Submitted to: Sustainable Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 15, 2002
Publication Date: November 30, 2003
Citation: Ritchey, K.D., Boyer, D.G., Turner, K.E., Snuffer, J.D. 2003. Surface limestone application increases ammonia volatilization from goat urine in abandoned pastures. Sustainable Agriculture. 23(2):111-125. Interpretive Summary: Many pastures in the Appalachian Region are abandoned, and contain unwanted brush. Some farmers use goats to clear pastures because it is relatively inexpensive and avoids use of herbicides. When a lot of goats are put on the pasture, there is a greater chance that urine deposits will overlap, and cause high rates of nitrogen addition. This can cause nitrate pollution of ground water. Sooner or later in the renovation program, farmers will apply agricultural limestone to the pasture under renovation. We tested whether early surface application of limestone would reduce the amount of nitrate pollution by converting some of the nitrogen to gaseous ammonia a part of which could be absorbed by nearby plants. We collected soil cores from an abandoned pasture. brought them to a greenhouse, and surface applied the equivalent of 6720 kg/ha limestone to half the columns. We then added goat urine one, two, or three times to simulate pasture receiving one, two, or three depositions of urine. The more urine applied to the columns, the more of it was transformed into ammonia gas. On average, limestone application more than doubled the amount of nitrogen released as ammonia. Three applications of urine damaged plant growth considerably. With time, plant cover in scorched treatments recuperated, but broadleaf plants tended to replace grasses in these columns. These results showed that early limestone application increased the amount of urine nitrogen transformed to ammonia gas, which should reduce N pollution of groundwater.
Technical Abstract: Concentrated application of N resulting from urine deposition by livestock can cause nitrate pollution of ground water. Use of goats at high stocking densities to clear unwanted shrubs from abandoned pasture during renovation increases the probability of multiple depositions of urine. We hypothesized that applying limestone early in the pasture restoration process would increase NH3 volatilization, thus improving N distribution over the area and reducing the potential for localized nitrate pollution. To study the effect of surface limestone application on NH3 generation, we collected 32 soil profile columns with intact vegetation from an abandoned pasture in southern WV. Urine was applied 18 weeks after surface application of 6720 kg/ha limestone. Columns received one, two, or three applications of 100 mL goat urine, adding a total of 9.8, 31.7, and 66.4 g/m2 N, respectively. Ammonia production decreased exponentially with time eafter each addition. The amount of NH3 increased markedly with increased urine application. Overall, limed columns generated 132% more NH3 than unlimed columns. Dry matter production was highest in the treatment receiving two urine applications and lowest in the control receiving no urine. Three urine applications damaged plants considerably; this scorching was related to amount of NH3 generated. With time, plant cover in damaged treatments recuperated considerably, with broadleaf plants tending to replace grass. Early limestone application should increase the amount of urine N volatilized to ammonia which should reduce N pollution of groundwater.