Long-Term Evidence for Sustainable Midwest Cropping Systems

Background/Question/Methods

Agricultural productivity gains since the 1950s resulted from the development of farming systems that rely extensively on external inputs of energy and chemicals to replace management and on-farm resources.  Cropping sequence in the Midwestern USA has increasingly evolved to a greater reliance on the corn-soybean rotation and even continuous corn over the last half of the century.  There are many reasons for this, among them the development of effective fertilizers and pesticides, government policies, and favorable economics. The objective of this paper was to determine the effect of crop rotation grain yield trends using data from an experiment established in 1966 to evaluate the profitability and agronomic sustainability of corn-based crop rotations.  Forty-five years later, the experiment has become one of the longest running rotation studies in the USA.  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).  

Results/Conclusions

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. 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.