滴灌施肥时序对不同质地土壤水氮分布的影响

Optimal Timing of Fertilization in Drip Fertigation for Bioavailable Water and Nitrogen in Soils of Different Textures

【目的】探究不同滴灌施肥时序下不同质地土壤水、氮的运移规律和分布特征。【方法】通过室内土槽试验,设置3种土壤质地:砂土、壤土、黏土,分别记为S1、S2、S3,4种施肥时序:仅灌水、1/2N-1/2W(前1/2时间施氮肥)、1/4W-1/2N-1/4W(前1/4时间灌水后在中间1/2时间施氮肥)、3/8W-1/2N-1/8W(前3/8时间灌水后在中间1/2时间施氮肥),分别记为T1、T2、T3、T4,分析了土壤湿润锋的运移以及水分、硝态氮在土体内的分布特征。【结果】在灌水量和滴头流量均相同的条件下,3种土壤的湿润锋分布特征存在明显差异。湿润锋的最大入渗深度:砂土(29.5 cm)>壤土(21 cm)>黏土(15 cm)。硝态氮在湿润体边缘累积,并且随着施肥次序向前推移,硝态氮向湿润体边缘运移的趋势越来越明显。不同施肥时序下,硝态氮在3种土壤中的分布存在差异。S1T4处理的硝态氮在砂土下层的比例最低;S2T3处理下壤土的硝态氮分布最均匀;S3T2处理可以降低硝态氮在黏土表层堆积。【结论】对于砂土、壤土和黏土,分别采用3/8W-1/2N-1/8W、1/4W-1/2N-1/4W和1/2N-1/2W的施肥时序,有利于降低氮肥淋失的风险,提高氮肥利用效率。

【Objective】Designing irrigation and fertilization scheduling needs to understand how water and fertilizer move in soil. The aim of this papers is to experimentally study the movement of water and nitrogen(N) in soils of different texture as impacted by timing of fertilization in drip fertigation.【Method】The experiment was conducted indoor using tanks repacked with sandy(S1), loam(2) and clay(3) soil. For each soil, there were four fertilizations with the fertilization lasting half of the irrigation duration but starting at different times: in the first half(T1), in the central half(T2), and commencing 3/8 way after the onset of irrigation(T3). Irrigation without fertilization was taken as the control(CK). In each treatment, we measured the movement of the wetting front and distributions of water and nitrate in the soil.【Result】When the irrigation amount and dripping rate were the same, there were significant differences in water movement between the three soil types. The maximum water infiltration depth in the sandy soil was 29.5 cm, compared to 21 cm in the loam soil and 15 cm in the clay soil. Nitrate accumulated at the edge of the wetting fronts, and delaying fertilization timing slowed down nitrate migration towards the wetting front.There were differences in nitrate distribution between the three soil types, and the difference varied with the timing of the fertilization. In the sandy soil, nitrate in the subsoil soil under T4 was least. In the loam soil, the nitrate distribution was more uniform than that in T3. In the clay soil, T2 reduced nitrate accumulation in the surface soil.【Conclusion】Soil texture and timing of fertigation had significant impacts on nitrogen distribution. For the sandy,loam and clay soil we studied, the best timing for fertilization under drip fertigation was 3/8 way after the irrigation commenced, in the central half and in the first half, respectively. These reduced the risk of nitrogen leaching while in the meantime improving nitrogen use efficiency by crops.