Cover Crops, no simple solution

Planting cover crops is a key tenet of conservation agriculture that involves planting non-cash crops on agricultural fields to provide soil cover between primary crop growing seasons. Cover crops primarily benefit future crops. They do this by reducing soil erosion and nitrogen runoff, crowd out weeds, control pests and diseases, increase biodiversity, and improve soil health soil health by helping to build soil carbon.

Building soil carbon serves also to reduce CO2 in theatmosphere. So, cover cropping was well funded under the United States Department of Agriculture's (USDA's) Environmental Quality Incentives Program that turned all agencies towards climate stewardship and has provided more than $100 million of incentives for cover crop adoption each year since 2016. An additional incentive of reduced insurance premiums was added through the Pandemic Cover Crop Program. 

Under these incentives, the total cropland area in the United States planted with cover crops in 2017 was  nearly 50% higher than reported in 2012 and has continued rising in the past five years. It sounds impressive until you realize that overall, in 2017 only about 5% of cropland  used cover crops.

Cover crops (grasses, legumes and forbs) recommended for seasonal cover and other conservation purposes include annual ryegrass, oilseed radish, winter cereal rye, and oats used for scavenging unused fertilizer and releasing nutrients back into the soil for the next crop to use. Good cover crops to break up compacted soils are forage radish  and forage turnip. Similar to commercial nitrogen (N) fertilizers, legume cover crops like crimson clover, hairy vetch and Austrian winter pea can provide some of the nitrogen needs of the primary crop.

Experimental field trials have often found slight yield losses for primary crops. However, these effects appear to vary considerably depending on many factors, including the agricultural region, the combination of cover and primary crop types, weather conditions, and management practices. Results from  field trial varied widely based on the type of cover crop, the level of fertilization, and the date of cover crop termination.

In a new study from Stanford scientists, examines yield loss by using data from actual farmer fields. They used satellite data to observe both the adoption of cover cropping and the yields of corn and soybeans throughout six states in the heart of the US Corn Belt. These observations, cover more than 90,000 fields, are then used in a algorithm developed by others to measure the incremental yield impact of adopting cover crops.

Using the satellite data they could determine the presence or absence of cover crops each year at field-level resolution. They used the previously published Scalable Crop Yield Mapper (SCYM) algorithm to forecast yield. The SCYM uses region-specific crop model simulations and weather to determine yields from satellite pixel data. Because they were using satellite data, their analysis could only represent the yield impacts of cover cropping as practiced in aggregate across the region.

The algorithm results indicated that fields where cover crops were adopted for 3 or more years experienced an average corn yield loss of 5.5%, compared with fields that did not practice cover cropping. The scientists also found on average, soybean yields were reduced by 3.5% following cover crop adoption. Nearly all locations appeared to experience negative effects. In general, impacts appeared most negative in Iowa and Northern Illinois compared with the rest of the study region. These areas were generally associated with better soil ratings, higher mid-season temperatures.

The scientists found greater yield losses for corn than soybean, which they felt was likely due to soybean's lower need for fertilizer nitrogen. They also found that corn yield impacts were significantly more negative on fields with a high soil productivity index (NCCPI). The scientists reasoned that those fields have higher yield potential, they accordingly have higher nitrogen needs to meet their yield potential.

Based on anecdotal observations in our own Prince William Soil and Water Conservation District.  “Small yield losses may be seen in certain situations,  in certain years, and the longer growers work with integrating covers in their systems the better they get at managing them thus reducing these losses.  The other thing they didn't look at was the economics.  Going no-till and using covers reduce fuel and fertilizer used.  Even though yield may be slightly reduced, profit may actually be better.” (Jay Yankey, former Manager PWSWC and current Farmer.)

There is on the ground research supporting the numerous benefits of introducing cover crops into a system, there are also challenges that growers may face in implementation or management. Cover cropping is different in different agricultural systems. Particularly in arid or drought-prone environments, the water needs by cover crops may cause a reduction in the amount available to the main crop, or require the use of supplemental irrigation.

In addition to potential increases in irrigation, there are other economic costs that must be considered. Expenditures for seed and soil preparations as well as labor requirements will change with the introduction of a cover crop. Because cover crops are left in the field, there is no direct profit to the farmer for harvested crop products. If improperly selected or managed, some cover crops can persist as weeds when the field is transitioned and prepared for subsequent plantings.

Sustainable Agriculture Equals a Sustainable Prince William

early summer at Yankey Farms

Since World War II, the world’s agricultural production has almost tripled while cultivated land area has grown only by 12%. This feat is often called the agricultural miracle or “Green Revolution” and was accomplished by doubling the amount of land under irrigation combined with the development of the chemical processes to manufacture fertilizers and pesticides, hybrid crops that more readily absorb nitrogen and mechanized agriculture. In the United States where agricultural production has even exceeded the world growth level, government policies were created that favored maximizing production. These changes allowed fewer farmers to feed more people and significantly reduced the relative cost of food, but favored mono-culture agriculture and have taken a toll on the environment.

For centuries the common practice in agriculture was a diversified farm integrating both crops and livestock in the same farming operation. Then with the advent of chemical fertilizers and pesticides and the government policies and economics resulting from those policies farmers were pushed to become more specialized, creating industrial agriculture and confined feeding operations and farms growing a one or two crops and a significant reduction in the diversity of those crops. Food security was vastly improved, but hunger was not eliminated. Today federal, state and local government policies often impede sustainable agriculture and local government seemingly encourages the conversion of agricultural land to suburban/urban uses and the continued consolidation of agriculture. Instead we should look to implementing sustainable agricultural practices. Sustainable agriculture within a community contributes to the quality of life and the overall sustainability of that community.

While post World War II government policies and farming practices increased agricultural yields and reduced the financial risks associated with farming, they also have resulted in the depletion of topsoil and contamination of groundwater and streams, the decline in family farms and rural communities. “In real life” I am the Treasurer of the Prince William Soil and Water Conservation District and I care deeply about the survival of our Rural Crescent as a sustainable agricultural community, the conservation of our soils and protection of the streams, rivers and groundwater. Sustainable agriculture is agriculture that does not deplete the soil, but builds it, does not contaminate groundwater or surface water, but uses water sustainable and responsibly, uses pesticides and fertilizers sparingly if at all, uses non-renewable resources responsibly and rests on the principle that we must meet the needs of the present without compromising the ability of future generations to meet their own needs. Sustainable agriculture is stewardship of the land and natural resources to maintain and enhance these vital resources for the long term, for the future generations. Organic, conservation and conventional agriculture can be practiced sustainably.

For the most part irrigated agriculture is not sustainable over the long run. Unless there is sufficient rain during the year, salinity will ultimately destroy the soil. In arid environments fresh water with very low levels of salt evaporates concentrating the salt over time and ultimately will make the land useless for agriculture. Low volume irrigation can slow this effect as can tile drainage, but over time the land builds up salt. Salinization of the land is a huge problem in California and parts of the southwest. However, large sections of the northeast, mid-Atlantic and Midwest have adequate rainfall (most years) to support agriculture. Even with supplemental irrigation to assure the success of valuable crops (think berries) these lands can be cultivated indefinitely. Water availability is the major limiting factor in much of agriculture, but mismanagement of pesticide and fertilizer use can contaminate groundwater and surface water with pesticides, nitrates and selenium.

Sustainable agriculture must utilize specific strategies that take into account topography, soil characteristic, climate, pests and water. Chemicals if used at all should be used strategically. Soil is a fragile and living medium that must be protected and nurtured to ensure its long-term productivity and stability. A "healthy" soil is a key component of sustainability; that is, a healthy soil will produce healthy plants that are less susceptible to pests. Properly managed diversity can improve soil. For example crop rotation can be used to suppress weeds and pests; cover crops can stabilize the top soil by holding soil and nutrients in place, conserving soil moisture by using the mowed mulches of the cover crops and by increasing the water infiltration during precipitation because of the root actions. Cover crops can also attract and sustain beneficial arthropods.

In addition, diversified farms are usually more ecologically (and economically) resilient. While it is more difficult to manage multiple crops, by growing a variety of crops, farmers spread their risks. A strategy that works particularly well with crop diversity is the locally popular community supported agriculture, CSA, model. Properly managed crop diversity can also buffer a farm in a biological and ecological sense. For sustainable agriculture to work consumers must play an important role in creating a sustainable food system. Through their purchases, consumers can send a powerful message to producers and others in the system about what they think is important. Food cost has always been at the top of the list, but buying a farm share or CSA is an important statement and support of farming. Sustainable agriculture providing local food to our community is what the Rural Crescent in Prince William County should be used for- connecting us to the land and the environment. In addition, the costs of conversion of local farmland to suburban/urban uses have to be considered as well as the loss of locally grown food.

Maintaining the rural nature of the Rural Crescent can ensure that Prince William County is sustainable. The Rural Crescent also provides a significant portion of the green infrastructure that connects the still intact habitat areas providing corridors for wildlife movement and trails as well as pathways for pollinators. Maintaining intact, connected natural landscapes is essential for basic ecosystem and watershed preservation to ensure that there will always be clean air and water in Northern Virginia. The Rural Crescent is also about water, groundwater and watershed preservation. Maintaining adequate open ground surface for groundwater and surface recharge are vital to ensuring safe water supplies, water recreation and the ecological integrity of the region. Sustainable agriculture is an important part of a sustainable Prince William County.