Direct Quantification of Manure Derived N Retention in Cover Crops After Fall Applications via 15N Enrichment

Commodities

Practices

The project title is "Direct Quantification of Manure Derived N Retention in Cover Crops After Fall Applications via ¹⁵N Enrichment". The three expected project outcomes are:  1. Direct quantification of manure derived N within cover crops will provide convincing evidence for widespread utilization of cover crops in conjunction with fall manure applications. 2. Producers will be able to adapt knowledge from this project to inform farm-specific management goals, like cover crop selection and termination strategies. 3. Increased producer confidence and improved attitudes towards cover crop implementation with fall manure applications will translate to a higher rate of practice adoption, which translates to increased economic and environmental sustainability for producers and the surrounding communities.

Fall manure applications are a standard practice across Wisconsin, primarily due to manure storage constraints and unpredictable spring field conditions. Unfortunately, manure derived N is at risk for runoff and leaching into groundwater without an appropriate mechanism for N retention leading up to spring planting. Planting winter cover crops with fall manure applications can be well utilized in integrated agricultural systems, especially after silage harvest, for benefits such as N retention. cover crop variety selection is a critical management decision in this regard, specifically when it comes to termination. While winter-killed varieties maximize N uptake and complete plant growth by late fall, overwintering varieties continue growing into the spring, utilizing available N. Consequently, overwintering varieties require spring termination, meaning cost and labor. With those differences in mind, they may vary greatly in their manure N retention capacity. In cover crop research, non-isotopic methods to quantify N uptake in cover crops rely on assumptions of N source (manure or soil derived), but an accurate estimation of N source cannot always be made. Direct quantification and tracing of manure derived N via isotopic labeling provides an opportunity to differentiate N source in cover crop’s and accurately describe N availability within the soil.

We will evaluate the success of our outreach efforts regarding these project results through two sets of surveys. The first survey will be designed to be submitted within two weeks of outreach events with two goals in mind: 1. Gauge the attendee’s response of the research presented 2. Determine if we extended the reach of our presentation through the attendees to other end-users. The second survey will be a follow-up gauging whether any change in practices occurred in response to the presented research in the following year.

There are two main learning outcomes. First, through direct quantification of manure derived N in cover crops, producers will be presented convincing evidence to implement cover crops with fall manure applications. Producers will learn exactly how much manure N they can expect cover crops to retain without relying on assumptions typically made in cover crop N uptake research. Cover crop implementation is a labor and monetary investment, met with skepticism by those looking out for the well-being of their operation potentially, so direct and transparent research is critical. Secondly, producers will learn to adapt the project results to inform individual or farm level management goals. For example, cover crop variety selection based on winter survival and termination requirements is a decision that weighs on many farmers. Comparing manure N uptake between winter-killed and overwintering cover crop varieties will provide useful information that can assist in decision making. The main action outcome is increased producer confidence regarding implementation of cover crops with fall manure application, thereby decreasing N leaching at a regional level and promoting cleaner waterways. A change in producer perception and practice will result from the communication of this research. The change in perception and practice among producers will be measured via surveys at extension and conference presentations. Surveys conducted at events the first year will ask how the research changed their perception, and follow-up surveys the next year at events or through mail will ask if it led a change in practice.