Irrigation Sends Nitrogen and Phosphorus Seeping Underground in China’s Hetao Farmland

Researchers have measured how much nitrogen and phosphorus seep sideways through the soil into drainage channels at a typical field in the Hetao Irrigation District, China’s third largest irrigation district, located in Bayannur. Over the full drainage period from April to November 2023, the team sampled groundwater and estimated lateral subsurface seepage of water and nutrients, reporting that total nitrogen fluxes via this pathway reached 8.773 to 9.654 kilograms per hectare over the whole growing season, while total phosphorus fluxes were 0.306 to 0.334 kilograms per hectare.

The chemical composition of the losses differed sharply between the two nutrients. Nitrate-nitrogen was the dominant form of total nitrogen, with dissolved organic nitrogen the second most significant component. For phosphorus, the pattern was reversed: dissolved organic phosphorus dominated total phosphorus, while dissolved inorganic phosphorus was the least significant component.

The timing of water movement lagged behind irrigation itself. Irrigation amounts were highest in May and decreased from May to November, but lateral subsurface seepage increased from April to July and then fell gradually from July to November, showing a delay relative to the irrigation schedule. The annual irrigation schedule in the district repeats the same sequence each year, which the authors note is relevant to understanding nutrient dynamics in groundwater for regional water resources and ecological environmental security in arid and semi-arid agricultural areas.

Nutrient fluxes fluctuated over the season, and the study links these fluctuations to irrigation amount, precipitation and evaporation, and fertilizer applications. Because the quantification of irrigation-induced lateral nutrient fluxes in drainage channels had remained poorly understood, the authors describe their work as providing methodological guidance for estimating agricultural non-point source pollution in similar irrigation districts. The findings, published as an open-access research article in Environmental Sciences Europe, offer a field-scale baseline for one growing season in a single typical field, so the flux estimates apply to the conditions measured there rather than to the entire irrigation district.

Subject of Research: Nutrient fluxes via irrigation-induced lateral subsurface flow in a Chinese irrigation district

Article Title: Irrigation-induced nitrogen and phosphorus fluxes via lateral subsurface flow in a typical field of the third largest irrigation district in China

Article References: Zhang, Q., Li, C., Cai, X., Ye, C., Zhao, R., Xie, Z., Zhou, X., & Ye, Z. (2026). Irrigation-induced nitrogen and phosphorus fluxes via lateral subsurface flow in a typical field of the third largest irrigation district in China. Environmental Sciences Europe. https://doi.org/10.1186/s12302-026-01535-0

Image Credits: AI Generated

DOI: 10.1186/s12302-026-01535-0

Keywords: Hetao Irrigation District, nitrogen, phosphorus, lateral subsurface flow, groundwater, agricultural non-point source pollution, irrigation, nutrient fluxes, Bayannur, water quality, Irrigation-induced, fluxes