The state of phosphorus balance on 58 Virginia dairy farms

Abstract

Managing a sustainable dairy farm requires balancing phosphorus (P) imports and exports that enter and leave through the farm gate. Over the long term, P surpluses will elevate soil‐test P concentrations above crop requirements through routine land applications of manure. The objectives of this study were aimed at Virginia dairy farms (a) to determine P mass balances, (b) to define potential guidelines for a sustainable and feasible zone of operation based on P balance and P use efficiency, and (c) to assess risk factors driving P surplus and P use inefficiencies. Data on farm‐gate P imports and exports via feed, manure, crops, fertilizers, bedding, animals, and milk were collected for 58 dairy farms in Virginia. There was no relationship between farm P balance and milk production, indicating that a P surplus was not necessary for good milk productivity. A feasible P balance limit was calculated below which 75% of farms could operate, and this was 18.7 kg P ha−1. Two risk factors were identified for farms having a P balance above this limit: (a) land application of poultry litter and (b) excessive import of P through feed. Combined dairy and beef operations generally had more land and a lower P balance, whereas having combined dairy and poultry did not raise the P balance as long as poultry litter was exported. Dairy farms in Virginia can operate with a sustainable P balance as long as they avoid using excessive poultry litter and pay attention to P imported through purchased feed.

Intensification of Grassland-Based Dairy Production and Its Impacts on Land, Nitrogen and Phosphorus Use Efficiencies

“…A relative constancy of P surpluses with intensification level (Fig. 3(a)) has also been reported for dairy farms in Virginia, USA; P input via manure and fertilizers decreased as soil P status increased [60] . However, in many intensive grassland-based dairy systems, both N and P surpluses increase with the intensity of dairy production [23,59,61] .…”

Unraveling feed and nutrient use efficiencies in grassland-based dairy farms

“…The externalization of the (in)efficiencies of feed production also contributed to a high PUE; assigning a P use efficiency coefficient to purchased feed strongly decreased overall mean farm PUE and strongly decreased the differences among FE groups in farm PUE (Table 2). A relative constancy of PUE farm has also been reported for dairy farms in Virginia, USA (Pearce and Maguire, 2020).…”

Confronting our Agricultural Nonpoint Source Control Policy Problem

“…Such diversity of producer behavior is real and can be substantial (Ribaudo 2015). One recent study in a portion of the Chesapeake Bay watershed showed that P mass balances on adjacent farms can vary by a factor of 10 (Pearce and Mcguire 2020). Agency funding is allocated to staff and their offices that can “get BMPs on the ground” as measured by contracts processed.…”