土壤酸碱性质对尿素转化特征的影响

Effects of Acidity and Alkalinity on Urea Transformation in Soil

试验研究了3种酸性土壤和3种碱性土壤施入尿素后，对土壤pH值变化、氨挥发特性、氮素转化及Al元素活性的影响。试验结果表明：土壤酸碱性对尿索水解的影响与尿素浓度有关，在常温25℃下，3种酸性土壤的pH值在短期内都随着加入尿素浓度的增大而急剧上升，而3种碱性土壤的pH值却是随着加入尿素浓度的增加先增加再减少然后又增加，且其变化的幅度较之酸性土壤小；动态试验表明，pH值上升的现象是短期的，6种土壤pH值达到最大值后缓慢下降，2周后3种碱性土壤的pH降到比原来更低的程度。氨挥发强度与土壤pH变化同步；在酸性土壤和碱性土壤中，氨气日挥发量都是先从小到大出现峰值，然后又降低；酸性土壤氨挥发高峰期约在7—9天，碱性土壤的氨挥发高峰期约在第3天左右。各处理NH4^＋ -N含量和NO3^- -N含量与土壤pH变化趋势相似，在前2—4星期增加到峰值，而后开始下降并保持不变。短期内，交换性灿随着尿素浓度的增大而急剧下降，交换性舢含量与土壤pH变化呈显著负相关，施用尿素短期内能显著降低酸性土壤交换性铝的含量。

Changes of pH, volatilization of ammonia （NH3 ） volatility ,transformation of urea- N and activity of AI in 3 acidic and 3 alkali soils as induced by urea were studied. The results indicated that effects of acidity and alkalinity of soil on urea hydrolysis was related to the concentration of urea. At 25℃, the changes of pH in 3 acidic soils increased quickly, however, the changes of pH in 3 alkali soils increased at the beginning and then fell to some extent, but rose again after sometime, The dynamic experiment revealed that the increase of soft pH was short -lived, with a subsequently slow decline after reaching its maximum. Ammonia volatilization intensity, NH4^＋ - N and NO3^- - N followed the changes of soil pH. The peak of NH3 volatilization occurred between the 7^th and 9^th day of urea fertilizer addition in the 3 acidic soils, but on the 3^rd day in alkali soils, NH4^＋ - N and NO3^- - N in the 6 soils increased to maximum after 2 -4 weeks, and then decreased to a constant value. Soil exchangeable Al decreased sharply with the increasing concentrations of urea in the 3 acidic soils, and there was an obviously negative relationship between soil exchangeable AI and soil pH in a short -term period. Applying urea to acidic soils could obviously decrease the content of exchangeable Al in the acidic soils in the short- term.