With decreasing land availability and increasing regulations for animal agriculture in the United States, disposal and utilization of horse manure is becoming a major concern. Composting may serve as a viable treatment option for horse manure prior to land application, yet research on the composting of horse stall materials (HSM) and its value as a fertilizer is limited. The objectives of this dissertation were: (1) to evaluate various rates and sources of nitrogen (N) amendment and their effects on the ease of composting horse manure mixed with hay or wood shavings bedding; and (2) to examine the performance of unprocessed and composted HSM on forage production in north Florida. To study these effects, two composting studies and five land application trials were conducted from 2005 to 2007.

Farm-scale composting was conducted using a multiple-bin system under roof cover. HSM containing either wood shavings or hay bedding were amended with urea or slow-release nitrogen sources to achieve specific carbon:nitrogen (C:N) ratios ranging from 15 to 60:1 and composted for either 84 or 120 d. Composting reduced the total mass of HSM by 15-60%. Composting HSM containing wood shavings bedding, but not hay, resulted in temperatures high enough to destroy parasite eggs, pathogens, insect larvae and weed seeds. Manure mixed with wood shavings showed a greater degree of decomposition and nutrient stability after composting than HSM containing hay bedding. Slow-release N sources reduced the loss of N during composting, but did not enhance the rate or extent of decomposition compared to urea. Slowrelease N sources did not sustain microbial populations for an extended time beyond that observed for urea-treated or unamended HSM. HSM amended with N had higher concentrations of soluble N in the form of NO₃ and NH₄. Soluble N can increase the value of compost as a fertilizer by providing plant available forms of N; however, if applied in excess, the potential for surface and groundwater pollution exists. More research is needed to determine an economically feasible and timely method of promoting decomposition of bedding in HSM to form a higher quality end product.

Investigations of land application of HSM were conducted during the growing season in Gainesville, FL (2006) and Live Oak, FL (2007). Unprocessed (STALL) and composted (COMP) HSM were either surface applied onto or incorporated into soil of Coastal bermudagrass (Cynodon dactylon), Argentine bahiagrass (Paspalum notatum), Pensacola bahiagrass or Florigraze perennial peanut (Arachis glabrata) forages. Application rates ranged from 11,200 to 37,000 kg ha^-1 STALL and 8,400 to 18,500 kg ha^-1 COMP. Fertilization with STALL or COMP improved yields for bahiagrass and bermudagrass compared to unfertilized control. Yields of bahiagrass and perennial peanut were greater with STALL than COMP, but yields were comparable between the fertilizer sources for bermudagrass. Across all forages, soil ammonium-N (NH₄) and nitrate-N (NO ₃) did not vary due to fertilization or fertilizer source and did not increase soil residual NH₄ or NO₃ levels. Application of STALL or COMP had no measurable effect on soil phosphorus. STALL provided a greater fertilizer response than COMP during a single season, but effects of repeated application require further study.