利用HYDRUS-2D模拟膜下滴灌玉米农田深层土壤水分动态与根系吸水

河套灌区农田地下水埋深普遍较浅且年内波动较大,明确不同膜下滴灌条件下深层土壤水分对根区的补给作用及作物根系吸水的响应差异有利于膜下滴灌技术的完善和推广。本研究开展了连续2 a(2017—2018年)的春玉米田间试验,设置3个膜下滴灌灌溉水平,分别控制土壤基质势下限为-10 kPa(S1)、-30 kPa(S3)和-50 kPa(S5)。利用HYDRUS-2D模型模拟0～120 cm深度土壤含水量、根层下边界(100 cm深度处)水分通量和作物根系吸水速率。结果表明,经过率定后的HYDRUS-2D模型对0～120 cm深度土壤含水量模拟结果的根均方差(RMSE)和决定系数(R~2)分别为0.039～0.042 cm~3·cm~(-3)和0.78～0.73,模拟结果可靠。膜下滴灌农田100 cm和120 cm深度处土壤含水量较高且处理间差异不大,说明不同滴灌条件对于100 cm以下深层土壤含水量影响较小;但不同处理显著影响根区下边界的水分通量和根系吸水速率。基质势下限控制水平越低,深层土壤水分对于根区的补给量(毛管上升)越大,S1、S3、S5生育期内累积补给量在31.9～49.6 mm之间。S5处理根系吸水速率较低,根系吸水受到显著抑制,从而造成作物生长指标和产量显著低于S1和S3处理(P0.05);而S1和S3之间籽粒产量差异不显著。综上,在本研究所设置的3个滴灌处理中,S3生育期内灌溉定额为240～300 mm,既较S1显著减少灌水量、提高水分利用效率,又具有较好的根系活力,有效利用深层土壤水分,因此建议该地区春玉米膜下滴灌的灌水下限为-30 kPa。

Modeling of dynamics of deep soil water and root uptake of maize with mulched drip irrigations using HYDRUS-2D

The Hetao Irrigation District (HID) of Inner Mongolia, which is located in the arid area in Northwestern China, generally has a shallow groundwater with a great fluctuation annually. Understanding the water recharge effect from the deep to root layer and water uptake by root under mulched drip irrigation helps to revamp and promote drip irrigation technology in the HID. A two\|year (2017-2018) field experiment was conducted, in which three soil\|water matric potential (SMP) threshold values including -10 kPa(S1),-30 kPa(S3), and -50 kPa(S5), were used to schedule the mulched drip irrigation for spring maize. Then, the HYDRUS-2D model was used to simulate the water content in the 0~120 cm soil layer, the cumulative water flux at the lower boundary,and the water uptake rate by root under different drip irrigation regimes.The results showed that comparing the simulated soil moisture contents with the measured, the calibrated HYDRUS-2D was reliable to simulate water movement in the studied soil layers under drip irrigation, gave the acceptable root mean square error (RMSE) (0.039-0.042 cm³·cm^-3) and determination coefficient (R²) of 0.78~0.73. The soil moisture contents in the deep layers of 100 cm and 120 cm depth were not significantly different among the different treatments, indicating that the different drip irrigations had little effect on water movement in the deep layers. The different drip irrigation levels significantly affected the cumulative water flux at the lower boundary of root zone and root water uptake. The recharge (capillary rising) from deeper to root layer increased from 31.9 mm to 49.6 mm with decreasing SMP threshold values of S1, S3 and S5. When the SMP threshold value was -50 kPa (S5), the lowest root water uptake intensity was predicted, showing a stressed root activity and resulting in the significantly restricted growth and yield in S5 relative to S1 and S3 (P<0.05); while the difference in leaf area index, aboveground biomass, and grain yield between S1 and S3 was not significant (P>0.05). That means the S3 treatment with the SMP threshold value of -30 kPa, which irrigation quota was 240~300 mm, improved water use efficiency and maintained the root activity of water uptake. Therefore, the SMP threshold value of -30 kPa was recommended to schedule mulched drip irrigation for spring maize production in the studied area.