Increasing fertility phosphorus use efficiency through organic matter cycling enhanced maize production in Kenya

Phosphorus has been identified as a major District) and the botlener considered a 'lop bottleneck to improved crop production ~tioIJ i1f' fixmg' soil at Mau SLlmmit (NakulJJ.Qhct). soils with high P-retention capacities. Tne,stl The following treatments and e applied in soils occupy large areas of the production, Fertilizer 1997 and 1998: NIL7It:g super phosphate lands in Kenya and the highlands of" Bast P ha-', FYM at ) t ha-1 dry matter, FYM + Africa. Several management options h~ 'aye 25 kg Pf]11n ombination and 75 kg been suggested to provide solutions to the- To .1'") supphosphate P ha-I all in four replicates nutrition limitation. However then arandomised block design.Alltreatments applicability under smallholder systems have received 100 kg N ha-1. Maize was the test not been evaluated. Similarly the crop. There was no significant correlation transformation of the applied fertilizer P to in either year at both sites between soil P, soil under the various management options measured as NaHC03-extractable P, resin has remained unclear. The aim of this POl' NaOH-extractable P and maize yield. experiment was to evaluate the impact of However the different soil P fractions were some of the available management options closely correlated with each other. There on yield in soils having high P-retention was a significant positive relationship capacities. The fate of the applied P-fertilizer (P0.05) between biomass P and crop yield, under some management options is also again at both sites and in both years. The traced and measured through P- treatment FYM+P gave the best yield and fractionation scheme and the option that the largest biomass P. The results indicate ensures adequate availability of applied P that combined use of organic and inorganic for crop uptake is recommended for use by fertilizer inputs in these low input systems the smallholders. Two approaches were may promote better biological cycling, adopted. Firstly to attempt to saturate the enhanced availability and consequently p.fixing sites in the soils by applying a large improved plant uptake of soil and fertiliser annual application ofP (75 kg P ha'I), which P. The results also indicate that biomass P should serve for several seasons. Secondly, measurements may provide a better toattemptto keep the fertilizer P in biological indicator of soil P availability in these soils forms by supplying fertilizer P and manure than the more conventional chemical mcombination i.e. promote the cycling ofP extractants. However, both findings require through the soil microbial biomass and further evaluation. Associated metabolites and so help increase plant availability. These treatments were Investigated under field conditions on