soil health and fertility - food and agriculture · pdf filemain objectives to conserve soil...

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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3-13

13-26

26-52

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Conventional tillage

Organic matter content (%)

Soil depth (cm)

Micro-organisms

0

10

20

30

40

Harvest Sowing Flowering Harvest Sowing Flowering Harvest

Numb

er of

P di

ssolv

ing ba

cteria

(*10

5 ) Conventional tillageConservation agriculture

Root nodule bacteria

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10

20

30

40

50

60

S/W/M S/W M/W S/W/M S/W M/W

Popu

lation

size

Bra

dyrh

izobiu

m (#

cells

*100

)

Conventional tillage Conservation agriculture

Mycorrhizal fungi

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10

20

30

40

50

60

70

Naturalvegetation

Conventionaltillage (1 year)

Conservationagriculture(10 years)

Conservationagriculture(20 years)

Aver

age r

oot c

oloniz

ation

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Maize

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Soya

Earthworm activity

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200

400

600

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1000

1200

10 20 30 40 50Soil depth (cm)

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er of

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worm

burro

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r m3

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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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14

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Bulk density (g/cm3)��

Macroporosity (% )

Water infiltration

0

20

40

60

80

100

120

140

1 2 3 4 5 6 7Time (hours)

Rainw

ater in

filtra

tion (

mm)

ForestNatural grass vegetationConventional tillageConservation agriculture

Water storage

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10

20

30

0-7.5 7.5-15 15-30Soil depth (CM)

Wate

r con

tent o

f the s

oil (%

)

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Conserv ation agriculture

Soil temperature

20

30

40

50

60

1 3 5 7 9 11 13 15 17 19 21 23

Time of the day (hours)

Soil t

empe

ratur

e ( o C)

With cov er

Without cov er

Chemical properties

Ability of the soil to exchange nutrientsAddition of plant nutrientsIncrease in organic matter

Soil acidity - pH

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4.5

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Soil depth (cm )

pH

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Phosphorus content

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20

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100

120

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Soil depth (cm)

P co

ntent

(mg k

g-1)

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Conventional tillageoats/maize

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oats/maize

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Calcium and magnesium levels

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Soil depth (cm)

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ble C

a+Mg

(cmo

l kg-1 so

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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50

100

150

200

250

300

0-7.6 7.6-15.2 15.2-22.9 22.9-30.5

Soil depth (cm)

Nutrie

nt co

ntent

(mg k

g-1 so

il)

��P - Plough

��P - Direct seeding

��K - Plough��

K - Direct seeding

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

soil health and fertility - food and agriculture · pdf filemain objectives to conserve soil...

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