Water quality enhancements in corn cropping systems through optimization of cover crop establishment technologies

Principal Investigator: M. Scott Wells  
Organization: University of Minnesota, Department of Agronomy and Plant Genetics
Award Amount: $243,910
Start Date: 4/29/2014 | End Date: 6/30/2017 
Project Manager: Heidi Peterson 

Publication: View in ACSESS Digital Library "Establishment and Function of Cover Crops Interseeded into Corn"   January 2018

Research Objectives

1. Evaluate cover crop establishment methods and cover crop species/mixture in a corn-based cropping system using three establishment techniques: direct broadcast via highboy seeder with and without soil disturbance; and interseeder drill.

2. Assess potential groundwater quality improvements resulting from cover cropping using a calibrated Nitrogen Loss and Environmental Assessment Package (NLEAP) model and estimate soil reductions using Revised Universal Soil Loss Equation (RUSLE).

3. Contribute to an educational program to share research findings and demonstrate cover crop establishment technologies to farmers and agricultural professionals.

Background

Due to a short fall season in Minnesota, establishing cover crops in corn-based cropping systems is a challenge. Most Minnesota farmers harvest corn in mid-October, but best management practices (BMPs) recommend planting cover crops six-to-eight weeks prior to a killing frost, well before corn harvest. Aerial seeding between August and mid-September has mixed results due to soil moisture, improper seed placement and vulnerability to animal/insect predation. More research is needed to improve cover crop establishment in corn-based cover cropping systems.

Project Description

For this project, researchers established cover crops when corn was at the V7 to V8 growth stage (approximately 38 inches tall, 30-40 days after planting). At that point there is good soil moisture and also cover crops remain in a vegetative stage throughout the growing season and have a higher likelihood of surviving winter. Applying cover crop seed much before the V7 to V8 stage can lead to increased cover crop competition with the corn.

 
Image from Purdue University

New Equipment and Technology

Broadcasting cover crop seeds (applying them on top of the soil surface) into corn is the simplest seeding method. However, broadcast seeding often produces inconsistent results. Without soil disturbance to incorporate the seed and achieve adequate seed-to-soil contact, cover crop establishment can be low if rainfall does not occur soon after seeding.

New technologies have been developed to allow for earlier planting and to capitalize on the benefits of broadcast inter-seeding. For example farmers have modified high-boy seeders to be capable of planting directly into growing corn.

The need for improved cover crop establishment has prompted other technologies and research. Pennsylvania State University developed a 3-in-1 inter-seeder capable of direct-drilling cover crop seed in corn as late as the V8 stage, while simultaneously applying fertilizers and herbicides. Combining field activity is cost effective. Also, applying nitrogen during the growing season can reduce the potential for nitrogen losses. 

Methods and Data Collection

Key Findings

• Corn grain and silage yields were not affected by cover crop species or planting method, indicating that the interseeded cover crops did not interfere with corn production when planted at the V7 growth stage.
• Spring cover crop biomass was greater overall with the DRILL and DBC+INC planting methods (average 641 kg/ha) compared to DBC (514 kg/ha).
• All cover crop species were successfully established, although rye and red clover were consistently among the greatest in spring biomass and N uptake.
• The overall findings indicated that RUSLE@ generally overestimated soil loss compared to empirical measurements. However, RUSLE2 estimations were valuable to inform relative comparisons between cropping practices and environments.
• Cover crops did not affect soil nitrate N content in the Fall. In the spring, however, soil nitrate N was reduced by rye cover crops at Lamberton compared to other treatments, and by rye, hairy vetch, red clover, and pennycress at Waseca compared to the MIX and CHK treatments. An important finding is that differences in spring soil nitrate N coincided with spring cover crop biomass production. This supports that cover crop biomass can serve as an indicator for ecological services in the reduction of excess soil nitrate N.
• In this study, the greatest effect was from the interseeded rye cover crops, which reduced spring soil nitrate N compared to the no cover crop check by 53 kg nitrate-N/ha at Waseca and by 39 kg nitrate-N/ha at Lamberton
• Rye cover crops also reduced volumetric soil water content compared to the no-cover CHK at the time of cover crop termination at Waseca in 2015. Although the rye cover crops did not affect measured soil moisture in other site years.

Concluding Remarks

Overall these findings support that:

1. cover crops can be interseeded into corn at the seven leaf collar stage in the upper Midwest without risk of reducing corn yield,
2. interseeded cover crops can sequester excess soil nitrate-N in the spring, and
3. cover crops should be completely terminated prior to no-till planting soybean to avoid potential yield reductions.

If farmers are interested in interseeding cover crops, the researchers advise they start with a small area as a test. Select a uniform acre or two of the field and split it into test strips. Winter rye is relatively cheap and has shown to be one of the most hardy and productive cover crop options. Rye is also easily terminated with glyphosate. If legumes, such as red clover and hairy vetch are tested, a sound termination plan needs to be developed, as these species were difficult to terminate with glyphosate alone.

To keep tests at a low cost, farmers can adapt their own broadcast and incorporation mechanism to a high clearance tractor. Alternatively, some custom operators in Minnesota are interseeding cover crops and could potentially plant a small area at low cost to the farmer. These tests would best be done in swaths the same width as the farmer's combine, so that any effects on main crop yield can be detected. Strips should be replicated at least four times in a field to obtain a good coverage.

In addition to the agronomic findings of this research, this work supports that cover crops can provide an improvement to water quality issues in Minnesota by reducing the amount of water-mobile N in the soil during otherwise fallow periods.

Education and Outreach

Research results target agricultural professionals, farmers, state agencies and environmental groups to include:

• A series of crop-specific field days, winter workshops and grower meetings

• Articles in leading agricultural magazines and newspapers

• University of Minnesota-Extension articles distributed to the > 1,500 subscribers of Minnesota Crop News blog

• A University of Minnesota-Extension factsheet

Events included:

• Four University of Minnesota-Extension web bulletins and research updates

• Four field day demonstrations (including the Southern Research and Outreach Summer Crops Field Day)

• Four University of Minnesota-Extension workshops

• Two eLeaming webinars

• Six media interviews

Education and outreach topics will focus on: Cover crop inter-seeding technologies and subsequent impacts on water quality; explanation of best management practices; agronomic and environmental risk assessments for various management practices; economic projections for cover crop inter-seeding technologies into current com cropping systems.