Green manuring and mulching in a three-crop sequence in the Bolivian Amazon.

Three successive crops (maize – common beans – rice) were cultivated in the same plots in the Amazon basin in Bolivia between 1996 and 1998. A split-plot design was used. The presence/absence of mulch (80% Panicum maximum plus 20% Brachiaria decumbens) was considered as the main plots and the manure sources (control – Mucuna pruriens var. utilis – Pueraria phaseoloides – mineral fertilizer) as subplots. Top cuttings of kudzu and mucuna were incorporated with a hoe to a depth of 10 cm before every planting. Grass mulch significantly decreased weed number until 28-35 day after emergence (DAE) compared to the bare plots. Weed reduction was 48, 45 and 50% for maize, beans and rice, respectively. The effects of legume incorporation and chemical fertilizer application on yields were different for each crop. In maize crop, the mucuna and kudzu top cuttings produced yields of 50 and 68%, respectively of that obtained with mineral fertilizer (3.4 t ha-1). The incorporation of kudzu in common beans produced yields significantly higher than the control, but 45-50% of the grain obtained in comparison to chemical input. Only mineral fertilizer application significantly increased grain production compared to the control (by 45%). It can be concluded from this study that: 1. grass mulch decreases weed population and reduces competition. 2. in the absence mineral fertlizers, the incorporation of kudzu in maize and beans significantly increases crop yields when compared to control. 3. the different effects of organic additives within a crop can be directly attributed to specific changes in the physical-chemical characteristics of soil induced by organic incorporation and grass mulch; 4. the potential use of incorporated green manure and the mulching practice may be significant for small farm.