Effect Of Alternate Partial Root-zone Irrigation On Microbial Biomass C, N And Enzymatic Activity In Soil

Alternate partial root-zone irrigation creates a heterogeneous soil moisture distribution that may affect soil microbiological activity and crop water-and nutrient-use. In order to understand such effect, this study investigated soil microbial biomass C (MBC) and N (MBN), soil enzymatic activity and water-and nutrient-use efficiency of maize under different water and nitrogen treatments. Pot experiment1included three irrigation methods, i.e. conventional irrigation (CI, soil was evenly irrigated in each watering), alternate partial root-zone irrigation (AI, watering was alternately applied to the two halves soil in consecutive watering) and fixed partial root-zone irrigation (FI, watering was fixed to one side), and two irrigation levels, i.e. normal irrigation (W1,70%-80%field capacity) and mild water deficit (W2,60%-70%field capacity), and two ratios of inorganic to organic N, i.e.100%inorganic N (F1) and70%inorganic N+30%organic N (F2). Pot experiment2included four irrigation methods, i.e. conventional irrigation (CI) and alternate partial root-zone irrigation (AI)(respectively carried out at seedling-early grain filling, seedling-jointing and jointing-tasselling stages, i.e. All, AI2and AI3), two irrigation levels (W1, W2) and two ratios of inorganic to organic N (F1, F2). The main results were outlined in the following:1. The pot experiment1shows that AI increased soil MBC at jointing stages, but reduced soil MBN. And soil MBN and CO2release quantity of induced respiration in the dry side of FI were significantly reduced. Compared to only inorganic N, combined application of organic and inorganic N increased soil MBN at jointing stages, dissolved organic carbon (DOC) and catalase activity. 2. The pot experiment2shows that:(1) Alternate partial root-zone irrigation at jointing-tasselling stages increased soil MBC and DOC and soil MBN at the tasselling stage, but reduced CO2release quantity of induced respiration in soil. Under certain soil moisture conditions (W1CI, W1Al1and W1AI2), combined application of organic and inorganic N increased soil DOC at the jointing and tasselling stages and CO2release quantity of basic and induced respiration in soil at the early grain filling stage when compared to only inorganic N.(2) Compared to CI, AI increased soil urease and invertase activity at the tasselling and early grain filling stages, mild water deficit increased soil urease and invertase activity at the early grain filling stage and catalase activity at the three stages, F2increased soil urease and invertase activity at the early grain filling stage under AI3conditions.(3) Compared to CI, all AI treatment increased root N content, and AI2increased shoot N content under F2conditions, AI2and AI3significantly increased shoot and total N uptakes of maize, but the K content of maize under All was lower than the other treatments. Combined application of organic and inorganic N significantly increased shoot and total N contents under AI2, but significantly reduced soil available N and K contents.(4) Under mild water deficit condition, alternate partial root-zone irrigation at jointing-tasselling stages increased total dry mass and water use efficiency of maize by23.2%-27.4%and23.3%-26.7%, respectively. Combined application of organic and inorganic N increased total dry mass of maize.Therefore, alternate partial root-zone irrigation at the jointing-tasselling stage could increase total dry mass and water use efficiency of maize, soil microbial biomass carbon, soil dissolved organic carbon, and soil urease and invertase activity under mild water deficit condition.