Effects of potassium fertilizer on some major food crops in Kenya
2000
Gikonyo, E.W(Kenya Agricultural Research Institute, Nairobi (Kenya). National Agricultural Research Laboratories) | Smithson, P.C.(International centre for Research in Agroforestry, Nairobi, Kenya) | Nandwa, A.M.(International centre for Research in Agroforestry, Nairobi, Kenya) | Janssen, B.(Wageningen Agricultural University, Wagenigen, The Nehterlands)
Potassium (K) content is generally thought to be sufficient in Kenyan soils, but K deficiency is being reported in some areas. This study evaluated the effects of K fertilization on five major food crops and established crop specific soil critical potassium levels (SCKLs) using the method of Cate and Nelson (1965). Data for the analysis were from the 1987-1993 Fertiliser Use Recommendation Project, and from ICRAF trials in western Kenya. Two laboratory methods for exchangeable K were examined: modified Olsen and Mehlich 1. In most sites there was no response to K, probably due to the high soil test K levels of the soils: only 23% of sites were low in soil test K « 0.20 cmolc kg-l). Maize (Zea mays L.) responded positively to K at 4 of 36 sites and sorghum (Sorghum bicolor L.) at 1 of 10 sites. An equal percentage of sites showed negative K responses for both crops, mostly where soil K was 0.5 cmolc kg-l. The Olsen SCKLs established for maize, sorghum, beans (Phaseolus vulgaris L.), potato (Solanum tuberosum L.)and cabbage (Brassica oleracea L.) were about 0.12 to 0.2 cmolc kg-l for all the crops, but responsive sites and sites with low-K soils were few, so the SCKL still needs to be refined with further data. The ICRAF trials tested maize only, at 32 sites in Vihiga and Siaya Districts, 22 of which had modified Olsen K::; 0.20 cmolc kg-l. The SCKL from these sites was about 0.18 cmolc k\{ Results of modified Olsen and Mehlich methods were highly correlated: Mehlich K = 1.19 * Olsen K + 0.004, r2 = 0.91.
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