Phosphorus use efficiency and productivity as influenced by microbial inoculants in vegetable Cowpea

Abstract

An experiment was conducted at the Instructional Farm attached to the College of Agriculture, Vellayani during December 1998 - April 1999 with the objectives of finding out the role of bioinoculants viz. arbuscular mycorrhizal fungi (AMF) and phosphate solubilising microorganisms (PSM) in improving the phosphorus use efficiency and productivity in vegetable cowpea var. Sharika. The experiment was laid out in 3 x 4 + 2 factorial randomised block design with three replications. The treatments included three levels of microbial inoculants and four levels of phosphorus along with two control treatments. The study revealed that crop failed to show a significant response to the use of bioinoculants and phosphorus levels in a soil with low available nitrogen and medium phosphorus status. Biometric characters except length of vine at vegetative stage was influenced by phosphate solubilising microorganisms as well as dual application of PSM and AMF. Phosphorus application as well as interaction effect did not show a positive response on growth parameters except LAI at harvest stage where in interaction effect was significant. Bioinoculants and phosphorus application exerted a profound influence on root length and volume. Dual inoculation of AMF and PSM significantly improved root length and volume. Phosphorus application at all

levels improved root mass where as maximum root length and volume were reco;ded at P2 level. Interaction effects were significant only with respect to root volume and root mass. Mycorrhizal colonisation percent was highest with M3P2 (AMP + PSM + 15 kg P20S ha-I) and showed a decreasing trend with higher doses of phosphorus. Microbial inoculants showed only limited role in improving yield and yield attributes. In general, crop responded positively to phosphorus application only up to 30 kg P20S ha-I but it was on par with 15 kg P20S ha-I. Among the interaction effects, dual application of AMP + PSM along with 30 kg P20S ha-1 gave the highest yield. The effect of microbial inoculants in promoting growth and yield of crop was found to decline in the presence of higher doses of applied phosphorus. Quality characters of pod viz. protein and fibre content were significantly improved by bioinoculants and graded doses of phosphorus. Dual inoculation of AMP and PSM significantly increased protein content as well as reduced fibre- content of pod . . Available nitrogen content in soil after harvest did not show any significant variation among treatments but bioinoculants significantly improved residual K20 content in soil. Available P20S content at vegetative, flowering and harvest stages recorded higher values compared to initial status. Treatments M3 and P2 recorded the maximum available P20S content at vegetative and flowering stages. But at harvest stage, lowest residual P20S

content was recorded at P3 level indicating higher uptake by the crop at later stages. Interaction effects were significant with respect to P20S content only at vegetative stage. The results of economic analysis revealed that the net income and benefit-cost ratio was maximum by dual inoculation of arbuscular mycorrhizal fungi and phosphate solubilising microorganisms along with a phosphorus level of30 kg P20S ha-I.