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Serving: NE
cover crops in field
LATE TERMINATION: A Nebraska Extension study found delaying cover crop termination reduced yield for the subsequent corn crop.

Managing cover crops in semiarid western Nebraska

While cover crops gain traction in western Nebraska, water use by noncash crops remains a top concern.

Cover crops are becoming popular across Nebraska and much of the Corn Belt. Producers in western Nebraska are interested to know whether 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. However, one of the major concerns surrounding cover crops in the wheat-corn-fallow rotation is the amount of water used by these noncash species and potential yield reduction of the subsequent crop.

Cover crop planting, termination
In the wheat-corn-fallow rotation, cover crops can be planted right after the 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).

A recent study conducted by University of Nebraska Extension at sites near Grant and North Platte evaluated:

• three cover crop planting times: three, six and nine weeks after winter-wheat harvest

• four cover crop termination times: no cover crop, terminated during winter (winterkill), terminated with herbicide two weeks before corn planting and terminated with herbicide at corn planting.

• winter-sensitive cover crop species mix: black oats, spring barley, spring lentil and daikon radish; seeding rate of 63 pounds per acre

• winter-hardy mix: winter barley, winter triticale, hairy vetch and daikon radish; seeding rate of 57 pounds per acre

• soil water content biweekly during early corn growing season using a time-domain reflectometer (TDR), which is a type soil moisture 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 subsequent corn grain yield reduction. The winter-hardy late planting and early termination treatment combination had the least effect on corn yield.

Cover crop species selection
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 included no cover crop, spring triticale (60 pounds per acre), cereal rye (60 pounds per acre), spring oat (60 pounds per acre), purple top turnip (20 pounds per acre), kale Siberian (20 pounds per acre), balansa clover (20 pounds per acre) and hairy vetch (40 pounds per acre).

The study found the following results:

• 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 biweekly using the TDR sensor.

• Weed counts and biomass were collected at corn V6 growth stage.

• In general, cover crops reduced the weed population. Cereal rye had the biggest effect on weed suppression.

• Overall, cover crop species reduced corn grain yield. In wet years, there is less of an effect of cover crop species in corn grain yields.

In semiarid rainfed areas, the timing of cover crop termination is key to avoiding excessive cover crop growth, water use and nitrogen immobilization, and consequently, reducing 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, and it also has the highest detrimental effects on corn yield. Moreover, wheat farmers are concerned about the weediness potential of cereal rye. 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.

This report comes from UNL CropWatch.

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