Cycling phosphorus and nitrogen through cropping systems in an intensive dairy production region

Authors: Leytem, April; WILLIAMS, PAULA - University Of Idaho; ZUIDEMA, SHAN - University Of New Hampshire; MARTINEZ, AUDREY - University Of Idaho; CHONG, YEN LENG - University Of Idaho; VINCENT, ALYSSA - University Of Idaho; VINCENT, AARON - University Of Idaho; CRONAN, DANIEL - University Of Idaho; KLISKEY, ANDREW - University Of Idaho; WULFHORST, JD - University Of Idaho; ALESSA, LILIAN - University Of Idaho; Bjorneberg, David - Dave

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2021
Publication Date: 5/19/2021
Citation: Leytem, A.B., Williams, P., Zuidema, S., Martinez, A., Chong, Y., Vincent, A., Vincent, A., Cronan, D., Kliskey, A., Wulfhorst, J., Alessa, L., Bjorneberg, D.L. 2021. Cycling phosphorus and nitrogen through cropping systems in an intensive dairy production region. Agronomy. 11(5):1005. https://doi.org/10.3390/agronomy11051005.
DOI: https://doi.org/10.3390/agronomy11051005

Interpretive Summary: As pressure on the dairy industry to reduce its environmental impact increases, efficient recycling of manure nutrients through local cropping systems becomes crucial. The aim of this study was to calculate annual nitrogen (N) and phosphorus (P) budgets in six counties located in the Magic Valley, Idaho and estimate what distance manure would need to be transported to be in balance with crop nutrient demand given current dairy cattle populations and cropping systems. Our study suggests that a more sustainable system could be attained in this region by wider distribution of manures to meet crop nutrient needs and maintain nutrient balance. Assuming that N is distributed across all cropland, our results suggest that volatilization and slow rates of mineralization result in a slight deficit of N for crop production. However, N, as well as P, are concentrated around dairies due to the cost and inconvenience of transporting manures away from the facility. Phosphorus is in surplus in all counties in this region which has led to regulation of the dairy industry by the state. Many dairies do not have enough cropland for manure application, while staying within the bounds of their nutrient management plans, therefore forcing them to transport manure further distances or stockpile for future use. Dairy and crop producers consider economic returns and crop yields as the two most important factors in decisions about nutrient application. Although transporting manures farther could reduce economic re-turns, crop yields may improve from application of manures. Motivating wider transport could involve both monetary incentives to do so, combined with educating producers, and the people they employ to make nutrient application decisions, of the benefits of manure application. It is also important to address potential conflicts of interest of those making nutrient application decisions, as well as to address the regulatory gap between dairy producers and crop farmers.

Technical Abstract: As pressure on the dairy industry to reduce its environmental impact increases, efficient recycling of manure nutrients through local cropping systems becomes crucial. The aim of this study was to calculate annual nitrogen (N) and phosphorus (P) budgets in six counties located in the Magic Valley, Idaho and estimate what distance manure would need to be transported to be in balance with crop nutrient demand given current dairy cattle populations and cropping systems. Our analysis suggests that crop N needs will not be met solely by manure, and synthetic fertilizer will need to be applied. However, to balance P with crop production, manure would need to be transported a minimum of 12.9 km from dairies and would have to replace synthetic fertilizer P on 91% of regional cropland. Education of producers and technical specialists would be necessary to improve the management of manure use in regional cropping systems. Technical solutions such as alternative diets for cattle and nutrient capture from manure streams will also likely be necessary to bring regional P into balance to protect environmental quality and improve the sustainability of the regional dairy industry.