地下水位波动对不同施氮量农田土壤硝态氮运移影响

Effects of groundwater fluctuation on nitrate nitrogen transport after nitrogen application in cropland soil

明确地下水位波动对农田土壤剖面和地下水NO3--N运移的影响,可为减少土壤氮素淋失、降低地下水硝酸盐污染风险提供依据。本研究采用大型土柱温室种植甘蓝,研究2种水位波动(水位不变、水位每隔10 d波动20 cm)和3种施氮量[0 kg(N)·hm−2、225 kg(N)·hm−2、450 kg(N)·hm−2]对土壤含水量、土壤溶液NO3-N-浓度、地下水NO3--N浓度和作物产量的影响。结果表明,水位波动和施氮肥对NO3-N-运移的影响与土壤剖面深度有关。0~20 cm包气带土壤NO3--N含量受施氮量影响,过量施氮肥[450 kg(N)·hm−2]导致该剖面NO3--N累积。20~60 cm水位波动带土壤NO3--N含量受施氮量和水位波动的共同作用:施氮量增加提高NO3-N-含量;水位波动降低剖面土壤NO3--N含量,水位上升和下降均促进土壤NO3-N-随着水流运动向下层迁移;剖面土壤硝态氮含量高,增加NO3--N进入地下水的风险。60~80 cm淹水区剖面土壤NO3--N含量较低。作物产量受水位波动影响不显著。在地下水位埋深较浅的农业区进行氮素污染防控时,不可忽视水位波动对NO3--N运移的影响。

Understanding the effects of groundwater fluctuations on nitrate nitrogen(NO3--N)transport in the soil vertical profile is important for reducing nitrogen(N)leaching and nitrate pollution in croplands with shallow groundwater.This study investigated effects of groundwater fluctuations and nitrogen application rate in a greenhouse cabbage with large soil column experimental devices.Two groundwater fluctuation levels(W0,stable;W1,20 cm fluctuation per 10 days)and three levels of nitrogen application(N0,0 kg(N)·hm−2;N1,225 kg(N)·hm−2;N2,450 kg(N)·hm−2)were tested to determine water contents and NO3--N concentration changes at different soil depths,NO3--N concentration in groundwater,and crop yield.The results showed that fluctuating groundwater affected NO3--N transport depending on the soil depth and nitrogen application rate.At 0–20 cm depth(part of the vadose zone),excessive N application led to NO3--N accumulation in soil,but there was no correlation with groundwater fluctuation.At 20–60 cm depth(groundwater fluctuation zone),increased N fertilizer increased the soil NO3--N,and groundwater level changes promoted NO3--N migration into deeper soil,increasing the NO3--N groundwater pollution risk(especially in soil with already high NO3--N concentrations).At 60–80 cm depth(the flooding area),there was less NO3--N in soil,mainly due to denitrification.Crop yield did not significantly correlate with groundwater level changes.Groundwater fluctuations affected NO3--N transport and should be considered in agricultural areas with shallow groundwater levels to prevent and control nitrogen pollution.