Crop rotation with nine-year continuous cattle manure addition restores farmland productivity of artificially eroded Mollisols in Northeast China

Soil erosion has been recognized as a major agricultural problem of the world. This study was conducted to ascertain the effects of simulated erosion on soil productivity and methods for its amendment. Field experiments were conducted from 2005 to 2013 on a Mollisol farm field with 5% steepness. Five simulated-erosion levels were established in the autumn of 2004 by removing up to 30 cm of top soil in 5-cm and 10-cm depth increments. The plots were cropped in corn-soybean or soybean-corn rotations with two soil amendments. The two soil amendments were: nitrogen, phosphorus, potassium (NPK) chemical fertilizer at the normal farm rate for each crop, and chemical fertilizer plus 15 Mg/ha of cattle manure. Greatest yield decline was observed in the first year of the 30-cm topsoil removal for corn with 40.9% reduction in grain yield, and 31.8% reduction in grain yield for soybean compared to the non-eroded treatment with chemical fertilizer alone. The negative impact of loss of topsoil depth on yield reduction was gradually alleviated with crop rotation. Compared to non-eroded plots, the average grain yield during nine years on the chemical fertilizer treatment declined 5.1%, 5.9%, 12.3% and 18.6% for soybean, and 6.6%, 9.4%, 14.4% and 25.1% for corn in the 5-cm, 10-cm, 20-cm and 30-cm topsoil removal treatments respectively. In contrast, compared to non-eroded plots with chemical fertilizer alone, the grain yield with the addition of manure treatment declined 0.01%, 3.4% and 5.1% for soybean, and 0.70%, 4.7% and 10.8% for corn with 10-cm, 20-cm and 30-cm topsoil removal treatment respectively, while grain yield was slightly increased by 2.5% for soybean and 1.4% for corn at the 5-cm topsoil removal treatment. Addition of cattle manure with crop rotation and chemical fertilizer had significant yield-enhancement effect, especially in the first five years of the treatment. As the depth of topsoil removal increased, the average residual effect (2005-2013) of manure increased, for example, on the 5 cm removal, the residual effect (over the equivalent soil loss with chemical fertilizer treatment) for soybean was 8.0%, and increased to 16.7% for the 30 cm removal depth, while the respective effect was 7.6% and 19.1% for corn. Based on the yield data from the nine-year growing periods, 1-cm topsoil loss reduced 14.0 kg/ha for soybean and 69.1 kg/ha for corn with chemical fertilizer alone under crop rotation, while1-cm topsoil loss reduced 9.1 kg/ha for soybean and 48.4 kg/ha for corn with addition of cattle manure plus chemical fertilizer under a similar crop rotation. The integrated use of chemical fertilizers with cattle manure under a corn-soybean rotation was an excellent option for restoring the eroded soil productivity in Chinese Mollisols.