s:1828:"TI Agronomic and economic evaluation of organic and inorganic sources of phosphorus in Western Kenya 
AU Jama, B.A. 
AU Swinkels, R.A. 
AU Buresh, R.J. 
AB Manys oils in the highlands of East and Central Africa are depleted of soil nutrients, particularly P. Ouro bjective was to comparec attle manure, Calliandra calothyrsus Meissner leaf biomass, and triple superphosphule (TSP) as sources of P for maize (Zea mays L.), both individually and as mixtures of organic (manure or calliandra) and inorganic (TSP + urea) sources. Field experiments were conducted on a Kandiudalf at two sites in western Kenya. Net benefits were computed as the difference between the value of additional maize yield accruing from nutrient inputs and the associated additional costs. Maize grain yield was 0.6 Mg ha1 for application of urea without P. Application of 10 kg P ha1 as organic, inorganic, and mixtures of organic and inorganic sources significantly increased maize yield. Grain yield for manure at least equaled and sometimes exceeded (P 0.05) yield for calliandra and TSP + urea. Net benefits in U.S. dollars (USD) for two seasons were highest for manure spot placed in the planting bole (293 USD ha1), broadcast manure (255 USD ha1), and broadcast TSP + 44 kg urea-N ha1 (313 USD ha1 at P = 30 kg ha1 and 98 USD ha1 at P = 10 kg ha1). Net benefits for calliandra leaf biomass were highest (136 USD ha1) when biomass was valued at cost of production and integrated with TSP, such that it provided all the N for maize and TSP provided the additional P not supplied by calliandra. Cailiandra valued at its opportunity cost as a protein supplement for dairy cattle was not an economic source of P. Sensitivity analyses suggest that organic materials most suitable for use as P sources have high P content and low cost of production. 
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