Effects of Rates of Inorganic and Organic Fertilisers on Desmodium uncinatum Nodulation, Dry Matter and Seed Yields on Phosphorus and Nitrogen Deficient Soils

Forage legumes are important in the smallholder farming system since they increase the quality of livestock feeds and soil fertility through quality manure. The legumes can also concurrently enhance soil fertility through nitrogen fixation for companion grasses and subsequent cereal crops. Farmers in Kenya are aware of the importance of forage legumes but stunted/slow growth during the establishment year and non availability of low cost seed has limited adoption of this technology. Two experiments were carried out on nitrogen and phosphorus-deficient soils at the National Agricultural Research Centre Kitale. In experiment 1 the effects of nitrogen applied at the rates of 0, 10, 20, 40, 60, 80 and 100 kg N/ha were evaluated for nodulation and dry matter accumulation of Desmodium uncinatum. Experiment 2 evaluated the effects of 0, 23, 46, 69, 92, 115 kg P₂O₅/ha in the form of single superphosphate fertiliser and 10, 20, 30 and 40 t/ha of farm yard manure on nodulation, herbage dry matter and seed yields of Desmodium uncinatum. A randomized complete block design with 3 replicates was used in each experiment. Nitrogen fertilisers did not increase nodulation and dry matter yields significantly. Increasing nitrogen fertiliser rates beyond 20 kg N/ha resulted in a significant (P<0.01) decline in the total and number of effective nodules produced per plant. Herbage dry matter yields also significantly (P<0.01) declined with application of more than 40 kg N/ha. Application of 23 and 46 kg P₂O₅/ha significantly (P<0.05) increased nodulation (total and effective number of nodules) and herbage dry matter yields. However, for 2 years there was no advantage in applying rates exceeding 46 P₂O₅/ha. Farm yard manure also significantly (P<0.5) increased nodulation but there were no significant differences between application of 10 t/ha and higher rates of 20, 30 or 40 t/ha. Herbage dry matter yields were increased by application of farm yard manure though the results were not significant at P>0.05. Seed yields were not significantly increased by phosphate or farmyard manure application.