关键词: 降雨分布, 渭北旱地, 春玉米, 临界氮浓度, 氮营养指数

Abstract:

The excessive nitrogen (N) applications, large rainfall variations and poor water-nitrogen couplings are main problems to efficient nitrogen fertilizer uses in spring maize production of Weibei dryland. Critical nitrogen dilution curves under different rainfall scenarios in Weibei dryland were constructed in this study to analyze the feasibilities of diagnosing and evaluating nitrogen nutritional conditions in terms of nitrogen nutrition index (NNI), which would provide a theoretical basis for reasonable nitrogen fertilizations application of dryland maize in response to different rainfalls. The experiment design using Zhengdan 958 (ZD958) and Shaandan 8806 (SD8806) as tested materials was five treatments level, N applied at 0(N0), 75(N1), 150(N2), 270(N3), and 360(N4) kg hm^-2 in 2016 and 2017, and at 0(N0), 90(N0), 180(N2), 270(N3), and 360(N4) kg hm^-2 in 2018 and 2019, respectively. It was rainy at the ear stage and dry at the grain stage in 2016 and 2018, whereas dry at the ear stage and rainy at the grain stage in 2017 and 2019. Critical nitrogen dilution curve models for spring maize with two precipitation patterns were constructed and verified using the data collected in the four-year position nitrogen fertilization experiment. The results showed that: (1) increased nitrogen fertilizer application significantly increased aboveground biomass and plant N concentrations, and there were significantly different among different treatments. Both critical nitrogen concentrations (N_c) and aboveground biomass conformed the exponential relations with the two precipitation patterns, but there were differences between the parameters of the models for these relations (a. Rainy at the ear stage: N_c = 35.98DM^-0.35; b. Dry at the ear stage: N_c = 35.04DM^-0.23). The relatively stable model had a linear correlation between the fitted and actual plant N concentrations, which shown that the RMSE and n-RMSE were 1.03 and 5.75% at the ear stage over the rainy years and 1.53 and 6.78% at the ear stage in the dry years, respectively. (2) at the different growth stages, NNI were increased with the increased application, and there were differences in the optimal nitrogen application under different precipitation conditions. The optimum N rate in the form of basal fertilizers was 150-180 kg hm^-2, and in the form of top dressing fertilizers was 45-75 kg hm^-2 at the ear stage in the rainy years. The nitrogen nutrition index (NNI) was significantly correlated with relative nitrogen uptake (RN_upt), as were relative aboveground biomass (RDW) and relative yield (RY). When the NNI was 1.02 at the ear stage in the rainy years, the maximum RY was 0.95; and when the NNI was 1.08 at the ear stage in the dry years, the maximum RY was 0.92. The critical nitrogen dilution curve model and nitrogen nutrition index model constructed in this study were able to accurately predict nitrogen nutrition conditions from jointing stage to maturity stage under the two precipitation patterns of spring maize. They would provide an important guidance for nitrogen diagnosis and fertilization application in maize growing stage.

Key words: precipitation pattern, Weibei dryland, spring maize, critical nitrogen dilution curve, nitrogen nutrition index