RZWQM simulation of nitrogen transport and loss under winter wheat/ summer maize rotation system in the North China Plain

Rational management measures involving crop selection, tillage, crop rotation, fertilization, etc. are important for prevention of contamination and protection of soil and water resources. A number of field studies conducted under subsurface drainage conditions with various management practices have focused on reducing N loss through runoff. Also several models have been developed to evaluate the effects of the management measures on N loss through runoff. Models such as SWAT, DNDC and RZWQM were developed to simulate physical, chemical and biological responses of root-zone soil system to various agricultural management practices. Most of these models have been extensively tested under various soil, climate and agricultural management conditions. They have been used to assess the effects of agricultural practices on crop production or crop rotation systems and the related water and nitrate transport processes. In this study, the Root Zone Water Quality Model (RZWQM) was used to simulate water and nitrate nitrogen accumulations in the soil profile, nitrate nitrogen leaching and ammonia volatilization and yield of winter wheat/summer maize rotation systems in the North China Plain. The objective of the study was to explore the feasibility of predicting optimum nitrogen fertilization process using the RZWQM. A rotation trial of winter wheat and summer maize was conducted on Dahe Experiment Station of Hebei Academy of Agricultural and Forestry Sciences. Four nitrogen fertilizer rates 575 kg·hm^-2 (N3), 400 kg·hm^-2 (N2), 215 kg·hm^-2 (N1), and 0 kg·hm^-2 (N0) were set for the winter wheat/summer maize rotation system. While data for maize was used to calibrate the RZWQM, data for wheat was used to validate the model. The results showed the deviations in the model calibration and validation were acceptable. The Root Mean Square Error (RMSE) of soil water content was as low as 0.019 cm³ cm^-3 and the Mean Relative Error (MRE) was 15.98%. RMSE and MRE for accumulated soil nitrate were 4.580 mg kg^-2 and 52.63%, respectively. There were significant linear correlations between nitrogen use and nitrate leaching as well as ammonia volatilization in winter wheat/summer maize rotation systems. In summary, the RZWQM effectively simulated the transport processes of water and nitrogen in the soil profile in the North China Plain. Thus the study provided a convenient and reliable method of prediction and estimation of transport processes of water and fertilizer in root-zone soil. Irrespectively, there was the need for further research on extended RZWQM model application and robust calibration of critical parameters to increase the model simulation efficiency.