滴灌条件下施氮时段对土壤氮素分布的影响研究
Effect of nitrogen application time on the distribution of soil nitrogen under drip fertigation

采用单点源滴灌试验模拟土壤入渗，并分不同时段施氮肥，灌水施氮肥结束后，在不同时间段和湿润体不同位置采集土样，并测定土壤中速效氮的含量，分析比对湿润体中不同位置硝态氮与铵态氮的时空分布，结果表明：滴灌全程施肥，土壤湿润体中高氮区始终分布在滴头附近；滴灌前1/2时段施肥，硝态氮含量的最大值(107.50 mg·kg-1)出现在距滴头水平距离15～20 cm，垂直距离15～30 cm范围内；后1/2时段施肥，高氮区始终也分布在滴头附近，但含量值表现极高(184.36 mg·kg-1)；中间1/2时段施肥，硝态氮主要分布在距滴头水平距离为15 cm左右，垂直深度也为15 cm左右的土层范围内。随着时间的推移，土壤湿润体中NO3--N的含量均表现为到第5天前后达到最高值，此后又开始降低；NH4Institution of soil and water Conservation, Chinese Academy of Science, Shaanxi, Yangling 712100, China；-N在时间上转化速率相对较快，在灌水施肥结束后的第3天硝化作用最强，从第3天到第5天NH4+-N浓度急剧降低。
Using single-point infiltrational simulation, an experiment on different nitrogen application time under drip fertigation was conducted. Soil ammonium and nitrate content in different location was measured at different time after drip irrigation. The results showed that the region with high nitrogen content was always near the drip emitter for fertigation during the whole drip irrigation. Maximum NO3--N content occurred at 15～25 cm horizontal distance and 15～30 cm vertical distance for fertigation during the first half time of drip irrigation. The region with high nitrogen was always near the drip emitter for fertigation during the second half time of drip irrigation，but the content is rather high. Maximum NO3--N content existed at 15cm horizontal distance and 15 cm vertical distance for fertigation in the middle half of the time. The peak content of NO3--N in wetted soil body occurred on the 5th day and then became smaller with time. The transforming rate of NH4+-N was relatively fast, and the nitrification was most strong on the third day after irrigation, resulting in the ammonium content decreased sharply from the third day to the fifth.