Comparison of crop management strategies involving crop genotype and weed management practices in conventional and more diverse cropping systems

Cropping systems that include forage legumes and small grains in addition to corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] can achieve similar or higher crop productivity and economic return than simpler corn–soybean rotations. We hypothesized that this rotation effect occurs regardless of the crop genotype planted and the herbicide and cultivation regime selected for weed management. To test this hypothesis, we conducted a 3-year experiment that compared three cropping systems: a conventional 2-year corn–soybean rotation, a 3-year corn–soybean–oat (Avena sativa L.)/red clover (Trifolium pretense L.) rotation, and a 4-year corn–soybean–oat/alfalfa–alfalfa (Medicago sativa L.) rotation. Within each cropping system, two contrasting sets of management strategies were used: (i) genetically engineered corn with resistance to insect pests (Ostrinia nubilalis Hübner and Diabrotica spp.) plus the broadcast application of pre-emergence herbicides, followed in the rotation by a genetically engineered soybean variety with resistance to the herbicide glyphosate plus the post-emergence broadcast application of glyphosate; and (ii) non-genetically engineered corn plus the banded application of post-emergence herbicides, followed in the rotation by a non-genetically engineered soybean and banded application of several post-emergence herbicides. The two management strategies were identified as ‘GE’ and ‘non-GE.’ Corn yield was higher in the 3-year (12.51Mgha⁻¹) and 4-year (12.79Mgha⁻¹) rotations than in the conventional 2-year (12.16Mgha⁻¹) rotation, and was also 2% higher with the GE strategy than with the non-GE strategy. Soybean yield was similar among rotation systems in 2008, but higher in the 3- and 4-year systems than the 2-year rotation in 2009 and 2010. Soybean yield was similar between management strategies in 2008, but higher in the GE strategy in 2009, and similar between strategies in the 3- and 4-year rotations in 2010. Increases in rotation length were accompanied by 88–91% reductions in synthetic N fertilizer application, and the use of the non-GE rather than the GE strategy was accompanied by a 93% reduction in herbicide active ingredients applied. Averaged over the period of 2008–2010, net returns to land and labor were highest for the 3-year rotation managed with either the GE ($928ha⁻¹yr⁻¹) or non-GE ($936ha⁻¹yr⁻¹) strategies, least in the 2-year rotation managed with the non-GE strategy ($738ha⁻¹yr⁻¹), and intermediate in the other rotation×management combinations. Our results indicate that more diverse crop rotation systems can be as profitable as conventional corn–soybean systems and can provide farmers with greater flexibility in crop management options.