Phosphomonoesterase Activities, Kinetics and Thermodynamics in a Paddy Soil After Receiving Swine Manure for Six Years

Soil phosphomonoesterase plays a critical role in controlling phosphorus (P) cycling for crop nutrition, especially in P-deficient soils. A 6-year field experiment was conducted to evaluate soil phosphomonoesterase activities, kinetics and thermodynamics during rice growth stages after consistent swine manure application, to understand the impacts of swine manure amendment rates on soil chemical and enzymatic properties, and to investigate the correlations between soil enzymatic and chemical variables. The experiment was set out in a randomized complete block design with three replicates and five treatments including three swine manure rates (26, 39, and 52 kg P ha−1, representing low, middle, and high application rates, respectively) and two controls (no-fertilizer and superphosphate at 26 kg P ha−1). The results indicated that the grain yield and soil chemical properties were significantly improved with the application of P-based swine manure from 0 to 39 kg P ha−1; however, the differences between the 39 (M39) and 52 kg P ha−1 treatments (M52) were not significant. The enzymatic property analysis indicated that acid phosphomonoesterase was the predominant phosphomonoesterase in the tested soil. The M39 and M52 treatments had relatively high initial velocity (V0), maximal velocity (Vmax), and activation grade (lgNa) but low Michaelis constant (Km), temperature coefficient (Q10), activation energy (Ea), and activation enthalpy (ΔH), implying that the M39 and M52 treatments could stimulate the enzyme-catalyzed reactions more easily than all other treatments. The correlation analysis showed that the distribution of soil phosphomonoesterase activities mainly followed the distributions of total C and total N. Based on these results, 39 kg P ha−1 could be recommended as the most appropriate rate of swine manure amendment.