Compounding soils to improve cropland quality: A study based on field experiments and model simulations in the loess hilly-gully region, China

Increasing the quantity and improving the quality of cropland can alleviate the human-land contradiction and promote the sustainable development of agriculture especially in mountainous areas. With the support of the central government’s policies, Yan’an, Northern Shaanxi, China implemented a major land consolidation engineering project in the loess hilly-gully region from 2013 to 2018, achieving 33,333.3 ha of new cropland. However, the poor quality of some newly-constructed cropland at the initial stage hindered its efficient utilization. In order to overcome this problem, red clay and Malan loess were compounded in different volume ratios to explore the method to improve the cropland quality. The Root Zone Water Quality Model was used to simulate the effects of different soil treatments on soil water, nitrogen and maize growth. Experimental data were collected from 2018 to 2019 to calibrate and validate the model. The root mean square error (RMSE) of soil water content, nitrate nitrogen concentration, above-ground biomass, leaf area index were in the range of 11.72–14.06 mm, 4.06–11.73 mg kg−1, 835.21–1151.28 kg ha−1 and 0.24–0.47, respectively, while the agreement index (d) between measured and simulated values ranged from 0.70 to 0.96. It was showed that, compared with land constructed with Malan loess only (T1), the soil structure and hydraulic characteristics of land with a volume ratio of red clay and Malan loess of 2:1 (T3) was better. Simulation indicated that, compared with T1, the soil water content and available water content of T3 increased by 14.4% and 19.0%, respectively, while N leaching decreased by 16.9%. The above-ground biomass and maize yield of T3 were 7.9% and 6.7% higher than that of T1, respectively. Furthermore, the water productivity and nitrogen use efficiency of T3 increased by 21.0% and 16.6% compared with that of T1. These results indicated that compounding red clay and Malan loess in an appropriate ratio was an effective method to improve soil quality. This study provides a technical idea and specific technical parameters for the construction or improvement of cropland in loess hilly-gully region, which may also provide reference for similar projects in other places.