Soil fertility analysis associated to land use in Western Kenya. B2

A total of 112 samples were collected from Busia Township and Angurai sites in Busia and Teso Districts respectively. These comprised 25 from Busia and 87 from Angurai in two sampling dates, 2002 and 2004 to determine soil fertility change over the two year period. In order to assess the soil fertility from the sites, and in different land uses, soil chemical and texture analysis was carried out and values compared with crop recommended agronomically adequate values for specific elements. Texture for purposes of soil hydrologie behaviour was also considered in respect to soil water. Average organic carbon in the soils was 1.39% with mean in Busia and only 64% of the farms had adequate levels of carbon. In Angurai site, mean organic carbon increased over the two year period from 1.13% to 1.41% with the number of farms with adequate (moderate) levels increasing from 13% to 35%. However, overall carbon levels were still below threshold levels during the two sampling intervals. These levels of nitrogen indicated that the soils were very low in organic matter as revealed by the analysed total nitrogen, which ranged from very low to just moderately adequate. Generally the sites showed low soil fertility status as indicated by the soil organic C, total nitrogen, available phosphorous and soil PH. Exchangeable potassium was adequate in the two sites although the second sampling (after two years) in Angurai showed slightly low but above threshold levels of the same. Available phosphorous was very low to sustain optimal crop yield in both sites even after two years sampling interval (in Teso District). 96% of points in Busia and 89% of points in Angurai and 80% of points after second sampling same site had deficient levels of available phosphorous. Some farms within the sites were applied phosphate fertilizers at planting time while others received no fertilizers. Majority of soils from these sites were also found to be strongly acidic thereby limiting availability of phosphorous. In these situations, phosphorus tends to be “fixed” by the soil. The low available P levels needs to be corrected through application of 100kg/ha of triple super phosphate or compound fertilizer containing N, P and K at planting time and top dress with 80kg/ha CAN. Acidifying fertilizers like diammonium phosphate (DAP), ammonium sulphate (AS) or ammonium sulphate nitrate (ASN) should be avoided due to their acidifying reaction. Alternatively, agricultural lime need to be applied at a rate of 2t/ha one month before planting. Exchangeable potassium (me%) was on average adequate but there were a good number of sites, which were K deficient and required K replenishment for balanced crop fertilizer application. Two year sampling interval in Angurai led to an increase in the points with potassium deficiency from 24% to 29%. It is recommended that in Busia site and Angurai in Teso District, compound fertilizer containing nitrogen, phosphorous and potassium e.g. N: P: K 17:17:17 at 300kg/ha per year should be used at planting to correct N, P and K deficiencies in the soil. All the sites in Busia and Angurai (will) will require application of 5t/ha FYM or compost on sites with crops to raise soil organic matter and hence total nitrogen. In Angurai site foliar feed containing zinc, should be sprayed on crops. On the effect of time interval on soil fertility status in Teso District, it can be concluded that farming activities at this site led to change in soil fertility status and almost coincides with the KARI-NARL recommendations that oil should be resampled after very three years. Most of the land (60%) in Busia is under bushland/ grazing land/ grassland/fallow and least under nappier grass indicating most farmers here practice with free range grazing and limited zero grazing. Land under crops is just 36% of the land implying that farmers are slowly 2 adapting crop farming. The most important crops in Busia are maize (18%) and sweet potatoes (12%) followed by cassava (8%). In Angurai site during the first sampling, 83% of the land was under crop farming with the rest under bush/fallow while during the second sampling (2004), only 64% was under cultivation. Only 18% of the farms were fallow/bush for grazing. There was pure groundnut and groundnut intercropped with maize. The nitrogen fixed by groundnuts benefit the maize crop. The %sand, %silt and %clay indicated that soils taken from these two sites had a mean textural class of sandy loam (SL) even after an interval of two years sampling in Angurai. This texture implies that the soils have been subjected to erosion and hence the low %clay range of 5.8-57.3 % clay for Angurai and 11.1-41.2 % clay for Busia. Soil texture can only change due to erosion as both water and wind erosion would take away the fine particles first leaving large particles. (Resume d’auteur)