Construction and screening of complex microbial system for efficient degradation of rice straw and their application effects under field condition

  Objectives  To overcome the adverse effect of slow in situ degradation of rice straw, high-efficiency multifunctional complex microbial agents suitable for rapid in situ decomposition of rice straw were screened and constructed.

  Methods  Straw decomposition strains were screened and isolated from the surface soil with rotten straw in a rice field. The carboxymethyl cellulase activity, filter paper disintegration, and rice straw degradation ability of these strains were determined by DNS, shake flask culture observation, and weight-loss method. The strains with high degradation effects were identified by 16S rRNA or 18S rRNA. Complex microbial agents were constructed by selecting the strains without antagonistic effect. We used filter paper to measure enzyme activity, and used rice straw to measure the degradation rate under laboratory conditions. We selected the agents with higher degradation effects for field experiments. The straw degradation rate, soil organic matter, available nutrients, and rice yield were investigated.

  Results  Strains B2, B5, B6, F1, F5, and F12 were identified as Bacillus velezensis, Bacillus halotolerans, Bacillus subtilis, Aspergillus oryzae, Aspergillus niger, Trichoderma longibrachiatum, respectively. The degradation rates of these strains were all higher than 19.8%. The degradation rate of F12 was the highest (29.1%). Seven complex microbial agents were constructed with the six strains identified. Complex microbial agents B2+F12, F1+F5+F12 and B2+F5+F12 showed good degradation effects in the straw liquid medium, and the degradation rates were 32.9%, 29.8%, and 40.3%, respectively. B2+F5+F12 showed the highest potential for application in field. Compared with no agent, the in situ degradation rate of rice straw increased by 37.1 percentage point. Soil organic matter, alkali hydrolyzable N, available P, and readily available K increased by 2.1 g/kg, 1.9 mg/kg, 0.6 mg/kg, and 1.7 mg/kg, respectively. Similarly, rice yield (P<0.05) increased by 6.3%.

  Conclusions  Complex microbial system B2+F5+F12 had good rice straw degradation ability. It increased the contents of soil organic matter, alkali hydrolyzable N, available P and K, which promoted crop yield improvement. Therefore, we conclude that complex microbial agent B2+F5+F12 has good application potential.