Effects of conservation tillage and grass-hedge on soil, water, nitrogen and phosphorus loss in sloping cropland

Soil and water loss in sloping croplands has been a major environmental problem across the globe. It has been reported that 28% of soil loss was from sloping croplands that account for only 7% of cultivated land areas. In other words, sloping croplands have been the primary source of runoff and sediment. It is therefore urgent to develop strategies for controlling soil and water loss on sloping croplands across the globe. Although various soil protection techniques (e.g., terrace and contour tillage) have been used in sloping croplands in recent years, the effects of these techniques on soil and water loss remained limited. Conservation tillage with grass-hedge has been effective in reducing soil and water loss in sloping croplands especially in tropical and subtropical regions. These techniques have, however, not been adequately evaluated in North China, thus, which has led to limited adoption by local farmers in this region. In this study, the effects of conservation tillage with grass-hedge on soil, water, nitrogen and phosphorus loss were evaluated under simulated rainfall (rainfall intensity of 60 mm·h-1) from farmland on slopes with 5%, 10%, 15% and 20% gradients in the Changping District of Beijing, China. The results showed that conservation tillage with grass-hedge significantly limited soil, water, nitrogen and phosphorus loss and in the order as follows: conservation tillage with grass-hedge > conventional tillage with grass-hedge > conservation tillage without grass-hedge > conventional tillage without grass-hedge. Runoff under conventional tillage with grass-hedge, conservation tillage without grass-hedge, and conservation tillage with grass-hedge decreased by 56%, 44% and 68%, respectively, compared with conventional tillage without grass-hedge. Correspondingly, soil loss decreased by 66%, 49% and 82%; total nitrogen loss dropped by 56%, 43% and 66%; and total phosphorus decreased by 54%, 40% and 70%, respectively. These results suggested that the integration of conservation tillage and grass-hedge was more effective than sole application of either conservation tillage or grass-hedges in terms of soil, water and nutrient loss control. The results further showed that the effectiveness of conservation tillage and grass-hedge gradually decreased with increasing slope gradient. Although the results suggested that both conservation tillage and grass-hedge significantly limited soil and water loss, their effectiveness was limited under steep slope conditions. Some other engineering techniques (e.g., micro-basin, fish-scale pit, mulch or even landscape shaping) therefore needed to be used in combination in order to prevent soil and water loss under steep slope and intense rain conditions. It was, however, concluded that conservation tillage and grass-hedge were critical for controlled soil, water, nitrogen and phosphorus loss in sloping croplands. These finding was useful in the remediation of soil and water loss in sloping croplands in northern China and other similar landscape regions.