This article was originally produced for Dairy’s Bottom Line, a PDPW publication.
Traditional Wisconsin forage systems usually include some combination of corn silage and alfalfa. The ultimate ratio of different crops that end up in front of dairy cows in this state depends on multiple factors. Water quality is one of those factors on many farms. Discovery Farms has monitored surface water quality on 25 farms in Wisconsin and Minnesota since 2001. The water quality parameters we monitor are runoff volume, and pounds per acre of sediment, nitrogen and phosphorus contained in that runoff. We queried the database of 203 site years to come up with answers to ‘What are the water quality risks and benefits of our current forage systems?’
Runoff happens, crop type influences the soil and nutrients in it.
While runoff happens no matter the crop type, the amount of soil and nutrient loss does vary by crop. Overall, alfalfa and corn grain show low soil losses (usually less than 400 pounds per acre annually). This can be related to a lack of tillage after alfalfa is established and plant cover or residue on the soil surface throughout the year. However, data show that there is more risk for soil loss during the establishment year of alfalfa and also in corn silage years. This is based on the amount of soil disturbance or tillage and the amount of time that the soil is bare (or bare and disturbed) in the spring and early summer.
Reduce soil disturbance and increase cover to decrease losses after corn silage.
Overall, most soil losses occur during May and June (figure 1), and in years following corn silage, the soil is largely bare from September throughout the spring and early summer. In order to lower the risk of soil loss in fields where corn silage needs to be part of the rotation, consider switching to no-till on that field and/or planting a cover crop immediately after harvest. Discovery Farms data shows that average monthly soil loss following corn silage is three to five times higher on tilled fields compared to no-till fields. Wisconsin farmers are even seeing success with planting the following year’s crop directly into the green cover crop. This amount of soil protection during May and June when the risk for soil loss is the highest will certainly keep valuable soil in the field where it is needed most.
Figure 1. May and June see high soil losses when soil is left bare. Green cover during these risky time periods can help mitigate soil loss.
Consider ways to establish alfalfa that provide more protection.
Establishing alfalfa is critical to ensuring a reliable crop for years to come. Through Discovery Farms monitoring, we have observed losses of nearly 1,800 pounds per acre when spring rain interacts with freshly tilled and planted alfalfa fields. Several participants with Discovery Farms have adopted methods for establishing alfalfa in the spring into a growing rye crop that was planted after corn silage harvest the previous fall. These methods reduce the amount of bare and disturbed soil in the spring and do not negatively impact alfalfa performance or quality. Do some asking around of fellow farmers and check out resources on the University of Wisconsin Division of Extension Team forage site to learn more about this practice. https://fyi.extension.wisc.edu/forage/
Conservation practices aren’t just for soil.
When soil leaves the field, we aren’t just losing productivity value and moving sediment somewhere downstream, phosphorus also goes with it. Most particulate phosphorus (phosphorus attached to soil particles) is lost during the growing season. If we can increase cover on the soil and reduce soil disturbance in forage rotations, phosphorus losses will also decrease. Discovery Farms data indicates that decreasing soil loss is the first step to decreasing phosphorus loss, and thus improving your farm’s water quality impact. While focusing on these practices is not the final step in reducing phosphorus losses, it is a tremendous first step.
Wisconsin is the dairy state, and a large part of that heritage stems from our incredible ability to produce a large quantity of quality forages. As you continue to evaluate your farm’s future, consider ways to decrease the vulnerability of your current system to soil and nutrient loss. There are also positive reports on new alternative forage varieties that are working very well for farmers across the landscape. These varieties could provide more ground cover, manure application windows, and plant diversity while making quality feed.