Integrating Legume-Based Forages and Short-Season Grain Corn into Double-Cropping Systems.

Double-cropping can increase biomass production and reduce soil nitrate runoff compared to single-cropped, full-season corn (Zea mays L.) rotations. However, yield reductions in warm-season crops due to delayed planting dates can limit the profitability of double-cropping. A study was conducted in Lamberton, MN and Rosemount MN from 2014 to 2015 investigating whether the combination of high-value forage, reduced nitrogen (N) fertilizer applications, and early-maturing grain crops can increase nitrogen use efficiency and profitability of double-cropping in Minnesota, compared to a single-cropped, full-season corn rotation. A high-value forage mixture of pea (Pisum sativum L.) and barley (Hordeum vulgare L.) was double-cropped with an early-maturing, dual purpose silage/grain corn (relative maturity = 89) in 2014. A second rotation of hybrid grain corn (RM = 102) was planted with no prior forage crop. Six N fertilizer rates were applied to both rotations at corn planting, ranging from 0 kg N/ha to 224 kg N/ha. Due to slow maturation, dual purpose corn was harvested as silage in October. Winter rye (Secale cereale L.) was planted in both rotations following corn harvest, and was harvested as forage in spring 2015. Pea-barley forage mixture yielded 8.3 Mg/ha in Lamberton and 22 Mg/ha in Rosemount (reported at 65% moisture). Total forage yields in the double-cropping rotation ranged from 31.4 Mg/ha in Lamberton to 56 Mg/ha in Rosemount. Returns on full-season corn rotation ranged from $38/ha (0 kg N/ha) to $159/ha (179 kg N/ha). Returns from double-cropping ranged from $78/ha (0 kg N/ha) to $117/ha (90 kg N/ha) in Rosemount. For all treatments, rye production was unprofitable due to low yields and high costs of production.  In Rosemount, double-cropping rotations compared favorably to full-season corn rotations at N fertilizer rates of 0, 45, and 90 kg/ ha. Low biomass yields in Lamberton resulted in negative returns for double-cropping at all N-rates.  High operational costs and variable biomass yields and the opportunity for higher returns from corn grain indicates that double cropping only compares favorably at the margins.