Studies on the plant debris in rice paddy soils

Abstract

Samples described in the previous paper (1) were measured for microbial respiration and enzyme activities (β-g1ucosidase and β-acetylglucosaminidase). The samples obtained by physical fractionation from the plough layer of Nagano and Yamanashi soils were plant debris (>2 mm, 2-1 mm, 1-0.5 mm, 0.5-0.25 mm, 0.25-0.15 mm, 0.15-0.075 mm, and 0.075-0.037 mm), silt, and clay fractions. The results were as follows: 1) Microbial respiration and enzyme (β-g1ucosidase and β-acetylglucosaminidase) activities in various fractions of plant debris decreased with the decrease in particle size. Microbial respiration and enzyme activities in the clay fraction were much areater than those in the clay fraction. 2) Microbial respiration and enzyme (β-g1ucosidase and β-acetylaglucosaminidase) activities in each fraction were found to have a high correlation. This result suggests that specific enzyme assays may be a good index of microbial metabolic activities in the soils. 3) Microbial respiration, β-glucosidase, and β-acetylglucosaminidase activities of the plant debris fractions comprised 40–43%,36–45%, and 36–45%, respectively, of total activities in the soils. This fact suggests that plant debris in paddy soil, although referred to just as “plant debris zone” in this paper, is not only a suitable habitat for various microorganisms, but also plays an important role as active sites of soil metabolism.