Effect of organic and inorganic sources of nutrients on soil mineral nitrogen (ammonium and nitrate N) and maize yields in western Kenya

Ayuke FO, Opondo-Mbai ML, Rao MR, Swift MJ. "Effect of organic and inorganic sources of nutrients on soil mineral nitrogen (ammonium and nitrate N) and maize yields in western Kenya.". In: proceedings of the 8th Tropical Soil Biology and Fertility and Programme African Network meeting. Arusha, Tanzania; 2001.

Date Presented:

7-10 May


The effects of organic and inorganic fertilizers on soil mineral N and maize yields were evaluated in a Kandiudalfic Eutrodox soil of western Kenya. Leaf biomass of tithonia (Tithonia diversifolia [Hemseley] A. Grey) and senna (Senna spectabilis D.C. & H.S. Irwin) at 5 t ha-1 dry weight were incorporated into the soil and compared with the response obtained from control without any input and fertilizer at 120 kg N, 150 kg P and 100 kg K ha-1 from urea and triple super phosphate (TSP). Soil mineral (inorganic), N, was measured at the beginning of the trial and subsequently at 1, 2, 4, 8 and 12 weeks after applying the treatments. Maize grain and stover yields were estimated at harvest. Total inorganic nitrogen in the soil at the beginning of the season was at a similar level in all treatments. It increased rapidly after applying the materials and at the onset of rains for all treatments probably because of rapid nitrogen mineralisation in all treatments. After four weeks, inorganic nitrogen decreased progressively until end of the experiment in all the treatments. The highest contribution of mineral N to the soil by the organic residues was noted at four weeks stage and this was significantly higher with tithonia than senna. This could be due to rapid N mineralization by these residues. Senna treatment that had the lowest mineral N during the first weeks of the trial, showed that N mineralization was slow with the mineral N reaching highest level at four-week stage. However, it is interesting to note that while soil N under tithonia was statistically higher than in senna at four weeks, it was higher under senna at later stage observations. Thus tithonia decomposed completely in about four weeks, while senna was still mineralizing at 8 weeks. Fertilizer use increased maize grain yield by 63% over the control. Although tithonia biomass increased maize grain yield by 38% over the control and did not differ significantly from fertilizer treatment, senna increased maize yield by only 6% over the no input control. Higher yield with tithonia than senna was partly because of higher nutrient concentration and hence greater amounts of nutrients added for the same quantity of material applied. The study indicates that high quality residues such as tithonia can be used as sources of nutrients to improve crop yields.

Keywords: Biomass transfer, Tithonia diversifolia, Senna spectabilis, mineral nitrogen, maize yield.

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