Finding fields that need manure If we connect the barns with the fields, we can understand when manure transport is really needed. by Curtis Dell, Sheri Spiegal, John Baker, and Peter Kleinman
T
he concept of a manureshed was developed to describe the amount of cropland needed to use the manure nutrients produced by a livestock operation without negative environmental impacts. Consider the manureshed as a cropland balance sheet to accommodate the nutrients from an operation’s manure. Manuresheds have changed dramatically over time. Historically, dairies produced all, or most, of their own forages and feed. Manure nutrients could be reused for crop production on the farm without exceeding crop demand. So, the manureshed of these dairies was contained within individual farms. Today’s manuresheds have grown. Trends toward larger farms in many regions of the U.S. have led to many dairies importing more forage and feed than in the past. The cropland available for manure application on individual dairies is often not sufficient to safely use the manure nutrients produced. In those cases, the manureshed becomes larger than the individual operation. Manureshed area can vary greatly in different parts of the country. In regions that are dominated by small and medium-sized dairies, manuresheds generally remain small. However, the larger herds on many western U.S. dairies lead to large manuresheds.
Watching the water Although the manureshed is a sound agronomic concept, its real relevance can
This map highlights four regional “manuresheds”: clusters of counties with surplus manure P (brown) and the surrounding “sink” counties required to assimilate the surplus P (gray). The black symbols represent the livestock industries that dominated manure production in the source area. Source: “Manuresheds: Advancing nutrient recycling in U.S. agriculture.” Agricultural Systems 182: 102813. be found in water. Water quality concerns are the main factor limiting the amount of manure nitrogen (N) and phosphorous (P) that can be safely applied. Phosphorus buildup in soil from years of manure application can elevate P in field runoff to water bodies where that P can trigger algal blooms and other harmful microbial growth. Another important concern is the leaching of nitrates to groundwater, especially in sandy soils or areas with
12 | Journal of Nutrient Management | May 2022
F3 12-13 May 2022 Finding Fields.indd 1
shallow water tables. The nutrient guidelines that have been developed in most states help farmers create manure and fertilizer application plans. These plans prevent excess nutrient accumulations and avoid application where the risk of nutrient losses is high.
Mapped by county To understand the diversity of manuresheds within the United States, jofnm.com
5/12/22 1:55 PM
