County Level Analysis of Land-Based Manure Utilization

Part of the recent Natural Resources Conservation Service (NRCS) resource assessment mandated by the Resource Conservation Act (RCA) included a national assessment of manure nutrients available for crop and pasture fertilization. Personnel from the South Central Water Management Center (SCWMC) were instrumental in determining available manure nutrients at a regional level and helping to manage the over-all assessment.

The assessment was made using county level animal numbers and cropland and pastureland acreage from the 1992 Census of Agriculture. Manure nutrients (nitrogen, phosphorus, and potassium) available for crop and pasture production were calculated using a series of coefficients that accounted for recovered manure at a regional level, and an estimate of manure nutrients lost during collection, storage/treatment, and application. The manure "coefficients" were multiplied by animal numbers to determine the pounds of available nitrogen, phosphorus, and potassium for the county.

A national agronomy database was used to match crop and pasture production with nutrient removal per acre. In determining acreage of crop and pastureland receiving nutrients, only non-legumes were considered. The nutrient removal per acre by crop was multiplied by the number of acres of crop or pasture occurring in the county, and the results summed to determine a county level nutrient requirement.

The total available manure nutrients were then divided by the nutrient requirement, and the results expressed as a percentage of the nitrogen, phosphorus, and potassium requirements of non-legume crop and pastureland in the county that could potentially be supplied by manure. Click on the appropriate state to view the tables that provide county level data for each of the four states in the South Central Region. ARKANSAS LOUISIANA OKLAHOMA TEXAS

A county level analysis of the balance between manure nutrients and crop and pasture requirements can be misleading, most likely underestimating any problems that exist. Not every farm with pasture and cropland produces livestock, and there is no evidence of wide-scale movement of manure off-farm. Very seldom are the livestock and poultry facilities spread evenly across the county. In addition, manure is normally not evenly applied to all the acres of crop and pastureland on the farms where it is produced. The result tends to be a concentration of manure nutrients in portions of the county and on certain fields on a particular farm. Commercial or inorganic fertilizer use continues, and often is in addition to manure applications.

There is no "rule-of-thumb" or other measure to tell when the calculated percentages indicate "problems." Certainly when the percentage of potential crop and pasture nutrient requirements supplied by manure in a county approaches or exceeds 100 percent, a problem most likely exists. One mitigating circumstance could be the application of manure to non-legume crop and pastureland as well as other land uses; however, these are not the "normal" crops and land uses receiving manure; and in some cases the application of manure could cause unintended consequences such as changes in plant communities.

The analysis does reflect census numbers that are approaching five years of age. Expansion of the livestock and poultry industry into some counties in the past five years has been dramatic and will not be reflected by these numbers. In that regard, the user of this information will need to have a good understanding of the livestock and poultry industry in the area of interest. On the positive side, the analysis has been automated and well documented so it can be readily updated when better information becomes available with the 1997 census results.

In addition, the data reflects at the best a regional assimilation of manure characteristics. In counties where manure handling is appreciably different than the rest of the region, this analysis could greatly under or over estimate the percent of crop and pasture nutrient needs potentially supplied by manure.

Even with the obvious limitations associated with this analysis, it still provides useful information to planners and others involved in targeting resources. Where manure resources could provide thirty to fifty percent of the nutrient requirements of crops normally receiving fertilizer, some further study and investigation seems appropriate.

REFERENCES

Ault, Klaus, C. Lander and D. Moffitt, "Fertilizer Nutrients from Livestock Manure - Documentation of Computation of Manure Credit Estimates," Unpublished working document, USDA-Natural Resources Conservation Service, Washington, DC, November 1996

Lander, Charles H., D. Moffitt, and K. Ault, "Nutrients Available from Livestock Manure Relative to Crop Growth Requirements", Resource Assessment and Strategic Planning Working Paper 98-1, USDA-Natural Resources Conservation Service, Washington, DC, February 1998.

Moffitt, Dave, C. Lander, "Using Manure Characteristics to Determine Land-based Utilization," ASAE Paper No. 97-2039, USDA-Natural Resources Conservation Service, Fort Worth, TX, (To be presented in Minneapolis, MN August 1997)

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