Evaluating Canola and Winter Cover in Alternative Cropping Systems in Iowa

Evaluating Canola and Winter Cover in Alternative Cropping Systems in Iowa

Summary

The overall purpose of this research project is to provide demonstrations of and more information about practical alternative and sustainable cropping systems for farmers in Iowa. These cropping systems include oilseed, cereal, and perennial legume species uncommon to current Iowa crop rotation, which is primarily dependent on two species, corn and soybean. Improving farmer economic stability and reducing the negative ecological impacts of current Iowa farming practices are additional goals of this project.
Three different crop rotations are being evaluated on an Iowa State University research farm. The first rotation (Rotation A) represents a corn-soybean system common to Iowa. The two other rotations represent alternatives to the common and include ‘third’ crops, double-cropping, and legume interseeding. In one alternative rotation (Rotation B), a corn crop will be succeeded by a double- crop of spring wheat and winter canola. In the other alternative rotation (Rotation C), corn will be succeeded by a double-crop of spring canola and winter wheat. The winter annual is planted shortly after the spring annual is harvested, thus providing ample time for the winter annual to establish and the best opportunity for winter survival. Red clover is then frost-seeded into the winter annual (canola or wheat) the following late winter/early spring. The red clover remains after harvest of the winter annual and over-winter into the following spring before being terminated for another corn crop completing the rotation. These latter two rotations ensure winter cover (in the form of a winter annual or perennial legume) in two of the three winters in each rotation. Moreover, these alternative rotations include three cash crops (corn, canola, and wheat) as well as a green manure legume crop (red clover) that may also increase farmer profitability by reducing farm input costs incurred by pest control and fertility requirements. The reduced reliance on these inputs may play a role in reducing the ecological footprint of farming practices. Furthermore, the increased winter cover can serve to reduce system leakages contributing to farm ecological footprint in the form of soil erosion and nutrient leaching.

Objectives/Performance Targets

Ecological implications, such as entire-system fertility and mechanical input requirements among the rotations are being assessed. These implications will surely impact the financial competitiveness of the rotations. The diverse rotations generally require more passes through the field, yet costs of seed and fertility may in fact be greater in the conventional rotation making them more expensive. We continue to hypothesize that the reduction of synthetic fertilizer and weed control methods due to the inclusion of the alternative crops, compared to conventional cropping systems, will result in the economical competitiveness of rotations incorporating alternative crops.

Accomplishments/Milestones

In 2012, numerous interviews in popular press, including the Ames Tribune and the Leopold Center for Sustainable Agriculture website, shared with the public some results and benefits a project studying alternative cropping systems that include canola, wheat, and red clover. General research findings were presented in the class, Organic Agriculture Theory and Practice (Agron 484/584) as well as on-campus poster sessions organized by the Agronomy Department and the Graduate Program in Sustainable Agriculture. More results will be presented at the ASA-CSSA-SSSA joint meetings in Tampa, FL in November 2013. Furthermore, journal articles are tentatively planned at the outcome of the experiment to comply with our expected goals and end ‘deliverables’.

Impacts and Contributions/Outcomes

In 2012, grain yield of corn in the common rotation, A (133 bu/acre), was greater than the alternative rotations, B and C (99 and 103 bu/acre, respectively). The lesser yields in B and C were not due to insufficient available nitrogen as evidenced by stalk nitrate tests (excess levels observed in corn in B and C; optimal observed in A). The state corn yield average for 2012 according to the USDA-NASS (county data not yet available) was 140 bu/acre. Problems with proper seed placement into tilled strips of terminated red clover coupled with the extreme drought conditions and high temperatures are credited for the lower corn yields in the extended rotations in 2012. This can be illustrated by the fact that under equivalent nitrogen fertility management, end-of-season corn stalk nitrogen levels tended to be in upwards of 300% greater in the alternative rotations compared to the common rotation indicating potentially greater levels of plant-available nitrogen in the alternative rotations. Indeed, above ground red clover cover crop biomass preceding the corn in B and C contained over 100 lb N/acre with the potential to be mineralized and become plant-available. Soil nitrogen will be continually assessed throughout the remainder of the project to determine if a particular rotation contributes to an enhancement of soil fertility. Additionally, weed pressure in Rotations B and C (19 and 34 g m-2) was lesser than weed pressure in Rotation A (40 g m-2). These differences can likely be attributed to the red clover mulch resulting from chemical surface termination in Rotations B and C.
Of particular interest was the maintaining of successful yields of winter canola (1,400 lb/acre) and winter wheat (53 bu/acre) in the moisture and heat stressed year of 2012. Yields were no different than in 2011 and were similar to yields produced in the more traditional canola and wheat production regions of the country. Winter canola and winter wheat took advantage of adequate moisture and temperatures in the spring, matured in June, and escaped much of the drought that stressed and reduced yields of crops in Iowa in 2012. In addition to escaping the drought, the winter crops are inherently more competitive with weeds than corn. The production of the winter crops in 7.5-inch rows closes to the crop canopy much earlier than corn and additionally included no chemical pest control while industry standard rates of glyphosate and dimenthenamid-P were used to control weeds in corn production.
Collectively, the plots in the extended rotations provided on average at least 70% ground cover between May and October. By comparison, the plots in the conventional corn/soybean rotation provided at least 70% ground cover between July and September. By design, the extended rotations provide greater ground cover over a longer period during the year potentially reducing some negative effects of agriculture on the environment (i.e. nutrient leaching, soil erosion). Implications concerning soil, water, and weeds will be explored with respect for these data.

Collaborators: