Maize-grain legume intercropping is an attractive option for ecological intensification that reduces climatic risk for smallholder farmers in central Mozambique.

摘要

Many farmers in central Mozambique intercrop maize with grain legumes as a means to improve food security and income. The objective of this study was to understand the farming system, and to evaluate the suitability of maize-legume intercropping to alleviate the biophysical and socio-economic constraints faced by smallholder farmers in Ruaca and Vunduzi villages, central Mozambique. To achieve this we characterised the farming systems and measured grain yields, rainfall infiltration, economic returns and acceptability of maize-legume intercrops under different N and P application rates. Two intercropping strategies were tested: (a) an additive design of within-row intercropping in which legume was intercropped with alternating hills of maize within the same row; maize plant population was the same as sole crop maize, and (b) a substitutive design with distinct alternating rows of maize and legume (local practice). Fertiliser treatments imposed on all treatments were: (i) no fertiliser, (ii) 20 kg P ha-1, (iii) 20 kg P ha-1 +30 kg N ha-1, and (iv) 20 kg P ha-1 +60 kg N ha-1. Intercrops were relatively more productive than the corresponding sole crops; land equivalent ratios (LER) for within-row intercropping ranged between 1.1 and 2.4, and between 1.0 and 1.9 for distinct-row intercropping. Average maize yield penalty for intercropping maize and pigeonpea in the within-row was small (8%) compared with 50% in the distinct-row design; average (season x fertiliser) sole maize yield was 3.2 t ha-1. Intercropping maize and cowpea in within-row led to maize yield loss of only 6%, whereas distinct-row intercropping reduced maize yield by 25% from 2.1 t ha-1 of sole maize (season x fertiliser). Cowpea yield was less affected by intercropping: sole cowpea had an average yield of 0.9 t ha-1, distinct-row intercropping (0.8 t ha-1) and the within-row intercropping yielded 0.9 t ha-1. Legumes were comparatively less affected by the long dry spells which were prevalent during the study period. Response to N and P fertiliser was weak due to poor rainfall distribution. In the third season, maize in rotation with pigeonpea and without N fertiliser application yielded 5.6 t ha-1, eight times more than continuous maize which was severely infested by striga (Striga asiatica) and yielded only 0.7 t ha-1. Rainfall infiltration increased from 6 mm h-1 to 22 mm h-1 with long-term maize-legume intercropping due to a combination of good quality biomass production which provided mulch combined with no tillage. Intercropping maize and pigeonpea was profitable with a rate of return of at least 343% over sole maize cropping. Farmers preferred the within-row maize-legume intercropping with an acceptability score of 84% because of good yields for both maize and legume. Intercropping increased the labour required for weeding by 36% compared with the sole crops. Farmers in Ruaca faced labour constraints due to extensification thus maize-pigeonpea intercropping may improve productivity and help reduce the area cultivated. In Vunduzi, land limitation was a major problem and intensification through legumes is amongst the few feasible options to increase both production and productivity. The late maturity of pigeonpea means that free-grazing of cattle has to be delayed, which allows farmers to retain crop residues in the fields as mulch if they choose to; this allows the use of no-tillage practises. We conclude that maize-legume intercropping has potential to: (a) reduce the risk of crop failure, (b) improve productivity and income, and (c) increase food security in vulnerable production systems, and is a feasible entry point to ecological intensification.