层状土壤条件下地下滴灌水氮运移模型及应用

基于土壤水分运动的动力学方程和溶质运移的对流-弥散方程,考虑地下滴灌灌水器流量随时间的变化,建立了层状土壤地下滴灌施用硝酸铵(NH4NO3)条件下水氮运移的数学模型。利用均质砂土(S)、均质壤土(L)、上砂下壤(SL)和砂土夹层(LSL)四种土壤的试验数据对模型进行了验证。结果指出,考虑土壤中灌水器流量随时间变化可稍改善土壤含水率和硝态氮的模拟精度。利用验证后的数学模型研究了灌水器流量(1.1、1.75和2.6L/h)、灌水器与犁底层相对位置对地下滴灌水氮分布的影响,模拟结果表明灌水器流量对含水率分布的影响不明显,但灌水器流量的增大可明显增加20~40cm土层硝态氮含量;灌水器与犁底层相对位置对水氮分布影响显著,灌水器位于犁底层中(埋深25cm)土壤表层干土层较薄、水氮向下运移深度较小,有利于减小土壤蒸发和避免水氮淋失。

Modeling of water and nitrogen transport in layered-textural soils under subsurface drip fertigation

A model was established to simulate the transport of water and nitrate in layered-textural soils from a buried line source of ammonium nitrate (NH4NO3). In the model, a variable flux boundary condition was used to describe the discharge performance of the buried line source. The model was verified by the laboratory experiments conducted in the soils of uniform sandy (S), uniform loam (L), sandy over loam (SL) and loam sandy loam (LSL) under different lateral depths. The simulated distributions of water and nitrate show that the variable flux boundary condition produced slightly better simulated results than that of constant flux boundary condition. Then the model was used to investigate the effects of the relative positions of emitters to the interface between plow pan soils and emitter discharge on water and nitrate distributions under subsurface drip fertigation. The simulation results demonstrate that emitter discharge had no significant effect on water distributions, but the nitrate content in 20~40cm soil layer significantly increased with the increase of emitter discharge. The relative positions of emitters to the interface between plow pan soils had significant effect on water and nitrogen distributions. It is suggested that a buried depth of 27cm with emitters buried in plow pan may be beneficial to decreasing soil evaporation and avoiding water and nitrate leaching out of the root zone.