Quantification of Atmospheric N2 Fixed by Cowpea, Pigeonpea and Greengram Grown on Ferralsols in Muheza District, Tanzania

Abstract

Legume crops are usually intercropped with cereals in small-scale farming systems in Tanzania. This aims at taking advantage of legumes to replenish soil nitrogen (N due to legumes’ N2 fixation). Glasshouse pot
experiments and field trials were carried out atMlingano Agricultural Research Institute in Tanga, Tanzania, with the objective to find out how much N2 can be fixed by cowpea, pigeonpea and greengram using native
Rhizobia, thus substituting for the use of N-mineral fertilizers in maize production on Ferralsols. In the glasshouse pot experiment, the legumes were grown in 5L plastic pots for 40 days in soil sampled from 0 –20 cm layer. The field experiment was maize – legumes intercropping whereby the N2 fixation assessment was done 35 days after planting. In both cases, maize (Katumani variety) was the non- N2- fixing reference crop. The legumes formed effective nodules with the native Rhizobia. Different quantities of N2 gas were fixed by the different legumes, the differences being attributed to the legumes’ differences in their genetic characteristics. In the field, monocropped cowpea, pigeonpea and greengram fixed 38, 21, and 49 kg N2, respectively. In the intercrop system cowpea, pigeonpea and greengram fixed 16, 4, and 24 kg N2, respectively. In both cases, the quantities of N2 fixed were less than 50% of their total N accumulation. It was concluded that in Muheza, maize grown in association with the legumes would continue to need supplementation of mineral N fertilizer to maximize its yields.

Key words: Ferralsol, intercropping, legumes, nodules, N2 fixation, N requirement