Differentiating the early impacts of topsoil removal and soil amendments on crop performance/productivity of corn and soybean in eroded farmland of Chinese Mollisols

Farmland soil erosion affects crop productivity. Field experiments were conducted from 2005 to 2006 on a typical Chinese Mollisol at a farm in Hailun, Heilongjiang, China, to differentiate the early impact of topsoil removal on corn and soybean yield, and to determine the effectiveness of soil amendments for restoring the productivity of eroded soils. The simulated erosion levels were established in the autumn of 2004 by removing up to 30 cm of topsoil in 5-cm and 10-cm depth increments. The two soil amendments were: nitrogen, phosphorus, potassium (NPK) chemical fertilizer at the normal farm rate, and NPK chemical fertilizer plus cattle manure. Above-ground dry matter was substantially reduced by topsoil removal at later stages of vegetative growth, while a reduction in root dry mass was observed earlier. Plant height at harvest and photosynthetic rates during reproductive stages were also reduced. Across the 2 years in the normal fertilizer rate, the 5 cm and 10 cm topsoil removal reduced soybean yield by 5% and 9%, and corn yield by 10% and 13% respectively, while 20 cm and 30 cm topsoil removal reduced soybean yield by 37% and 53%, and corn yield by 46% and 73% respectively. Corn was more sensitive to topsoil removal and responded more to application of cattle manure than soybean. The addition of manure did not improve above-ground dry matter accumulation in soybean but greatly increased dry matter in corn in 2006 with a lesser increase in 2005. A significant increase in root growth was found with the addition of chemical fertilizers plus cattle manure in 2006, especially for corn. The addition of cattle manure was an excellent amendment to restore productivity through an enhanced effect on the photosynthetic rate, particularly in corn. Addition of cattle manure with chemical fertilizer restored crop yield in the slightly eroded soil (5 cm topsoil removal). The use of chemical fertilizers with cattle manure for improving crop yields on eroded soils is important in the regions similar to the Chinese Mollisols.