Comparative study of enriched compost, inorganic fertilizer and PGPR on soil fertility status and physiology of wheat (Triticum aestivum L.)

Abstract

Present investigation was aimed to formulate an efficient phosphatic bio-fertilizer to supplement or substitute chemical fertilizers and to evaluate its effect on the availability of P for growth and yield of wheat. For this purpose rock phosphate enriched compost (RPEC) was prepared and the effect of plant growth promoting rhizobacteria (PGPR) was evaluated for phosphorus availability through composting. Impact of PGPR alone or in combination with different (organic and inorganic) fertilizers were studied on wheat crop grown under natural conditions of field and axenic condition of pots. In the first experiment, poultry litter alone and in combination with rock phosphate was composted with and without PGPR (Pseudomonas sp. and Proteus sp.) inoculation in pits for 120 days (d) and shuffled with 10 d interval for proper aeration. The RPEC prepared by the combination of poultry litter, rock phosphate (RP) and Pseudomonas sp. inoculation showed maximum total phosphorus, available (Mehlic-3 extracted) phosphorus, microbial biomass (carbon and phosphorus), but lower total organic carbon, total nitrogen and carbon/nitrogen ratio over poultry litter without inoculation and addition of RP. Pseudomonas sp. enhanced P solubilization from rock phosphate (RP) and showed 79% higher P availability from RP added poultry litter over un-inoculated treatment on 120th day of composting. Experiments under natural condition of field as well as under axenic condition in pots were conducted for two consecutive years. The residual impact of the treatments were also studied on soil chemical and biological properties. The wheat seeds were surface sterilized and inoculated with Pseudomonas sp. (Accession No. KF307201) and Proteus sp. (Accession No. KF307202) at the rate 106cells ml- 1 prior to sowing. Seven treatments; simple poultry litter (SPLC), Rock phosphate enriched compost (RPEC1, inoculated with Pseudomonas sp. during composting), RPEC2 (solubilized with Proteus sp. during composting), Rock phosphate, Half recommended dose of inorganic P fertilizer (HDP) and Full recommended dose of inorganic P fertilizer (FDP) were applied with and without seed inoculation of PGPR (Pseudomonas sp. and Proteus sp.). Average of two year data on field and pot experiments showed increase in plant height, number of tillers, grain yield, dry matter yield, seed phosphorus and plant P-uptake with application of Pseudomonas sp. solubilized rock phosphate enriched compost compared to recommended dose of inorganic (single super phosphate) fertilizer. The chlorophyll content and phytohormones (Indole Acetic Acid and Gibberellic Acid) in flag leaves were also enhanced with application of rock phosphate enriched vii compost. Post-harvest soil phosphorus availability, nitrate nitrogen content, extractable potassium, alkaline phosphatase activity and microbial biomass increased with the application of rock phosphate enriched compost over full recommended dose of inorganic fertilizer. Moreover, seed inoculation with PGPR (Pseudomonas sp.) also significantly increased yield and yield parameters of wheat and post-harvest soil properties over un-inoculated treatments. Economic analysis in terms of value cost ratio showed 3.23:1 from the treatment where RPEC in combination with Pseudomonas sp. seed inoculation was applied. Thus rock phosphate enriched compost can be used as an alternate to inorganic phosphatic fertilizers and seed inoculation with Pseudomonas sp. can enhance wheat growth and yield applied in combination with enriched compost. In another experiment, wheat (AGS2060) root phosphatase activity was also determined in presence of different P sources; compost (C), rock phosphate (RP), single super phosphate (SSP), C + RP, C + SSP, RP + SSP, C +RP + SSP and results showed maximum (447%) increase in P mineralization with compost (C) grown roots over SSP. It was inferred that compost is the best source to mineralize organic P for better crop production.