Slot drainage of clay soils under sugarcane in Cuba

SLOT DRAINAGE OF CLAY SOILS UNDER SUGARCANE IN CUBAy

LUCIANO VIDAL1*, PEDRO CAIRO2, PETER MENNING3, HERMANN KONKER3,NORBERTO ALONSO2 AND ARNALDO GUTIERREZ1

1Instituto de Investigaciones de la Cana de Azucar, Estacion Territorial de la Cana de Azucar, Ranchuelo, Villa Clara, Cuba2Centro de Investigaciones Agropecuarias. Facultad de Ciencias Agropecuarias. Universidad Central de las Villas. Santa Clara, Cuba

3Agrar- und Umweltwissenschaftliche Fakultat der Universitat Rostock, Rostock, Germany

ABSTRACT

To perform agricultural drainage of clay soils under sugarcane monoculture, a new kind of slot drainage was

developed. A special implement produces slots of approximately 6 cm width and 95 cm depth, which are filled with

crumbly soil substrate. After heavy rain, a large amount of water will be discharged very quickly through these

slots. Under the economic conditions of Cuba, slot drainage pays for itself within 3–5 years. Furthermore, time

periods of inhibited harvesting machine operation are cut short, enabling sugar factories to operate with fewer

interruptions. Copyright # 2006 John Wiley & Sons, Ltd.

key words: clay soils; drainage; land improvement; slot drainage; sugarcane

Received 4 April 2006; Revised 19 September 2006; Accepted 24 September 2006

RESUME

Pour parvenir a drainer les sols argileux sous monoculture de canne a sucre une nouvelle forme de drainage par

rigoles a ete developpee. Un outil special effectue des tranchees d’environ 6 cm de large et 95 cm de profondeur, qui

sont ensuite remplies de substrat en miettes. A la suite de fortes pluies, d’importants volumes d’eau peuvent etre

tres rapidement draines par ces rigoles. Dans les conditions economiques de Cuba, le drainage par rigoles s’amortit

en 3 a 5 ans. En outre, les temps morts pour les machines a recolter se trouvent reduits, permettant ainsi aux

sucreries de fonctionner avec moins d’interruptions. Copyright # 2006 John Wiley & Sons, Ltd.

mots cles: sols argileux; drainage; amelioration des terres; drainage par rigoles; canne a sucre

INTRODUCTION

In Cuba, the coastal lowlands are the main regions of sugarcane cultivation. At present, in these regions two-thirds

of the agricultural area is used for the cultivation of sugarcane as a monoculture.

The soils of these regions were formed on marine clay deposits and consist mainly of gley soils, which are

periodically waterlogged. To reduce waterlogged conditions, surface drainage (Carter, 1999; Spoor and

Leeds-Harrison, 1999) has been used until now. Unfortunately, the effect of surface drainage by using furrows is

insufficient. Because of the unevenness of the soil surface and the presence of large pores in the topsoil, 15–30 lm�2

water are retained after heavy rain (Vidal, 1990, 2001). This water can be removed only by evaporation.

To drain surplus water, a different method is needed that is applicable under the conditions in Cuba and that

creates more favourable conditions for the cultivation of sugarcane.

IRRIGATION AND DRAINAGE

Irrig. and Drain. 55: 511–521 (2006)

Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/ird.279

*Correspondence to: L. Vidal, Instituto de Investigaciones de la Cana de Azucar, Estacion Territorial de la Cana de Azucar, Ranchuelo, VillaClara, Cuba. E-mail: [email protected] par rigoles des sols de canne a sucre argileux a Cuba.

Copyright # 2006 John Wiley & Sons, Ltd.

SITE CONDITIONS

The experiments were carried out on the northern coastal lowland in the Villa Clara region. Here, soils developed in

the late glacial epoch on marine deposits with a high clay content. The majority of soils are mollic and eutric

gleysols. These soils may be characterized by specific properties as follows:

� High clay content (�60%), increasing with depth and predominantly consisting of smectite, which shows a high

plasticity index (Ip� 0.7 g g�1);

� Topsoil is of small thickness (Ap-horizon< 30 cm) and exhibits sharp-edged interfaces to the subsoil caused by

tillage;

� Subsoil is bleached by reduction and exhibits iron coatings on crack surfaces and slickensides (G-horizons).

Organic matter content is much lower than 1%;

� Cation exchange capacity is high. Acidity increases with depth (pH< 4.5);

� Topsoil exhibits polyedric structure; upper part of subsoil contains prisms, coherence getting stronger with

increasing depth;

� In spite of the low bulk density (dB¼ 0.9–1.1 g cm�3) and thus, high porosity (PV� 60 vol.%), soils show a

deficiency of large pores, especially in the upper parts of the subsoil. This is reflected by a low saturated hydraulic

conductivity (kf< 0.002m day�1) impeding the discharge of drainagewater, causing ponding of water on the soil

surface, and generation of perched groundwater tables.

After heavy rain, waterlogged conditions of topsoil prevail for up to 10 days during summer and up to 30 days

during winter. On average, soils are waterlogged for 30–40% of the total time. In wet years, this may increase to

70% (Garcia, 1985; Guillen, 1986). Waterlogged conditions hamper root growth and soil structure development in

the subsoil. Therefore, the water supply of sugarcane becomes restricted during dry periods. This will reduce the

growth of the sugarcane from May to October, delays its ripening, makes harvesting more difficult and impedes

agricultural machinery operation. Because of the waterlogged conditions, tillage operations on clayey gley soils

may be performed only during the dry period between January and April. Furthermore, wetness makes topsoil

aggregation worse and leads to an overall degradation of soil structure in these soils.

AGRICULTURAL DRAINAGE OF CLAYEY GLEY SOILS: STATE OF THE ART

Because of the small proportion of large pores and low subsoil hydraulic conductivity common techniques of

agricultural drainage, such as drainage by ditches or tile drainage, have turned out to be of limited success, even if

drainage spacing were very narrow.

In these clay soils, very narrow drain spacing associated with traditional mole and slot drainage is more effective

(Feichtinger, 1960; Feichtinger and Schleifer, 1962; Muller et al., 1989).

Slot drainage, which requires filling of the slots with material of high hydraulic conductivity, is much more

expensive than mole drainage. For that reason we first tried to apply mole drainage on the field of the Sagua

experimental station (Villa Clara district) and worked with a special gadget designed by Muller and Schindler

(1989). In spite of yielding good results on heavy soils in Germany, the method failed to give expected results in

Cuba. Investigations have shown that the expander of that plough pressed soil material into the lower part of the

slot. This impeded perched water from entering the mole drain. Furthermore, mole drains disappeared very quickly

because of soil swelling.

Interestingly, we observed that the slots generated by the leg were partially filled with dry aggregated topsoil

material. Most of the slots contained such material filling the middle section of the slots. There were many slots

filled up to the topsoil. All slots showed a hydraulic connection between topsoil and mole channel. Perched water

from the soil surface entered the slots and moved laterally (Bloch, 1990).

Based on these observations, the idea of a special slot drainage technique was developed, which may be

characterized by complete filling of the slots with aggregated and crumbly topsoil substrate.

Copyright # 2006 John Wiley & Sons, Ltd. Irrig. and Drain. 55: 511–521 (2006)

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512 L. VIDAL ET AL.

DEVELOPMENT OF SLOT DRAINAGE

Development of a device

To design the equipment necessary to produce drainage slots, we followed the design of a mole drainage plough

(Figure 1). It produces a slot of 60mm width by a chisel tine. Near the lower part the slot is widened to 100mm.

The chisel tine andwheels (Figure 2 (1) and (2)) are adjustable in such away that the slot depth may vary between 55

and 95 cm. An expander that widens slots (Figure 2 (3)) is installed immediately behind the leg. Up to a depth of 15 cm,

it forms funnel-shaped slots of 25 cm width. Larger aggregates are pushed away. Behind that device a moulder is fixed

(Figure 2 (4)). It pushes a surplus of aggregated topsoil material into the slot forming a soil roller on the surface like a

ridge plough. Behind the moulder a plough blade (Figure 2 (5)) is fixed to prepare a furrow where sugarcane seedlings

may be planted. The entire device was tested on the terrain of the Sagua experimental station (Villa Clara region).

Effect of soil moisture conditions on performance of drainage slots

We observed a close relationship between slot performance and soil water content affecting soil consistency.

Stiff-plastic subsoil conditions corresponding to a soil water content between (WPþ 0.1IP)1 and (Wpþ 0.2Ip) turned

out to be best suited to produce drainage slots (Figure 3).

In the subsoil under investigation, this so-called optimum range of soil water content corresponds to a

gravimetric water content of 0.46–0.52 g water per gram soil, thus being smaller than field capacity. Under this

condition, slots are well formed and filled with topsoil material that is at that time in general rather dry and crumbly.

In general, favourable conditions like these prevail only during the dry season.

Figure 1. Implement for slot drainage (units: mm)

1(Ip¼ index of plasticity¼WL�WP, (WL denotes the Atterberg liquid limit, estimated by the Casagrande device, see Kezdi, 1969.)


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SLOT DRAINAGE OF CLAY SOILS 513

If the subsoil water content is even lower (W< (WPþ 0.1IP)), slots will not run in a straight line anymore and cannot

be filled easily with topsoil material. This leads to more soil swelling during rewetting and partial closing of slots.

In soil of higher water content (W> (WPþ 0.2IP)) the mole channel is squeezed by the weight of surrounding soil

immediately after its formation. This becomes more pronounced by traffic on the soil surface, e.g. by driving the

mole plough to establish the adjacent mole drain.

To obtain slots and mole drains of sufficient quality, the topsoil between 5 and 15 cm depth should be dried as far

as necessary to become crumbly and free flowing. In most cases this condition will be met when the subsoil is in a

suitable condition. However, after rain events during the dry season this might be different. Slots filled with topsoil

material are permeable, enabling perched water to flow easily to the ditch.

EFFICACY OF SLOT DRAINAGE

Under conditions similar to agricultural practice, the efficacy of slot drainage was examined in the Sagua

experimental station on an area of 7.7 ha (Figure 4 and Table I).

Figure 2. Plough for mole slot drainage-construction plan

Figure 3. Favourable soil moisture range for mole slot drainage (numerical values valid for Sagua)


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514 L. VIDAL ET AL.

Both of the layouts A and C contained 1.6m spaced slot mole channels of 0.75m depth. The spacing corresponds

to the lateral distance between sugarcane rows. Slot mole channels opened out on both ends into a collector

drainage pipe trench running across and filled with permeable material. The collector drainage pipes consisted of

perforated PVC pipes of 125mm diameter. The spacing interval of these pipes was 60m (layout A) or 120m (layout

C), respectively. Collector drain trenches were filled with flint chipping up to the topsoil.

Lots B and D, containing no artificial drainage, were located immediately adjacent to lots A and B. The entire

area was equipped with furrows to provide surface drainage as commonly done in Cuba. Because the conditions of

the experiment did not allow for carrying out replications, it was impossible to apply ANOVA (Analysis of

variance, Dougherty, 1990, p. 520). Since soils of the experimental station are very homogeneous and there are no

deviations of the remaining site conditions from their typical characteristics, it may be permitted to regard results as

being representative.

Forming of drain slots

One year after establishing the experimental set-up 12 slot mole channels were investigated. All of them looked

very similar. Figure 5 shows representative cross-sections of slot mole channels.

Figure 4. Position sketch of the experimental area in Sagua

Table I. Test areas in the Sagua experimental arrangement

Test plot Length (m) Width (m) Area (m2) Distance to seepage collectors (m)

A 245 80 19 600 60B 245 77 18 865 Without seepage collectorC 245 80 19 600 120D 245 77 18 865 Without seepage collector

Notes: Test areas A and C with slot drainage: depth 75 cm beneath sugarcane row (spacing 1.6m).Seepage collector: chipping Ø 9–13mm, PVC tube Ø 125mm (test area A und C only, see Figure 4).Each test area equipped with surface drainage and furrrow irrigation.


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The different shape of the slots is due to the heterogeneity of soil moisture and thus, consistency conditions at the

time of their manufacturing. To a large extent, all of the slots were backfilled with topsoil material. Three of the

slots were backfilled up to the crumb. The remaining slots were backfilled up to 40 cm depth. Two slots were filled

up only to a larger depth. In spite of this incomplete backfilling, the hydraulic connection between topsoil and lower

part of the slot was obvious. In most cases, the backfilling of the slots was 42–45mm wide. The backfilling was not

consolidated but incoherent, porous and, therefore, highly water permeable.

Drainage effect

Drain discharge. To assess the effect of slot drainage, drain discharge of both of the layouts was measured

continuously. To achieve this, all of the slots of one layout were connected to one outlet and flow rates were

measured bymeans of a Thompson weir. Because only oneweir was available, measurements of both layouts had to

be carried out one after another. For that reason results are only conditionally comparable with one another

(Table II).

It can be seen that—dependent on the distance between slot drain and collector as well as on initial soil moisture—

a major part of precipitation during the measuring period discharged. As expected, layout A with 60m spaced

collectors yielded higher discharge (27% of precipitation) than layout C with a collector spacing of 120m (22% of

precipitation). Longer flow paths in layout C delayed the discharge, made drainage slower, and lowered peak flow

rates.

Figure 5. Drainage slots in the experimental area in Sagua 12 months after making

Table II. Discharge capacity of slot drains

Slot drainage layout

A C

Number of precipitation occurrences 14 10Total precipitation N, mm 392 350Precipitation amount per occurrence 9 . . . 52 9 . . . 73Total discharge A, mm 105 78Discharge ratio A/N 0.27 0.22Length of discharge time, h 546 580Length of discharge time per precipitation occurrence, h 6 . . . 109 6 . . . 109Average discharge rate, mmh� 0.30 0.11Peak discharge rate, mmh�1 7.1 2.6


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516 L. VIDAL ET AL.

Discharge of perched water. To observe the effect of slot drains on perched groundwater in the topsoil,

groundwater observation tubes were installed close to the slot drains. They extended 8–10 cm into the subsoil. The

lowest 15 cm of the tubes were perforated. The groundwater table was measured regularly during periods of

perched water. Results show that the drawdown of the slot-drained groundwater table was much faster than that of

lots without artificial drainage (Figures 6–8).

The major portion of perched groundwater was discharged speedily from topsoil. The time it takes to lower the

perched groundwater table beneath 40 cm depth is highly dependent on the length of the flow path inside the slot

drain and, therefore, on the spacing of collectors. With a collector spacing of 60m the duration of soil wetness

compared to lots without drainage is reduced to less than 50%. A collector spacing of 120m yields a wetness time

reduction of 30%.

Effects of slot drainage on soil

Soil density. Using either a g-radiation device or soil cores, soil bulk density was measured twice, namely 22

and 60 months after making the drainage slots (Table III).

In spite of increased soil dryness and thus, pronounced soil shrinkage, topsoil bulk density was lower in

slot-drained plots than in plots without slot drainage. We observed values of bulk density and porosity very similar

Figure 6. Depth to perched groundwater table beneath soil dam surface, experimental plot AHydrograph over 6 days after 100mm rain. Spacingof collectors 60m, depth of observation tube beneath soil dam 40 cm

Figure 7. Depth to perched groundwater table beneath soil dam surface, experimental plot C Hydrograph over 6 days after 100mm rain. Spacingof collectors 120m, depth of observation tube beneath soil dam 40 cm


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to those values which prevailed in that region before initiation of mechanized sugarcane monocropping (Bennet and

Allison, 1966). Sixty months after establishment of slot drainage, bulk density all over the place had returned to

higher values again because of the burden exerted by heavy machinery. In contrast to these findings, 30 cm beside

slots the soil was loosened and more porous than without slot drainage. Even looser was the filling of slots. For that

reason perched groundwater could percolate easily and the aeration of topsoil and of subsoil as well was favourable.

One year after establishing slot drainage beneficial effects on soil were observed. The soil got dryer and vertical

fissures of 60 cm depth were present. The interface between topsoil and subsoil lost its former colour, which had

been due to reduction conditions.

Figure 8. Hydrograph after 100mm rain at time¼ 0, Mean values of all field observation tubes. Depth of observation tube beneath soil dam40 cm

Table III. Influence of slot drainage on bulk density and porosity in the Sagua experimental arrangement

(a) 22 months after construction of slot drainage (measurement by TROXLER 3440 gamma ray gauge, approx. 30 cm next todrainage slot)

Depth (cm) Bulk density (g cm�3) Volumetric water content (%) Volumetric air content (%)

SD� No SD SD No SD SD No SD

0–10 0.99 1.03 43.9 47.2 20.4 14.910–20 1.10 1.12 41.9 46.6 18.4 12.220–30 1.12 1.16 43.5 47.2 14.4 9.00–30 1.07 1.10 43.2 47.0 17.6 12.3

(b) 5 years after construction of slot drainage (measurements on soil cores)

Depth (cm) With slot drainage Without slot drainage

Inside drainage slot 30 cm next to drainage slot Bd (g cm�3) wV (%) LV (%)

Bd1 (g cm�3) wV

2 (%) LV3 (%) Bd (g cm

�3) wV (%) LV (%)

0–20 1.01 52.6 10.9 1.09 54.3 6.3 1.05 60.9 0.520–40 0.98 59.4 3.8 1.02 59.1 2.6 1.07 59.5 0.140–60 0.99 60.7 4.6 1.04 59.6 3.9 1.09 61.8 0.060–80 1.04 59.3 4.0 1.05 60.8 2.1 1.11 60.8 0.0X0–80 1.01 58.0 5.7 1.05 58.5 3.8 1.08 60.8 0.1

�SD¼ slot drainage.1Bulk density.2Volumetric water content.3Volumetric air content.


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518 L. VIDAL ET AL.

Effect of slot drainage on growth and crop yield of sugarcane

Shortly ahead of the first harvest, the proliferation of sugarcane roots was investigated 20 months after planting.

Six pits were excavated crossways to crop rows on plots with and without slot drainage, and 96 soil samples were

taken from points at up to 80 cm depth containing 32 dm3 volume each (Figure 9).

We obtained the following results.

Plots not treated with slot drainage.� High root density in topsoil. About 85% of total root mass was found in shallow soil up to 30 cm depth;

� More than 40% of total root mass was present in soil up to 10 cm depth;

� Little root penetration into subsoil;

� Maximum root depth 60 cm.

Plots treated with slot drainage.� Increase of total root mass by 16%, approximately;

� Maximum root density between 10 and 20 cm depth;

� Root mass in subsoil was doubled compared to plots not treated with slot drainage;

� Maximum root depth 80 cm.

In these clayey gley soils, slot drainage contributes to making subsoil accessible to deeper and more intensive

root penetration. In this way, water supply to the crop during dry periods is greatly improved. During the field

experiment, which took 4 years, we observed better growth of seedlings. Later, seedlings showed more and taller

sprouts. In the average of three harvests, sugar yield increased by about 11 t ha�1 (approximately 35%) compared to

plots having no drainage system (Table IV).

Figure 9. Effect of the slot drainage on root development of sugarcane


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CONCLUSIONS

Using a newly developed plough-like appliance in a tropical clayey gley soil, we were able to establish highly

permeable slots of 75 cm depth filled with in situ topsoil substrate. Slots were able to drain perched groundwater

occurring periodically and to discharge that water into collectors running crossways. The collectors consist of a

drainage pipe trench that was filled with permeable material. The collector drain pipes consisted of perforated PVC

pipes. Collectors, which were spaced at intervals of 60m, enabled the system to reduce wetness time by 50%;

spacing at intervals of 120m would reduce wetness time by about 30%. Speedier drying of waterlogged topsoil by

slot drainage shortens the interruptions of harvesting operations and hence, the idle time of sugar refineries due to

waterlogged conditions.

Deeper and more intense drying of soil causes an improvement of soil structure, which can be observed in terms

of increased porosity in topsoil and in subsoil as well. Even 5 years after their making, we observed within drainage

slots considerably lower bulk density and a significantly increased fraction of large pores. This enabled roots to

proliferate up to a depth of 75 cm, yielding a substantial increase of root mass in subsoil. This would improve crop

water supply during dry weather periods. Filling topsoil material into subsoil and generation of deeper shrinkage

fissures because of speedier drying initialises the development of clay soils towards vertisols.

Compared to mere surface drainage, slot drainage increased sugar yield by 35%. Under the economic conditions

prevailing in Cuba, the costs of slot drainage including collectors are paid by the surplus yield of a single cultivation

period. Furthermore, soil mechanical conditions improved by slot drainage make employment of machinery more

effective. After one period of cultivation–that is after 6–8 years–slot drainage has to be rebuilt and new seedlings

planted. Because collectors may be usable further on, this subsequent slot drainage is muchmore cost-effective than

the first one.

Especially with cultivation of sugarcane, slot mole drainage with slots filled by aggregated topsoil material is an

effective method of improving soil physical conditions of waterlogged tropical clay soils.

REFERENCES

Bennet HH, Allison RV. 1966. The Soils of Cuba Tropical Plants Foundation. Washington (1928), (Los suelos de Cuba y algunos nuevos suelos).

Edicion Revolucionaria: La Habana, Cuba; 410 pp.

Table IV. Sugarcane development and sugarcane yields in the experimental field of Sagua

Test statistic Monthsafter planting

Options Fraction (%)(with/without slot drainage)

Without slotdrainage

With slotdrainage

Development of seedlingsThriving seedlings (% of all plants) 2 84 92 110Height, cm 4 139 148 106Number per metre length 4.9 6.7 137Height, cm 6 198 222 112Number of seedlings, m�1 6.7 7.7 115Sugarcane yield (t ha�1)1st harvest 23 108.3 144.4 1332nd harvest 35 56.2 76.4 1363rd harvest 48 49.8 65.1 131Total 214.3 285.9 133Sugar yield (t ha�1)1st harvest 23 15.2 20.8 1372nd harvest 35 7.8 10.8 1383rd harvest 48 6.9 9.1 132Total 29.9 40.7 136


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520 L. VIDAL ET AL.

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Rostock, Rostock, Germany, 88 pp.

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Spoor G, Leeds-Harrison PB. 1999. Nature of heavy soils and potential drainage problems. In Agricultural Drainage, Skaggs RW, Schilfgaarde

Jvan (eds). American Society of Agronomy Monograph 38: Madison, Wisconsin, USA; 1328.

Vidal L. 1990. El denaje con topos en los suelos pesados del norte de Villa Clara. II Conferencia Cientıfica de la Universidad de Ciego de Avila,

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Slot drainage of clay soils under sugarcane in Cuba

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