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. Keywords: Ferralsol; Incubation; Intercropping; Mineral N East African Journal of Sciences Vol. 2 (2) 2008: pp. 119-12