Nitrogen Fertilizer Equivalency Values for Different Organic Materials Based on Maize Performance at Kabete, Kenya
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Decline in crop yields has been a major problem facing small holder farming in Kenya and the entire sub-Saharan region. This is attributed mainly to the mining of macronutrients due to cropping without external addition of adequate nutrients. Inorganic fertilizers are expensive hence unaffordable by most small holder farmers. Although organic nutrient sources are available. information about the right proportions of application is scanty. An experiment was set up in 1999 at the National Agricultural Research Laboratories (NARL)at Kabete, with the overall objective of determining nitrogen fertilizer equivalencies based on high quality organic inputs. The specific objectives of the study included determination of the nitrogen fertilizer equivalency values of Tithonia diversifolia, Senna spectabilis and Calliandra ca/othyrsus and the investigation of nitrogen use efficiency from combined organic and inorganic inputs. The experiment consisted of maize plots to which freshly collected leaves of Tithonia diversifolia (tithonial, Senna spectabilis (senna) and Calliandra calothyrsus (calliandra) (all with % N >3) obtained from hedgerows grown ex situ (biomass transfer from outside) and urea (inorganic nitrogen source) were applied. Results obtained indicated that a combination ofboth organic and inorganic nutrient sources gave higher maize grain yield than when each is applied separately, except for tithonia whose sole application gave better grain yield than a combination of the same with mineral fertilizer. Maizegrain yield production after organic and inorganic application was in the order of tithonia > tithonta-urea = calliandra+urea > urea> senna-urea > calliandra > senna > control. The percentage N recovery was highest in sole application of urea followed by a combination ofboth urea and tithonia while sole application of tithonia biomass had relatively lower percentage N recoveries. In both seasons, the mineral Ncontent was high in sole application of tithonia than in senna and calliandra treatments. The three organic materials (senna, calliandra and tithonia) gave fertilizer equivalency values of 68%, 72% and 119% respectively.