Double-cropping with forages can increase yields and N-use efficiency over sole-crop systems, but reductions in primary crop yield can limit economic returns. This study assessed whether the combination of high value, forage, early maturing corn varieties, and reduced N inputs constitutes an economically viable, low N-input double crop system for Minnesota. Biomass yield, N uptake, and residual soil N were measured in two double-crop (DC) and one sole-crop (SC) systems at site-years in MN, from 2014 to 2016. In DC treatments, a pea- (Pisum sativum L.) barley (Hordeum vulgare L.) forage bi-culture was double-cropped with early-maturing hybrid (DC-HC) or semidwarf (DC-SD) corn (Zea mays, L.) varieties. In SC treatments, 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 for each yield component. 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.
University of Minnesota M.S. thesis. September 2016. Major: Applied Plant Sciences. Advisors: Julie Grossman, M Scott Wells. 1 computer file (PDF); iii, 66 pages.
Below-ground plant residues as a source of nitrogen in double-crop forage systems.
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