Effects of Water and Nitrogen Management on Root Morphology, Nitrogen Metabolism Enzymes, and Yield of Rice under Drip Irrigation

This paper explores the effects of water and nitrogen management on drip irrigated rice root morphology, nitrogen metabolism and yield, clarifies the relationship between root characteristics and yield formation. Normal irrigation (W-1, 10,200 m(3)/hm(2)) and limited irrigation (W-2, 8670 m(3)/hm(2), 85% of W-1) were set with nitrogen-efficient variety (T-43) and nitrogen-inefficient variety (LX-3) as the materials. Under the condition of a total nitrogen application rate of 300 kg/hm(2), three kinds of nitrogen management methods were applied, N-1: a seedling: tiller: panicle: grain ratio of 30%:50%:13%:7%; N-2: a ratio of 20%:40%:30%:10%; and N-3: 10%:30%:40%:20%. Their effects on root morphology, root architecture, and nitrogen metabolism enzyme activities were studied. The results showed, drip irrigated rice yields were highest under W1N2, reaching 9.0 t/hm(2) for T-43 and 7.3 t/hm(2) for LX-3. Compared with W-2, the root length density (RLD), surface area density (SAD), and root volume density (RVD) of finely branched roots, coarsely branched roots and adventitious roots increased by 49.5%, 44.6%, and 46.7%; the RLD, SAD, RVD, and root architecture RLD beta values of the 0-30-cm soil layer increased significantly (p < 0.05); and the yield and nitrogen partial factor productivity increased by 20.7% and 23.3%, respectively, under W-1. Compared with N-1, RLD, SAD and RVD in 0-10 cm soil layer under N2 increased significantly by 24.8%, 35.6% and 31.4%, and RLD beta decreased significantly (p < 0.05); Leaf GS, GOGAT and GDH were increased by 37.9%, 17.0% and 40.9%; all indexes showed a downward trend under N-3. Compared with LX-3, T-43 RLD, SAD, RVD increased significantly (p < 0.05), nitrogen metabolism enzyme activity increased, and yield increased by 21.8%. Rational water and nitrogen management can optimize the root growth and distribution characteristics and achieve simultaneous improvement of rice yield, nitrogen absorption, and nitrogen utilization efficiency under drip irrigation.