Potential of local plants as a source of N P K on small holder fields in southern Ethiopia

Improving food production and security in the face of soil infertility and high cost of inorganic fertilisers is a challenge for smallholder farmers. Erythrina spp. and Ensete ventricosum are indigenous to Ethiopia and noted as N-fixing agroforestry and high value food producer trees respectively. These trees have been identified with a high potential use as organic fertilisers for increased crop production. The study sought to determine nutrient and chemical compositions of the species, their mineralisation rate and N-equivalence value of E. brucei. Composite leaf samples from HagreSelam and Wolaita in southern Ethiopia were analysed for N, P, K, lignin and total polyphenol (TP). The effect of E. brucei biomass on wheat grain and straw yields and its N-equivalence value were also observed from 2010-2011. The results revealed that E. abyssinica had significantly higher (p<0.05) N content (4.2%) than E. brucei (3.5%) and E. ventricosum (2.4%). All the three plant species had lignin and polyphenol <15 and 5% respectively, implying the likelihood to decompose faster in soil. Based on the N, lignin and polyphenol contents, both Erythrina spp. are considered as high quality (Class-1) organic materials. Enset, is rated as a Class-3 plant material hence should be composted or mixed with inorganic fertiliser before applying on field. The mean P contents of E. abyssinica, E. brucei and E. ventricosum were found to be 0.39, 0.38 and 0.26 % respectively. In Contrast E. Ventricosum had significantly higher (4.2%) K content than E. abyssinica, (2.6%) and E.brucei (2.0%).The mineralisation results showed that both Erythrina spp released more than 80% of their N content within two weeks of incubation. E. ventricosum achieved maximum N-mineralisation after four weeks of incubation.The experiment on the effect of E. brucei biomass on wheat yield and N-equivalence value showed that the application of 2.5 t DM/ha increased wheat grain and straw yields by 127% and 194% respectively. E. brucei biomass resulted in N-equivalence value of 43kgha-1 of N-fertiliser with relative fertiliser equivalence value of 93%. The study has provided both field and laboratory information on the beneficial effect of E. bruei biomass as organic fertiliser for improving crop yield. Thus, dissemination of the technology in areas where the tree is found abundantly in Ethiopia is recommended. Further, real time field experiment on the effect of E. abyssinica and E. ventricosum biomass on yields and soil quality should be studied extensively.