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Benefits of Cover Crop Growth Prior to Soybeans
by LuAnn Rolling, District Conservationist
According to a  study funded by the United Soybean Board (USB), winter cereal rye that grew an extra three weeks prior to soybean planting produced about 300-400% more biomass (Figure 1) with a 100% increase in nitrogen retention (Figure 2), when compared with early terminated cover crops.

Results from this study showed no difference in soybean yield following a cover crop killed 3 weeks prior to soybean planting compared to a cover crop that was killed one day before soybean planting.

The more cover crop biomass production, the greater the benefits to farmers and the environment. Identification of management decisions that maximize cover crop biomass without affecting yield make cover crops an economical choice that benefits crop production.

This United Soybean Board research showed that cover crops before soybeans provided more benefit than cover crops before corn because they have more time to grow. Cover crops produce more biomass before soybeans for two reasons:
1. Soybeans are planted on average three weeks after corn.
2. Cover crops can be terminated as little as one day before soybean planting without impacting soybean yield. Many producers are waiting until several weeks after planting to terminate and feel they are not impacting their yields.

The short-term economic benefit is by letting the cover crop grow an extra three weeks, the data showed no negative effect on soybean yields. By increasing biomass production and retaining nitrogen, the system will build soil health and have a positive impact on water quality challenges.

In the long-term the economic benefit is leaving cover crops in the ground three weeks longer resulted in a 300-400% increase in biomass production.

This extra growth should improve soil health by leading to lower compaction, greater aeration, more organic matter, increased water-holding capacity, and nutrient retention.

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