Effects of CA and manure application on maize grain yield and soil organic carbon: a comparative analysis - Leonard Rusinamhodzi
Effects of conservation agriculture andmanure application on maize grain yieldand soil organic carbon: a comparative analysis Leonard Rusinamhodzi PhD Student Plant Production Systems Group
The challenge of soil fertility decline…. 70% of smallholder farms are on infertile sandy soils Majority of farmers use mouldboard ploughing 90 80 Clay soil Sandy soil 80 60 70 SOC (t ha-1) 60 40 50 20 40 30 0 0 5 10 15 20 0 2 4 6 8 10 12 14 16 Time of cultivation (years) Time of cultivation (years) Source: Rusinamhodzi et al (2011)
Farmers’ response………. Use of cattlemanure to improvecrop productivity Use of cropresidues to improve manurequantity and qualityof manure
Manure use………… Manure is spread on soil surface and ploughed under Some farmers are now applying manure in planting basins Strategy make small quantities cover a large area
Crop residue use………Example: Manjonjo village, Murehwa, Zimbabwe Crop residues produced 40 ha 43 ha Collected Left in fields 4.6 ha 13.5 ha3 ha 5.6 ha 13 ha 1.1 ha 1.9 ha 40 ha Mulch Mulch Available (ex- Compost Burnt Livestock Bedding (in- Burnt for situ) feed situ) livestock Kraal CR from 70% of cropped area is used for feed/bedding
Trade-offs ……………….. The allocation of crop residues for livestock feed meets two out of three critical objectives; it ensures feed during the dry season improves quantity and quality of manure but does not ensure permanent soil cover required under conservation agriculture (CA).
Trade-offs……………… There are strong trade-offs for either allocating crop residues for livestock feed or using the crop residues directly for mulch thereby reducing the amount and quality of manure available and compromising the condition of livestock
Study objective…….To perform a comparative analysis of maizegrain yield and soil organic carbon (SOC)changes in CA systems versus conventionaltillage systems (with manure application). • Crop yield- food security and income, • SOC - important determinant of soil fertility, productivity and sustainability
Field experiments…………….• Data obtained from two sets of long-term experiments under continuous sole maize (Zea mays L.) • experiment on manure application under conventional tillage • Experiment on no-tillage with mulch cover
Manure experiment• Established from 2002 to 2010 on both clay (Chromic Luvisols) and sandy (Haplic Lixisols) soils and two field types (homefield and outfield) in Murehwa, Zimbabwe.• Tillage- mouldboard ploughing • Fertiliser treatments • control, • 100 kg N ha-1, • 100 kg N ha-1 + 5 t manure ha-1 • 100 kg N ha-1 + 15 t manure ha-1.
Tillage experiment • Established in 1988 to 1999 at three sites, Domboshawa (sandy soils, Haplic Lixisols), Makoholi (sandy soils, Ferralic Arenosols) and Institute of Agricultural Engineering (IAE) (red clay soils, Chromic Luvisols) • Two tillage treatments • Conventional mouldboard ploughing, 23 cm depth. • Mulch ripping (MR), ripping to a depth of 20 – 25 cm , crop residues maintained on the soil surface (40 and 60 % cover). • All treatments received 114 kg N ha-1, 22 kg P ha-1 and 25 kg K ha-1
Soil analysis Total C was determined by dry combustion using a LECO TRUSPEC C and N auto-analyser (LECO Corporation, 2003). Grain yield advantages were calculated as difference between yield in control and treatment
Results…….maize grain yield 6 6 Red clay soil (homefield) Red clay soil (outfield) Weighted mean difference (t ha ) -1 5 ha-1 5 Addition of 5 t 4 4 manure resulted in 3 2 3 2 more than double maize 1 1 0 grain yield over the 0 100N 5T 15T 100N 5T 15T 5 5 Sandy soil (homefield) Sandy soil (outfield) Weighted mean difference (t ha ) -1 control 4 3 4 3 2 2 1 1 0 0 -1 -1 100N 5T 15T 100N 5T 15T Fertilization strategy Fertilization strategy
Results……..maize grain yield 3 Effect of mulch and reduced tillage on yield Weighted mean difference (t ha ) -1 2 was marginal with a yield 1 gain of only 0.2 t ha-1 over a nine year period 0 -1 -2 Domboshawa Makoholi IAE Pooled
Results…………SOC 4 3.5 Soil organic carbon (%) Manure application 3 (5 t ha-1) under 2.5 2 conventional tillage 1.5 increased SOC by 1 0.13% and 0.09% 0.5 per year on clay 0 and sandy soils Control 5t 15t Control 5t 15t Control 5t 15t Control 5t 15t respectively Red HF Red OF Sandy HF Sandy OF
Results………….SOC 2 Reduced tillage 1.8 and mulch 1.6 Soil organic carbon (%) 1.4 retention led to 1.2 an increase of 1 0.02% per year 0.8 for both sandy 0.6 and clay soils 0.4 0.2 0 CT Red clay MR Red clay CT sandy soil MR sandy soil
Discussion points the opportunity cost of losing mulch is offset by gains in animal productivity given that communal grazing is not adequate during the dry season The results suggest that the decision by farmers to allocate crop residues to animals as feed and use manure is most suitable for their circumstances manure application in combination with fertilizer provides calcium, magnesium and micronutrients that ensure high yields especially on degraded soils
Conclusion• An optimal procedure for retaining adequate crop residues while providing sufficient feed for livestock is thus required to facilitate the adoption of CA on smallholder farms.