Growth and nutritional response of sesbania sesban (L) merr to rock phosphate, biofertilizer and rhizobial applications

Abstract

Sesbania sesban (L.) Merrill is a leguminous tree currently planted in western Kenya and other regions within East and Central Africa as an improved fallow species. This species is planted to restore soil fertility of degraded smallholder farms through production of high-quality biomass that, when applied as green manure or mulch, usually improves yields of food crops planted after the fallow periods. Most studies testing leguminous trees in improved fallow agroforestry practices take .little account of rhizobial inoculation or P requirements of planted trees which may enhance biological nitrogen fixation (BNF). Therefore, it is important to know the extent to which the presence of effective Rhizobium and soil nutrient status,especially P, affect biomass production, biological N2-fixation and overall nutrient uptake by S. sesban. A greenhouse experiment was set up in 2 x 2 x 2 factorial design to study the. effects of three treatments on growth and nutritional responses of S sesban to Rhizobium (KFR 647) inoculant, Minjingu rock phosphate,and commercial biofertilizer. Rhizobial inoculation significantly increased root nodulation by about 50% exclusively when P was added as rock: phosphate. Phosphorus fertilization increased plant height (58.3 cm vs. 29.6 cm in the control}. Approximately 90% more biomass was obtained with P fertilization alone compared to the control or sole rhizobia inoculation treatments, and 68% more compared to the· commercial biofertilizer alone or when combined· with rhizobia. Fertilization with rock phosphate significantly improved biological N2-fixation rates and overaIl nutrient uptake, while biofertiIizer application enhanced plant nutrient uptake. However, a significant interaction between rock phosphate and biofertilizer increased growth performance of S. sesban.