Changes in Enzyme Activities in Salt-Affected Soils during Incubation Study of Diverse Particle Sizes of Rice Straw

Soil enzymes are linked to the plant–soil–enzyme–soil nutrients of the soil system, which play an important role in carbon cycling and phosphorus mineralization in soil. Monitoring soil biological quality, particularly enzyme activities, after receiving organic amendments is a prerequisite for the sustainable management of soils. An incubation study was conducted to evaluate the effect of different particle sizes of rice residue (control, powdered, 1 cm, 2 cm, 5 cm, and 10 cm) on the enzymatic activities in three soils (normal, saline, and sodic). The soils used in the study were alkaline in reaction with a pH range of 7.05–8.86 and an electrical conductivity (EC) gradient from 0.41 to 2.5 dS m−1. Significant changes in the soil enzyme activity (dehydrogenase, fluorescein diacetate, and alkaline phosphatase) were observed with the incorporation of rice residue as compared to control. The enzymatic activities were substantially enhanced with a decrease in the size of the residue up to 28 days during the incubation period. The maximum enzymatic activity in the three soils was found to be in the order of normal > sodic > saline soils. These results suggest that the particle size of rice residues and salt levels should be considered important factors in residue decomposition in soils, as they directly influence the activity of soil enzymes for the overall improvement of the biological pools in soils.