求翻译：宁夏引黄灌区的农田退水污染对黄河的水质安全影响越来越严重，正在发展成为主要的污染源，退水污染主要来源于土壤中硝态氮的淋失。因此研究如何控制硝态氮淋失的技术是保证黄河水质安全的主要途径。是什么意思？

Ningxia Yellow River Irrigation farmland retreat of water pollution is increasingly serious impact on the Yellow River water quality and safety, is being developed as a major source of pollution, the retreat of water pollution comes mainly from the leaching of nitrate in the soil. Study how to contr

Ningxia irrigation areas from Huang of the field of river water pollution affecting water quality and safety of the increasingly serious and is becoming a major source of pollution, water pollution comes mainly from nitro gas nitrogen in the soil of the shower. Therefore, the study how to control ni

The Ningxia Huang river irrigated area farmland draws back the water pollution to be more and more serious to Yellow River's water quality safe influence, is developing into the main source of pollution, draws back the water pollution main origin in the soil the nitric nitrogen leaching out.How ther

Rolling farmland on water pollution of the Yellow River in Ningxia irrigation area water quality safety of more and more serious, is being developed into a major source of contamination, back water pollution mainly from the leaching of nitrate-nitrogen in the soil. Study on technology of control of

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