Response of the vertical distribution of soil water and nitrogen in the 5 m soil layer to the conversion of cropland to apple orchards in the Loess Plateau, China

In the Loess Plateau, apple (Malus pumila Mill.) orchards converted from cropland are expanding because of the economic value of apples. Understanding the effects of the conversion of cropland to apple orchards on soil water and nitrogen distributions, as well as the potential soil nitrate accumulation, is important and necessary. In this study, apple orchards (Red Fuji) of different growing ages (5, 15, and 28 year old), an abandoned apple orchard, a wheat field, and a maize field in Changwu County of the Loess Plateau were selected to evaluate the soil water content (SWC), nitrate-nitrogen (NO3--N), and other soil parameters within the 0-5 m soil depth. Results showed that SWC of maize field (21.22%) was the highest, followed by that of the 5-years-old apple orchard (20.24%) and wheat field (18.83%). The SWC of the 28-years-old apple orchard (16.09%) was the lowest of the six treatments. Soil NO3--N storage within the 0-5 m soil profile under 5-, 15-, and 28-years-old, abandoned apple orchards, wheat fields, and maize fields reached approximately 613.2, 1929.4, 4277.9, 1282.4, 95.2, 275.9 kg ha 1, respectively. The SWC deficits were found severe, and high nitrate accumulation was found in 15-and 28 years-old apple orchards. Soil water deficits and nitrate accumulation in abandoned apple orchards can persist for ten years. The soil NO3--N content was significantly (P < 0.01) negatively correlated with SWC. After converting croplands to apple orchards, soil water deficit and nitrate accumulation were the main soil environmental problems, which worsened with age. A reasonable amount of fertilizer should be applied in orchards to reduce contaminants in the soil environment. Coupling enhancement of the utilization efficiency of fertilizers and limited soil water resources could be important for establishing the soil environment in arid and semi-arid areas.

Automated summary

This study investigated the effects of converting cropland to apple orchards on soil water and nitrogen distributions in the Loess Plateau. The results showed that there were severe soil water deficits and high nitrate accumulation in apple orchards, especially in older orchards. The soil water deficits and nitrate accumulation in abandoned apple orchards can persist for ten years. It is important to apply a reasonable amount of fertilizer in orchards to reduce contaminants in the soil environment.