基于密切值法和水氮管理模型的华北平原农田水氮优化管理

优化农田水氮管理措施可为实现粮食高产、资源高效及环境友好的目标提供科学依据。该研究以华北平原泰安地区为例,利用农田生态系统水热碳氮过程耦合模型(soil water heat carbon and nitrogen simulator,WHCNS)分别对冬小麦季设置的165个水肥组合和夏玉米季设置的55个水肥组合进行了情景模拟分析,在综合考虑农学、环境和经济效益的基础上,采用密切值法优化了农田水肥管理方案。结果表明:受到华北地区年内降雨分配不均的影响,冬小麦产量随着灌水量的增加呈先增加后稳定的趋势;而夏玉米产量与灌水量没有明显的关系。冬小麦和夏玉米产量均随着施肥量的增加而增加,后保持稳定。水分渗漏和氮素淋洗量均随着灌水量或施肥量的增加而显著增加。在研究区作物秸秆全部还田及高累积氮的条件下,冬小麦季灌水240 mm和施肥60 kg/hm~2(以N计,下同),夏玉米季不灌溉和施肥90 kg/hm~2分别为研究区当年冬小麦季和夏玉米季最佳的水肥管理方案。在所有水肥组合情景中,优化的水肥管理方案不仅能保证冬小麦-夏玉米最大周年产量的97%、具有较高的水氮利用效率和最佳的产投比,而且氮素淋洗和气体损失分别比最大值降低了77%和71%。因此,该方法可以用来优化华北平原农田的水肥管理措施。

Optimal management of water and nitrogen for farmland in North China Plain based on osculating value method and WHCNS model

Abstract: Optimizing water and nitrogen (N) management is important for high grain yield, resource-efficient and environment-friendly targets in North China Plain (NCP). In this study, the Soil Water Heat Carbon and Nitrogen Simulation (WHCNS) model was combined with the osculating value method to achieve this objective. A 2-year experiment involving 4 integrated management practices was conducted in Tai''an City, Shandong Province in the NCP. These management practices were designed as follows: 1) traditional farming practice (FP); 2) optimized combination of cropping and fertilization (OPT-1); 3) practice for high yield (HY), which did not consider the cost of resource inputs to maximize grain yield; and 4) further optimized combination of cropping and fertilization (OPT-2), which was based on the HY practice. The dynamics of soil water content and soil nitrate concentration in different soil depths were monitored, crop dry matter and leaf area index at the key crop growth stages and yield were measured. These dataset was used to test the WHCNS model. After calibration and validation, the scenario analysis was conducted by the validated WHCNS model, which included 165 scenarios of winter wheat and 55 scenarios of summer maize with different water and N management combinations. The osculating value method was then employed to obtain the best management practices (BMPs). This method took into account agronomic, environmental and economic benefits. The results showed that the winter wheat yield increased firstly with the amount of irrigation and then kept steady when reached the maximum. There was no significant relationship between maize yields with irrigation due to the summer maize growth was synchronized with rains in NCP. The yield of winter wheat and summer maize increased with the amount of fertilizer firstly, and then remained stable when reached the maximum. The amount of water drainage and nitrogen leaching increased significantly with the irrigation amount and fertilizer application rates. The optimal irrigation amount and fertilization rates were 240 mm and 60 kg/hm2 (based on N) for winter wheat, respectively. The fertilizer-N application at a rate of 60 kg/hm2 with no irrigation was the BMPs for summer maize. Of all the scenarios, the BMPs could guarantee 97% of the maximum annual yield (16 220 kg/hm2), higher water and N use efficiency and the highest value-cost ratio (VCR), whilst N leaching and gas loss reduced by 68% and 56%, respectively. Thus, this method can be used to optimize management of water and nitrogen in farmland effectively.