Moraes L E, Burgos S A, DePeters E J, Zhang R, Fadel J G
Department of Animal Science, University of California, Davis 95616.
Department of Biological and Agricultural Engineering, University of California, Davis 95616.
J Dairy Sci. 2017 Mar;100(3):2388-2394. doi: 10.3168/jds.2016-11927. Epub 2017 Jan 11.
The objective of the study was to quantify the rate of urea hydrolysis in dairy cattle manure under different initial urea concentration, temperature, and pH conditions. In particular, by varying all 3 factors simultaneously, the interactions between them could also be determined. Fresh feces and artificial urine solutions were combined into a slurry to characterize the rate of urea hydrolysis under 2 temperatures (15°C and 35°C), 3 urea concentrations in urine solutions (500, 1,000, and 1,500 mg of urea-N/dL), and 3 pH levels (6, 7, and 8). Urea N concentration in slurry was analyzed at 0.0167, 1, 2, 4, 6, 8, 12, 16, 20, and 24 h after initial mixing. A nonlinear mixed effects model was used to determine the effects of urea concentration, pH, and temperature treatments on the exponential rate of urea hydrolysis and to predict the hydrolysis rate for each treatment combination. We detected a significant interaction between pH and initial urea level. Increasing urea concentration from 1,000 to 1,500 mg of urea-N/dL decreased the rate of urea hydrolysis across all pH levels. Across all pH and initial urea levels, the rate of urea hydrolysis increased with temperature, but the effect of pH was only observed for pH 6 versus pH 8 at the intermediate initial urea concentration. The fast rates of urea hydrolysis indicate that urea was almost completely hydrolyzed within a few hours of urine mixing with feces. The estimated urea hydrolysis rates from this study are likely maximum rates because of the thorough mixing before each sampling. Although considerable mixing of feces and urine occurs on the barn floor of commercial dairy operations from cattle walking through the manure, such mixing may be not as quick and thorough as in this study. Consequently, the urea hydrolysis rates from this study indicate the maximum loss of urea and should be accounted for in management aimed at mitigating ammonia emissions from dairy cattle manure under similar urea concentration, pH, and temperature conditions reported in this experiment.
本研究的目的是量化不同初始尿素浓度、温度和pH条件下奶牛粪便中尿素水解的速率。特别是，通过同时改变所有三个因素，还可以确定它们之间的相互作用。将新鲜粪便和人工尿液溶液混合成浆液，以表征在2个温度（15°C和35°C）、尿液溶液中3种尿素浓度（500、1000和1500 mg尿素-N/dL）和3个pH水平（6、7和8）下尿素水解的速率。在初始混合后的0.0167、1、2、4、6、8、12、16、20和24小时分析浆液中的尿素氮浓度。使用非线性混合效应模型来确定尿素浓度、pH和温度处理对尿素水解指数速率的影响，并预测每种处理组合的水解速率。我们检测到pH与初始尿素水平之间存在显著相互作用。将尿素浓度从1000 mg尿素-N/dL提高到1500 mg尿素-N/dL会降低所有pH水平下的尿素水解速率。在所有pH和初始尿素水平下，尿素水解速率随温度升高而增加，但仅在中等初始尿素浓度下观察到pH 6与pH 8之间的pH效应。尿素水解的快速速率表明，尿素在尿液与粪便混合后的几个小时内几乎完全水解。由于每次采样前进行了充分混合，本研究估计的尿素水解速率可能是最大速率。尽管在商业奶牛场的牛舍地面上，牛走过粪便时会使粪便和尿液有相当程度的混合，但这种混合可能不如本研究中那么迅速和彻底。因此，本研究的尿素水解速率表明了尿素的最大损失量，在旨在减轻本实验报道的类似尿素浓度、pH和温度条件下奶牛粪便氨排放的管理中应予以考虑。
