Efficacy of polymer coated diammonium phosphate bioaugmented with endophytic bacteria on growth, yield and phosphorus use efficiency of wheat (Triticum aestivum L.)

Abstract

Efficiency of applied phosphatic fertilizers on calcareous soil is very low, 10–25%. This is due to high calcium activity that substantially retards P availability to plants. Saving of phosphate fertilizer from calcium or solubilizing the fixed P is in fact improving its availability to plant. Coating granules of diammonium phosphate (DAP) fertilizer with polymer-entrapped bacteria can improve availability of P and deliver microbe in rhizosphere for improving P use efficiency and crop production. A series of experiments including laboratory, wire house and field were conducted to investigate the efficacy of polymer coated DAP bioaugmented with endophytic bacteria on growth, yield and P use efficiency of wheat (Triticum aestivum L.). Polymer including carboxymethyl cellulose (CMC), polyacrylamide (PAM) and alginate and pre-isolated wild type and their derivatives endophytic bacteria strains Enterobacter sp. MN17 and Burkholderia phytofirmans PsJN were taken for experiments. Polymer solutions and endophytes inocula were mixed by unit ratio. In laboratory experiments, different concentrations (0.5, 1 and 1.5%) of three polymers CMC, PAM and alginate were taken to check the microbial survival over different time intervals. Selected concentrations of alginate (1.5%), CMC (1%) and PAM (0.50%) and carbon sources [(G) 1%, glycerol (Gly) 1% in separate and then combination (G 1% + Gly 1%)] prototype solution was prepared to determine microbial survival at different time intervals. The best selected polymers concentration and carbon source (polymer + (1% G + 1% Gly) + MN17 or PsJN) prototype solution was coated on DAP granules and recovery of microbes from coated DAP surface was counted at different storage temperatures i.e.10, 25 and 40°C up to three months. Maximum microbes survive rate was recorded on DAP granules surface stored at temperature 10°C in order of alginate, PAM and CMC entrapped microbes, respectively, followed by 25 and 40°C storing temperature, respectively. Coated DAP fertilizer with alginate (1.5%), CMC (1%) and PAM (0.50%) along with {(G + Gly) + MN17 or PsJN)} was placed in cups containing 200 g soil at rate 1 g 100-1 g soil along with alone polymer coated and uncoated DAP as control to elucidate the P release pattern in soil at different field capacity (FC) moisture levels (50, 75 and 100% of FC) and temperatures (10, 25 and 40°C) up to two month. Best performing organically complex polymer-entrapped endophytic bacteria coated DAP fertilizer i.e. alginate (1.5%) and PAM (0.50%) along with {(1% G + 1% Gly) + MN17 or PsJN)} was selected and tested under wire house and field conditions. Results revealed that application of alginate-entrapped MN17 coated DAP at recommended rate increased plant height (36%), chlorophyll content (41%), photosynthesis rate (67%), grain yield (83%), grain P (39%), Straw P (30%), total P uptake (90%) as compared to uncoated DAP. Maximum phosphorus recovery efficiency (165%) and agronomic efficiency (181%) was recorded in the treatment of alginate entrapped MN17 coated DAP applied at half of recommended rate over recommended rate of uncoated DAP treatment. Application of PAM entrapped MN17, alginate and PAM entrapped PsJN coated DAP at recommended rate were followed this treatment. Regarding microbial enumeration in rhizospheric soil and root endosphere results of pot trial showed that application of alginate entrapped MN17 coated DAP showed maximum recovery of MN17 in rhizosphere soil and root endosphere i.e. 12 ± 0.54 × 107 CFU-g soil and 3.78 ± 0.74 × 106 CFU-g root, respectively. So, it can be summarized that polymer entrapped microbes coated DAP is a novel approach that could effectively carry required count of microbes into the rhizosphere that is under conditions improve growth, yield and phosphorus use efficiency of wheat crop compared to alone either polymer coated DAP.