By Alexandre Tonon Rosa, Roger Elmore, Daran Rudnick, Cody Creech, Rodrigo Werle
Cover crops are becoming popular across Nebraska and much of the Corn Belt. Producers in western Nebraska are interested in knowing whether and/or how cover crops could be incorporated into their cropping systems. Cover crops have the potential to reduce soil erosion and compaction, increase water holding capacity and soil organic matter, and suppress weeds. One of the major concerns regarding the inclusion of cover crops in the wheat-corn-fallow rotation is the amount of water used by these “non-cash” species and potential yield reduction of the subsequent crop.
Figure 1. No cover crop (left) and cover crop late terminated (right) treatments at North Platte.
Cover Crop Planting and Termination Time
In the wheat-corn-fallow rotation, cover crops can be planted right after winter wheat harvest in July. Winter-sensitive species will grow during the fall and winter-kill after the first frost. Winter-hardy species resume growth in the spring and need to be terminated either chemically (herbicide) or mechanically (incorporated into the soil).
- Three cover crop planting times: 3, 6 and 9 weeks after winter-wheat harvest.
- Four cover crop termination times: no cover crop, terminated during winter (winter-kill), terminated with herbicide two weeks prior to corn planting, and terminated with herbicide at corn planting.
- Cover crop winter-sensitive species mix: black oats, spring barley, spring lentil, and diakon radish; seeding rate of 63 lbs/ac.
- Cover crop winter-hardy species mix: winter barley, winter triticale, hairy vetch, and diakon radish; seeding rate of 57 lbs/ac.
- Soil water content was monitored during early corn growing season bi-weekly using the TDR sensor.
- Early cover crop planting resulted in higher cover crop biomass during the fall. Late winter-hardy mix planting resulted in higher cover crop biomass in the spring.
- Delayed cover crop termination resulted in corn grain yield reduction. The winter-hardy late planting and early termination treatment combination had the least impact on corn yield.
Cover Crop Species Selection
Figure 2. Hairy vetch (left) and purple top turnip (right) treatments at Grant.
Different cover crop species may have distinguished effects on cropping systems of western Nebraska. Brassicas may reduce soil compaction and increase nutrient cycling; legumes can fix nitrogen to the soil, and grasses have the greatest potential for biomass production, giving an opportunity for grazing and helping suppress weeds.
- Cover crop species treatments and seeding rates: no cover crop, spring triticale (60 lbs/ac), cereal rye (60 lbs/ac), spring oat (60 lbs/ac), purple top turnip (20 lbs/ac), kale Siberian (20 lbs/ac), balansa clover (20 lbs/ac) and hairy vetch (40 lbs/ac).
- Spring triticale, spring oat, purple top turnip, and kale Siberian died in the winter. Cereal rye, hairy vetch and balansa clover were terminated with herbicide in the spring.
- Brassicas and spring oat produced the highest biomass in the fall.
- Cereal rye reached the highest biomass accumulation during the spring.
- Soil water content was monitored during early corn growing season bi-weekly using the TDR sensor.
- Weed counts and biomass were collected at corn V6 growth stage.
- In general, cover crop reduced weed population. Cereal rye had the biggest impact on weed suppression.
- In general, cover crop species reduced corn grain yield. In wet years, there is less of an impact of cover crop species in corn grain yields.
In semi-arid rainfed areas, the timing of cover crop termination is key to avoiding excessive cover crop growth, water use, and nitrogen immobilization, and consequently, reduce corn grain yield. Brassicas and oats have the greatest potential for biomass accumulation during the fall. Cereal rye has the greatest potential for biomass accumulation during the spring, but also has the highest detrimental effects on corn yield. Moreover, wheat farmers are concerned about the weediness potential of cereal rye; thus, an alternative cool-season grass species such as triticale may be a better option. Also, some cover crops can host wheat diseases and that is an important consideration when selecting cover crop species.