Nutrition of Horticultural Crops

Monica Ozores-Hampton University of Florida/IFAS/SWFREC

Spring 2013

Essential Nutrients - List O MACRONUTRIENTS: O Nitrogen (NO3, NH4) O Phosphorus (P) O Potassium (K) O Calcium (Ca) O Magnesium (Mg) O Sulfur (S)

O “Free elements”: C, H, O

O MICRONUTRIENTS: O Boron (H2BO3

-) O Chlorine (Cl) O Copper (Cu) O Iron (Fe) O Manganese (Mn) O Molybdenum (MoO4

-) O Zinc (Zn)

Ca: chemistry background

O Calcium (Ca). Atomic weight: 40 O Between K and Sc (Scandium) in periodic chart O Main source: primary (apatite; silicates; sulfates) and secondary

(carbonates) minerals O 5th most abundant element on earth (O, Si, Al, Fe) O Clays typically have more Ca than sand O Form taken up: Ca++ (not subjected to redox reactions) O Ca-P and Ca-S have very low solubility (<2g/L)

CEC and BS values

O Target BS = 80% of CEC

O Target Ca: 70% BS O Target K: 20% BS O Target Mg: 10% BS

K+, Ca ++, Mg++ H+

0 20% 100%

Ca Uptake

O Ca moves in the soil by mass flow O Ca++ is taken up by the transpirational stream (passive) O Ca++ taken up is not chemically altered O Uptake occurs only at the root tip in which the cell wall

of the endodermis is still unsuberized O In the plant, Ca++ may remain in solution or

precipitated as oxalate O Ca moves in the xylem, but it is poorly relocated (low

level in phloem) O In the cell, high Ca++ concentration in apoplast,

vacuole, and mitochondria; lower in cytosol

Factors Affecting Ca Uptake

O Ca++ concentration in soil solution

O Moisture availability (and ETo)

O Architecture of root system

O Nematodes will reduce Ca uptake

Ca Essential Roles

O Structural function in the middle lamellae of cell walls (binds with free carboxyl groups of pectin); involved in cell elongation

O Detoxify by precipitating with oxalate, carbonate, sulfate or phosphate in the vacuole

O In cytoplasm, Ca-calmodulin complex is involved in the activation of several enzymes

O Loss of Ca++ is part of leaf abscision

Blossom-end rot (BER) in tomato caused by Ca deficiency

Names of Ca-related Disorders

Crop Disorder name Fruiting (tom, peppers, eggplants) BER

Celery Black heart

Lettuce, leafy vegetable, cabbage Tip burn

Apple Bitter pit

Mango Soft nose

Pear Cork spot

Cauliflower Whiptail

Ca in Fertility Programs O Lime (pre-plant) O Gypsum (when Ca needed, but pH adequate) O Calcium nitrate (injected) O Irrigation water (40 to 50 mg/L of Ca in FL ground water)

Common Calcium Sources

Calcium, Relative Material (%) neutralizing value*

Calcitic limestone 32 85-100 Dolomitic limestone 22 95-108 Basic slag 29 50-70 Gypsum 22 None Marl 24 50-90 Hydrated lime 46 120-135

Burned lime 60 150-175 *Based on pure calcium carbonate at 100% Note: Relative neutralizing value is used interchangeably here with calcium carbonate equivalent

Adequate Ca Range O Vegetables: 0.8% to 2% O Leafy vegetables: 1% to 3% O Trees:0.2% to 2% These broad ranges need to be fine-tuned based on production system

Soil pH and

Liming

What is Soil pH?

Acidity generally increases with

soil depth

Why Acid Soils Should Be Limed

O Increases CEC in variable charge soils

O Increases availability of several nutrients

O Supplies Ca and Mg to plants

O Improves symbiotic N fixation in legumes

O Improve crop yields

• Reduces Al and other metal toxicities

• Improves the physical condition of the soil

• Stimulates microbial activity in the soil

Soil Acidity Affects Plant Growth

OAluminum, Fe and Mn can reach toxic levels because of increased solubilities in acid soils

OReduced activity of organisms responsible for the breakdown (mineralization) of organic matter

Soil Acidity Affects Plant Growth

OThe performance of soil-applied herbicides can be adversely affected

OReduced activity of symbiotic N fixing bacteria OClay soils high in acidity are less highly

aggregated OAvailability of nutrients such as P, K and Mo is

reduced OTendency for K to leach is increased

How Lime Reduces Soil Acidity (I) O Carbonates, oxides, hydroxides: O CaCO3 (Lime), CaO, Ca(OH)2

O It is the CO3 or OH group that changes pH, not Ca or Mg:

O CaCO3 + H2O Ca++ +2 OH- + CO2

O 2 OH- + 2 H+ H2O O Liming source efficacy is represented by the

Calcium Carbonate Equivalence (CCE)

How Lime Reduces Soil Acidity (II) Ca2+ ions from aglime replace Al3+ at the exchange

sites. The Al3+ reacts with water releasing H+: O Al-CEC + Ca++ Al3+ + Ca-CEC O Al3+ + H2O Al (OH)2

+ + H+ OCarbonate ions (CO3

2-) from aglime react in the soil solution, creating excess OH- (hydroxyl) ions which combine with H+ ions forming water

OThe pH increases because the acidity source (H+) has been reduced

For best results, apply lime well ahead of planting to allow sufficient

time to neutralize soil acidity

Relative Neutralizing Values of Some Common Liming Materials

Relative Liming neutralizing material value, %

Calcium carbonate 100 Dolomitic lime 95-108 Calcitic lime 85-100 Baked oyster shells 80-90 Marl 50-90 Burned lime 150-175

Burned oyster shells 90-110 Hydrated lime 120-135 Basic slag 50-70 Wood ashes 40-80 Gypsum None By-products Variable

Relative Liming neutralizing material value*, %

*Relative neutralizing value is used interchangeably here with calcium carbonate equ

Particle Size Determines Lime Reactivity

0

20

40

60

80

100

4-8 8-20 20-50 50-100

Lim

e re

acte

d in

1 to

3 y

ears

, %

Finer particle size (logarithmic scale of mesh size)

Placement Another important factor

determining the effectiveness of lime

How Soil pH is Measured

O Electronic pH meters O More accurate method, used in

laboratory

• Indicator dyes – Used in field diagnosis to

determine pH

Lime requirement depends on soil pH and CEC.

The more clay and organic matter, the higher the buffering capacity and the more aglime needed

Soil Acidity

O pH = free acidity O Buffer pH = ‘latent’ pH O Lime requirement determined with a ‘buffer pH’ (most

common: SMP or Adams Evans) O Lime requirement based on texture (CEC), target pH, depth

to be treated, material used O Lime needed = Rate * fineness * purity O Ex: Lime needed = Rate * 80% * 90%

Calcareous soils usually have pH values

in the range of 7.3 to 8.4

Mg: chemistry background

O Magnesium (Mg). Atomic weight: 24 O Between Na and Al in periodic chart O Main source: ferromagnesian minerals (biotite, serpentine,

hornblend and olivine) and secondary clay minerals (chlorite and vermiculite) and carbonates (dolomite)

O Mg seldom associated with OM O Form taken up: Mg++

Some Facts about Soil Magnesium

O Held in exchangeable form by soil colloids O Present in soil solution O Most Mg deficiencies occur on coarse-

textured, acidic soils O Deficiencies on calcareous soils where

irrigation water contains high bicarbonates O Mg can be deficient on sodic soils

Mg uptake

OMg moves to the roots by mass flow OMg++ uptake is passive, possibly

mediated by ionophores OMg++ taken up is not chemically altered OMg++ is mobile in the xylem and phloem

Mg essential roles

OChlorophyll (15% to 20% of Mg in the plant)

OMg is co-factor of enzymes (kinases)

OStabilizes the tails of AXP

N

N N

N

Magnesium is the Central Atom in the Chlorophyll Molecule

Mg in Fertility Programs O Dolomitic lime (preplant) O MgSO4 (when Mg needed, but pH adequate) O Sul-Po-Mag (preplant)

Dolomitic limestone 3-12 (Mg carbonate) Magnesia (Mg oxide) 55-60 Basic slag 3 Magnesium sulfate 9-20 Potassium-magnesium sulfate 11 Magnesium chloride (solution) 7.5

Common Magnesium Sources

Material Magnesium (%)

Adequate Mg Range

OVegetables: 0.15% to 0.40%

OThis broad range needs to be fine-tuned based on production system