Ye Yuan-Hang, Chen An-Qiang, Li Lin, Min Jin-Heng, Wang Chi, Yan Hui, Zhang Dan
College of Resources and Environment, Yunnan Agricultural University, Kunming 650201, China.
Agricultural Environment Resources Institute, Yunnan Academy of Agricultural Sciences, Kunming 650201, China.
Huan Jing Ke Xue. 2024 Jun 8;45(6):3225-3233. doi: 10.13227/j.hjkx.202306133.
Soil nitrogen accumulation in cropland and groundwater nitrogen pollution can be effectively alleviated by reducing exogenous nitrogen input, and fallow is an important measure for reducing exogenous nitrogen input. To explore the effects of fallow on nitrogen accumulation in the soil profile and shallow groundwater, the soil profile and shallow groundwater in cropland around Fuxian Lake were selected as research objects. The changes in nitrogen accumulation in the 0-100 cm soil profile and nitrogen concentration in shallow groundwater before (December 2017) and after (August 2020 and April 2021) fallow and their relationships were analyzed. The results showed that the content and storage of nitrogen in soil profiles were significantly reduced by fallow, and the contents of TN, ON, DTN, NO-N, and NH-N in 0-30, 30-60, and 60-100 cm soil profiles after fallow decreased by 18.4 %-36.5 %, 16.1 %-26.8 %, 54.0 %-130.2 %, 59.5 %-90.8 %, and 60.1 %-110.6 %, respectively. The storages of TN, ON, DTN, NO-N, and NH-N in 0-100 cm soil profiles before fallow were (17.20 ±0.97) t·hm, (15.50 ±1.23) t·hm, (0.68 ±0.06) t·hm, (266.8 ±31.17) kg·hm, and (18.7 ±3.04) kg·hm, respectively. However, their storages after fallow decreased by 25.5 %, 23.3 %, 44.7 %, 80.1 %, and 59.9 %, respectively. Fallow also changed the concentration and composition of different forms of nitrogen in shallow groundwater. The concentrations of TN, ON, NO-N, and NH-N in groundwater after fallow decreased by 88.4 %, 82.7 %, 92.1 %, and 65.8 %, respectively, and ON/TN and NH-N/TN increased from 26 % and 6 % before fallow to 39 % and 17 % after fallow, respectively, whereas NO-N/TN decreased from 61 % before fallow to 41 % after fallow. Changes in nitrogen concentrations and their forms in groundwater were closely related to DTN, NO-N, and NH-N in the soil profile and pH, ORP, and DO in groundwater before and after fallow. Our study highlights that fallow effectively reduced nitrogen accumulation in cropland soil profiles, further alleviating nitrogen pollution in shallow groundwater, and was conducive to preventing the deterioration of water quality in plateau lakes.
通过减少外源氮输入，可有效缓解农田土壤氮素积累和地下水氮污染，休耕是减少外源氮输入的一项重要措施。为探究休耕对土壤剖面和浅层地下水中氮素积累的影响，选取抚仙湖周边农田的土壤剖面和浅层地下水作为研究对象。分析了休耕前（2017年12月）、休耕后（2020年8月和2021年4月）0-100cm土壤剖面中氮素积累的变化以及浅层地下水中氮浓度的变化及其相互关系。结果表明，休耕显著降低了土壤剖面中氮的含量和储量，休耕后0-30cm、30-60cm和60-100cm土壤剖面中总氮（TN）、有机氮（ON）、溶解态总氮（DTN）、硝态氮（NO₃-N）和铵态氮（NH₄-N）的含量分别下降了18.4%-36.5%、16.1%-26.8%、54.0%-130.2%、59.5%-90.8%和60.1%-110.6%。休耕前0-100cm土壤剖面中TN、ON、DTN、NO₃-N和NH₄-N的储量分别为(17.20±0.97)t·hm⁻²、(15.50±1.23)t·hm⁻²、(0.68±0.06)t·hm⁻²、(266.8±31.17)kg·hm⁻²和(18.7±3.04)kg·hm⁻²。然而，休耕后它们的储量分别下降了25.5%、23.3%、44.7%、80.1%和59.9%。休耕还改变了浅层地下水中不同形态氮的浓度和组成。休耕后地下水中TN、ON、NO₃-N和NH₄-N的浓度分别下降了88.4%、82.7%、92.1%和65.8%，ON/TN和NH₄-N/TN分别从休耕前的26%和6%增加到休耕后的39%和17%，而NO₃-N/TN从休耕前的61%下降到休耕后的41%。地下水中氮浓度及其形态的变化与土壤剖面中的DTN、NO₃-N和NH₄-N以及休耕前后地下水中的pH、氧化还原电位（ORP）和溶解氧（DO）密切相关。我们的研究强调，休耕有效减少了农田土壤剖面中的氮素积累，进一步减轻了浅层地下水的氮污染，有利于防止高原湖泊水质恶化。
