Krishna Paudel, Keshav Bhattarai, Wayne Gauthier and John Westra

Dairy producers face the challenge of minimizing the costs of manure disposal while at the same time complying with environmental regulations. Manure contains nitrogen, phosphate and potash – nutrients valuable for use as fertilizer. Managing dairy manure, however, remains costly for both physical and economic reasons.

Physically, the substitution of manure nutrients for commercial fertilizer is limited by interactions between the manure, soil types to which it is applied and the particular crops being grown. Failure to recognize these interactions can create conditions of either nitrogen or phosphorus buildup in soil. These conditions increase potential nutrient leaching or runoff from the land into waterways.

Manure removal and disposal are necessary management practices that consume costly resources. Economically, the substitution of manure nutrients for commercial fertilizers depends on nutrient recommendations for crops grown in a given area. Transportation costs account for the majority of costs associated with using manure nutrients and vary with distance and size of the load transported between the originating dairy farm and the disposal land parcel.

The economic problem facing the Louisiana dairy sector concerning manure disposal is identifying the least-cost combinations of routes for transporting manure from dairy farms   in the principal milkshed to crop and pasture lands within and adjacent to that milkshed without applying excess nitrogen and phosphorus. For this study, figures from 2005 were used, and in 2005, Louisiana’s principal milkshed consisted of 204 dairy farms distributed as shown in Table 1 across five parishes: St. Helena, Tangipahoa, Washington, Livingston and St. Tammany. The quantity of nutrients produced in each of these parishes and the magnitudes of their nutrient deficiencies are found in Table 2. (The LSU AgCenter’s Ag Summary figures indicate that in 2009, there were 166 dairy farms in Louisiana.)

Researchers developed a unique GIS model containing specific road mileage, speed and load-bearing data for transporting dairy manure between source dairies and disposal sites to determine the appropriate values for an economic model designed to optimize manure disposal. In addition to the milkshed-specific data presented in Tables 1 and 2, the model includes the distribution of dairy farms and their manure volume, the physical properties of the roadbeds that influence transportation costs, and the natural obstructions imposed by water bodies and man-made structures that influence the distances between source farms and disposal sites. It also accounts for the interactions of the physical properties of the manure, the soils and the crops being grown on those soils relative to environmental impacts being monitored.
 
Nutrient supply and deficit levels reported in Table 2 indicate that the quantity and size of dairy farms within the milkshed are not evenly distributed. Of the 204 dairies in the study area, 116 were located within one mile of the receiving lands while 88 dairies were more distantly located. The disparity between the source of dairy manure production and the receiving or disposal lands calls for transporting manure from one place to another. In Louisiana, the majority of farmers collect manure in lagoons. When lagoons are emptied, the solids get stockpiled. The moisture content of stockpiled manure varies between 30 percent and 50, depending on weather and storage conditions. Table 2 identifies the amounts of nitrogen, phosphate and potash production from dairy manure with a 30 percent moisture content for each of the five parishes in the milkshed.

Using the GIS model, 2,805 cropland and pastureland parcels were identified as potential recipient sites of dairy manure from the 204 dairy farms. Parcel selection in the model was based on delivered-cost comparisons between dairy manure nutrients and commercially a vailable fertilizer for different disposal sites from each of the 204 source farms. By identifying source farms and receiving sites, nitrogen-, phosphate- and potash-consistent rules ensured environmental compliance in the analysis. A manure transportation rate of 10 cents per ton-mile was used in comparing costs of dairy manure nutrients with commercial fertilizers.

The optimization model compared differences in margins of profitability between dairy manure nutrients and commercial fertilizers as a function of the distances between source dairy farms and receiving sites. Origin-to-destination cost comparisons meeting the nitrogen and phosphate needs of an oat-ryegrass hay parcel revealed that dairy manure transportation is not economically feasible at distances in excess of 18 miles for nitrogen and 8.9 miles for phosphate and potash (Figure 1). Breakeven distances for nutrients vary by crop requirements for each nutrient.

Modeling that reflects these interactive variables can help the public policy process by establishing levels of subsidies for manure removal and disposal that would help existing dairy farms remain in business. Equally important, this particular GIS model can be applied to other situations where actual distances between origins and destinations are critically important to the decision-making and policy-formulation processes. These can include activities such as siting processing plants and value-added facilities, staging disaster relief facilities, and other activities in which space considerations are important. This research is another example of how scientists working in the Louisiana Agricultural Experiment Station can create tools for using society’s resources more efficiently and effectively.

Krishna Paudel, Associate Professor,Department of Agricultural Economics & Agribusiness, LSU AgCenter, Baton Rouge, La.; Keshav Bhattarai, Professor of Geography, University of Central Missouri, Warrensburg, Mo.; Wayne Gauthier, Associate Professor, and John Westra, Associate Professor, Department of Agricultural Economics & Agribusiness, LSU AgCenter, Baton Rouge, La.

(This article was published in the spring 2010 issue of Louisiana Agriculture.)