Contribution of Legumes and Phosphorus Fertilizer to Nutrient Balances in a Sorghum Based Cropping System in Njoro Kenya

Aim: To determine nutrient balances in a sorghum based cropping system, following integration of legumes and phosphorus application.

Study Design: Two field experiments were set up. They comprised either white lupin or chickpea, and are subsequently referred to as lupin-sorghum and chickpea-sorghum, respectively. A split plot in a randomized complete block design was used. Main plots were cropping systems; sorghum monocrop, legume-sorghum rotation and legume/sorghum intercrop. Subplots were phosphorus sources; triple super phosphate and minjingu phosphate rock.

Place and Duration of Study: Njoro Kenya, in the short rains of 2012 and long rains of 2012 and 2013.

Methodology: N, P and K balances were determined using NUTrient MONitoring (now known as MonQi) Tool box.

Results: Nutrient balances were negative in both experiments, with nitrogen showing more negative values than phosphorus and potassium. Effect of cropping system and phosphorus sources on nutrient balances were significant (P = .05) in both experiments. Sorghum monocrop had more negative nitrogen and potassium balances, in both experiments. Phosphorus balance was more negative in the intercrop and monocrop in lupin-sorghum and chickpea-sorghum experiments, respectively. In the lupin-sorghum experiment, more negative nitrogen balance occurred with use of triple superphosphate in all cropping systems; for P with minjingu phosphate rock in intercropping and sole sorghum systems while for K, balances were more negative with minjingu phosphate rock in sorghum monocrop and intercrop. For the chickpea-sorghum experiment, N balance was more negative with the use of minjingu phosphate rock in the monocropping and intercropping system, for P, values were more negative with triple super phosphate in sorghum monocrop and intercropping systems while for K with triple superphosphate in all cropping systems.

Conclusion: Greater nutrient losses occurred in sole sorghum, hence unsustainable. Integration of white lupin or chickpea, in rotation and/or intercropping systems, with application of either phosphorus sources is recommended for enhanced sustainability of the system. An economic analysis of the farms is also recommended in future studies.