Organic Manures in Relation to Rhizosphere Effect III. Effect of Organic Manures on Population of Ammonifying Bacteria and Mineralization of Nitrogen in Rice and Succeeding Wheat Rhizosphere Soils

Abstract

Summary Ammonifying bacteria were stimulated in the rhizosphere of rice with green manuring (control), while depressed with town compost (TC) at early tillering stage. The growth of cellulose decomposers was greatest with ammonium sulphate (AS). Except under control and farm yard manure (FYM), the number increased with time and with the age of the crop at final harvest, the highest was with rice straw (RS) + rock phosphate (RP). At this stage, the abundance of cellulose decomposers was greatest with RS + AS. AS induced the best residual effect on the proliferation of ammonifying bacteria and RS + RP on cellulose decomposers in the rhizosphere of wheat. Green manuring (control) promoted the growth of ammonifying Bacillus, which was further intensified with TC in the rice rhizosphere. Residually Pseudomonas was stimulated by the manures in the wheat rhizosphere. At early tillering stage of rice, mineralization of nitrogen in the rhizosphere decreased with the manures, excepting AS and AS + RP. Barring under RS + RP, the transformation declined with the age of the crop. AS and RP, either alone or together, also provided a favourable condition for nitrogen mineralization, residually in the rhizosphere of wheat. In this respect, the rhizosphere effect of wheat under the residual influence was superior to that of rice under the direct influence of the manures. The process was positively correlated with the number of ammonifiers, being significantly in the wheat rhizosphere at final harvest.