DECOMPOSITION RATES OF INTERCROPPED GREEN MANURE CROPS IN OAXACA, MEXICO

In the Central Valleys of Oaxaca, Mexico, crop production is seriously limited by soil moisture and fertility, as well as by land scarcity. To try to alleviate these constraints, an experiment to evaluate the feasibility of producing green manure crops intercropped with maize (Zea mays), residue decomposition rates and nitrogen content at full bloom was conducted. The mung beans (Vigna radiata) and dolichos beans (Dolichus lablab), planted as single crops, out yielded widely the other species evaluated, but decreased significantly their dry matter production when intercropped with maize, particularly mung beans. Maize production was also affected by the intercrops, especially crop grain yields when grew associated with crotalaria (Crotalaria juncea). On average, biomass production of intercropped legumes decreased 31.3 %, with extreme values of 22.1 % for crotalaria and of 37.4 % for mung beans. Using the methodology of burying residues contained in mesh bags, it was found that mung and dolichos beans showed the highest decomposition rates (8.8 and 9.1 g ha-1 per day, respectively), while crotalaria and common beans reached values of 4.1 and 5.7 g ha-1 per day, respectively. Decomposition rates were significantly related to soil temperature and water content, as well as to C/N ratios of the residues. Given its characteristics of high drought tolerance and rate of height increase when intercropped, crotalaria is a species suitable for intercropping with maize in more marginal areas. Because of its growth habit and long life cycle, which minimizes competence with maize during its critical stages, dolichos bean has a good potential to grow well in association with maize in deep soils under rain-fed conditions.