Field trials were conducted to determine the economically optimum fertilizer rates for soybean production and for optimizing net profits in Dedza, Lilongwe and Salima Districts of Malawi. The effects of PK fertilizer rates on rain use efficiency (RUE), harvest index, agronomic use efficiency of phosphorous (AEP) and potassium (AEK), and value cost ratio (VCR) were evaluated. The applied dia gnostic PK fertilizer rates significantly improved soybean grain yields, harvest index, rainwater use efficiency, AEP, AEK and returns to fertilizer use expressed as value cost ratio (VCR). However, the results differed significantly (P < 0.01) among the three agro-ecological zones. The VCR values indicated that the most economical and profitable fertilizer rate was 7.5 kg/ha P in Salima, Dedza and Lilongwe. The lowest economical and profitable NP fertilizer rate was 22.5 kg/ha P plus 20 kg/ha K for Dedza and Lilongwe and 15 kg/ha P plus 30 kg/ha K for Salima District. All the VCR values obtained from applying different PK fertilizer nutrient rates were above two implying that all the applied fertilizer rates had a good value of returns to adequately cover against any risks associated with using fertilizers at small-scale under smallholder farms with inadequate financial resources. The results also presented different available NP fertilizer application rate options for maximizing profits for the financially constrained smallholder farmers.
KeywordsSoybeanNet ReturnsEconomically Optimum RatesAgronomic Use Efficiency of Phosphorous and PotassiumNutrient CombinationValue Cost Ratio
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