Economic analysis of waste management systems on Tennessee dairy farms

The purpose of this research was to make a comparative evaluation of the various waste management systems most commonly found on Tennessee dairy farms. Systems deemed to be most typical were classified as: (1) daily haul (DH); (2) dry stack (DS); (3) earthen pit (EP); (4) above- ground tank (ACT) (steel or concrete); (5) single stage lagoon (SSL); and (6) two stage lagoon (TSL). Storage capacity of 3-months and 6-months was assumed for DS, EP, and ACT systems. The dairy waste management systems were compared for various sizes of milking herds and alternative confinement systems. The sizes of milking herds modeled were 80, 160, and 320 cows. Alternative confine-ment systems were defined as partial and total confinement. Seventy- eight distinct dairy waste systems resulted from incorporating the three herd sizes, two confinement systems, and seven waste systems (with associated variation in storage capacity and collection methods) into the analysis. Based upon technical data synthesized and primary cost data col-lected, each specific dairy waste management system was modeled with regard to economic parameters of initial investment and annual costs/- returns. It was assumed that quantifiable economic returns from any system were restricted to the fertilizer value of the waste nutrients preserved by that waste system. System comparisons were then made based upon these estimated economic parameters. With regard to initial investment, DH systems were least cost in each case analyzed. Generally, EP (particularly EP/3) systems were the next least cost system. AGT systems consistently required the greatest initial investment. Typically, SAGT systems required larger capital outlays than similar CAGT systems. Definite economies accrued to herd size. Per cow investment costs fell by as much as 70% when herd size was increased from 80 to 320 cows. Additionally, doubling storage capacity on those systems for which this parameter was varied resulted in less than double investment costs. When compared with respect to net annual costs, DH systems were least cost for modeled dairy herds utilizing partial confinement. How ever, EP systems (EP/3 and EP/6) tended to be least cost on modeled dairy herds incorporating total confinement. At the very large herd size (320 cows) lagoon systems, especially the SSL/FC system, became quite competitive with EP systems. AGT systems, specifically SAGT systems, were consistently the most costly systems. Certain critical parameters were varied to test the stability of the performed net annual cost analysis. Parameters deemed to be criti-cal included nutrient loss rates, manorial nutrient values, and labor costs. Generally, variation of these parameters did not significantly im-pact on relative net annual costs. Systems remained relatively stable when compared to one another. However, net annual costs for particular dairy waste systems were significantly affected in absolute terms. Only when nutrient values were increased by 50% did positive re-turns accrue to any dairy waste management system. Increases of this magnitude in prices of manorial fertilizer nutrients are not anticipated in the near future.