Combining field phosphorus runoff risk assessments with whole‐farm phosphorus balances to guide manure management decisions

• Published in: Journal of environmental quality 2020-03, Vol.49 (2), p.496-508
• Main Authors: Ros, Mart B.H., Czymmek, Karl J., Ketterings, Quirine M.
• Format: Article
• Language: English
• ISSN: 0047-2425; 1537-2537
• DOI: 10.1002/jeq2.20043

Phosphorus (P) loss from agricultural fields contributes to water quality degradation. A phosphorus index (PI) is a tool that scores fields based on P loss potential. Recently, a new transport × best or beneficial management practice (BMP) approach was proposed for the New York PI (NY‐PI), which first scores fields using landscape‐based transport factors (raw scores) and then offers various BMPs to reduce the score (i.e., risk of P transport). The final score is assigned a management implication (N needs based, P removal based, or zero P application), taking into account field‐specific soil‐test P (STP) and the farm's whole‐farm P balance. With farmer and nutrient management planner input and data on field‐specific transport factors and whole‐farm P balances of 18 New York dairy farms, we set coefficients for transport factors, BMPs related to P application, and STP limits and determined the impact of implementation of the new NY‐PI on manure management options. Based on raw scores, the proposed NY‐PI initially limited manure application to 51% of the total cropland area of the participating farms (28% N‐based, 23% P‐based). Implementation of BMPs (i.e., changing the method and ground cover or timing of P application) allowed 43–98% of the land area to receive manure at N‐based rates. For farms with whole‐farm P balances within the feasible limits set for New York, an additional 0–50% of the land base was classified as N‐based management, depending on BMP selection. These results show the ability of the new NY‐PI to limit P applications on fields with high transport risk while incentivizing adoption of BMPs and improvements in whole‐farm P management.