Characteristics of water supply and demand in an agroforestry ecosystem under long-term continuous cropping assessed using the RZWQM2 model

Sustainable agricultural management is one of the important factors for ensuring food security. In recent years, many wheat and maize fields on the Loess Plateau of China have been transformed into apple orchards for better economic returns. However, the evapotranspiration of apple orchards is far greater than the precipitation supply, resulting in a reduction in water resources that are available for apple trees. In this study, an experiment was conducted from 2012–2015 on apple orchards of different ages and maize and wheat fields. The field experiment and the Root Zone Water Quality Model (RZWQM2) were combined (1) to explore the feasibility of RZWQM2 in simulating soil water conditions under the three cropping systems and (2) to simulate long-term soil water dynamics and plant water use in different cropping systems from 1981–2019. The results showed that RZWQM2 was able to simulate the growth of wheat and maize and the water use of the three land use patterns (R2>0.70, −3.86 %<PBIAS<0.49 %, and D>0.89). Under the long-term continuous cropping system, the water consumption in the apple orchard was the highest, followed by that in the maize and wheat fields. The turning point of evapotranspiration in the apple orchard occurred at the 22nd year, but it decreased with increasing years of cultivation in the maize and wheat fields. Therefore, the planting of winter wheat after 22 years of apple planting should be considered to restore the soil water in the apple orchard to ensure the sustainable development of agriculture in this area.