Fertilizer nitrogen recovery as affected by soil organic matter status in two sites in Kenya

Management of nitrogen (N) nutrition is a vital aspect in maize production systems of Kenya. In Central and Western parts of Kenya, high population density has eliminated the use of traditional fallow farming systems for replenishing soil fertility while high unevenly distributed rainfall increase chances of N leaching. A study was conducted at Maseno, and Kabete to investigate the fate of fertilizer N in the soil-plant system using treatments that had been receiving leaf prunings of Calliandra calothyrsus and Tithonia diversifolia. Two microplots were installed in the main treatments to which labelled fertilizer was applied. At the beginning and at the end of 2002 long rains, soil was sampled to 200 cm for N and N-15 enrichment analysis at the two trials. Also at the end of the season plant samples were collected for N and N-15 analysis. At Maseno trial, evenly distributed rainfall and the influence of organic resource quality enhanced good fertilizer nitrogen recovery in the maize crop. Also substantial nitrate movement down the soil profile was observed in the control followed closely by calliandra at the end of the 2002 long rains season. At Kabete trial recorded the poorest fertilizer N recovery due to unevenly distributed rainfall. Limited soil moisture reduced both soil and fertilizer N uptake which was reflected in high N in the top soil and low recovery in plant. Most of the nitrate-N was left in the tp soil as a result of low rainfall which couldn't move it into the lower soil depths.