Manure Nutrients Relative to the Capacity of Cropland and Pastureland to Assimilate Nutrients:
Spatial and Temporal Trends for the United States
Data from the Census of Agriculture were used to estimate livestock populations, quantities of manure produced, and land available for manure application for 1982, 1987, 1992, and 1997. Livestock include beef cattle, dairy cattle, swine, and poultry. A descriptive analysis is presented of the temporal and spatial changes in the number, size, and kind of livestock operations, and the changes in animal units, quantity of manure nutrients produced, land available for manure application, and excess manure nutrients at both the farm level and the county level.
The analysis shows that the structure of animal agriculture has changed dramatically over the last two decades. Small and medium-sized livestock operations have been replaced by large operations at a steady rate. The total number of livestock has remained relatively unchanged, but more livestock are kept in confinement. The number of confined animals per operation has increased for all major livestock types. A significant shift in the mix of livestock types occurred as dairy cattle decreased in number and poultry and swine populations increased. Livestock populations have become more spatially concentrated in high-production areas. The number of animal units per acre of land available on the farm for manure application for the largest operations is often high, averaging more than eight confined animal units per acre for large poultry and fattened cattle operations.
These changes in animal agriculture have resulted in increased problems associated with the utilization and disposal of animal waste. As livestock production has become more spatially concentrated, the amount of manure nutrients relative to the assimilative capacity of land available on farms for application has grown, especially in high production areas. Consequently, off-farm export requirements are increasing. In some counties the production of recoverable manure nutrients exceeds the assimilative capacity of all the cropland and pastureland available for manure application in the county. The number of these counties has significantly increased since 1982, indicating that problems associated with animal waste utilization and disposal have become more widespread over the last two decades as the structure of animal agriculture has shifted toward fewer, but larger livestock operations.
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APPENDIX: List of Maps and Data
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