Decay Kinetics of Enzymes as Influenced by Manuring Under Varying Hydrothermal Regimes in a Wheat–Maize Cropping System of Subtropical Cambisols in India

Abstract

This study highlighted the impact of different organic manuring on the decay kinetics and temperature sensitivity (Q10) of three enzymes viz. dehydrogenase (DHA), fluorescein diacetate hydrolase (FDA) and β-glucosidase (GLU) under varying hydrothermal regimes in the subtropical Cambisols in India. We hypothesised that along with organics, water content and temperature will also affect enzyme activities. Soil samples were collected from five treatments, viz., control, 100% nitrogen-phosphorus-potassium (NPK), vermicompost, compost and farmyard manure (FYM)–treated plots in an on-going maize-wheat field experiment, and were incubated at 25 and 35 °C temperatures and 0.033 and 0.1 MPa soil water contents. Activities of all enzymes were found higher in organic-treated plots than NPK-treated plots throughout the incubation period due to higher substrates and energy supply. At constant water content, the increased temperature significantly increased the decay rates of all the enzymes owing to dissolution and diffusion of carbon substrates towards active sites of enzymes. However, at a specified temperature, water stress decreased the decay rates in vermicompost- and compost-treated soils but increased in FYM-treated soils, indicating a significant influence of soil amendments on the decay kinetics due to specific microbial adaptation mechanisms and substrate biochemistry of FYM. The Q10 values of DHA and FDA increased by ~ 59 and 46%, respectively but that of GLU decreased by ~ 44% with declining water content due to their capacity to degrade diverse substrates in the soils. FYM application could be beneficial for nutrient mineralisation under adverse conditions to support plant nutrient demand.