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Eric Young for Progressive Forage Published on 26 November 2019
Cover crops

Climate can be defined as the long-term average of weather. Weather is the largest source of variability with respect to annual crop yield variation.

In many U.S. agricultural regions, average annual temperature and precipitation have increased over the past century. Average temperature has increased more than 1.5ºF since 1900 for many areas in the U.S. Between 1958 and 2012, precipitation increased 37% in the Midwest and 71% for the Northeast U.S. During this same time, the frequency of extreme precipitation events has also increased.

Weather variability not only impacts crop yield and quality, but also affects environmental risk since it drives runoff, erosion, leaching and greenhouse gas emission. Given the importance of weather on both crop production and water quality, determining practices that optimize crop yield potential and minimize nonpoint source pollution risk is critical.

The goal of nutrient management is optimizing the amount, form, timing and placement of crop nutrients and ideally enhances crop nutrient recovery, termed nutrient use efficiency (NUE). A plan based on realistic crop yield goals and identification of high-runoff-risk fields is important.

The plan should also identify where practices are needed to mitigate water quality risk. Cover crops, manure incorporation and reduced tillage are three practices that can increase NUE, reduce surface runoff and erosion, and help manage environmental risk.

Cover crops

Cover crops mitigate erosion and sediment transport by physically stabilizing soil via root systems, reducing raindrop impact forces and slowing surface runoff velocity. They also have the potential to increase water infiltration, thereby decreasing runoff and nutrient losses. Effective use of cover crops requires producer flexibility. For example, cover crops in corn systems may require shorter-day corn hybrids or other modifications to accommodate possible delays in planting depending on geography (particularly in Northern regions).

A wide range of species are used as cover crops, and the most appropriate one depends on climate, cropping system and goals. In some cases, cover crops work well in double-cropping systems, where annual crop harvest is followed by planting and harvest of the cover crop in the same season or the following spring.

A good example is planting a winter forage crop (rye, wheat or triticale) after harvesting corn silage with subsequent harvest the following spring as a hay crop forage. A two-year study at the Miner Institute showed a winter rye cover crop planted after corn silage significantly reduced nitrogen (N) and phosphorus (P) loss in surface runoff while increasing NUE. In the second trial year, rye was harvested as hay, and rye and control plots had similar yields in the fall.

Reducing tillage

Reduced tillage is another practice that lowers water quality risk while enhancing soil health. Soil organic matter (SOM) is the backbone of soils given its foundational effects on physical and biochemical properties. The basic idea of reduced tillage is to minimize soil disturbance and promote SOM accumulation and biological activity, soil macropore development for improved aeration and drainage, and reduce overall inputs (i.e., labor, time, fuel, etc.).

Opinions vary on no-till and tillage methods in general; however, it is well-established that reduced tillage (mulch-, strip-, zone- and pure no-till) lowers soil erosion potential compared to more aggressive tillage. In general, lower erosion also translates to less soil-bound phosphorus (P) and nitrogen (N) (termed particulate N and P) loss in surface runoff.

Incorporating manure

Manure incorporation or injection is a third practice that substantially reduces environmental risk while increasing NUE. Notwithstanding, many farms use broadcast manure application because it is easier and presumed to be more efficient (i.e., lower labor, time and equipment costs). Since liquid and semi-solid manure typically have a high fraction of ammonia-N, N is rapidly lost to the air if not incorporated soon after application. Compared to broadcast, incorporating also increases NUE and reduces nutrient and pathogen loss risk in surface runoff.

Studies in the U.S. and other countries demonstrate that incorporating manure reduces nutrient loading and concentrations in surface runoff. Research at the USDA Dairy Forage Research Center showed that both tillage and low-disturbance incorporation of liquid dairy manure increased corn silage yield and NUE while decreasing runoff N and P loss.

More recent work found that shallow disk injection significantly reduced runoff N and P concentrations and loads in alfalfa-grass plots compared to broadcast. Using a calibrated whole-farm system model, research led by Dr. Al Rotz (USDA-ARS, University Park, PA), suggested shallow disk injection was the most cost-effective method for hay crops with the lowest runoff loss risk.


Trade-offs in cropping systems occur when a particular management practice has a beneficial effect on one outcome and a negative effect on another. In tile-drained fields, consistent no-till may present a trade-off between reduced erosion or surface runoff and greater N loss in tile flow. While cover crops may alleviate N leaching in tiled fields, they can also reduce crop yield in some cases. Manure incorporation may also present trade-offs compared to broadcast application (more time and equipment), but may end up being more cost-effective from higher NUE.

Despite possible farm- and site-specific trade-offs with cover crops, reduced tillage and manure incorporation, each contributes to improved soil quality (Figure 1).

Effects of cover cropsCompared to their traditional counterparts (i.e., no cover crop, conventional tillage and tillage incorporation), each contributes to greater SOM. Both reduced tillage and low-disturbance manure application decrease soil disturbance and create more potential to build SOM.

Cover crops reduce erosion and add SOM via roots and above-ground biomass residue. Less soil disturbance contributes to more SOM, improves soil structure and aggregation, and enhances aeration or drainage (critical for soil biology and root growth). Improved drainage leads to higher water infiltration and lower erosion, contributing to consistently higher crop yield potentials, NUE and lower environmental risk. Importantly, higher crop yield potential, NUE and lower production risk all contribute to greater profitability.

Start somewhere

Logistics, financial status and other factors affect technology and practice adoption by farms. Adopting new practices need not be an “all or nothing” approach. Starting with a few select fields or sections of a field is a good way to start. Choosing fields where the practice can be consistently done each year with careful monitoring of input costs and yield or quality is important. It may also be beneficial to work with other farmers, NRCS staff, soil-water districts, extension, crop consultants and/or industry partners to develop a detailed plan for comparing practices.  end mark

PHOTO: A wide range of species are used as cover crops, and the most appropriate one depends on climate, cropping system and goals. This mix includes pearl millet, oats, alfalfa, clover and kale. Staff photo.

References omitted but are available upon request. Click here to email an editor.

Eric Young
  • Eric Young

  • Research Soil Scientist
  • USDA – Agricultural Research Service
  • Email Eric Young