Partial root-zone irrigation enhanced soil enzyme activities and water use of maize under different ratios of inorganic to organic nitrogen fertilizers

Partial root-zone irrigation (PRI) is an effective water-saving irrigation method but the heterogeneous soil moisture distribution that may affect soil enzymatic activities and crop water use. With pot-grown maize, we investigated the dry mass accumulation, crop water-use efficiency and the activities of four major soil enzymes from jointing to grain filling stages of maize plants subjected to PRI and also different ratios of inorganic to organic N fertilizers. Three irrigation methods, i.e. conventional irrigation (CI), alternate PRI (APRI) and fixed PRI (FPRI) and three ratios of inorganic to organic N, i.e. 100% inorganic (F-1), 70% inorganic + 30% organic (F-2) and 40% inorganic + 60% organic (F-3), were applied. Compared to CI, PRI reduced total dry mass and water consumption of maize by 9.5 and 15.7%, respectively, which led to an increase of canopy water-use efficiency by 7.4%. Within the same irrigation method (Cl, APRI or FPRI), added organic N increased total dry mass and canopy WUE. During the whole period, maximal soil catalase, urease and acid-phosphatase activities occurred in the wet root-zone of PRI, but maximal invertase activity occurred in the dry root-zone of PRI. When organic N was the most (F-3), APRI increased soil catalase, urease and invertase activities at jointing stage if compared to CI, but PRI reduced the acid phosphatase activity from jointing to filling stages. Soil catalase, urease and invertase activities generally increased with more organic manure, but the maximal acid-phosphatase activities occurred under moderate amount of organic N (F-2). Our results indicate that APRI increases canopy WUE and the catalase, urease and invertase activities in its wet zone and organic N plays a major role in enhancing canopy WUE and soil enzymatic activities. (C) 2009 Elsevier B.V. All rights reserved.