Plant growth and fate of nitrogen in mixed cropping, intercropping and crop rotation. III. Nitrogen content of corn in association with soybean, cowpea or kidney bean.

Corn (Zea mays L.) was grown alone or in association with soybean (Glycine max (L.) Merill), cowpea (Vigna sinensis Endlichen) or kidney bean (Phaseolus vulgaris L.) under the Condition of small top competition for light in pots containing nitrogen-poor soil. In association with soybean, the effects of growth stage and clipping of tops of soybean and nitrogen application on the nitrogen content of associated corn were examined. The results are summarized as follows. 1. Nitrogen content of corn tops in association with soybean, cowpea or kidney bean was remarkably less than that grown alone 96 days after planting (Fig. 1). This reduction was more remarkable when associated with cowpea or late-maturing soybean than with kidney bean or early-maturing soybean. 2. Regardless of the rate of nitrogen application (0, 5, 10 and 15 kg/10 a), corn growth associated with soybean was less than that grown alone (Fig. 4). 3. Nitrogen content of corn tops was reduced by association with soybean either in the vagetative phase under long day condition or in the reproductive phase under short day condition (Fig. 5). Clipping of the tops of soybean plant increased nitrogen content of corn tops 2 months after clipping (Fig. 5 and Table 2). 4. Cropping associated with three legumes and corn increased nitrogen content of the succeeding wheat, varying with species and cultivars of the legumes (Table 1). 5. Association with soybean reduced nitrogen derived from fertilizer and soil by the corn plant on the 38th day after planting (Table 2). It is found from these results that nitrogen content of corn is reduced by association with these three legumes by their growth stages. It is suggested that this reduction is caused by competition for nitrogen in soil between legume and corn from the early stage of cultivation.