施肥时机对土壤水氮运移转化规律的影响

为揭示不同施肥时机（全过程、前1/2和后1/2入渗水量施肥）下土壤水氮运移转化规律，以砂壤土和黏壤土质地的一维垂直肥液（尿素）入渗试验为基础，重点分析不同施肥时机下土壤水氮分布与再分布过程中的运移转化规律，并量化比较其对土壤中氮素含量的影响。结果表明，施肥时机对土壤累积入渗量和湿润体中水分分布影响微小，但对不同形态氮素运移转化影响显著；砂壤土和黏壤土入渗结束时刻，全过程和后1/2入渗水量施肥时，其尿素态氮、铵态氮（NH₄⁺—N）和硝态氮（NO₃^-—N）含量均随土层深度增大而减小；前1/2入渗水量施肥时，尿素态氮和NO₃^-—N含量在湿润体边缘累积，NH₄⁺—N呈先增大后减小趋势，且主要分布在5—25 cm土层；再分布阶段，全过程和后1/2入渗水量施肥时，砂壤土和黏壤土中尿素态氮分别在再分布3天和5天时基本水解完成，同时NH₄⁺—N含量达到峰值，NO₃^-—N含量再分布10天内未出现下降趋势；前1/2入渗水量施肥时，尿素态氮再分布10天时基本水解完成，NH₄⁺—N含量再分布5~10天达到峰值，NO₃^-—N含量则呈先增加后减小趋势；后1/2入渗水量和全过程施肥条件下，砂壤土和黏壤土再分布10天时0—40 cm土层中NH₄⁺—N和NO₃^-—N含量均大于前1/2入渗水量施肥，说明其氮素潜在利用效率高，故推荐畦（沟）灌合理施肥时机为后1/2入渗水量或全过程施肥。研究结果可为农田畦（沟）灌施肥系统的设计和管理提供理论基础和技术支撑。

Effects of Fertilization Timing on Soil Water and Nitrogen Transport and Transformation

In order to reveal the law of soil water and nitrogen transport and transformation under different fertilization timing (the whole process, the first 1/2 and the last 1/2 infiltration water fertilization), we analyzed the migration and transformation law of soil water and nitrogen distribution and redistribution under different fertilization timing, and compared their effects on soil nitrogen content quantitatively based on the one-dimensional vertical fertilizer solution (urea) infiltration experiment of sandy loam and clay soil. The results showed that fertilization timing hadlittle effect on the cumulative infiltration of soil and the distribution of water in moist body, but it had a significant effect on the transport and transformation of different forms of nitrogen in the process of distribution and redistribution. At the end of infiltration in sandy loam and clay loam, during the whole processand fertilization of the last 1/2 infiltration water, the content of urea nitrogen, ammonium nitrogen (NH₄⁺-N) and nitrate nitrogen (NO₃^--N) decreased with the increasing of soil depth. When the first half of the infiltration water was fertilized, the content of urea nitrogen and NO₃^--N accumulated at the edge of the wet body, andNH₄⁺-N increased first and then decreased, mainly distributed in 5-25 cm soil layer. In the redistribution stage, urea nitrogen in sandy loam and clay loam was basically hydrolyzed after 3 and 5 days of redistribution during the whole process and the last 1/2 infiltration water fertilization, respectively. At the same time, NH₄⁺-N content reached the peak, and NO₃^--N content did not decline within 10 days of redistribution. When the first half of the infiltration water was fertilized, the hydrolysis of urea nitrogen was basically completed after 10 days of redistribution, the content of NH₄⁺-N reached the peak after 5-10 days of redistribution, and the content of NO₃^--N increased first and then decreased. Under the condition of the last 1/2 infiltration water and the whole process of fertilization, when sandy loam and clay loam were distributed for another 10 days, the content of NH₄⁺-N and NO₃^--N in the 0-40 cm soil layer both were greater than those of the first 1/2 infiltration water, indicating that its potential nitrogen utilization efficiency was high. Therefore, it was recommended that the rational fertilization time of border (ditch) irrigation was the last half of the infiltration water or the whole process of fertilization. The results of this research could provide theoretical basis and technical support for the design and management of farmland border (ditch) irrigation and fertilization system.