Corn grain yield response to crop rotation and nitrogen over 35 years
Crop rotation and N are management methods that can increase corn (Zea mays L.) grain yields. Our objective was to determine the corn grain yield response to six crop rotation sequences and four N rates in a long-term (35-yr) study. The rotations were continuous corn (CC), corn–alfalfa (Medicago sativa L.) (CA), corn–soybean [Glycine max (L.) Merr.] (CS), corn-corn-corn-alfalfa-alfalfa (CCCAA), corn-corn-oat (Avena sativa L.) with alfalfa seeding-alfalfa-alfalfa (CCOaAA), and corn-soybean-corn-oat with alfalfa seeding–alfalfa (CSCOaA). From 1970 to 2004, first-yr corn grain yields (CCCAA, CCOaAA, and CSCOaA) increased from 79 to 100 kg ha–1 yr–1. Increasing N rates did not influence grain yield trends, indicating that an alfalfa crop produced the N required by first-yr corn. However, 224 kg N ha–1 was needed to improve second and third-yr grain yield trends 69 and 58 kg ha–1 yr–1, respectively. Grain yield trends for CC did not improve despite increasing N treatments, although grain yield tended to increase over time at 224 kg N ha–1 (P < 0.10). From 1989 to 2004, corn grain yield trends of CA and CS decreased by 161 kg ha–1 yr–1 if no N was added. The 2-yr rotation was not sufficient to improve grain yield trends, whereas the 5-yr rotation was able to enhance corn grain yield and decrease the need for fertilizer N. Effects on pathogens and insects were not evaluated but warrant further investigations. Overall, this data shows that extended rotations involving forage crops reduce N inputs, increase corn grain yields, and are more agronomically sustainable than current short-term rotations.