Diet modification to reduce phosphorus surpluses: a mass balance approach

Area of Science:

• Agricultural Science
• Environmental Science
• Animal Nutrition

Background:

• Environmental concerns over phosphorus (P) losses from animal agriculture to surface waters have driven research into manure management.
• Dietary modifications in livestock are being explored to reduce P concentrations in manures.

Purpose of the Study:

• To assess the impact of diet modification on manure P production and surpluses at a county scale.
• To evaluate the effectiveness of reducing P in animal diets for mitigating regional P imbalances.

Main Methods:

• Utilized USDA-NASS statistics on animal numbers and crop production for county-scale mass balance calculations.
• Calculated manure P production, P removed by crops, and the potential effects of dietary P reduction.
• Analyzed regional variability in manure P surpluses and the impact of diet modification.

Main Results:

• In 89% of counties, a deficit of manure P relative to crop P removal was observed; 11% had a manure P surplus.
• Diet modification decreased the percentage of states with a manure P surplus from 11% to 8% (a 27% reduction).
• Diet modification reduced counties with the highest manure P surpluses (>30 kg ha(-1)) from 3% to 1% of all counties.

Conclusions:

• Diet modification is an important strategy for alleviating environmental concerns associated with surplus manure P in many agricultural areas.
• While beneficial, diet modification alone is insufficient to address manure P surpluses in all regions.
• Additional strategies are necessary to manage persistent manure P surpluses effectively.