Nitrogen fluxes in soils amended with animal manure and Tithonia biomass on a soil degradation chronosequence

Nitrogen (N) and Phosphorus (P) deficiencies affect 80% of the soils in western Kenya, but fertilizer use among farmers is limited due to high prices. We studied the use of animal manure and Tithonia diversifolia biomass as potential sources of N and P for maize production along a 100 year cultivation chronosequence. Tithonia is a shrub belonging to the family compositae. It’s biomass contains 3.5 % N, 0.37 %P, 4.1 % K while the animal manure used contained 1.1 % N, 0.4 % P, 6.3% K. These organic materials were applied to supply the equivalent of 25 kg of P per hectare. Similar P fertilizer rates were applied to provide the equivalent inorganic treatment. We monitored inorganic N fluxes using 2.5cm radius field soil cores buried to 10cm and recovered on a monthly basis. Soil samples were extracted for nitrate and ammonium. The difference in total inorganic N min minus N leach provided an estimate of plant N uptake. At time zero, there were no significant differences in the levels of extractable ammonium among the treatments. Recent conversion sites had higher extractable nitrate compared to old conversions for all the treatments. We also observed higher rates of N mineralization on the recently cultivated farms. In addition, we will report agronomic yield responses to all sources of nutrients applied

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