Goat Urine and Limestone Affect Nitrogen and Cation Distributions in an Acidic Grassland

Authors: Ritchey, Kenneth; Boyer, Douglas; Turner, Kenneth; Snuffer, Josie

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/23/2007
Publication Date: 4/9/2008
Citation: Ritchey, K.D., Boyer, D.G., Turner, K.E., Snuffer, J.D. 2008. Goat Urine and Limestone Affect Nitrogen and Cation Distributions in an Acidic Grassland. Soil Science Society of America Journal. 72(3):626-633.

Interpretive Summary: Some farmers use goats to clear abandoned pastures or scrubland because it is relatively inexpensive and avoids use of herbicides. When a lot of goats are put on an area, there is greater chance urine deposits will overlap, and cause high rates of nitrogen addition. This can result in nitrate contamination of ground water, causing a potential health hazard and contributing to pollution of streams and lakes. We collected vegetated soil cores from an abandoned pasture, brought them to a greenhouse, and surface-applied limestone to half the columns. We added goat urine 0, 1, 2, or 3 times to simulate pasture soils receiving 0, 1, 2 or 3 depositions of urine. Plant growth improved in the treatments receiving one and two applications, but scorching in the three-urine application killed most of the vegetation. In the leachate from this treatment nitrate-nitrogen concentration reached levels much higher than the safe limit for drinking water. The three-application treatment received only five times more N than the one-application treatment, but it leached more that 12 times more N. This study shows that in situations where plant growth is damaged by trampling, heavy grazing, or, in our case, scorching, there are two factors that worsen leaching losses of N: (i) lack of vegetation severely restricts plant uptake of N, and (ii) absence of plants means that the amount of rainwater that would normally be used by plants is greatly reduced, thus increasing the amount of water draining through the profile and increasing the rate of N leaching. Soil pH and extractable levels of calcium and magnesium in the soil profile were decreased by urine and increased by limestone application, and extractable aluminum was increased by urine and decreased by limestone. Thus, surface application of limestone can alleviate some of the detrimental effects of high rates of urine addition to acidic infertile soils.

Technical Abstract: Use of goats (Capra aegagrus hircus L.) to clear overgrown pastures and woodlots of unwanted vegetation may result in high rates of urine deposition where goats congregate. Surface application of limestone to dystrophic acid soils before clearing is known to augment ammonia gas volatilization from added urine, but it is not clear what will occur deeper in the soil profile. Our objective was to determine effects of previous limestone surface applications and various rates of goat urine additions on N transformations and leaching in an infertile acidic soil. A quantity of limestone equivalent to 0 and 6720 kg ha-1 was surface applied to vegetated columns of Typic Hupludult soil collected from an abandoned Fescue spp. grassland in southern WV. After 18 wk, one, two, or three applications of urine supplying a total of 36, 98, or 177 g m-2 of N were made. One and two applications of urine increased vegetative growth and decreased the amount of water leaching through the column, but the third addition killed plants and increased leachate volume compared to the two-application treatment. Soil solution inorganic N present as NO3- generally increased with time, depth, and rate of added N. Limestone slightly increased soil solution Ca concentrations in the three-application treatment, and approximately doubled Mg concentrations, but had little or no effect on K concentrations. In leachates, mean NH4+-N levels were less than 8 mg L-1 except in the three-application treatment where they reached 70 mg L-1 at about 12 wk, and then declined, indicating that the bulk of the soil solution NH4+ had passed out of the column. Mean NO3--N in leachate reached 170 mg L-1 in the three-application treatment, peaking at about 23 wk. Leachate levels of Ca, Mg, and K were increased by urine application. Extractable levels of soil NH4+ between 28 and 40 cm in the three-application columns were higher in the unlimed than in the limed treatment, and extractable NO3- levels tended to show the same pattern. Soil pH and extractable levels of Ca and Mg were decreased by urine and increased by limestone, and extractable Al was increased by urine and decreased by limestone applications. The net amounts of N recovered as (i) NH3 gas released to the atmosphere, (ii) N taken up into above-ground plant material, (iii) NH4+ and NO3- extracted from soil, and (iv) NH4+ and NO3- in drainage water, ranged from 49% to 77% of the amount added, with treatments that received two and three N applications showing the higher recoveries. Surface application of limestone can alleviate some of the detrimental effects of high rates of urine addition observed in acidic infertile soils.