Effects of partial root-zone irrigation and ratio of organic to inorganic N on the enzyme activities in maize-planting soil

Partial root-zone irrigation (PRI) creates a heterogeneous soil moisture distribution which may affect soil enzymatic activities. Activities of four soil enzymes were investigated using PRI pot experiments under different ratios of inorganic to organic N fertilizers from jointing to grain filling stages of maize. There were three irrigation methods, conventional irrigation (CI), alternate PRI (APRI) and fixed PRI (FPRI), and three ratios of inorganic to organic N, 100% inorganic (F1), 70% inorganic+30% organic (F2) and 40% inorganic+60% organic (F3) in the experiment. The results show that highest values of soil catalase, urease and acid-phosphatase activities are in the wet root-zone of PRI, while the highest of invertase activity is in the dry root-zone of PRI from the jointing to grain filling stages. Under the F3 fertilization and APRI, soil catalase, urease and invertase activities are increased at the jointing stage compared to CI, while under the F3 fertilization and PRI, the acid-phosphatase activity is reduced from the jointing to filling stages. Soil catalase, urease and invertase activities are generally enhanced with increasing organic N ratio, but maximal acid-phosphatase activities occur under the moderate amount of organic N (F2). Our results indicate that APRI stimulates the catalase, urease and invertase activities in its wet zone, and organic N plays a major role in enhancing soil enzymatic activities.