Testing agricultural production simulator model (APSIM) with machanga (Embu) long-term manure application experimental data
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A long-term study was conducted at Machanga, in arid and semi -arid lands (ASALs) of eastern Kenya to assess the mfluence of manure application on soil nut6ent and the resultant crop productivity. T!1edata fi"om a long-term experiment (19891002) were also used to validate the perfonnance ofthe Agricultural Production Simulator (APSIM) model in predicting the crop dry matter yield, soil phosphorus (soilP) and soil organic carbon (SOC) on P deficient soils.The experimental treatments comprised a control (no inputs), jand 10 t ha-' rates of high quality (26% C; 2,0% N; 0.48% P) manure from a single source applied annually in October. Other treatments were residual manure, where manure application ceased from 1993, and a NP fertilizer application in control plots from 1993. The experiment was simulated using the APSIM P-aware maize module even though maize was not the test crop prior to the November 1999 season. The model performance was tested in terms of dry matter yields, soil P and organic carbon. There was a wide agreement between observed and predicted dry matter yields, soil labile P but poor in organic C. For example the observed and predicted organic was not significantly different between 5 ndlOt ha-1, the decline of soil C in the :sidual treatment, and the magnitude of the crease in oil C when fertilizer was applied. The model model prediction ability need to be tested on different environment and crop and soil parameters before being recommended as a management tool.