Waterlogging and Salinity The downward movement of residue irrigation water below the root zone is restricted by a barrier. This leads to accumulation and rise of saline water that reduces productivity. This problem can be solved by drainage effort. Drainage canals are expensive. Waterlogging can be slowed by adoption of higher efficiency irrigation technologies. They can be induced by incentives. Waterlogging and salinity cost $11 billion annually. 20% of the irrigated land worldwide is affected by salinity. 1.5 million hectares are taken out of production each year as a result of high salinity levels in the soil.

"Waterlogging" is defined as the state of land in which the subsoil water table is located at or near the surface with the result that the yield of crops commonly grown on it is reduced well bellow for the land, or, if the land is not cultivated, it cannot be put to its normal use because of the high subsoil water table.

"Salinity control" is defined as the physical control, management, and use of water and related land resources in such a way as to maintain or reduce salt loading and concentrations of salt in water supplies.

Drainage of irrigated land is required to reduce waterlogging and soil salinization that inevitably accompanies waterlogging in arid zones. At present, about 20-30 million hectares of irrigated land are seriously affected by salinity.

WATERLOGGING AND SALINITY

* Basic Concepts in Waterlogging and Salinity

* Control of Waterlogging and Salinity Problems

* Irrigation Water Quality

BASIC CONCEPTS IN WATERLOGGING AND SALINITY

Excess water in the plant root zone restricts the aeration required for optimum plant growth. It may affect the availability of several nutrients by changing the environment around the roots.

Excess salts in the root zone inhibit water uptake by plants, affect nutrient uptake and may result in toxicities due to individual salts in the soil solution. Excess exchangeable sodium in the soil may destroy the soil structure to a point where water penetration and aeration of the roots become impossible. Sodium is also toxic to many plants.

Waterlogging and salinity in the soil profile are most often the result of high water tables resulting from inadequate drainage or poor quality irrigation water. Adequate surface drainage allows excess irrigation and rain water to be evacuated before excess soil saturation occurs or before the water is added to the water table. Adequate subsurface drainage insures that water tables are maintained at a sufficient depth below the soil surface to prevent waterlogging and salt accumulation in the root zone. Salinization of the soil profile is prevented because upward capillary movement of

water and salts from the water table does not reach the root zone. Adequate subsurface drainage also allows salts to be removed from the soil profile through the application of excess irrigation water (leaching).

To understand how we may prevent, eliminate or otherwise deal with a waterlogging or salinity problem, we must first understand how crops and soils respond to excess water and salts.

Waterlogging and High Groundwater Tables

The growth of most crops is affected when groundwater is shallow enough to maintain the soil profile in the root zone wetter than field capacity. This excess water and the resulting continuously wet root zone can lead to some serious and fatal diseases of the root and stem. Working the soil when overly wet can destroy soil structure and thus restrict root growth and drainage further. The chemistry and microbiology of waterlogged soils is changed due to the absence of oxygen. This can result in changes which affect the availability of many nutrients. For example, nitrogen can undergo denitrification more readily and be lost to the atmosphere as a gas. The anaerobic (reducing) environment results in changes to metals and other cations that can result in deficiencies or toxicities. For example, sulfide, ferrous and manganese ions will accumulate in waterlogged soils.

Crops vary in their tolerances to waterlogging and a high water table. Some crops, such as rice, are adapted to these conditions and can thrive. The table below presents the different tolerances of some crops.

Tolerance Levels of Crops to High Groundwater Tables and Waterlogging

GROUNDWATER AT 50 CM WATERLOGGING

HIGH TOLERANCE sugarcane, potatoes, rice, willow, plum, broad beans strawberries, some grasses

MEDIUM TOLERANCE sugarbeet, wheat, oats, citrus, bananas, apple, barley, peas, cotton pears, blackberries,

onion

SENSITIVE maize, tobacco, peaches, cherries, olives, peas, beans, date palm

The capillary fringe is a saturated zone that extends some distance above the water table. Water moves into this zone by capillary movement. The roots on many crops do

not generally penetrate closer than 30 cm above the water table. The capillary fringe is thinner in sandy soils than in loam or clay soils. Thus the following depths to groundwater are suggested as a minimum for most crops:

Sandy Soils ----------- Rooting Depth + 20 cm

Clay Soils ------------ Rooting Depth + 40 cm

Loam Soils ------------ Rooting Depth + 80 cm

Soil and Water Salinity

Crop yields decrease linearly with increasing salt levels above a given threshold level. This threshold level will vary according to the tolerance of the crop. Yield decreases in the absence of toxic salts such as boron are mainly due to the difficulties the crop has in taking up water due to the high concentration of salt in the soil solution. Often crops present a droughty or dry appearance in high salt soils.

The table below presents the tolerance of different crops to soil and water salinity levels, and the effect that increasing salinity levels has on yield. In this table, the ECe (Electrical Conductivity of the Saturated Paste Extract) is a measure of soil salinity, ECw (Electrical conductivity of the Irrigation Water) a measure of water salinity. The Max ECe is the highest ECe that the plant can tolerate. The Yield Potential is the percent of an optimum yield that can be attained under given growing conditions.

Crop Salt Tolerance Levels for Different Crops as Influenced by Irrigation Water or Soil SalinityYIELD POTENTIALFIELD CROPS 100 90 % 75 % 50% 0%

ECw ECe ECw ECe ECw ECe ECw ECe ECw ECeBarley 8 5.3 10 6.7 13 8.7 18 12 28 19Cotton 7.7 5.1 9.6 6.4 13 8.4 17 12 27 18Sugarbeet 7 4.7 8.7 5.8 11 7.5 15 10 24 16Sorghum 6.8 4.5 7.4 5 8.4 5.6 9.9 6.7 13 8.7Wheat 6 4 7.4 4.9 9.5 6.3 13 8.7 20 13Wheat, Durum 3.8 7.6 5 10 6.9 15 10 24 16Soybean 5 3.3 5.5 3.7 6.3 4.2 7.5 5 10 6.7Cowpea 4.9 3.3 5.7 3.8 7 4.7 9.1 6 13 8.8Peanut 3.2 2.1 3.5 2.4 4.1 2.7 4.9 3.3 6.6 4.4Paddy Rice 2 3.8 2.6 5.1 3.4 7.2 4.8 11 7.6Sugarcane 1.7 1.1 3.4 2.3 5.9 4 10 6.8 19 12

Corn(Maize) 1.1 3.4 2.3 5.9 4 10 6.8 19 12Flax 1.7 1.1 3.4 2.3 5.9 4 10 6.8 19Broadbean 1.5 1.1 2.6 1.8 4.2 2 6.8 4.5 12 8Bean 1 0.7 1.5 1 2.3 1.5 3.6 2.4 6.3VEGETABLE CROPSZucchini Squash 3.1 5.8 3.8 7.4 4.9 10 6.7 15 10Beet, Red 4 2.7 5.1 3.4 6.8 4.5 9.6 6.4 15 10Squash 3.2 2.1 3.8 2.6 4.8 3.2 6.3 4.2 9.4 6.3Broccoli 2.8 1.9 3.9 2.6 5.5 3.7 8.2 5.5 14 9.1Tomato 2.5 1.7 3.5 2.3 5 3.4 7.6 5 13 8.4Cucumber 2.5 1.7 3.3 2.2 4.4 2.9 6.3 4.2 10 6.8Spinach 2 1.3 3.3 2.2 5.3 3.5 8.6 5.7 15 10Celery 1.8 1.2 3.4 2.3 5.8 3.9 9.9 6.6 18 12Cabbage 1.8 1.2 2.8 1.9 4.4 2.9 7 4.6 12 8.1Potato 1.7 1.1 2.5 1.7 3.8 2.5 5.9 3.9 10 6.7Sweet Potato 1 2.4 1.6 3.8 2.5 6 4 11 7.1Pepper 1.5 1 2.2 1.5 3.3 2.2 5.1 3.4 8.6 5.8Lettuce 1.3 0.9 2.1 1.4 3.2 2.1 5.1 3.4 9 6Radish 1.2 0.8 2 1.3 3.1 2.1 5 3.4 8.9 5.9Onion 1.2 0.8 1.8 1.2 2.8 1.8 4.3 2.9 7.4 5Carrot 1 0.7 1.7 1.1 2.8 1.9 4.6 3 8.1 5.4Turnip 0.9 0.6 2 1.3 3.7 2.5 6.5 4.3 12 8FORAGE CROPSRyegrass,per. 3.7 6.9 4.6 8.9 5.9 12 8.1 19 13Vetch,Common 2 3.9 2.6 5.3 3.5 7.6 5 12 8.1Sudan Grass 1.9 5.1 3.4 8.6 5.7 14 9.6 26 17Forage Cowpea 1.7 3.4 2.3 4.8 3.2 7.1 4.8 12 7.8Alfalfa 2 1.3 3.4 2.2 5.4 3.6 8.8 5.9 16 10Clover,Berseem 1 3.2 2.2 5.9 3.9 10 6.8 19 13Other Clover 1 2.3 1.6 3.6 2.4 5.7 3.8 9.8 6.6FRUIT CROPSDate Palm 4 2.7 6.8 4.5 11 7.3 18 12 32 21Grapefruit 1.2 2.4 1.6 3.4 2.2 4.9 3.3 8 5.4Orange 1.7 1.1 2.3 1.6 3.3 2.2 4.8 3.2 8 5.3Peach 1.7 1.1 2.2 1.5 2.9 1.9 4.1 2.7 6.5 4.3Apricot 1.6 1.1 2 1.3 2.6 1.8 3.7 2.5 5.8 3.8Grape 1.5 1 2.5 1.7 4.1 2.7 6.7 4.5 12 7.9Almond 1.5 1 2 1.4 2.8 1.9 4.1 2.8 6.8 4.5

Plum, Prune 1 2.1 1.4 2.9 1.9 4.3 2.9 7.1 4.7Blackberry 1 2 1.3 2.6 1.8 3.8 2.5 6 4Strawberry 0.7 1.3 0.9 1.8 1.2 2.5 1.7 4 2.7

An example of how to use this table is as follows: A farmer can produce 50 Kg per Hectare of corn on good soil. The farmer has a field with an ECe of 3.8 which gives him or her many problems. Using the table, an estimate can be made of an expected yield of roughly 37 Kg per Hectare (i.e. a 75% Yield Potential) for this field.

This table represents general information about relative tolerances to salt, but varietal differences are also very important. Much effort has been put into developing salt tolerant varieties of many crops because of the worldwide salinity problem. In some cases, minor problems can be alleviated by selecting the correct variety.

Electrical Conductivity (EC) is the reciprocal of Resistance (1/ohms), and is measured in mmhos/cm or in dS/m (dS/m = mmhos/cm). EC is measured with a salinity or conductivity meter, which is a standard piece of equipment in all soil labs and can often be purchased at a reasonable price for field use. ECw (salinity of the water) is measured by simply inserting the conductivity meter in the irrigation water, with adjustment made for temperature. ECe (soil salinity) is a little more complicated, requiring a saturated paste of the soil from which the water is then extracted and the salts measured.

Exchangeable sodium in the soil becomes a problem when the predominant salts in irrigation water or in the soil solution are sodium salts. Soil constituents which determine soil structure, such as clays and organic matter (soil colloids), have negative charges (exchange sites) on their outer surface which loosely attach to positive ions and molecules (cations) such as Calcium (Ca++), Ammonium (NH4+), and Sodium (Na+) (see Figure 7.1). These cations can readily be replaced by other cations (they are exchangeable). If there is excessive sodium in the soil solution, it will take over most of the exchange sites. Sodium is a small cation, so when present in large quantities on the exchange sites, it destroys the separation between soil particles. What happens then is that the clay or organic matter collapses on itself leaving no air spaces or pores (deflocculation). In some cases, the structureless organic matter is dispersed and can be lost in the drainage water, hence the old-fashioned term for these soils is Black alkali soils.

Sodium is measured as the Exchangeable Sodium Percent (ESP) or as the Sodium Absorption Ratio (SAR ). The ESP is simply the percent of all the exchange sites in the soil which are holding sodium on them. The SAR is more complicated, and is merely an index of the extent of the problem.

Very high sodium levels not only affect soil structure, but are toxic to many crops.

Classification of Salt Affected Soils

Saline Soils

These soils contain sufficient amounts of soluble salts to interfere with germination, growth and yield of most crop plants. They do not contain enough exchangeable sodium to alter soil characteristics. Technically, a saline soil is defined as a soil with an ECe greater than or equal to 4 mmhos/cm and an Exchangeable Sodium Percent (ESP) less than 15. The soil pH is usually less than 8.5. These soils may have a white crust or white salt crystal accumulation on the surface (salt blooms) so they are sometimes called "white alkali soils". Excess soluble salts can be removed by leaching if drainage permits as will be discussed.

Saline-Sodic Soils

These soils contain soluble salts and exchangeable sodium in sufficient quantities to interfere with the growth of most crops. Technically, a saline-sodic soil is defined as a soil having an ESP greater than 15 and an ECe greater than or equal to 4 mmhos/cm. The soil colloids (charged particles) are collapsed (deflocculated), and drainage and aeration are very poor. pH is usually in the range of 8-10.

Sodic Soils

These soils contain sufficient exchangeable sodium to interfere with the growth of most crops, but do not contain appreciable quantities of soluble salts. Technically, they are soils with an ESP greater than 15 and an ECe of less than 4 mmhos/cm. Drainage and aeration are very poor because soil colloids are very dispersed. The pH is generally above 8.5. These soils are sometimes called "black alkali soils". High pH values generally can be used as a indicator of possible sodium problems, but this is not always true.

Evaluating Waterlogging and Salinity Problems

The evaluation of the extent of waterlogging and salinity problems can usually be conducted through simple observation, communication and possibly some soil analysis. The following steps can be followed:

1) Interview local agronomists, agricultural technicians, and agribusiness personnel. Ask them questions about water table depths, salinity problems etc. If such problems exist, how are local farmers taking care of them?

2) Conduct a field reconnaissance to find out if the problem exists in your area. Wells, gravel pits and deep channels which show the depth to groundwater should be observed. If there are few of these, then install pits or auger small observation wells into the soil to depths of 30 to 80 cm below the expected rooting depths (30 cm for sandy soils, 80 cm for loams and fine textured soils). If soil horizons are reached which are grey, wet and may contain black or red mottles, you have hit "gleyed" or waterlogged horizons. You can assume at this point that soils are poorly drained at this level.

As part of the reconnaissance, observe fields for signs of excess water or salinity such as:

a) White crusts on the soil surface. There may be a problem even when these are not present.

b) Plants which are stunted, appear droughty or irregular even though the soil is fairly moist. In cases of high salinity, the leaves may be curled up and yellow. The margins of the leaves may burn, a reddish color is often seen and in some cases the plant may actually die during or shortly after germination and emergence.

c) Use of drainage water, tailwater or water which has been used extensively for washing, irrigation or industrial purposes before reaching the field. This may be a problem when the farmer is a tail-end user on a major irrigation system. This water can accumulate salts.

d) Soils with poor structure, which appear sticky and plastic when wet and which do not grow a crop. Hard, structureless soil pans can develop at different depths in sodic soils.

e) Standing water or wet spots in parts of the field where crops grow poorly. Standing water in spots after a prolonged drying period are also useful indicators.

f) When soil is dry and smooth or has slicked over areas without vegetation, sometimes with a thin peeled up skin, it can indicate infiltration and sodic soil problems

g) Absence of field drains for removing excess water.

h) Condition of field drains: Are surface drains full of vegetation or plugged up? Are surface and subsurface drains operating properly?

i) If the opportunity presents itself, take soil samples and have them analyzed if you suspect a salinity problem, or look at past samples if any are available.

CONTROL OF WATERLOGGING AND SALINITY PROBLEMS

Surface and Subsurface Drains

The first requisite in the prevention or elimination of waterlogging and salinity problems is an adequate drainage system. Very often, the natural drainage in an area along with good water management is sufficient to eliminate excess water and to preclude the need for expensive subsurface drainage systems. However, almost every farmer who applies water by surface irrigation or who deals with significant rainfall should have adequate surface drainage facilities to remove excess water. This will allow the farmer to avoid waterlogging and possible salinity problems at the tail end of borders, furrows or basins after irrigation or intense rainstorms. It will also allow the prevention of erosion associated with natural movement of the excess water over the soil surface.

Surface drains are open channels which collect water as it runs off of, or into irrigated fields. These drains convey water to a stream or channel where it can be carried safely. The design procedures for these drains are the same as for any open channel (see Chapter 5). The main requirement is that they are able to convey the maximum expected flow rate without erosion. At the tail-end of irrigated fields, these drains are often broad and shallow to allow farm machinery to operate efficiently.

Subsurface drainage may be accomplished either through the construction of open trenches or through buried clay or concrete tiles or perforated pipe. Subsurface drainage systems can be classified as Natural, Herringbone,GridironorInterceptor (Cutoff) types.

The Natural systems are used in fields where there are small and isolated wet areas. The buried drain lines follow natural draws or depressions.

The Herringbone systems are useful in situations where the land slopes toward a draw on either side. The main line follows the draw, and the laterals empty into this from both sides.

The Gridiron systems are similar to the Herringbone except that they enter the main drain from only one side.

Interceptor drains are installed across a slope to intercept the passage from higher ground. These drains can prevent the waterlogging of soils below irrigation ditches, springs or at the foot of a hill. They can be useful in collecting water for recycling into the irrigation system.

The design, drain size, spacing and depth are a function of the water table depth desired, the soil permeability (hydraulic conductivity), amount of water to be drained, economics of construction, etc. Generally, the deeper the drains are

installed, the wider the spacing between drains can be. In humid regions, drain spacings of 10 to 50 meters (30 to 150 feet) are common. The closer spacing is used in heavier soils with higher value crops and greater rainfall. In more arid irrigated areas, spacings of 50 to 200 meters (150 to 600 feet) are common.

Tile drain is common in 10, 13 and 15 cm (4, 5 and 6 inch) sizes, but can be obtained in greater sizes as can corrugated drainage pipe. Minimum grades are sometimes based on a minimum velocity of 0.45 m/s (1.5 feet per second) at full flow. Surface inlets, outlets and cleanouts, envelope filters and other structures must be properly designed if the drain system is to operate correctly.

The design of subsurface drains is generally more complex than for surface drains and requires significant knowledge of groundwater hydrology. Thus the reader should seek the assistance of a drainage engineer before undertaking the design of expensive subsurface drains. The one possible exception is the Interceptor drain which can be installed as an open channel below the level of an irrigation canal to provide drainage to land which would otherwise be waterlogged by the canal.

Reclamation of Salt Affected Soils

The chemical and physical analysis of soils provides a basis for the diagnosis, treatment and management of salt affected soils. After diagnosing the problem but before actual reclamation, two steps must be observed.

1. Establishing adequate drainage in the area. The water table should be lowered if it is high and water should be at least 3 to 4 meters below the surface.

2. The land should be level or contour farmed so that the surface of the soil will be covered uniformly by water.

Saline Soil

If the soil is only saline, it can be reclaimed simply by leaching the excess salts below the root zone. The quantity of water depends on the texture of the soils, the concentration of salts in the soil and in the leaching water (the higher, the more water needed) and the amount of salts to be leached. On the average, 0.5 to 1.25 meters of water are required.

Saline Sodic Soil and Sodic soil

If leaching is conducted on a saline-sodic soil, the soil will become sodic and could present more problems than it would have originally. Saline-sodic soils require the leaching process to be accompanied by the application of amendments. The amendments that are used are the same ones that would be utilized on a sodic soil. Sodic soils are generally very poor in infiltration, so amendments are slow to enter soil. For this reason, both compacted saline-sodic soils and sodic soils should undergo deep cultivation such as deep ripping to break up hardpans which prevent infiltration.

Correcting Sodium Problems with Amendments:

The presence of lime (free calcium carbonate) in soil allows for the widest choice of amendments. To test for this, a spoonful or clod of soil is treated with a few drops of sulfuric acid or hydrochloric acid. If bubbling or fizzing occurs where the acid drops fall, then lime is present. The greater the fizzing, the more lime is present. If the soil contains lime, any of the amendments listed in Table 7.3 can be used. If no lime is present, then only amendments containing soluble calcium are recommended.

Commonly Used Amendment Materials and Their Equivalent Amendment ValuesTons of Amendment Material Equivalent to:

Amendment Chemical Formula 1 Ton of 1 Ton of(100% Basis) Pure Gypsum Soil SulfurGypsum CaSO4.2H20 5.38Soil Sulfur S 0.19 1Sulfuric Acid H2SO4 0.61 3.2Ferrous Sulfate Fe2(SO4).9H2O 1.09 5.85Lime Sulfur CaSx 0.78 4.17Calcium Chloride CaCl2.H2O 0.86 ---Calcium Nitrate Ca(NO3)2.H2O 1.065 ---Aluminum Sulfate Al2(SO4)3 --- 6.34

The percent purity is generally given on the bag.

Types of Amendments

Calcium containing amendments such as gypsum react in the soil as follows:

GYPSUM + SODIUM-SOIL _ CALCIUM SOIL + SODIUM SULFATE

Leaching is then undertaken to wash out the sodium sulfate. Repeated applications are necessary in many cases. The amount of gypsum used is substantial, often 1.5 or more tons of material per hectare, because it is not highly water soluble, and in many cases, the reaction described above takes a long period of time. It needs to be incorporated to speed up reaction. A more precise measurement of the "gypsum requirement" is available from most soil labs, assuming a material of 100% purity.

Acids such as sulfuric acid undergo a two step process:

1. SULFURIC ACID + SOIL LIME _ GYPSUM + CO2 + WATER

2. GYPSUM + SODIUM-SOIL _ CALCIUM SOIL + SODIUM SULFATE

Acids are dangerous and corrosive, so handling can be a problem. The volume applied has to be controlled because of excessive frothing. Occasionally, cheap industrial sources are available but must be used with caution because of the potential for heavy metal contamination. An analysis of spent acids is recommended. They are much faster than other reclamation procedures because the reaction is instantaneous.

Acid forming materials such as sulfur are much slower because they undergo a three step process, the first step requiring microbial intervention in the oxidation reaction:

1. SULFUR + OXYGEN + WATER _ SULFURIC ACID

2. SULFURIC ACID + SOIL LIME _ GYPSUM + CO2 + WATER

3. GYPSUM + SODIUM-SOIL _ CALCIUM SOIL + SODIUM SULFATE

These steps can take years.

Effectiveness and Amount of Amendments:

In the absence of a soil analysis for gypsum requirement, a rule of thumb is that something is better than nothing. Gypsum is usually used in large quantities, so 0.5 to 2 metric ton applications per hectare are not unusual. To convert the gypsum requirement to an amount of some other amendment, Table 7.3 offers a simple guideline. Simply multiply the gypsum ton equivalent by the gypsum requirement.

If the material being considered is not 100% pure, a simple calculation will indicate the amount needed to be equivalent to 1 metric ton of pure material:

100 % / % purity = m Tons per 1 m ton of pure material.

For example: If gypsum is 60 percent pure, the calculation would be 100/60 = 1.67 m tons. In other words, 1.67 tons of 60 percent pure gypsum is equivalent to 1 m ton of 100% material.

Sulfur presents an additional challenge, since not only purity but the fineness of the granules must be accounted for. The finer the material, the faster microbial oxidation will occur. Coarse grade materials are highly insoluble and may take years to be active.

Management of Saline and Sodic Soils

Often, it is too expensive or impractical to reclaim saline or sodic soils, or even to maintain them at low salinity levels. It may be impossible to adequately drain an area, amendments may not be available or may be too expensive, or the water used for irrigation may be of poor quality.

In these situations, there are various management practices that will aid in controlling or reducing the impact of salts or sodium:

1. Selection of crops or crop varieties that have higher tolerances for salt or sodium (See Table 7.2)

2. Use of special planting procedure that will minimize salt accumulation around the seed. (See Figure 7.2)

3. Use of the appropriate irrigation method for the root characteristics of the crop (See Figure 7.3).

4. Use of sloping beds and other special land preparation procedures and tillage methods to provide a low salt environment

5. Use of irrigation water to maintain a high water content to dilute the salts or to leach the salts out for germination or from the root zone.

6. Use of physical amendments such as manure, compost, etc. for improving soil structure and tilth. Conservation tillage to incorporate crop residues will help create drainage.

7. Deep ripping of soil to break up sodic and other hardpans or other impervious layers to provide internal drainage.

8. Use of chemical amendments as described.

9. Good, sound farming practices and careful fertilizer management.

IRRIGATION WATER QUALITY

An understanding of the quality of the irrigation water is essential in any salinity or sodium control program. Often, poor quality water is the source of the salinity or sodium problem. Table 7.4 presents some quality guidelines for evaluating the riskiness of the water. If water is of poor quality, tactics such as dilution with other water sources, or applications of larger leaching amounts can be implemented.

Effect of Irrigation Water Quality on Soil Salinity, Permeability, ToxicityNone Moderate Severe

Effect on:Salinity ECw (mmhos/cm) < 0.75 0.75 - 3.0 > 3.0Permeability ECw (mmhos/cm) > 0.50 0.50 - 0.20 < 0.2adj. SARMontmorillonite 1 < 6.0 6.0 - 9.0 > 9.0Illite 2 < 8.0 8.0 - 16.0 > 16.0Kaolinite 3 < 16.0 16.0 - 24.0 > 24.0Toxicity (most tree crops)Sodium (adj. SAR) 4 < 3.0 3.0 - 9.0 > 9.0Chloride (meq/l) 5 < 4.0 4.0 - 10.0 > 10.0Boron (mg/l) < 0.75 0.75 - 2.0 > 2.0MiscellaneousNitrogen (mg/l) 6 < 5.0 5.0 - 30.0 > 30.0Bicarbonate (HCO3) < 1.5 1.5 - 8.5 > 8.5pH Normal Range: 6.5 - 8.4

1 Temperate clay soils, highly expandable, not suited for ceramics or clay tiles.

2 Temperate clay soils or tropical soils in low rainfall or wet/dry climates. Not highly expandable. Can be used for ceramics.

3 Tropical clay soils in high rainfall areas. Usually have a distinct red or yellow color.

4 For most field crops

5 Sprinkler irrigation may cause leaf burn when >3 meq/l.

6 Excess nitrogen causes excessive vegetative growth, lodging, and delayed crop maturity.

Salinity problems can occur due to saline water being used in irrigation. Decreased soil infiltration rates can be the result of irrigation water which is low in salts but high in sodium, or water which has a high sodium to calcium ratio. If infiltration problems are due to high sodium water, the effect will be noticed in the surface few centimeters of the soil.

Other water quality problems to be on the look-out for include:

1. Water high in iron, bicarbonate or gypsum which can result in unsightly deposits on cash crops.

2. Highly acid (low pH) or corrosive water which can result in severe corrosion of irrigation hardware such as pipelines and wells.

3. Other pH abnormalities (high or low) which can result in encrustation or other effects on crops.

4. Risks from diseases such as Bilharzia (schistosomiasis), malaria and lymphatic filariasis; or risks from vectors of diseases such as mosquitoes. Vector breeding can often originate in situations where there is low water infiltration rates, use of wastewater for irrigation or poor drainage.

5. Sediments which can clog up irrigation structures, build films on leafy cash crops which make them unacceptable for marketing and seal-off soils due to the depositing of structureless silt on soil surfaces.

Wealth from Water factsheet Waterlogging in soil Symptoms and causes Waterlogging occurs when the soil profile or the root zone of a plant becomes saturated. In rain-fed situations, this happens when more rain falls than the soil can absorb or the atmosphere can evaporate. Lack of oxygen in the root zone of plants causes their root tissues to decompose. Usually this occurs from the tips of roots, and this causes roots to appear as if they have been pruned. The consequence is that the plant’s growth and development is stalled. If the anaerobic circumstances continue for a considerable time the plant eventually dies. Most often, waterlogged conditions do not last long enough for the plant to die. Once a waterlogging event has passed, plants recommence respiring. As long as soil conditions are moist, the

older roots close to the surface allow the plant to survive. However, further waterlogging-induced root pruning and/or dry conditions may weaken the plant to the extent that it will be very poorly productive and may eventually die. Many farmers do not realise that a site is waterlogged until water appears on the soil surface (see picture above). However, by this stage, plant roots may already be damaged and yield potential severely affected. Key points Waterlogging occurs when roots cannot breathe due to excess water in the soil profile. Water does not have to be on the soil surface for waterlogging to be a potential problem. Improving drainage can decrease the time that the crop roots are subjected to anaerobic conditions. Open trenches are the simplest drains and are the first requirement of a drainage system with more intensive drainage such as underground pipes, raised beds or hump and hollow, providing more effective drainage. Background Waterlogging can limit agricultural productivity in many areas of Tasmania as the State enjoys relatively high rainfall which normally occurs with an excess of rainfall over evaporation in winter and spring. Many soils experience parts of the year when they are saturated due to high regional water tables, low rates of water conductivity, perched water tables or seepage. Waterlogging occurs whenever the soil is so wet that there is insufficient oxygen in the pore space (anaerobic) for plant roots to be able to adequately breathe. Other gases detrimental to root growth, such as carbon dioxide and ethylene, also accumulate in the root zone and affect the plants. Plants differ in their demand for oxygen and a plant’s demand for oxygen in its root zone will vary with its stage of growth. Wealth from Water factsheet Contact: Ph 1300 368 550 Email: wfwp@dpipwe.tas.gov.au Wealth from Water Local call on 1300 368 550 email wfwp@dpipwe.tas.gov.au www.dpipwe.tas.gov.au/wealthfromwater Produced by Dr Bill Cotching, TIA Last updated March 2012 Identifying problem areas Diagnosing your waterlogging problem is the key to achieving success with any drainage. You need to know the source of the water and where it is moving in the soil. This will ensure correct selection of drain type to install and depth of installation. In winter it is easier to identify the limits of wet areas, particularly seepage areas, and to identify soil horizons on which a perched watertable occurs. For the initial investigation, dig a series of holes up to one metre deep in and around wet areas. A number of pegs are useful to mark out drainage lines and potential drain locations. Signs of waterlogging to look for on the soil surface include ponding, pugging by stock and ruts from machinery, poor crop establishment and growth, and patches of excessive weed growth. Benefits of improved drainage Reducing the length of time soils remain waterlogged by the installation of appropriate drainage systems, results in greater ease of soil management, increased plant growth by improving aeration and soil temperature, plus control of plant diseases. Improving drainage results in the soil becoming friable rather than plastic, and less likely to be compacted or pugged. A more aerated soil encourages organisms which metabolise organic matter and stabilise soil aggregates. Improved drainage increases the depth of aerated soil allowing plant roots to explore a greater soil volume. This increases the pool of nutrients available, and with a greater volume of soil to draw on for water, plants are able to continue growing for longer during dry summer periods, which is often one of the unexpected benefits of improved drainage. Drainage can lessen the incidence of fusarium and phytophthora root rots which can occur when plants are stressed by waterlogged conditions and poor aeration. Poor soil drainage may be limiting plant growth to the extent that no responses are gained from increased fertiliser use. Drainage is also an important way of improving working conditions by removing the unpleasantness of muddy, wet soil. Disclaimer Information in this publication is intended for general information only and does not constitute professional advice and should not be relied upon as such. No representation or warranty is made as to the accuracy, reliability or completeness of any information in this publication. Readers should make their own enquiries and seek independent professional advice before acting or relying on any of the information provided. The Crown and Tasmanian Institute of Agriculture, their officers, employees and agents do not accept liability however arising, including liability for negligence, for any loss resulting from the use of or reliance upon information in this publication. Types of drainage Drainage is carried out either on the surface or

underground depending on the diagnosis of the problem. Surface drains can be open arterial ditches, grassed waterways or hump and hollow. Underground drains can be pipe drains, mole drains, or deep ripping. Surface drains are a minimal investment, last a long time provided stock are excluded, and can always be deepened or moved. Different soil types require different solutions to drainage problems. Plan your drainage in the winter, but install drains in the summer.

20.02.16

Waterlogging is happened when the soil is so filled or soaked with water that caused the roots of the plant to rot.

Waterlogging is 100% when water table rises to the surface. However the process of waterlogging starts even when the water table is quite below the

surface. In this case thereexists a capillary fringe. For example presence of water due to capillary action above the saturation line. Capillary fringe

depth depends upon the type of soil. If the soil is coarse and sandy, then its depth is low. Depth of capillary fringe is large for fine grained soil. The

other important factor is the depth of root-zone which varies from crops to crops. In case of wheat, the depth of root zone is about 2 feet, and if there is

a height of capillary fringe is 4ft. Then water logging process will start if the water table is at 6 meter from the surface.

Harmful effects of waterlogging and salinity are caused by unthoughtful planning of irrigation system.

With respect to water logging and salinity, there are following harmful effects:

1. Waterlogged soil provides excellent breeding grounds for misquitoes, and cause malaria.

2. It causes loss in crop yield.

3. When waterlogged soil are fully saturated, plant roots can not absorb water. Therefore, they are deprived of aeration. Due to absence of

aeration, anaerobic conditions exist killing the aerobic bacteria present in the root-zone of the plant. This aerobic bacteria helps to make food for the

plant. This aerobic bacteria transform chemical compounds into nitrogen and phosphorus and provides food to the plant. Due to waterlogging, killing

of this bacteria occured and ultimately causes the death of the plant.

4. In rainfall or irrigation, water after saturating the root-zone travels downward washing down excess salts. When the unsaturated conditions begin,

plant start taking up water. In waterlogged soil, water moves upwards due to  capillary. It bring up salts more and more in the root-zone. Thus making

soil solution excessively saline. The plant then faces hindrences in taking up moisture. This results in permanent wilting of the plant.

5. Where land is totally waterlogged, salinity causes destruction of vegetation and crops. Waterlogging causes depostion of salts in the root zone. If the

salts are alkaline, then soil pH increases. If the soil pH increases to 8.5, it effects the plant and if increases to 11.0 then plant becomes infertile. If the

salts are acidic, then its lower the pH. For acidic salts with pH low than 4, plants cannot absorb nutrients and die.

6. Destruction of roads occured due to reduced bearing capacity of waterlogged soil.

7. Rise of water through capillary in the buildings, causes dampness and therefore causes diseases. This also causes peeling off plasters and

appearance of salt patched on the walls of the buildings.

8. Certain weeds grow very fast in the waterlogged area and normal crops cannot compete with them. Thus suppressing the useful crops to grow.

9. Due to reduced bearing capacity, agricultural machinery cannot operate well in the fields.

10. Saline soil being unfit for agriculture is used for making bricks. The salts from these bricks appear on the surface whenever they get dry.

Definition:When the conditions are so created that the crop root-zone gets deprived of proper aeration due

to the presence of excessive moisture or water content, the tract is said to be waterlogged. To

create such conditions it is not always necessary that under groundwater table should enter the

crop root-zone. Sometimes even if water table is below the root-zone depth the capillary water

zone may extend in the root-zone depth and makes the air circulation impossible by filling the

pores in the soil.

The waterlogging may be defined as rendering the soil unproductive and infertile due to

excessive moisture and creation of anaerobic conditions. The phenomenon of waterlogging can

be best understood with the help of a hydrologic equation, which states that

Inflow = Outflow -I- Storage

Here inflow represents that amount of water which enters the subsoil in various processes. It

includes seepage from the canals, infiltration of rainwater, percolation from irrigated fields and

subsoil flow. Thus although it is loss or us, it represents the amount of water flowing into the

soil.

The term outflow represents mainly evaporation from soil, transpiration from plants and

underground drainage of the tract. The term storage represents the change in the groundwater

reservoir.

Causes of Waterlogging:After studying the phenomenon of waterlogging in the light of hydrologic equation main factors

which help in raising the water-table may be recognised correctly.

They are:i. Inadequate drainage of over-land run-off increases the rate of percolation and in turn helps in

raising the water table.

ii. The water from rivers may infiltrate into the soil.

iii. Seepage of water from earthen canals also adds significant quantity of water to the

underground reservoir continuously.

iv. Sometimes subsoil does not permit free flow of subsoil water which may accentuate the

process of raising the water table.

v. Irrigation water is used to flood the fields. If it is used in excess it may help appreciably in

raising the water table. Good drainage facility is very essential.

Effects of Waterlogging:The waterlogging affects the land in various ways. The various after effects are the following: 1. Creation of Anaerobic Condition in the Crop Root-Zone:When the aeration of the soil is satisfactory bacteriological activities produce the required

nitrates from the nitrogenous compounds present in the soil. It helps the crop growth. Excessive

moisture content creates anaerobic condition in the soil. The plant roots do not get the required

nourishing food or nutrients. As a result crop growth is badly affected.

2. Growth of Water Loving Wild Plants:When the soil is waterlogged water loving wild plant life grows abundantly. The growth of wild

plants totally prevent the growth of useful crops.

3. Impossibility of Tillage Operations:Waterlogged fields cannot be tilled properly. The reason is that the soil contains excessive

moisture content and it does not give proper tilth.

4. Accumulation of Harmful Salts:The upward water movement brings the toxic salts in the crop root-zone. Excess accumulation

of these salts may turn the soil alkaline. It may hamper the crop growth.

5. Lowering of Soil Temperature:The presence of excessive moisture content lowers the temperature of the soil. In low

temperature the bacteriological activities are retarded which affects the crop growth badly.

6. Reduction in Time of Maturity:Untimely maturity of the crops is the characteristic of waterlogged lands. Due to this shortening

of crop period the crop yield is reduced considerably.

Detection of Waterlogging:From the subject matter discussed above it is clear that the waterlogging is indicated when the

ground water reservoir goes on building up continuously. When the storage starts building up in

the initial stages the crop growth is actually increased because more water is made available for

the crop growth. But after some time the waters table rises very high and the land gets

waterlogged. Finally the land is rendered unproductive and infertile.

The problem of waterlogging develops in its full form slowly. Therefore its early detection is

possible by keeping a close watch over the yields and also on the variations in the groundwater

level. A comparative reduction in crop yields in spite of irrigation and fertilisation and early

maturity of crops indicate the symptoms of waterlogging. Also when harmful salts start

appearing on the fields as white incrustation or deposit it indicates that waterlogging is likely to

follow. In worst cases the water-table rises so high and close to the ground surface that the

fields turn into swamps and marshes.

The best way of keeping watch over the problem of waterlogging is by observing variations in

the groundwater level. It can be done by measuring the depth of water levels at regular interval

in the wells dug in the area. Continuous high water levels indicate that the groundwater storage

is building up which may create waterlogging in the area.

Solution to the Problem of Waterlogging:The problem of waterlogging may be attacked on two fronts. First is preventive measures, which

keep the land free from waterlogging. Secondly curative measures may be adopted to reclaim

the waterlogged area. But in principle both measures aim at reducing the inflow and augmenting

the outflow from the underground reservoir.

Preventive Measures:Preventive measures include the following:(a) Controlling the loss of water due to seepage from the canals:The seepage loss may be reduced by adopting various measures for example

i. By lowering the FSL of the canal:Loss may be due to percolation or absorption but when FSL is lowered the loss is reduced to

sufficient extent. It is course essential to see that while lowering the FSL command is not

sacrificed.

ii. By lining the canal section:When the canal section is made fairly watertight by providing lining the seepage loss is reduced

to quite a good extent.

iii. By introducing intercepting drains:They are generally constructed parallel to the canal. They give exceptionally good results for the

reach where the canal runs in high embankments.

(b) Preventing the loss of water due to percolation from field channels and fields:The percolation loss can be removed by using water more economically. It may also be affected

by keeping intensity of irrigation low. Then only small portion of the irrigable tract is flooded and

consequently the percolation loss takes place only on the limited area. It keeps the water-table

sufficiently low.

(c) Augmentation of outflow and prevention of inflow:It may be accomplished by introducing artificial open and underground drainage grid. It may

also be achieved by improving the flow conditions of existing natural drainages.

(d) Quick disposal of rainwater:Quick removal of rainwater by surface or open drains is a very effective method of preventing

the rise in water table and consequent waterlogging of the tract. It is needless to state that the

rainwater removed is net reduction in inflow.

Curative Measures:Curative measures include the following:(a) Installation of lift irrigation systems:When a lift irrigation project in the form of a tube well irrigation system is introduced in the

waterlogged area the water table gets lowered sufficiently. It is found to be very successful

method of reclaiming waterlogged land. Thus a combination of a canal system and a

supplementary tube well irrigation system may be considered to be most successful and

efficient irrigation scheme.

Of course it is true that it will create some complications while assessing the charges for

irrigation water. (The canal water being cheaper than tube well water). Implementation of

drainage schemes: The waterlogged area may be reclaimed by introducing overland and

underground drainage schemes.

(b) Implementation od Drainage Schemes:The waterlogged area may be reclaimed by introducing overland and underground drainage

schemes. 

Extent or Waterlogged Area:In our country water-logging is a problem of great concern. It is estimated that total area of

waterlogged land is 86.92 lakh hectares. It includes area in irrigation commands as well as other

area outside the command.

While the areas in the irrigation command get waterlogged due to rise in water table as a direct

consequence of inadequate drainage, other areas get waterlogged due to inundation, as

consequence of flooding for long durations. The States mainly affected and the extent of area

rendered infertile and unproductive are given in Table 11.1.

 

About 48 lakh ha are estimated to be affected by salinity and 25 lakh ha by alkalinity. Saline

soils include 10 lakh ha in arid and semi-arid regions of Rajasthan and Gujarat and 14 lakh ha in

black cotton soils. The alkali problem is mainly in Punjab, Haryana and Uttar Pradesh.

Steps are being taken to reclaim the waterlogged land in the country. The steps taken to reclaim

such areas include implementation of drainage schemes, provision of deep drains, excavation

of new channels and improvement of existing ones, construction of sluices with marginal

embankment and installation of tube wells.

The spread of conjunctive use of groundwater with that of surface water especially in Punjab,

Haryana and parts of Uttar Pradesh has substantially lowered the groundwater table and helped

in containing water-logging/salinity.

Summarising the most effective and efficient anti-water-logging measures are:i. Lining of channels (main canal, branches and field channels).

ii. Provision of surface drains for drainage of rainwater; and

iii. Implementation of tube well projects both extensive and local.

Water-Logging 

Key Points

Waterlogging occurs when roots cannot respire due to excess water in the soil profile. Water does not have to appear on the surface for waterlogging to be a potential problem. Improving drainage from the inundated paddock can decrease the period at which the crop roots are subjected to

anaerobic conditions. While raised beds (see Raised Bed Cropping fact sheet) are the most intensive management strategy, they are

also the most effective at improving drainage. Waterlogged soils release increased amounts of nitrous oxide (N2O), a particularly damaging greenhouse gas.

 

Background

Waterlogging occurs whenever the soil is so wet that there is insufficient oxygen in the pore space for plant roots to be able to adequately respire. Other gases detrimental to root growth, such as carbon dioxide and ethylene, also accumulate in the root zone and affect the plants.Plants differ in their demand for oxygen. There is no universal level of soil oxygen that can identify waterlogged conditions for all plants. In addition, a plant’s demand for oxygen in its root zone will vary with its stage of growth.

 

Symptoms and causes

Lack of oxygen in the root zone of plants causes their root tissues to decompose. Usually this occurs from the tips of roots, and this causes roots to appear as if they have been pruned. The consequence is that the plant’s growth and development is stalled. If the anaerobic circumstances continue for a considerable time the plant eventually dies.Most often, waterlogged conditions do not last long enough for the plant to die. Once a waterlogging event has passed, plants recommence respiring. As long as soil conditions are moist, the older roots close to the surface allow the plant to survive. However, further waterlogging-induced root pruning and/or dry conditions may weaken the plant to the extent that it will be very poorly productive and may eventually die.Many farmers do not realise that a site is waterlogged until water appears on the soil surface (figure 1). However, by this stage, plant roots may already be damaged and yield potential severely affected.

 

Figure 1: Waterlogging in a crop grown on a duplex soil in early winter, 1997, along the Esperance South Coast, Western Australia.

 

Waterlogging occurs when the soil profile or the root zone of a plant becomes saturated. In rain-fed situations, this happens when more rain falls than the soil can absorb or the atmosphere can evaporate.Western Australia’s ‘Mediterranean’ climate of cool and wet winters and hot dry summers produces more rain than the atmosphere can evaporate every winter. The amount of ‘excess’ rain is particularly large in the higher rainfall areas of the south-west.

 

Cost of waterlogging and inundation

Most data on the cost of waterlogging and inundation are from the Upper Great Southern (see McFarlane et al., 1992), although the problems are widespread. Cereal crop yields decrease by about 150 kg/ha for every 10 mm of rainfall in excess of the decile 5 rainfall during August in the Upper Great Southern. In the same study it was calculated that over a 10 year period in eight shires from that region, excess rainfall costs farmers about 14 % in lost wheat production each year.Waterlogging and inundation slow pasture growth in winter and delay the spring flush. Pasture growth in winter is at least five times more valuable than extra production in late spring. Waterlogged legumes grow more slowly than waterlogged grasses, so waterlogged pastures become grassy and weedy.In wet years, waterlogging reduces the area that can be cropped. When paddocks are waterlogged shortly after seeding, germination and emergence are often reduced; and crops may have to be re-sown when the soil is firm enough to support machinery.Waterlogged and inundated areas contribute recharge to saline aquifers, are very susceptible to water erosion and are prone to soil structure decline if cultivated or stocked when too wet.

 

Identifying problem areas

The best way to identify problem areas is to dig holes about 40 cm deep in winter and see if water flows into them (figure 2). If it does, the soil is waterlogged. Digging holes for fence posts often reveals waterlogging. Some farmers put slotted PVC pipe into augered holes. They can then monitor the water levels in their paddocks.Symptoms in the crop of waterlogging include:

Yellowing of crops and pastures. Presence of weeds such as toad rush, cotula, dock and Yorkshire fog grass.

 

Figure 2: Waterlogged duplex soil – sandy loam topsoil overlying a sandy clay subsoil at 30 cm. Seepage is entering the hole above the clay base.

 

Effects on plant growth

Low levels of oxygen in the root zone trigger the adverse effects of waterlogging on plant growth. Waterlogging of the seedbed mostly affects germinating seeds and young seedlings. Established plants are most affected when they are growing rapidly. Therefore, if a soil becomes waterlogged in July, final yields may not be greatly reduced; soils are cold, the demand for oxygen is low and plant growth is slow at this time of year. Prolonged waterlogging during the warmer spring period could be more detrimental, however the probability for this to occur is much lower than waterlogging in July.When plants are growing actively, root tips begin to die within a few days of waterlogging. The shallow root systems that then develop limit the uptake of nutrients (particularly nitrogen) and water, particularly when the soil profile starts to dry in spring. As a result plants may ripen early and grains may not fill properly.

Nitrogen is lost from waterlogged soils by leaching and denitrification (degassing). Denitrification leads to the gaseous loss of nitrous oxide (N2O) into the atmosphere, which is a major greenhouse gas. These losses, together with the lowered ability of plants to absorb nutrients from waterlogged soil, cause the older leaves to yellow. Waterlogging also directly reduces nitrogen fixation by the nodules of legume crops and pastures.

 

Solving waterlogging

Drainage can be improved on many sites and is the first thing to consider once a waterlogging problem has been identified. Options might vary from shallow surface drains (ie. Spoon- and ‘W’-drains) to more intensive drainage using wide-spaced furrows, to the intensive drainage form of raised beds (see Raised Bed Cropping fact sheet). The efficiency of surface drainage increases in that order as does the degree of management. Consult your local adviser for further advice.

Adverse effects.

In the irrigated areas of semi-arid regions, especially in northwest India, a considerable recharge to the groundwater leads to waterlogging and secondary salinization. In several sub-areas groundwater is mined, water tables fall, and salts are added to the root zone because a high proportion of irrigation water is derived from pumped groundwater of poor quality. Out of 1 million hectares of irrigation induced waterlogged saline area in northwest India, approximately half a million hectares are in the state of Haryana. Taking a homogenous physical environment as a starting point, the way and the extent to which farmers’ activities will affect the salinity and sodicity situation depend on farming and irrigation practices. In the past, soil salinity was mainly associated with high groundwater tables, which bring salts into the root zone through capillary rise when water is pumped. But nowadays, increasing exploitation of groundwater for irrigation purposes has led to declining groundwater tables and a threat of sodification and salinization due to use of poor quality groundwater. Farmers in northwest India are facing a situation in which they have to deal with salt volumes that are harmful for water uptake of crops. They are also facing the problem of sodicity, which has an adverse effect on the physical structure of the soil, causing problems of water intake, transfer and aeration. To mitigate the adverse effect of soil salinity on crop yield, the farmers irrigate frequently, either mixing canal water and groundwater, or alternately using canal water and groundwater. Due to differences in environmental parameters in the farming systems, such as groundwater quality, soil types and uneven distribution of irrigation water, income losses to the farming community are not uniform. This paper highlights the economic loss due to environmental degradation through the twin problems of waterlogging and soil salinity, which threaten the sustainability of agricultural production in Haryana state. Our analysis shows that the net present value of the damage due to waterlogging and salinity in Haryana is about Rs. 23,900/ha (in 1998–1999 constant prices). The estimated potential annual loss is about Rs. 1669 million (about US$ 37 million) from the waterlogged saline area. The major finding of the paper is that intensification per se is not the root cause of land degradation, but rather

the policy environment that encouraged inappropriate land use and injudicious input use, especially excessive irrigation. Trade policies, output price policies and input subsidies all have contributed to the degradation of agricultural land.

How do I manage waterlogging?

Key PointsUnderstanding the problem

Why is it important to me as a farmer? How and why it occurs How to recognise it in the paddock

Managing the problem

What is the best practice? How can you achieve this?

Case StudyOther related questions in the Brown BookResourcesReferences

Source: DEPI Victoria

Key Points

Significant problem for dairy farmers during wet winter and early spring

Manage water running onto the paddock before considering subsurface options

Water does not have to appear on the surface for waterlogging to be a potential problem

Before considering draining a wet area you should contact your local Catchment Management Authority for advice, as a permit may be required

Understanding the problem

Why is it important to me as a farmer?

Waterlogging is currently a significant land degradation threat across much of south-west Victoria

Vast areas including the Heytesbury Soldier Settlement and the Victorian Volcanic Plains represent landscapes significantly affected by waterlogging

Is a significant problem for dairy farmers during winter and early spring where soils can remain waterlogged for considerable periods

Causes poorer pastures, both in growth and quality

Makes it harder and more unpleasant to farm, particularly for dairy farmers:

o those jobs with critical timing (such as silage making and crop sowing) can be upset

o tractors leave deep furrows in paddocks when feeding out

o cows pugging pasture to the point where they require a full renovation

Waterlogging is also a major constraint to grain production in the region

Top of Page

How and why it occurs

Waterlogging may be a natural condition of the soil, but can worsen with deterioration in soil structure

It occurs when rainfall exceeds the ability of some soils to drain surplus water away

It is often perceived that waterlogging is a surface water problem that surface drains

will overcome. However, in many situations waterlogging is due to the soil profile (soil below the ground surface) being saturated and some type of subsurface drainage may be necessary to overcome this problem

Unfortunately, some soils and areas, due to their location, cannot be economically or feasibly drained by any means

Susceptibility maps indicate that waterlogging is high to very high over more than 50% of the Corangamite region and is:

o usually a seasonal problem

o caused by a relatively impermeable layer through which water moves only very slowly

o due to soil compaction, sodic soils, high rainfall

o ‘perched’ water-tables in topsoil

Figure 1 - Waterlogging susceptibility in the Corangamite region (DEPI FFSR). – Source: CCMA  [View larger image]  

o Generally located on low-lying heavy duplex soils in higher rainfall areas

o High to very high susceptibility to soil structure decline covers similar areas to that of waterlogging, predominant in the south-west section of the region

o Waterlogging is common in the higher rainfall pastures of the region particularly those on the clay soils of the Gellibrand Marl (Heytesbury) and Basalt

For detailed information about the physical extent of waterlogging in the Corangamite region, see following report - A terrain analysis assessment of waterlogging susceptibility 

For detailed information about regional soils, refer toSoils of the Corangamite Region online

Top of Page

How to recognise it in the paddock

Typically, waterlolgging can be easily observed on the soil surface, by the puddles as a result of perched watertables

o It is commonly associated with compaction, pugging, and sodic soils

Figure 2a – Waterlogging in the paddock. – Source: Soil Types and Structures Module, DEPI Victoria

Figure 2b – Waterlogging in the paddock. – Source: Soil Types and Structures Module, DEPI Victoria

The effects on plants include:o Reduced growth and yellowing or chlorosis of

older leaveso Damaged plant roots, resulting in restricted

water and nutrient uptake by the planto Chlorosis of older leaves is observed due to

poor root development and the consequential slow uptake of N by crop roots from the anaerobic soil

o Nitrogen deficiency symptoms (figure 3)

o Poor pasture utilisation by cattle

o The presence of weeds

Figure 3 – Loss of colour in older leaves of wheat indicating nitrogen deficiency. – Source: DAFWA

Figure 4 – Waterlogging can be detrimental to crop germination. – Source: Soil Types and Structures Module, DEPI Victoria

If surface waterlogging is not clearly evident, the best way to identify waterlogged problem areas:

o Dig holes about 40 cm deep in winter and see if water flows into them. If it does, the soil is waterlogged

o Digging holes for fence posts often reveals waterlogging

o Some farmers put slotted PVC pipe (piezometers) into augered holes. They can then monitor the water levels in their paddocks

Top of Page

Managing the problem

What is the best practice?

Proper installation and maintenance of surface drainage (including raised beds) is critical in minimising off-site impacts, especially where sediments and nutrients may enter waterways and threaten water quality 

1. Remove excess water (drainage options)

o Surface drainage – start with the perimeter

o Subsurface drainage

o Raised beds (cropping areas) - to reduce soil compaction and improve soil structure

2. Minimise compaction (non-drainage options)

o Controlled traffic flat beds (cropping areas) - to reduce soil compaction and improve soil structure

o Stock management - graze and spell (rotation) based on understanding of plant and soil needs

o Land class fencing

3. Improve water storage in profile

Top of Page

How can you achieve this?

1. Removal of excess water through drainage options

Surface and sub-surface drainage is commonly used to rehabilitate waterlogged land and improve soil structure

Currently, over 80% of dairy land has some form of surface drainage and up to 20% has sub-surface drainage (MacEwan 1998)

Questions to ask yourself when planning farm drainage: 

1. What is causing the waterlogging problem?2. Does this happen each year or is it only a problem in very wet years?3. Is there a sufficient outlet available?4. What are the likely benefits of draining this area?5. Which areas should be drained first?6. What type of drainage system is required?

- Surface drains- Subsurface drains

7. What are the non-drainage options?

Figure 5. - Humps and hollows in newly sown pasture. – Source: DEPI Victoria

8. Review the Water Act (1989)

Surface drainage - Is very useful in removing excess water from land in a controlled manner and as quickly as possible, to an artificial drainage system or a natural watercourse. This should be done with no damage to the environment. 

Types of surface drainage include: 

Ditches or open drains: 

o These vary in size and length and can be formed by spinner cuts or excavators

o Must be very wary of constructing open drains in dispersive soil as they are highly prone to erosion

Grassed Waterways: 

o These are usually shallow, varying in width from narrow to meters wide, but are constructed such that they are often grazed as part of the paddock

o They are sometimes used to bring drain outflows down slopes to prevent erosion without considerable expense

Humps and hollows (bedding): 

o Hump and hollowing is the practice of forming (usually while renovating pastures) the ground surface into parallel convex (humps) surfaces separated by hollows. The humped shape sheds excess moisture relatively quickly while the hollows act as shallow surface drains

o Humps and hollows are useful in areas or on soil types that are not suitable for tile or mole drainage

Figure 6 – Good water management. – Source: Soil Types and Structures Module DEPI, Victoria  [View larger image]  

Figure 7 – Poor water management. – Source: Soil Types and Structures Module DPI, Victoria  [View larger image]  

Subsurface drainage - Once you have taken care of the surface drainage, you may need to look at improving the drainage through the soil profile. Subsurface drainage aims to

Raised bed cropping: 

take away only the surplus water in the soil. Therefore, you need to know what the soil type is before any works start. 

Types of Subsurface drainage include: 

Mole Drains: 

o Mole drains are unlined channels formed in clay subsoil by pulling a ripper blade (or leg) with a cylindrical foot (or torpedo) attached on the bottom through the subsoil. A plug (or expander) is often used to help compact the channel wall. The foot is usually chisel pointed

o Mole drains are used in heavy soils where a clay subsoil near moling depth (400 to 600 cm) prevents downward movement of ground water. Mole drains do not drain groundwater but removes water as it enters from the ground surface

Figure 8 - Mole drains over a collector pipe system. – Source: Managing Wet Soils: Mole Drainage DEPI Victoria

Gravel mole ploughs: 

o Gravel mole ploughs incorporate a hopper to allow finely graded gravel to fall into the mole channel. These ploughs have been used successfully in the UK in heavy soils that cannot hold “normal” mole drains

o Experimental results from north east Victoria and Gippsland show they have promise on unstable clay soils, but are expensive because of the amount of gravel and close spacing needed. Unfortunately very few of these machines exist in southern Australia

o Over the past decade, extensive research efforts have been directed towards the factors that contribute to waterlogging and soil structure decline under broadacre cropping regimes. The biggest development has been with raised bed techniques, which currently cover about 10% of the annual crop area in the Corangamite region

o Raised beds aim to reduce machinery compaction by using controlled traffic and to reduce waterlogging by lifting the soil above the saturated zone. Where used, raised beds have significantly improved soil structure and reduced waterlogging on cropping land, while significantly increasing agricultural productivity in high rainfall areas

Case Study

Soil structure differences under raised beds in the Corangamite region

Figure 9 – Raised beds and a well planned grassed waterway. – Source: DEPI Victoria

The Water Act 

o The Water Act (1989) provides guidance for the management of waterways and swamps. Before considering draining a wet area you should contact your local Catchment Management Authority for advice, as a permit may be required

     2. Minimise compaction - non-drainage options 

Controlled Traffic o to reduce soil compaction and improve soil structure

Stock Management o Change land use (dedicate as a hay or silage paddock and graze only in summer, or remove from the grazing rotation)

o Remove stock as soon as pugging is imminent

o Allocate short grazing periods on restricted area to allow optimal feed intake prior to onset of pasture damage – use 'on-off' grazing   techniques:

This refers to removing cows from the pasture after a short period of grazing It has been identified as an effective method of reducing hoof compaction on broadacre grazing land as it

maintains good ground cover and higher organic carbon levels This practice is currently being adopted over 30% of broadacre grazing land in the Corangamite region

(MacEwan 1998)o Designate “sacrifice area” to which cows are moved in any wet weather

o Construct or designate “loafing area” (pad, laneway, barn or woodlot) to which stock can be moved in wet conditions

o Construct feed pad for all supplementary feeding in wet weather

We have had some flooding in vegetable crops due to heavy rains already this year and soils in some areas have remained waterlogged for extended periods. The majority of watermelons and other fresh market vegetables have been planted, peas are being harvested, lima bean planting has started and significant acres of pickles, snap beans, and sweet corn are in the field. Growers may be concerned.

Of course, low lying areas of fields are most affected by excess rainfall. However, cropping practices can also increase water ponding. Field compaction will reduce water infiltration and increase ponding. In plasticulture, water can accumulate and persist between rows of plastic mulch. Because much of the rainfall runs off of the plastic, water pooling can be more of a problem in plastic mulched fields, especially where row middles have become compacted. Vining crops that fruit into the row middles can have vines and fruits sitting in water and this produces an ideal environment for diseases of wet conditions such as Phytophthora capsici to infect plants.

When water overflows the bed tops of plastic mulched crops, whole beds become saturated as water enters the planting holes. This often leads to plant losses as beds take a long time to dry once saturated in this way and oxygen is very limited in the root zone.

To avoid water accumulation between beds, tilling with a deep shank or a subsoiler in row middles can help improve drainage. Cut drainage channels at row ends to reduce blockage that can back up water. Where practical, sectioning fields to go into plastic beds and installing cross drains to remove extra water can reduce water damage potential. Growers may also choose not to plant lower areas in the field prone to water damage where plastic is laid.

In flooded soils, the oxygen concentration drops to near zero within 24 hours because water replaces most of air in the soil pore space. Oxygen diffuses much more slowly in water filled pores than in open pores. Roots need oxygen to respire and have normal cell activity. When any remaining oxygen is used up by the roots in flooded or waterlogged soils, they will cease to function normally. Therefore, mineral nutrient uptake and water uptake are reduced or stopped in flooded conditions (plants will often wilt in flooded conditions because roots have shut down). There is also a buildup of ethylene in flooded soils; an excess of this plant hormone can cause leaf drop and premature senescence.

In general, if flooding or waterlogging lasts for less than 48 hours, most vegetable crops can recover. Longer periods will lead to high amounts of root death and lower chances of recovery.

While there has not been much research on flooding effects on vegetables, the following are some physiological effects that have been documented:

Oxygen starvation in root crops such as potatoes will lead to cell death in tubers and storage roots. This will appear as dark or discolored areas in the tubers or roots. In carrots and other crops where the tap root is harvested, the tap root will often die leading to the formation of unmarketable fibrous roots.

Lack of root function and movement of water and calcium in the plant will lead to calcium related disorders in plants; most notably you will have a higher incidence of blossom end rot in tomatoes, peppers, watermelons, and several other susceptible crops.

Leaching and denitrification losses of nitrogen and limited nitrogen uptake in flooded soils will lead to nitrogen deficiencies across most vegetable crops.

In bean crops, flooding or waterlogging has shown to decrease flower production and increase flower and young fruit abscission or abortion.

Ethylene buildup in saturated soil conditions can cause leaf drop, flower drop, fruit drop, or early plant decline in many vegetable crops.

Recovering from Flooding or WaterloggingThe most important thing that you can do to aid in vegetable crop recovery after floods or waterlogging is to open up the soil by cultivating (in crops that still small enough to be cultivated) as soon as you can get back into the field. This allows for oxygen to enter the soil more rapidly. To address nitrogen leaching, sidedress with 40-50 lbs of N where possible.

In fields that are still wet, consider foliar applications of nutrients. Since nitrogen is the key nutrient to supply, spraying with urea ammonium nitrate (28% N solution) alone can be helpful. These can be sprayed by aerial or ground application. Use 5 to 20 gallons of water per acre. The higher gallons per acre generally provide better coverage. As with all foliar applications, keep total salt concentrations to less than 3% solutions to avoid foliage burn. Research in on flooded vegetables in Florida showed the best response to foliar applications of potassium nitrate.