Growth of Crotalaria juncea and Sesbania cannabina under different underground water levels and their nitrogen contribution to the succeeding spinach plant

Dry matter production and nitrogen absorption of Crotalaria juncea and Sesbania cannabina grown under different underground water levels (16 cm [high] and 32 cm [low] below the ground) were evaluated in experiments conducted with 200 L volume containers, and the effect of incorporation on the nitrogen contribution to the succeeding spinach was also investigated, The dry weight and nitrogen content of tops at time of incorporation under low level were higher than those under high level in both plant species. No significant difference was noted in the decrement of dry weight and nitrogen content under high level between the two plant species, which was found to range from 30 to 35%. The yield and nitrogen content of the succeeding spinach plant under the high level were superior to those under the low level, regardless of the different dry matter production between water levels in both plant species. The proportion of nitrogen derived from soil and incorporated material to the total nitrogen content was higher than that derived from fertilizer, ranging from 86 to 92%. The inhibition against growth of the spinach plant after the incorporation of a greater amount of C. juncea tops was further investigated in a pot experiment. The fresh weight in a 300 g incorporated pot was significantly lower than those in 100 g and 200 g incorporated pots. The results were discussed in the possibility of introducing C. juncea to the upland fields from paddies.