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
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
What is Soil pH?
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)
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%
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
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