Cover Crops Following Sweet Corn and Processing Peas

Figure 1. Sweet corn following mechanical harvest, August 15, 2017.  No other field operations were performed between harvest and planting rye. 

In 2017, Minnesota ranked #1 in the US for both processing sweet corn and pea production with over 120,000 acres of sweet corn and 49,000 acres of peas planted.  Both of these crops have a relatively short growing season as they are harvested at an immature stage of growth and then processed for canned or frozen vegetables.  For peas planted early, a second crop of soybean is often planted for a double crop during that season.  For sweet corn and later planted peas, there is not enough growing season left to plant and harvest a second cash crop; however, there is ample opportunity to plant and establish a cover crop that can stabilize the soil and take up residual nutrients from pea or sweet corn residue.

Because peas and sweet corn are harvested as immature crops, significant nutrients and in particular nitrogen, remain in the residue.  In general, sweet corn stover can contain as much as 60-80 lbs of N/A with a C to N ratio of 30 or less.  Pea vines can contain even more nitrogen than sweet corn stover and the C:N ratio is less than 25. With these relatively low C:N ratios and a harvest time many weeks to months before freeze up, there is a high potential for nitrogen mineralization and subsequent leaching losses during the fall or following spring.  A properly planted cover crop can help to minimize these losses as well as provide additional benefits such as reduced erosion and in some cases disease suppression.   Potential cover crops that can be planted following peas or sweet corn include winter rye, tillage radish, rape (mustard) seed, and oats.   A feature of winter rye is that a living cover remains the following spring.  The other three crops will die after the first freeze.  Tillage radish planted in August will develop a thick taproot to provide a significant amount of biomass and will leave a large hole in the soil when the root dies. This can be beneficial for stand establishment of succeeding crops.

We are currently in the middle of a study funded by AFREC at the Southern Research and Outreach center in Waseca.  The objective of this study is to evaluate the effects of winter rye following sweet corn on nitrogen response by field corn the following year.  In that study, sweet corn was harvested with a mechanical harvester on August 15, 2017 (Figure 1). Winter rye was planted with a grain drill (Figure 2) on August 30, 2017.  Rye grew well that fall with adequate rainfall (figures 3 and 4) and reemerged in the spring with significant growth (figures 5-7).  Rye was disked on May 10, 2018, sprayed with glyphosate on May 15 disked again on May 18 (Figure 8).  Note that the timing of rye killing in this study is later than normal due to a cold and wet April.  The complete results showing field corn N response with and without a rye cover crop will be available following corn harvest this fall.   The study so far has shown that it is possible to establish a healthy rye crop following August harvested sweet corn, which in turn protects the soil and may help to reduce losses of nitrogen during the fall and following spring.

Figure 2. Grain drill used to plant rye. 

Figure 3.  Harvested sweet corn field planted with winter rye.  Rye is emerging – September 7, 2017

Figure 4. Rye growth on October 10, 2017.  

Figure 5. Rye cover crop April, 10, 2018. 

Figure 6. Rye cover crop April 25, 2018.  

Figure 7. Rye cover crop May 8, 2018 just prior to disking on May 10.  The rye was then sprayed with glyphosate on 15 May and disked again on May 18. 

Figure 8. Rye cover crop killed with glyphosate followed by disking May 18, 2018. Field corn was planted May 21, 2018.  

By: Carl Rosen, Professor and Department Head, Vince Fritz, Horticulturalist & Charlie Rohwer, Research Associate For the latest nutrient management information, like UMN Extension Nutrient Management on Facebook, follow us on Twitter or visit our website.

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

This article was first published in September 2018.