Effect of integrated nutrient management practices on soil enzyme activity and microbial population in paddy

Abstract

A field experiment was conducted at College Farm, S.V. Agricultural College, Tirupati during kharif, 2022-23 to study the effect of integrated use of organic manures, green manures, biofertilizers and inorganic fertilizers on enzymatic activity and microbial population in paddy. The experiment was laid out in a split-plot design with seven main plots and three sub plots with three replications. The main plots comprised of seven different combination of organic manures viz., M1: FYM @ 10 t ha-1 M2: Green manure seed (dhaincha) @ 25 kg ha-1), M3: FYM @ 5 t ha-1 + Green manures seed @ 12.5 kg ha-1, M4:FYM @ 10 t ha-1 + Azospirillum + PSB + KRB @ 1.25 l ha-1 each, M5: Green manure seed @ 25 kg ha-1 + Azospirillum + PSB + KRB @ 1.25 l ha-1 each, M6: FYM @ 5 t ha-1 + Green manures @ 12.5 kg ha-1 + Azospirillum + + KRB @ 1.25 l ha-1 each and M7:Control. Sub-plots comprised of three levels of fertilizers viz., S1: 50% RDF, S2:75% RDF and S3:100% RDF. The enzyme activity was estimated and total microbial population was recorded in soil at panicle initiation and harvest stage of paddy crop. Among the various organic combinations, significantly the highest urease, dehydrogenase and phosphatase activity was recorded with FYM @ 5 t ha-1 + green manures @ 12.5 kg ha-1 + Azospirillum + KRB @ 1.25 l ha-1 each which was on par with the application of green manures @ 12.5 kg ha-1 + Azospirillum + PSB + KRB @ 1.25 l ha-1 each (M5) and FYM @ 10 t ha-1 + Azospirillum + PSB + KRB @ 1.25 l ha-1 each (M4) and the lowest was recorded with control (M7). However, among the fertilizer levels, the highest enzyme activity was obtained with 100% RDF (S3) which was comparable with 75% RDF (S3) and 50% RDF (S3). Similarly, among various organic combinations, significantly the highest total bacteria, fungi and actinomycetes population were recorded with FYM @ 5 t ha-1 + green manures @ 12.5 kg ha-1 + Azospirillum + KRB @ 1.25 l ha-1 each (M6) which was on par with the application of green manures @ 12.5 kg ha-1 + Azospirillum + PSB + KRB @ 1.25 l ha-1 each (M5) followed by FYM @ 10 t ha-1 + Azospirillum + KRB @ 1.25 l ha-1 each (M4) and the lowest were recorded with control (M7). However, among the fertilizer levels, the highest microbial population was recorded with 100% RDF (S3) which was comparable with 75% RDF (S2) and 50% RDF (S1). The enzyme activity and microbial population were highest in combined application of FYM @ 5 t ha-1 + green manures @ 12.5 kg ha-1 + Azospirillum + KRB @ 1.25 l ha-1 each along with application of 75% RDF (M6S2) at both PI and harvest of paddy.