Double Cropping with Pea-Barley Biculture and Early-Maturing Corn As a Low N Alternative to Sole-Crop Corn in Minnesota.

Double-crop systems with cool season forages can increase yields and land- and resource- use efficiency over sole-crop summer annual rotations. Commonly, a cool-season forage crop is followed by a primary, warm-season crop. Minnesota’s short growing season limits growing degree units (GDU) and limits yield, necessitating a double-crop system that prioritizes economic value rather than season extension. This study assessed whether the combination of high value, forage, early maturing corn varieties, and reduced N fertilizer inputs constitutes a viable, low N-input double crop system for Minnesota. Two double-crop (DC) and one sole-crop (SC) rotations where studied from 2014 to 2016 at three locations in Minnesota. In DC rotations, a pea- (Pisum sativum L.) barley (Hordeum vulgare L.) bi-culture was double-cropped with early-maturing hybrid (DC-HC) or semidwarf (DC-SD) corn varieties as a primary crop. In SC rotation, full-season hybrid corn (SC-HC) was planted with no preceding forage. Corn was supplied with 6 N rates (0 to 224 kg N ha^-1). Biomass yield, N uptake, and residual soil N were measured for each yield component. Mean biomass yield of DC-SD was low (1.8 Mg ha-1) and showed no response to N rate. Corn yielded less biomass in DC-HC (8.2 Mg ha^-1) and DC-SD (1.8 Mg ha^-1) treatments yielded compared to SC-HC (16.3 Mg ha^-1). Biomass yield deficits lowered corn N demand in DC-HC treatments so that N rates >166 kg N ha^-1 did not limit biomass yield in DC-HC treatments, where SC-HC corn was limited by N rate in three of four site-years. Total biomass accumulation was similar between DC-HC and SC-HC treatments when forage bi-culture yielded >7 Mg ha^-1.This suggests that double-cropping with high-quality forages may constitute an economically viable low N-input alternative to sole-crop corn production in Minnesota.