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The Role and Importance of Residues The Role and Importance of Residues in Conservation Agriculturein Conservation Agriculture
Conservation AgricultureConservation Agriculture Training Course, Zimbabwe 2010 Training Course, Zimbabwe 2010
by Christian Thierfelder
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Minimum soil movement Minimum soil movement
Residue retentionResidue retention
Crop rotations and Crop rotations and GMCCsGMCCs
Basic principles of Conservation Basic principles of Conservation AgricultureAgriculture
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Residues – what are we talking about?Residues – what are we talking about?
Maize stover Maize stover covering a field covering a field before plantingbefore planting
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What are residues? What are residues? continued…. continued….
Maize residues in Maize residues in maize-cotton maize-cotton rotationrotation
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Sunnhemp Sunnhemp residues (left)residues (left)
Cotton Cotton residues (right)residues (right)
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How to manage residues - rolled maize stalks or How to manage residues - rolled maize stalks or sunnhemp sunnhemp
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The challenge – burning of stoverThe challenge – burning of stover
CIMMYT Research StationCIMMYT Research Station
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Competing uses for stover residues…!Competing uses for stover residues…!
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Water erosionWater erosion
Water infiltrationWater infiltration
Evaporation Evaporation
Soil temperatureSoil temperature
Weed controlWeed control
Soil organic matterSoil organic matter
Soil biological activitySoil biological activity
The Role and Importance of Residues in CAThe Role and Importance of Residues in CA
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Impact of raindrop on different soil Impact of raindrop on different soil surfacessurfaces
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Crusting and sealing leads to rill erosionCrusting and sealing leads to rill erosion
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Amount of soil being eroded after 7 years Amount of soil being eroded after 7 years of bare fallow of bare fallow (plot size 224 m²)(plot size 224 m²)
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Treatment Erosion in t ha -1 Runoff l m -2 Conventional ploughing (CP) 11.99 a 545.1 a Direct seeding (DS) 8.01 b 383.9 b Magoye ripper + M. pruriens intercropping (MR) 6.91 b 314.7 b LSD (p ≤ 0.05) 3.50 75.7
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About 50% of rainfall is lost on About 50% of rainfall is lost on conventional systemsconventional systems
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20 40 60 80
20
40
60
80100
2
4
6
8
Cover %
RelativeErosion %
Residue t/ha
Erenstein, 1997.Erenstein, 1997.Based on data of Shaxon et al., 1989, Based on data of Shaxon et al., 1989, Tripp and Tripp and BBarreto, 1993, and Kok and Thien, 1994.arreto, 1993, and Kok and Thien, 1994.
RelationshipRelationship between residue amount, between residue amount, ground cover and water erosionground cover and water erosion
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The soil needs to be permeable (no crusts)The soil needs to be permeable (no crusts)
The soil has to have pores (earthworms)The soil has to have pores (earthworms)
CA plots covered with residues provide for CA plots covered with residues provide for soil micoorganisms, build stable aggregates soil micoorganisms, build stable aggregates (natural swelling and shrinking) and increase (natural swelling and shrinking) and increase the organic matter which all improve the organic matter which all improve infiltrationinfiltration
Why soil erosion? Because water is not Why soil erosion? Because water is not infiltrating!infiltrating!
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Pore system has to be unsealed and easy to Pore system has to be unsealed and easy to moisten to enable infiltrationmoisten to enable infiltration
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Time to Pond – On-farm ResultsTime to Pond – On-farm Results
Conventional 6.26 b 6.60 bRip-line seed 11.50 a 11.50 aDirect Seed 11.99 a 10.88 aCV% 22.7 23.9SE Diff 1.30 1.24
Shamva Zimuto
C I M M Y TMRInternational Maize and Wheat Improvement Center
Infiltration rate (in l m-2) over time measured by a mini-rainsimulator, Henderson Research Station, Zimbabwe, 2005/2006
Time (min)
0 5 10 15 20 25 30 35 40 45 50 55 60 65
Infil
trat
ion
(in l
m2 )
20
30
40
50
60
70
80
90
100
Conventional Practice (CP)
Direct seeding (DS)Magoye Ripper + Mucuna pruriens (MR)
Cumulative infiltration over time measured by a mini-rainsimulator, Monze, FTC, Zambia, February 2006
Time (min)
0 5 10 15 20 25 30 35 40 45 50 55 60 65In
filtr
atio
n m
m h
-10
20
40
60
80
100
120
Conventional Ploughing (CP)Direct seeding (DS)Basins Planting (BS)
Infiltration is reduced on conventional Infiltration is reduced on conventional systemssystems
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Effects of mulch rate on soil water conservation during Effects of mulch rate on soil water conservation during fallow and on subsequent sorghum grain yield, Texasfallow and on subsequent sorghum grain yield, Texas
Source: Unger 1978Source: Unger 1978
Mulch rate, t ha- 1 Precipitation storage , mm Sorghum yield, t ha - 1 0 72 c 1. 8 c 1 99 b 2.4 b 2 100 b 2.6 b 4 116 b 3.0 b 8 139 a 3.7 a
12 147 a 4.0 a
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Mulch protects the soil from drying out!Mulch protects the soil from drying out!
Residues reduce radiation energy of the sun - less Residues reduce radiation energy of the sun - less radiation => less evaporationradiation => less evaporation
Drying forces of the wind are lowerDrying forces of the wind are lower
Vapour flux from the soil into the air is reducedVapour flux from the soil into the air is reduced
Capillary uptake in the soil maintains moisture Capillary uptake in the soil maintains moisture transportation from the subsoil to the soil surface transportation from the subsoil to the soil surface
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Comparison between capillar uptake in Comparison between capillar uptake in conventional and residue covered soilsconventional and residue covered soils
Conventional:Conventional: Radiation is high at the soil Radiation is high at the soil surface (less cover), surface (less cover),
capillary capillary uptake generally is uptake generally is not not sufficient sufficient from the subsoil. The from the subsoil. The consequence is drying out of the consequence is drying out of the upper layersupper layers
Residue covered:Residue covered: Radiation is lower, capillary Radiation is lower, capillary uptake can be maintained. uptake can be maintained.
Soils supply more Soils supply more moisture for moisture for germination and germination and plant growth.plant growth.
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Effect of Crop Residues on Soil Temperature Effect of Crop Residues on Soil Temperature (10 cm Depth)(10 cm Depth)
Bare soil
Days in August 1973
Tem
pera
ture
(°C
)
Source : Lal, 1978
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Effects of different residues on weed soil cover (in %) and Effects of different residues on weed soil cover (in %) and weed population (plants/mweed population (plants/m22) 7 and 58 day after roling) 7 and 58 day after roling
Source: Almeida and Rodríguez, 1985Source: Almeida and Rodríguez, 1985
2219
9
0 0
7
27
56
0
10
20
30
40
50
60
70
Mulch material
Wee
d co
ver (
%)
7 Days
139
5 26
31
83
6
0
10
20
30
40
50
60
70
80
90
100
Mulch materialW
eed
popu
latio
n (p
lant
s/m
2 )
58 days
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Residues build up the humus in the Residues build up the humus in the soilsoil
„„TheThe organic organic matter in matter in tropical soils is, tropical soils is, besides besides moisture, more moisture, more important than important than any other soil any other soil characteristic“ characteristic“ Young, 1976Young, 1976
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Residues increase organic carbon content over timeResidues increase organic carbon content over time
Plant available phosphorus, potassium, calcium and Plant available phosphorus, potassium, calcium and magnesium increases have been reportedmagnesium increases have been reported
Residues may lead to nitrogen lock-up initially Residues may lead to nitrogen lock-up initially especially when soils are very limited in nitrogen especially when soils are very limited in nitrogen (microbes use the nitrogen for their biomass)(microbes use the nitrogen for their biomass)
After some years the system is in equilibrium, N After some years the system is in equilibrium, N immobilization will no longer negatively effect nutrient immobilization will no longer negatively effect nutrient availabilityavailability
Effects of residues on nutrient availabilityEffects of residues on nutrient availability
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Decomposition in tropical climateDecomposition in tropical climate
Surface effects (protection, temperature, moisture Surface effects (protection, temperature, moisture retention, fodder for soil fauna and flora)retention, fodder for soil fauna and flora)
Slow nutrient release Slow nutrient release
Build-up of organic matter poolBuild-up of organic matter pool
Why is surface residue retention important? Why is surface residue retention important?
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40%
32%Microbial
DecompositionAsh
CO2
CO2
Soil OM 8%
Crop Residue
CO2 92%60%
Burn
Soil OM
Crop Residue
Microbial Decomposition
CO2 80%
20%
No Burn
Source: Albrecht et al., 1994 USDA-ARS Pendleton, OR
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Residues encourage earthworm Residues encourage earthworm activityactivity
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Effective destruction by ants and termites, fungi Effective destruction by ants and termites, fungi and bacteriaand bacteria
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Lignin contentLignin content C:N ratioC:N ratio Microbial preferences (maize/sunflower)Microbial preferences (maize/sunflower) Microbial variability (clay soils)Microbial variability (clay soils) Soil moisture contentSoil moisture content TemperatureTemperature pH pH
Factors influencing decompositionFactors influencing decomposition
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Effect of residue addition on biological activity (% increase in biological activity over control)
Day Wheat straw burned stubbles 1 80 29
4 61 9
7 47 0
10 28 0
Source: Albrecht et al., 1994 USDA-ARS Pendleton, OR
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Problems and challenges with residues Problems and challenges with residues (pests and diseases carry over)(pests and diseases carry over)
Perithecia of Perithecia of Pyrenophora Pyrenophora trichostoma trichostoma ((Helminthosporium tritici-Helminthosporium tritici-repentisrepentis) on wheat straw) on wheat straw
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Residues increase micro-, meso,- and macro-fauna Residues increase micro-, meso,- and macro-fauna thus facilitating a biological equilibriumthus facilitating a biological equilibrium
If a system is in If a system is in equilibrium, insects equilibrium, insects and pests are and pests are controlled by their controlled by their predatorspredators
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Some people just prefer „clean“ fieldsSome people just prefer „clean“ fields
The mindset is very The mindset is very importantimportant
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Thank you very much!Thank you very much!