EFFECTS OF PHOSPHORUS SOURCES ON SOYBEAN YIELD IN CENTRAL HIGHLANDS OF KENYA

Abstract

Farmers in Central highland Kenya continue to experience depressed land productivity and incomes mainly due to their farms’ low soil fertility status. Fertilizer costs have remained high beyond the reach of many farmers. Integrated soil fertility management (ISFM) is espoused as appropriate in intervention. Integration of legumes into smallholder farming system is one of the ISFM options. Using legumes can minimize nitrogen fertilizer requirement while improving farmers’ incomes and food security. Soybean is a versatile legume fixing more nitrogen (N) than most grain legumes but its production has not received adequate attention in spite of its huge demand and short supply in the country. The most limiting nutrient in soybean production is phosphorus (P), critical in soybean growth but is limited in the central highlands, needing replenishment. The study done at Kigogo in Meru South District and Kamujine in Tigania East District assessed selected sources of P. The sources of P were Triple Super Phosphate (TSP), Minjingu rock phosphate, Mavuno fertilizer, di-ammonium phosphate (DAP), manure and fortified manure (Manure with Minjingu fertilizer at 1:1 ratio) all providing 30 kg P ha-1. The trial was carried out in randomized complete block design (RCBD) having four replications with a plot size of 4.0 m by 4.5 m, being done in two seasons. Data was analyzed using analysis of variance (ANOVA) and means separated using Least Significant Difference (LSD) (p=0.05). Results showed DAP and Mavuno were among the best sources of Phosphorus. Farmers have an opportunity to enhance soybean production through use of either DAP or Mavuno fertilizer. The study recommends consistent use of manure in central highland farms alongside DAP and Mavuno use.