土壤酸碱性质对尿素转化特征的影响

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A l元素活性的影响。试验结果表明:土壤酸碱性对尿素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A l随着尿素浓度的增大而急剧下降,交换性A l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。

Effects of Acidity and Alkalinity on Urea Transformation in Soil

Changes of pH,volatilization of ammonia(NH_3) volatility,transformation of urea-N and activity of Al 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 soil pH was short-lived,with a subsequently slow decline after reaching its maximum.Ammonia volatilization intensity,NH_4~+-N and NO_3~——N followed the changes of soil pH.The peak of NH_3 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,NH_4~+-N and NO_3~——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 Al 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.