Alfalfa-corn rotation and row placement affects yield, water use, and economic returns in Northeast China

Planting systems in the corn belt of Northeast China (CBNC) have been adjusted to solve the problem of black soil productivity decline caused by long-term intensive cultivation. To this end, field experiments with the alfalfa (Medicago sativa L.)-corn (Zea mays L.) rotation and row placement were conducted to evaluate soil water, crop yield, and economic returns in the CBNC from 2014 to 2018. The three treatments included continuous corn (CC), continuous alfalfa (CA), and three years of alfalfa followed by two years of corn (3A2C). Corn was planted in the row (R) or interrow (IR) space of the previously planted alfalfa in the 3A2C treatment in 2017 and 2018. Planting alfalfa increased farmer income, and the 5-yr total revenue of the CA treatment was 41% greater than that of the CC treatment. There was no difference in total evapotranspiration (ET) between the CC and CA treatments, and the 5-yr biomass water use efficiency (WUEB) of the CA treatment decreased by 48%, compared with that of the CC treatment. The 3A2C treatment increased corn leaf area index, biomass, and yield. Corn yield of the 3A2C treatment was 8% greater than that of the CC treatment in 2017. The 5-yr net revenue of the 3A2C treatment increased by 24% compared with that of the CC treatment. Corn planting in the first year after alfalfa removal reduced ET. The ET of the 3A2C treatment decreased by 12% in 2017 compared with that of the CC treatment, The WUEB of the 3A2C treatment was 18% and 14% greater than that of the CC treatment in 2017 and 2018, respectively. Corn planted into the previously planted alfalfa row produced 4% and 6% greater yield and 12% and 18% greater WUEB than corn planted in the interrow space in 2017 and 2018, respectively. Therefore, an alfalfa-corn rotation system suitable for use in the CBNC and found to economically benefit farmers consisted of three years of alfalfa followed by two years of corn planted in the previous alfalfa crop row (3A2C-R).