Intercropping of maize and pulses: an evaluation of organic cropping systems

Field experiments were conducted at the National Agrobiology Research Center of the Brazilian Agricultural Research Corporation (Embrapa Agrobiologia) in Seropédica, Rio de Janeiro State, Brazil, from 1995 to 1998. Maize ( Zea mays L. cv. BR 106) was intercropped either with cowpea ( Vigna unguiculata (L.) Walp. cv. CNC 0434) or with jack bean ( Canavalia ensiformis (L.) DC.) by planting two rows of these pulses for each row of maize. At the flowering stage of maize, the pulses’ shoots were used as green manure for the maize crop. Three levels of green manure were applied: zero, one, or two rows for each row of maize, either incorporated into the soil or left as mulch cover. The applied nitrogen was mineralized and taken up quickly by the maize crop. Only 7 days after green manure application, a significantly ( p < 0.01) higher N content of maize leaves was determined in treatments with double-row application of green manure and its incorporation into the soil. Cowpea as well as jack bean shoot mass increased maize yield significantly ( p < 0.01) after double-row green manuring. Positive N balances were achieved only by treatments with harvest residues of jack bean, i.e., treatments with jack bean grain production. In the course of the experiment, soil organic matter (SOM) of the upper soil layers (0–20 and 20–40 cm) increased significantly ( p < 0.01 and p < 0.001, respectively) in intercropping treatments. In general, resources were used more efficiently by intercropping treatments: The land equivalent ratios (LER) of intercropping treatments without utilizing the pulses as green manure were significantly ( p < 0.05) higher than “1”. The utilization of intercropped pulses as green manure offered the opportunity of a quickly available nitrogen source for the maize crop. At the same time, these treatments caused a deficient N balance because the utilization of pulses as green manure alone could not make up for N exports via harvest products.