The Potential of Cowpea, Pigeonpea and Greengram to Supply Mineral Nitrogen to Maize under Intercropping on Ferralsol in Muheza-Tanga Tanzania

An incubation experiment was carried out at Mlingano Agricultural Research Institute, Tanga- Tanzania, to study the nitrogen mineralization in the Ferralsol under maize- cowpea, pigeonpea and greengram intercropping systems. Top soil (0 – 20 cm) samples were collected from previously maize intercropped and monocropped plots before the onset of rains in subsequent seasons. The fresh soil samples were sieved through a 6 mm screen, 250 g portions placed in 500 ml capacity volumetric flasks, then incubated at 60% field capacity for 42 days in a glasshouse. Destructive samplings were done at 14 day intervals and analysed for mineral N. The N mineralization increased with incubation time, with cowpea and pigeonpea having significantly higher quantities at the 42nd day sampling compared to the maize monocropped plots. The proportions of the mineral N at 14th day where maize stover was removed were 77%, 55%, 92% and 90% of that at the 42nd day for soil from the cowpea, pigeonpea, greengram and monocropped maize treatments, respectively. The respective proportions where the stover was incorporated were 81%, 53%, 96% and 77%. Such high proportions coupled with low maize N demand indicated possibilities of the N being leached, leading to maize plants’ N deficiency symptoms. It was concluded that the N mineralization in this cropping system is not in synchrony with the maize N demand, necessitating top dressing of N fertilizers.