Maize Productivity, Economic Returns and Phosphorus Use Efficiency as Influenced by Lime, Minjingu Rock Phosphate and NPK Inorganic Fertilizer

This study was conducted to examine the effects of Lime, Minjingu Rock Phosphate (MRP) and inorganic NPK fertilizer on maize productivity, profitability and phosphorus use efficiency (PUE) based on grain yield (PUE_Y) and economic returns (PUE_E). The study was carried out for two rain seasons in Kenya and the treatments were Lime, MRP, NPK, Lime + MRP, Lime + NPK, and a control. The highest height (185 cm) was recorded in MRP treated plots whereas the lowest values were observed in control (162 cm) and Lime (166 cm). The lowermost yield of 2.2 t ha^-1 was attained from the non-amended plots. The value increased by 4.0, 2.9, 1.8, 1.7 and 0.8 t ha^-1 in MRP, NPK, Lime + MRP, Lime + NPK and Lime treatments. The use of MRP proved to be the most lucrative with a disposable income of US$ 2122ha^-1. PUE_Y was such that Lime + NPK (95 kg of maize grain yield for every kg of p supplied) < Lime + MRP (116) < NPK (125) < control (139) < MRP (170) < Lime (188) whereas PUE_E was lowest in plots treated with Lime + NPK (38 $ kg^-1) and Lime + MRP (46 $ kg^-1), and highest in Lime (75 $ kg^-1) and MRP (68 $ kg^-1) plots. The results from the study indicate that MRP amendment is essential in optimizing not only maize productivity and economic returns but also phosphorus efficacy.