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Rye Cover Crops in Corn Production on Irrigated Sands

Natalie Ricks and Fabián Fernández

In Minnesota, approximately 500,000 acres of irrigated farmland are highly productive but susceptible to nitrate leaching to groundwater. Irrigated sandy soils are especially vulnerable to leaching. A recent study from University of Minnesota, with support from Pope County SWCD and the Minnesota Department of Agriculture, evaluated the use of winter rye as a cover crop in corn production. Early results show that a rye cover crop can help reduce nitrogen leaching in a corn after soybean rotation by 45 percent.

We conducted this study in 2016, an optimal year for corn, and 2017, a wetter and colder year. At the end of each season, the data were analyzed to determine what effect treatments had on nitrogen leaching, yield and economic optimum nitrogen rates (EONR). The addition of rye to a continuous corn (CC) rotation had no effect on nitrate leaching. However, under a corn/soybean (CSb) rotation, rye reduced nitrate leaching by 45 percent for 2016-17. This is likely because rye residue is tying up residual nitrate early in the spring when there is high precipitation and little crop uptake. As the season continues, the rye decomposes and nitrogen is released into the system when the plants are consuming nutrients. This allows the plants to utilize the nutrients, rather than losing them through leaching.

The preliminary data show promising results with rye decreasing nitrate leaching without negatively impacting yield or EONR. We found that rye had no effect on corn yield in either rotation. The presence of rye had an inconsistent effect on the EONR. In 2016, the EONR for rye plots in CSb was 50 lbs N/ac less than the conventional (no rye) treatments. In 2017, the EONR for rye plots in CSb was 17 lbs N/ac greater than for no rye treatments.
Two-year corn yield for continuous corn (CC) and corn-soybean rotation (CSb) with and without a rye cover crop present between fall and spring before corn seeding. 

So, why winter rye? Rye can survive the cold Minnesota winters, it is a vigorous nitrogen scavenger during critical nutrient loss (spring and fall) and it can be managed with chemical and mechanical termination.

Along with the rye cover crop, the crops received urease treated urea in four split applications at corn development stages V2, V6, V8, and V12. Nitrogen rates of 0, 90, 180, 225, and 270 lbs N/ac were used to predict the EONR.

What does this mean for your operation? In this study, the use of cereal rye on irrigated soils worked best for a CSb rotation. The use of fertigation to apply N in multiple split applications over the growing season may also help to reduce N loss. Researchers continue to evaluate new practices for nitrogen and water quality management. With the goal of helping farms perform more efficiently and reducing agricultural pollution, we will continue to investigate best management practices.

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Support for this project was provided in part by the Agricultural Fertilizer Research & Education Council (AFREC).

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  1. When was the rye terminated?
    Was stand establishment impacted by any allelopathy?

  2. The Rye cover crop was terminated approximately 10-14 days before planting corn and soybean each year. We did not see any evidence of allelopathy issues in the crop establishment.

  3. Natalie and I received a few additional questions by email, so we decided we would answer them all at once in here.

    Details on rye cover crop establishment
    The first year we wanted to get rye established early, so in 2015, rye was initially aerially-seeded at V6 corn and soybean development stage. Mid-season, after the spindly rye was about 5-6 inches tall, it died likely because it got too dark under the corn and soybean canopy. Because the rye did not survive as we had hoped, we re-seeded in the fall. We were able to get a good establishment that fall that remained strong until the following spring. Since this new approach was successful, we repeated this in fall 2016 by seeding rye at R6 in corn and at 50-75% leaf drop in soybean. We chose those stages based on the cash crops’ limited nitrogen uptake at that point in the season, adequate light penetration through the canopy, and to allow as much time as possible for rye to establish prior to a hard frost. The rye was seeded at 2 bu/ac (56 lbs/bu). While the seeds were not mechanically incorporated, we made sure the seeds received water by either rain or irrigation within one week of seeding. It is important to note that in 2015 and 2016 we had long and warm falls that helped with rye establishment. In contrast, fall 2017 was cool and corn maturity and harvest were delayed, which delayed rye seeding and resulted in poor establishment of the cover crop.

    Spring Termination:
    2016 - April 20 (at boot stage)
    2017 - Spray May 9 (at boot stage)
    2015 - June 18 (all V6) & September 17 (SbC – leaf drop)
    2016 - September 1 (SbC) & September 22 (CC/CSb)
    2017 - September 29 (SbC) & October 12 (CC/CSb)
    Corn/Soybean Harvest:
    2015 - October 2 (SbC) October 30 (CC/CSb)
    2016 - October 7 (SbC) October 6 (CC/CSb)
    2017 - October 17 (SbC) October 26 (CC/CSb)

    Were there differences on the growth and uniformity of the rye cover crop?
    Rye planted into soybeans was always more evenly distributed and robust than the planted into corn. Rye plants in soybean plots were between 6 to 15 inches tall by mid-April. Stands planted in the corn phase of the corn/soybean rotation were evenly distributed but the blades were thinner and the overall growth was delayed compared to the soybean phase planting, but plants still reached 6 to 15 inches. The stands in CC were the least established and range from 3 to 8 inches tall and were in patch clusters. We are now in the process of analyzing the actual rye biomass and N uptake data. While we do not have all the data yet, it is clear that most of the N uptake occurred in the spring when the cover crop was growing most vigorously.

    Was the growth of the cover crop different between different years?
    The 2016 (planted fall 2015) and 2017 (planted fall 2016) spring stands were comparable in coverage and plant biomass. Where we are seeing a difference is in plant biomass and coverage post-harvest between the fall 2016 and fall 2017 stands. The cooler temperatures and delayed planting in fall 2017 likely resulted in poor establishment and growth compared to 2016.

    How was the nitrate leaching measured?
    We collected weekly water samples from below the root zone throughout the growing season using permanently installed suction cup lysimeters. Those samples were then tested for nitrate concentration. Using a checkbook calculation of evapotranspiration, precipitation and irrigation, and total soil water holding capacity, we calculated weekly drainage amounts. The concentration and drainage amounts allowed us to calculate the load or amount of nitrate leached in lb/ac for the different treatments. The treatments were 0, 180, 225, and 270 lbs N/ac fertilizer application with and without rye. Averaged across N rates and the two years of the study we observed that the rye treatments reduced nitrate loading by 45% in the CSb rotation.

  4. Another question I received had to do with how well one can expect establishment of rye in other types of soils. I think that having the capability to irrigate is useful to enhance establishment (remember we were seeding without mechanical incorporation), but that doesn't mean a rye cover crop cannot be established successfully in finer textured soils or soils without irrigation. I have seen successful establishment in different environments. If what you are doing to establish a cover crop is working for you, I would not change it. Every situation is different, and sometimes the best way to learn is by trial and error. As I mentioned in my previous reply, during our first year we tried an early planting based on the fact that others had been able to do it successfully, but it did not work for us, and for that reason we adjusted to seeding at R6 in corn and leaf drop in soybean.

  5. what was rye biomass and N content across these years?


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