Objectives Many factors impact the promotion effect of some identified inoculants on straw decomposition under natural environment. Activities of extracellular enzymes are closely related to straw decomposition and nutrients release. We testified and compared the promotion effects of three kinds of inoculants from straw decomposition rate and the activities of main extracellular enzymes.
Methods The litter bag method was used in a straw returning field experiment that was carried out in the double-cropping rice planting area of Shanggao County, Jiangxi Province during the late rice season. The Pseudomonas, Bacillus, Penicillium and commercial inoculants were used as treatments, and no inoculant as control. The straw samples were collected on the 7th, 14th, 28th, 56th and 84th day since the straw bags were buried into field, and the straw mass were weighed, the nutrients contents and extracellular enzymes activities were measured. The decomposition rate of straw was calculated according to the mass loss between that on the sampling date and the initial.
Results 1) Whether adding inoculants or not, the decomposition rate of rice straw was fast at beginning and slow down gradually. Compared with control during 0–84 days, straw burying, the Pseudomonas significantly increased straw decomposition rate by 5.6%, and the C, N and P release rates by 9.09%, 11.66% and 7.87%; the Penicillium significantly increased straw decomposition rate by 5.2% and N release rate by 7.46%; commercial inoculant, however, only significantly improved straw decomposition rate on the 14th day, and the Bacillus did not have any significant promotion effect in all the sampling dates. 2) Decomposition time was the most important factor affecting enzyme activities, and microbial inoculants affected enzyme activities to different extent as well. Among the extracellular enzymes, N-acetyl-glucosamidase and β-glucosidase activity were the two dominant variable factors affecting straw decomposition, followed by phosphatase and β-cellobiosidase activity. Under Pseudomonas treatment, the activities of N-acetyl-glucosamidase, β-glucosidase (excluding the 14th day) and phosphatase were significantly higher than those in control treatment. However, the enzymes activities were not stable under Penicillium, Bacillus and commercial inoculants treatments. Penicillium significantly increased activity of N-acetyl-glucosamidase only in the initial 14 days. 3) Microbial inoculants showed different yield increase effect on late rice, with the highest increase of 9.92% by Pseudomonas inoculant treatment.
Conclusions Activities of N-acetyl-glucosamidase and β-glucosidase are closely related to straw decomposition and nutrients release. Penicillium and Bacillus have short and unstable promotion effect, so both of their inoculants have not showed satisfactory yield effect. Pseudomonas can significantly promote the activities of N-acetyl-glucosamidase and β-glucosidase during the whole decomposition period (0–84 day), therefore, the pseudomonas inoculant has significant yield increase effect on late rice when applied into soil.
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