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Termination Timing of a Rye Cover Crop When Planting Soybeans (05/28/20)

Planting soybeans into a rye cover crop is becoming more common in North Dakota.

Planting soybeans into a rye cover crop is becoming more common in North Dakota. A well-established rye cover crop in the spring can protect the soil from erosion, suppress weeds, reduce soil nitrate levels and use excess moisture that might otherwise limit timely planting of soybeans. The downside of a vigorous cover crop is that it may hinder soybean establishment if soil moisture is limiting and potently suppress soybean growth if it shades the emerging soybean seedlings. The timing of rye termination, therefore, can be critical to the success of this system. Experiments were conducted in 2019 at two locations (central and northern valley locations) to quantify the effect of when rye was terminated with glyphosate on soybean establishment and yield. Timings were at weekly intervals beginning two weeks before planting (during the first week of May) to two weeks after planting soybeans. When averaged across locations there was no effect of termination timing on soybean establishment and yield (Table 1). Weeds were more effectively suppressed by the heavier rye biomass when terminated later (also see Figure 1 which is a photo of one of the experiments about two weeks after the last rye termination timing). These data would point to later termination of rye being better than earlier.

We have continued this research this year. The rye cover crop developed little in April and early May. However, in the last 10 days rye has grown dramatically in both height and biomass. Rye at both experimental locations (south of Fargo this year), is now past the jointing stage. It has produced more biomass and is taller this year compared to last. Though the data from 2019 suggested that there were little negative impacts of terminating rye up to two weeks after planting soybeans, which may not be the case every year. Not only soil moisture status but the size of the rye plant can impact soybean establishment and early development. Soybean was planted at both locations last Friday (see Figure 2 for a picture of rye status at time of planting). There was adequate soil moisture to enable good germination. It will be interesting to see if the taller rye will interfere with the developing soybean plants significantly this year.

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Joel Ransom

Extension Agronomist, Cereal Crops

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