控制地下水位减少节水灌溉稻田氮素淋失

Reducing nitrogen leaching losses from paddy field under water-saving irrigation by water table control

为探讨高效的稻田灌排管理模式,降低稻田氮素淋失风险,该文利用装配有地下水位自动控制系统的蒸渗仪,研究地下水位调控对节水灌溉稻田氮素淋失的影响。结果表明,稻田排水控制限的提高可减少控制灌溉稻田地下排水量,控制地下水位处理1稻田地下排水量为179.4mm,分别较控制地下水位处理2(195.9mm)和控制地下水位处理3(285.8mm)稻田减少8.4%和37.2%。随稻田排水控制限的提高,控制灌溉稻田地下排水中铵态氮(NH4+–N)浓度增加,硝态氮(NO3-–N)浓度下降。与控制地下水位处理2和控制地下水位处理3稻田相比,控制地下水位处理1稻田地下排水中NH4+–N质量浓度均值分别增加9.3%和27.3%,地下排水中NO3-–N质量浓度均值分别减少32.6%和1.8%。稻田排水控制限的提高显著减少了控制灌溉稻田NO3-–N淋失量(P<0.05),控制地下水位处理1稻田NO3-–N淋失量为0.27kg/hm2,分别较控制地下水位处理2(0.43kg/hm2)和控制地下水位处理3(0.88kg/hm2)稻田显著减少0.16和0.61kg/hm2(P<0.05),控制地下水位处理2稻田NO3-–N淋失量较控制地下水位处理3稻田显著减少0.45kg/hm2(P<0.05)。采用控制排水技术,适当提高控制灌溉稻田的排水控制限,可有效降低稻田NO3-–N淋失对地下水污染的风险。该研究可为制定满足控污减排需求的稻田灌排管理模式提供指导。

Effects of controlled drainage（CD） on nitrogen leaching losses from paddy field under controlled irrigation（CI） were investigated. Water table control levels were managing with the use of a lysimeter equipped with an automatic water table control system. Three drainage treatments were implemented, namely, controlled water table 1, controlled water table 2, and controlled water table 3. For controlled water table 1, the water table control levels were adjusted daily based on the actual water table depths that were measured by using a water table observation well. Water table control levels in controlled water table 2 were controlled based on the rice root zone depths in different stages according to the water table management that was tested in the humid regions of Eastern Canada and Midwestern United States. For controlled water table 3, the water table control levels in different stages were selected based on previous studies in paddy field of Southeast China. The water table control levels in the later tillering stage and milk stage were also adjusted depending on the characteristics of rice growth and cultivation needs. Experiments were conducted in nine drainage type lysimeters with a mobile shelter and gallery. Each lysimeter had an area of 2.5 m × 2 m and a depth of 1.3 m. Influence of rainfall was avoided using the mobile shelter to strictly regulate the soil moisture in CI. Each lysimeter was individually irrigated and drained using a pipe installed with a water meter and a tube（40 mm in inner diameter） installed at 1.2 m below the soil surface, respectively. Subsurface drainage was conducted based on the water table control levels by using an automatic water table control system, which was installed on each drain tube in the gallery. Subsurface drainage water were collected twice at 2d intervals after each fertilizer application followed by 4d intervals. A 7d sampling interval was used during the rest time. NH＋4–N and NO-3–N concentrations in the water samples were analyzed using an ultraviolet-visible spectrophotometer. NH＋4–N or NO-3–N leaching loss was calculated by multiplying the subsurface drainage water volume between the two dates by the NH＋4–N or NO-3–N concentration in the sample taken at the latter date. The results showed increasing water table control levels resulted in less subsurface drainage water from CI paddy field. The subsurface drainage water from controlled water table 1 was 179.4mm, which was 8.4% and 37.2% lower than those from controlled water table 2（195.9 mm） and controlled water table 3（285.8 mm）, respectively. As the water table control levels increased, NH＋4–N concentration in subsurface drainage water increased, however, NO-＋3–N concentration decreased. Average NH4–N concentration in the subsurface drainage water from controlled water table 1 was 9.3% and 27.3% higher than those from controlled water table 2 and controlled water table 3, respectively. Average NO-3–N concentration in the subsurface drainage water from controlled water table 1 was 32.6% and 1.8% lower than those from controlled water table 2 and controlled water table 3, respectively. Significantly, less NO-3–N leaching loss from CI paddy field was observed as the water table control levels increased. NO-3–N leaching loss from controlled water table 1 was 0.27 kg/hm^2, with a significant reduction of 0.16 and 0.61 kg/hm^2, respectively, compared with controlled water table 2 and controlled water table 3. NO-3–N leaching loss from controlled water table 2 was significantly reduced by 0.45 kg/hm^2 compared with controlled water table 3. The application of CD with suitable water table control level could effectively reduce NO-3–N leaching loss from CI paddy field.