The “manureshed” refers to the land base needed to assimilate the nutrients produced by a livestock operation without presenting a danger to water, land, and air resources. Trends toward large dairies in many regions of the US, often with high density of livestock relative to the amount of land available for nutrient application, have increased in recent decades. Consequently, import of feed and forage often leads to nutrient surpluses and the need to transport manure off farm for land application. Our purpose was to evaluate the status of dairy manuresheds across the US to highlight challenges and opportunities to improve nutrient balances and facilitate manure nutrient redistribution when needed.
What Did We Do
Our group produced case-studies of manureshed management from four major dairy producing states across the US. We reviewed the predominate structure of dairies in those states and analyzed the primary challenges that must be addressed to safely assimilate nutrients. We focus on reviewing the extent of off-farm redistribution of manure that is needed in each of those states, limitations to redistribution, and approaches that can be built upon to facilitate redistribution. In the Minnesota case-study, where nutrient management data is publicly available for Confined Feeding Operations, GIS software was used to estimate manure transport distances for varying cropping systems and dairy cattle breeds. For Idaho, New Mexico, and Pennsylvania, whole-farm modelling is referenced to understand nitrogen (N) and phosphorous (P) balances on a range of dairies.
What Have We Learned
Soil P assimilation capacity was the predominate factor constraining manureshed land requirements in three of the four states studies. However, nitrate leaching potential was the largest constraint in New Mexico, where dairy forages were largely grown on irrigated lands near rivers. GIS analysis in Minnesota estimated that an average travel distance of 4.1 km for manure transport was required for dairy with 1000 or more cows. The Minnesota case-study also revealed smaller manuresheds were required, per unit of energy-corrected milk, for Jersey cattle compared to the larger Holsteins. Modelled nutrient budgets for Idaho indicated a greater need for off-farm transport, suggesting that expanded application of dairy manures on alternative crops (such as potatoes, sugar beets, and barley) should be considered. In New Mexico, large dairies and limited cropland has caused extensive import of feed from other states and Mexico, with informal nutrient brokering networks developing. In Pennsylvania, dairy producing counties are largely overall sinks for nutrients, but historic heavy manure applications on fields near dairy barns often necessitates greater redistribution of manure nutrients within individual dairies or transfer to local crop farms.
Multiple approaches for improving nutrient balances and distribution of manure were identified in the case studies. Continuing advances in dairy nutrition and cattle genetics are helping to improve nutrient balances and reduce quantities of N and P excreted. When nutrient surpluses necessitate off-farm transport, informal networks for connecting dairies with surplus nutrients with crop farms that have nutrient assimilation capacity, described in New Mexico, provide a basis for development of similar networks elsewhere. Manure processing developments also provide possibilities for more economical transport or reuse of manure nutrients from farms with liquid handling.
The current work provides an overview of the current status of manureshed management in dairy regions. Continuing work is needed to refine nutrient balances for individual farms and to continue to develop tools that assist farmers in understanding nutrient balances and manureshed requirements on their farms. Involvement of social scientists and economists is needed to further develop networks for manure redistribution. Our work also points to the need for greater federal and state cost sharing and more technical support from government, universities, and farm organizations to facilitate more intensive evaluation of manureshed requirements and transport of manure when needed.
Curtis Dell, Soil Scientist, USDA-ARS, Pasture Systems and Watershed Management Research Unit, University Park, PA
- John Baker, USDA-ARS, St. Paul, MN
- Sheri Spiegal, USDA-ARS, Las Cruces, NM
- Sarah Porter, Environmental Working Group, Minneapolis, MN
- April Leytem, USDA-ARS, Kimberly, ID
- Colton Flynn, USDA-ARS, Temple, TX
- Alan Rotz, USDA-ARS, University Park, PA
- David Bjornberg, USDA-ARS, Kimberly, ID
- Ray Bryant, University Park, PA
- Robert Hagevoort, New Mexico State Univ., Clovis, NM
- Jeb Williamson, New Mexico State Univ., Las Cruces, NM
- Amalia Slaughter, USDA-ARS, Las Cruces, NM
- Peter Kleinman, USDA-ARS, Fort Collins, CO
C.J. Dell et al., 2022. Challenges and opportunities for manure management across US Dairy systems: Case Studies from four regions. Journal of Environmental Quality. (In press in pending special edition on manureshed management).
USDA Agricultural Research Service and the Dairy Agroecosystems Workgroup (DAWG, USDA-ARS)
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