Evaluating Nitrogen and Water Management in a Double-Cropping System Using RZWQM

Simulation of water and nutrient processes can enhance intensive agriculture to help feed the world’s population in a sustainable manner. Due to excessive N application, environmental protection and agricultural sustainability have become major issues in agriculture. In this study, we calibrated and tested the RZWQM model to assess N management in a double-cropping system comprised of winter wheat (Triticum aestivum L.) and corn (Zea mays L.) at Luancheng, in the North China Plain. Data, including biomass, grain yield, soil water, and soil and crop N, were used from 2001–2003 field trials applying 200 to 800 kg N ha yr for five cropping seasons. In general, soil water, biomass, and grain yields were predicted better than plant N uptake or soil residual N. Once it had been tested and used to improve the understanding of N processes in this cropping system, the model was further used to evaluate the effects of alternative water and N management scenarios on N leaching. Typical application rates of bothwater andN could be reduced by about half based on these results, which would have high economic, social, and environmental impacts in China. The results also demonstrate the potential of RZWQM for evaluating N and water management practices in other regions and climates of the world with intensive agriculture. NITROGEN MANAGEMENTremains one of the most challenging tasks for sustainable agriculture, as it affects not only productivity and profit, but also other issues of importance to the environment such as NO3 contamination of ground and surface waters, greenhouse gas emissions and global warming. Elevated NO3 in groundwater has often been associated with overapplication of N fertilizers and irrigation water by producers anxious to achieve optimum yields (Schepers et al., 1991). Sexton et al. (1996) reported that NO3 leaching from corn grown on a sandy loam soil in central Minnesota increased rapidly as the N application rate exceeded 100 kg N ha yr. As N rates increased to about 250 kg N ha yr, NO3 leaching increased exponentially. Population and economic pressures worldwide have driven a general intensification of crop production. Sustained agricultural production is a particularly important issue for China, with its huge population of 1.3 billion. Winter wheat and summer corn are the staple grain crops. The deficit of grain (demand minus supply) has been about 27 million Mg yr recently in China (Zhou, 2004). In some high-yielding areas in the North China Plain (NCP), with great expansion of irrigated lands and large input of fertilizers (N application rates up to 450 kgNha yr) since the late 1970s, total grain production has increased three times and annual yield is up to 14 Mg ha. The NCP is one of the major agricultural areas in China (33 10 km) with a population of about 130 million people. It provides one-fifth of the nation’s food supply. In the future, increased total grain production will be mainly dependent on the increase of grain yield per hectare, because urbanization is decreasing the area of arable land. Fertilizer application is one of the key factors contributing to increased grain yield. Using 1Mg of fertilizer can cause an increase grain production by 8.84 Mg (Peng, 2000). Nitrogen fertilizer use is expected to rise continuously in China in the 21st century: 25millionMg in 2005, 27million Mg in 2010, and 30 million Mg in 2020 (Peng, 2000). Water management issues are coupled with fertilizer management. The mean annual rainfall of the NCP is about 480 to 500 mm. About 70% of the total rainfall occurs from July to September, the growing season of corn. Rainfall during the winter wheat growing season (October–June) is about 60 to 150 mm. Supplemental irrigation is required to support wheat production, as the consumptive water use of winter wheat is about 430 to 470 mm. Farmers in this region generally irrigate winter wheat four to five times each season, and corn is irrigated once or twice per year. Excess fertilizer application and overdraft of aquifers for irrigation have caused contamination and depletion of groundwater in the NCP (Zhang et al., 1995, 2003; Hu et al., 2005). Thus, for sustainable agriculture, it is necessary to develop comprehensive and improved N management recommendation tools to advise farmers. To maintain high yields while keeping adverse environmental impacts to a minimum, we need to effectively synthesize the knowledge accrued in various disciplines of agricultural research for timely solutions to practical problems in agriculture. Integration of information from field studies and processes through simulation modeling is recommended to identify solutions to such problems (Elliott andCole, 1989; Peterson et al., 1993).Agricultural systems simulation models can help synthesize much of the information accumulated from various experiments at various locations (Mathews and Blackmore, 1997). In general, all the reported studies for determining fertilizer recommendations for a locality made use of field experiments that have been done periodically with limited multiyear, multilocation replications, and conclusions are extrapolated statistically or otherwise. Fertilizer responses, depending on the soil and climate (especially rainfall) at the location, vary a great deal among years and locations. Field C. Hu and X. Li, Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences; S.A. Saseendran, T.R. Green, L. Ma, and L.R. Ahuja, USDAARS Great Plains Systems Research Unit, Fort Collins, CO 80526. Received 11 Jan. 2005. *Corresponding author ([email protected]). Published in Vadose Zone Journal 5:493–505 (2006).