Livestock Farm Phosphorus Import/Export Analysis and Strategies for Phosphorus Management

Objective of this project is to measure farm-gate phosphorus (P) import/export balances on Minnesota dairy farms and beef feedlots, identify imbalance sources, and examine strategies for reducing excess soil test phosphorus (STP) buildup. When livestock farms are land-limited relative to manure-P STP can rise, increasing dissolved and particulate P in runoff, and increasing algae growth in rivers and lakes. Detailed spreadsheet analyses of P imports and exports on fourteen dairy and five beef feedlots collected where there was expectation of excess P imports over exports. Excess P ranged from less than 1 to 130 kg ha-1 year-1. Feed and fertilizer were the largest P import sources with feed supplements usually the largest. There were case studies developed in four management areas: 1. Feed management: reduce ration P to National Research Council recommendations, and reduce feed waste. 2. Herd management: breed all heifers to freshen at 22-24 months, and reduce heifer inventory. 3. Crop management: increase crop yields and forage quality, and base P fertilizer applications (including starter) on university guidelines. 4. Manure management: transport manure to distant low STP fields, sell manure, and incorporate manure to conserve nitrogen (N), allowing reduced application rates to meet crop N requirements. Case studies presented at 21 workshops to dairy farms, beef feedlots, and agricultural professionals. Almost half of producer attendees stated their operations are likely out of balance; most are considering adopting one or more of the strategies presented. The case studies posted on completion at the UMN Extension website at z.umn.edu/manure