Best-fit residue allocation: a gate for legume intensification in nitrogen constrained cropping systems of Central Mozambique Nhantumbo, N., Dias, J, Mortlock, M, Nyagumbo, I., Dimes, J and Rodriguez, D INSTITUTO SUPERIOR POLITÉCNICO DE MANICA Getting things done

Presentation layout (1)Introduction (2)Materials and Methods (3)Results (1)Ex ante long term simulation (1)Conclusion (2)Legume intensification (4)General Conclusion

Conservation tillage, crop residue retention and legume integration in maize- legume cropping systems are being widely promoted as part of CA package in Central Mozambique and across SSA –Crop residues and fertilizers are limiting factors in smallholder cropping systems; –Legumes are mainly grown in unfavourable arrangements not allowing them to realise their yield and N-fixation potential The widely available and used crop residues have high C:N ratios which interacts strongly with soil N-supply during residue decomposition processes Therefore if high C:N residues are to be used, there is a need to create a much better understanding of residue and nitrogen interactions with yield in this N- constrained systems to improve resource allocation 1. Introduction

1.1 Research Question The overall research question posed in this study is what are the best fit resource allocations strategies and tactics that would best fit the nitrogen constrained systems of smallholder farmers from central Mozambique? What should be our research focus? Improving legume productivity is an affordable and environmentally friendly alternative to increase soil fertility and crop productivity in nitrogen constrained cropping systems of Central Mozambique. Innovative maize-legume cropping systems designs and smart resource allocation strategies need to be tested taking into account that achieving high productivity with African legumes, is of crucial importance to strengthen legume contribution in the SSA conservation agriculture initiative

2.Materials and Methods (1)Ex ante simulations with APSIM 7.4 to identify best-fit residue and fertilizer allocation strategies in maize- legume cropping systems (2)Use results from the simulations to aid trial design (1)Test a legume intensification possibility centered in the hypothesis that sowing legumes early in the season (October-November) instead of the recommended mid-January to March window can help improve legume performance and open the opportunity to sow a second legume crop.

Maize and cowpea crop response to: Residue type: maize and cowpea residues representing high (80) and low (20) C:N ratio material. Residue application levels: 0, 2, 4 and 8 t/ha at sowing N-application levels, 0, 23, 46, 92 and 184 kg/ha (higher rates split). Plant Material and sowing windows Maize = Tsangano, Cowpea = IT18 (Banjo) Plant population = 4.4 plts/m^2 and 8 plts/m^2 Planting Windows Maize Nov 1-Dec 15 Cowpea Jan 10 – Feb 10 and Nov1 – Dec 15 No weed competition Ex ante Long Term Simulations (61yrs)

APSIM Model Calibration Model Calibration Baseline yield expectation of RT (0.96 t/ha): Soil N-supply Adjustments of SC501 to Tsangano PAWC and SOC calibrated to reflect the experimental conditions Adjust soil description to fit trial site Model evaluation Simulation of maize response to tillage and mulch application: Curve Number (CN2_bare) method (Probert et al., 1998) Long Term Simulations Maize and cowpea crop response to: Residue type: maize and cowpea residues representing high (80) and low (20) C:N ratio material. Residue application levels N-application levels

3.Results

Maize Seasonal response to residue type and amount at different N-fertilizer levels Cowpea residues – maize yield benefits due to improved N and water supply Maize residues – maize yield response dominated by increased N-deficits, mask any moisture benefit At N no-limiting – moisture benefits of different types of mulch is evident 3.1 Long Term Simulations Results

Maize yield response to inputs of High and Low C:N ratio Residues at low and high N-levels 3.1 Long Term Simulations Results

Cowpea response to residue types and amounts at different N- application levels 3.1 Long Term Simulations Results

Cowpea yield response to inputs of maize and cowpea residues, at 0kg N/ha and different planting windows 3.1 Long Term Simulations Results

3.1.1 Preliminary conclusions LONG TERM SIMULATIONS Despite maize residues being the most available and effective in providing soil cover and protect against erosion, applying high C:N residues to a maize crop without investments in N fertilizers affects negatively the maize grain yields at lower N-levels; In N-constrained environments like Chimoio, maize residues could be applied to cowpeas in the normal growing period (January-February), with aim of increasing SOM content and protection against erosion loss, but do not contribute greatly to increased yields. Alternatively, the maize residues can be utilised to sow cowpea early in the season and extend cowpea production into a drier period of the season by providing an effective mulch and SWB benefits with improvements in cowpea yields with early sowing. In turn, this strategy opens the possibility of double cropping cowpea in a single season (increased N-fixation), for the benefit of the following maize crop

3.2 Legume Intensification Trials (1)Cropping systems i.Maize-cowpea intercrop and a sole cowpea (2)Experimental design: CRBD in a 3x3x2 Factorial arrangement i.Three Residue levels: 0, 2 and 4 t/ha ii.Three Nitrogen levels: 0, 23 and 92 kg N/ha. iii.Two Legume sowing windows: a)First legume was early sown with maize on 26 th November b)Second legume sown as a relay crop right after harvesting the first legume (2 nd March). c)A control maize-cowpea intercrop (Farmer practice) was sown in January 17 th. (3)Plant material: Tsangano, maize OPV with 137 days to harvest and IT18, a cowpea variety with 100 days to harvest were used.

3.2 Legume Intensification

4. General Conclusion For N-poor soils, with limited availability of crop residues, investing the available maize stubble on improving the performance of the sole legume crop (then intercrop) with early sowing is more productive, for the legume crop and the following cereal crop in the rotation; Despite having one distinct rainfall season there is a possibility of growing two legumes crops per season in Chimoio depending on how early the first legume is sown; For legume intensification systems, having a short duration variety for the second sowing is crucial to avoid having the legume growing into a cooler part of the season which reduces yield In nitrogen constrained maize-legume systems, investing the limited amounts of nitrogen fertilizer in improving maize yield is more beneficial than applying high C:N residues that immobilizes nitrogen and affects the overall performance of the maize crop.

Thank You