Soil health and fertility
Two statements:
“tillage reduces soil productivity”
“conservation agriculture benefits the soil”
Conventional tillageAdvantages
Machinery is presentIncorporates fertilizersNeeds less managementSuppresses weedsEliminates soil compaction
Disadvantages
Uses more fuelNeeds more labourNeeds more tractorsProvokes more compactionCauses more erosion
Conservation AgricultureAdvantages
Conserves soil humidityUses less fuelRequires less timeNeeds less machineryProvokes less compactionSaves money
Disadvantages
Difficult in clayey soil with bad drainageRequires specialized equipmentRequires high management levelPossibly increases pests in monocrop
Crop yield Soil productivity
Following factors need to be in optimum condition:
Water retention capacitySoil densitySoil porosityCompactionHealth
Main objectives to conserve soil
To reduce soil lossIncrease natural fertilityImprove soil structureLeave the soil in same or improved condition to next generations
Soil basics
m
m
m
m
m
m
Soilparticle
Microbes
Space forH2O & air
m
m
m
m
Humicacid
m
m
Polysaccharides
Soil problems that occur in conventional systems
CompactionSurface crustingErosionLow water holding capacity
All are caused through a reduction in soil organic matter
Effects of conservation agriculture on soil properties
Biological properties: organic matter, macro and micro-organisms
Physical properties: water, temperature, porosity, density
Chemical properties: nutrients and acidity
Carbon cycleCrop
residues
Humus
Immobilization
Proteins andpolysaccharides
Mineralization
Nutrients
Crop
Soilstructure
Microorganismsand soil biota
CO2 + H2O
Decomposition
Soil tillage activities
Organic matter
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Organic matter content (%)
Soil depth (cm)
Micro-organisms
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Harvest Sowing Flowering Harvest Sowing Flowering Harvest
Numb
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Root nodule bacteria
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S/W/M S/W M/W S/W/M S/W M/W
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lation
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Mycorrhizal fungi
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Nutrient concentration through insect activity
Soil depth(cm)
Organicmatter (%)
pH Al (me/100g) Ca(me/100g)
Mg(me/100g)
P(ppm)
K(ppm)
0- 5 5.8 5.1 0.18 5.7 2.2 8.9 >2005-10 3.8 5.2 0.17 5.5 2.0 8.5 164
10-15 3.3 4.9 0.49 2.2 1.2 1.4 16215-20 2.7 4.8 0.51 1.2 0.7 1.2 10420-25 2.4 4.8 0.48 1.0 0.7 0.7 8425-30 2.2 4.8 0.43 1.0 0.6 0.5 66
Bothynus sp.chambers
>9.4 5.3 0.17 9.3 3.7 7.6 >200
Physical properties
Aggregate stabilityBulk density and macroporesWater infiltrationWater storageTemperature
Higher aggregate stability
Mulch layer protects the soil against impact of raindropsNo soil disturbanceOrganic matter induces aggregationIncreased soil densityHigher concentration of calcium and magnesium
Bulk density and macroporosity
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Bulk density (g/cm3)��
Macroporosity (% )
Water infiltration
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20
40
60
80
100
120
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1 2 3 4 5 6 7Time (hours)
Rainw
ater in
filtra
tion (
mm)
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Water storage
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Soil temperature
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Time of the day (hours)
Soil t
empe
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Chemical properties
Ability of the soil to exchange nutrientsAddition of plant nutrientsIncrease in organic matter
Soil acidity - pH
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Soil depth (cm )
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Phosphorus content
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Conventional tillageoats/maize
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Calcium and magnesium levels
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il)
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Soil fertility management
Is different in CA systems, because reduction of land preparation may lead to:
accumulation of immobile nutrients reduction of mineralization of nitrogendecomposition of residues may lead to immobilization of nitrogensuperficial application of ammonia fertilizers can acidify the soil surface
Accumulation of immobile nutrients
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Soil depth (cm)
Nutrie
nt co
ntent
(mg k
g-1 so
il)
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Practices to avoid accumulation of nutrients in surface layers
Start with correct nutrient levelsApply part of the fertilizer in bandsAssess nutrient levels at different soil depthsGuard nutrient levels during first 2-3 yearsKeep surface homogeneously covered with residues
Nitrogen management
Three factors can hinder the availability of nitrogen for plants:
immobilizationmineralizationvolatilization
Practices to avoid lack of nitrogen for plant growth
Allow some time for organic matter to be decomposed before sowingApplication of N-fertilizer before sowingApply N-fertilizer as band placement during sowingUse nitrate fertilizers, because they dissolve easier
Acidification of soil surface through ammonium fertilizers
Acid formation
NH4
NO2-
Immobilization
Mineralization
Nitrification
O2
Nitrification
H+ + H2O
NO3-
O2
Ammonium fertilizer
Absorbed bycrops
Lime applicationUsually lime is incorporated into the soil
In CA this is not possible and thus lime is broadcast over the soil coverCover releases organic acids that bring lime to deeper soil layers