Figure 3. Concentration of NO3 N in soil water at 1.5 m depth. Evaluation of Best Management Practices on N Dynamics for a North China Plain C. Hu 1, J.A. Delgado 2, and X. Li 2 1 Chinese Academy of Sciences, 2 USDA, ARS, Soil Plant Nutrient Research Unit, Fort Collins CO * Corresponding Author We need to evaluate the reliability and performance of computer simulation models under different agroecosystems to improve the use of quick assessment tools that can contribute to develop better N management practices. The USDA, ARS NLEAP version 1.2 was tested for surface irrigated corn (Zea mays L.) and wheat (Triticum aestivum L.) systems grown in a North China Plain. The needed data to calibrate and test the model and current Best Management Practices (BMPs) for a Northern China Plain was collected. Initial NLEAP analyses showed that N use efficiency (NUE) can significantly be increased by incorporating urea after surface application on these alkaline soils to reduce NH3 volatilization and with realistic N rates and no over application of N. Evaluation of BMPs showed the need to develop N management plans that accounts for N budgets, including the initial residual soil NO3 N, to increase NUE and reduce NO3 N leaching and NH3 volatilization losses. Preliminary evaluations show that over application of N will not significantly increase yields but will increase N loses to the environment. NLEAP was a tool capable of evaluating and simulating the effects of BMPs on N dynamics and NUE for these cropping systems of the North China Plain. ABSTRACT CONCLUSION MATERIALS AND METHODS INTRODUCTION Simulated residual N (kg NO3-N/ha) Observed residual N (kg NO3-N/ha) Nitrogen is one of the most mobile and dynamic essential elements. Its worldwide use efficiencies have been reported to be between 33 to 50%. Raun and Johnson (1999) reported that worldwide grains NUE are about 33%. It is important that we continue developing BMPs that increase NUE and reduce N losses to the environment. Computer simulation models are tools that can be used to evaluate the effect of BMPs and N losses to the environment. All needed weather information such as precipitation, air temperature, and evaporation was collected (Delgado et al. 2001). We used the three layers 1.2 NLEAP model to evaluate BMPs for this region (Delgado et al., 1998). For additional information about uses of NLEAP as a tool to evaluate BMPs see Delgado et al & 2000, and Delgado Agricultural management practices were collected for these studies conducted at the Luancheng Agroecosystem Experimental Research Station. Planted and harvested dates for crops were June 2, 2001 / September 28, 2001 (corn); October 12, 2001/ June 8, 2002 (wheat); and June 15, 2002 / September 27, 2002 (corn), respectively. Two topdressing urea N fertilizer applications were applied at a rate of 100, 200, 300 and 400 kg N/ha each. Fertilizer was applied on July 5, and August 13, 2001 for corn; October 2, 2001 and March 15, 2002 for wheat; and July 17 and August 20, 2002 for corn. Right after topdressing corn received a 75 and 100 mm irrigation during the 2001 and 2002 seasons, respectively. Although wheat received five irrigations events of 60 mm, wheat was irrigated three and four weeks after fall and spring N fertilizer applications, respectively. Our rain data showed four precipitation events higher than 20 mm and one higher than 40 mm during 2001 and during The silt loam soil had 1.2% soil organic matter and a pH of 8.4. REFERENCES Figure 1. Collection of water samples at 1.5 m depths. Figure 2. Predicted vs observed residual NO 3 N for the 0 to1.5 m profile for small grains and N rates. Table 1. Average grain yields (kg/ha) with standard deviation (std), N fertilizer use efficiency (total N uptake/ N fertilizer applied), simulated NO3 N leaching from 1.5 m depths, and simulated NH3 volatilization. This preliminary study shows that with over application of N fertilizer, at rates greater than needed, we will not obtain significant increases in grain yields. For agricultural sustainability and increases in NUE that reduce N losses to the environment, while producing a high quality crop, N management practices should involve realistic N rates, incorporating applied urea fertilizer and developing N management plans that account for residual soil N. Delgado, J.A., M.J. Shaffer and M.K. Brodahl New NLEAP for shallow and deep rooted crop rotations. J. Soil and Water Conserve. 53:338/340. Delgado, J.A., R.F. Follett, and M.J. Shaffer Simulation of nitrate-nitrogen dynamics for cropping systems with different root depths. J. Soil Sci. Soc. Ame. 64:1050/1054. Delgado, J.A Use of simulations for evaluation of best management practices on irrigated cropping systems. p.355/381. In: M.J. Shaffer, L. Ma, and S. Hansen (ed.) Modeling Carbon and Nitrogen Dynamics for Soil Management. Lewis Publishers, Boca Raton, FL. Raun, W.R. and G.V. Johnson Improving nitrogen use efficiency for cereal production.Agron. J. 91:357/363. RESULTS To evaluate Current Best Nutrient Management Practices for the North China Plains we used the methods of Delgado et al. (2000) and Delgado (2001). We collected yields for a corn and wheat rotation, crop total N uptake, soil water content during the growing season (data not shown), and initial and final soil NO3 N for the 0 to 1.5 m depths. Additionally, we used lysimiters to monitor and assess NO3 N leaching from 1.5 m depths (Figure 1). The NLEAP model was able to simulate the N dynamics and residual soil NO3 N for these grain systems of the Northern China Plain (Figure 2). Over application of urea N fertilizer just increased the NO3 N leaching losses (Figure 3 and Table 1) and atmospheric N losses, reducing the NUE of the system (Table 1). Over application of N did not increase grain yields. Wheat yields for 2002 were 5480 (std: 212), 5627 (378), 5307 (378) and 6107 (760) kg /ha for the 200, 400, 600, and 800 kg N/ha N rates, respectively. r 2 = 0.88***