Cover crops: Are they a real fix for water quality?
The use of cover crops has been growing over the past decade or so. But, do the benefits to the landscape from using covers in a cash-crop system actually outweigh the risks of changing practices and modifying operations? Cover crops need to pay dividends to both the individual grower and the landscape as a whole. The in-field advantages are much better known and documented than the effects on water quality and how it moves through the agricultural landscape. These landscape-level effects are critical in telling the story of modern agriculture and how we are able to maintain top production while making positive steps in reducing the amount of agricultural inputs to surface waters.
To be successful in this quest, cover crops should decrease total water volume, suspended solids or soil leaving the field, and total phosphorus (P) and/or nitrates (N). The first two of these need to be measured, but we can make some educated assumptions when it comes to total water volume and soil loss. Cover crops increase surface cover and keep growing roots in the soil longer than cash crops alone. These additions will absolutely over time decrease soil loss and increase infiltration. But to what extent? Similarly, it’s reasonable to assume that the extra living plant uptake should reduce loss of N and P, but again, it is important to prove the extent to which the loss is mitigated.
For agriculture to remain “business as usual,” it’s critical to prove that cover crops can reduce losses of these pollutants. We need a success story to tell, and integrating cover crops can be a big one.
Recently, the Missouri Soybean Association and Missouri Corn Growers Association began a study that put water samplers on fields that were farmed using different practices. The samplers collect water any time there’s a runoff event. They track and measure total water volume, soil loss in suspended solids, N and P. For this study, these organizations used grant funding from EPA’s Clean Water Act Section 319 program, which specifically focuses on nonpoint sources of water pollution, such as agricultural runoff and soil erosion.
The information gathered from this research provides great insight about when losses are happening and what works to reduce total losses.
First, historical practices of grassed waterways and terraces seem to be working really well in reducing nutrient and sediment runoff. This is great news and proves the effectiveness of these practices that we’ve used for decades. Even when changing overall management to no-till or to include cover crops, it’s important to keep these structural practices in mind. When needed, nothing does a better job at stopping soil or nutrient loss than a good grass sod waterway.
Second, cover crops seem to be doing an overall good job at continuing to reduce nutrient and soil losses, especially in the spring. The large, intense rain events that come with spring not only hamper fieldwork, but they are also major contributors of those losses. Having a cover crop in place during these events can help. This also brings to mind some of the nutrient applications made that time of year. Those nutrients can be especially vulnerable to losses and show up in the runoff. Minimize this risk by not applying right before large rainfalls, or move those surface applications to other times of the year when precipitation is typically less intensive.
While it’s impossible to say that cover crops can reduce nutrient losses every time, it’s reasonable to say there are clear benefits. That conclusion is based on actual water sample data along with visual observations of field-level benefits. With the floods of 2019 fresh in our minds, the number of large rain events seem to be happening more often. For reasons both on and off the farm, cover crops are something to consider in row-crop agriculture.
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