Nitrate accumulation in an intensive small agricultural catchment: challenges and solutions

Nitrogen (N) fertilization in the intensive horticultural systems is usually high, especially in China during past decades. We have studied nitrate accumulation in soil profiles and nitrate in groundwater of a small catchment dominated by kiwifruit orchard at northern sloping region of Qinling Mountains in Shaanxi. We found that long-term N fertilization resulted in high nitrate accumulation in 4 m profile. The averaged NO3 – -N concentrations and δ 15N-NO3 – values of groundwater increased from natural forest to arable land and to the orchards; on the contrary, the δ18O-NO3 – decreased. The nitrate sources in the groundwater at different regions were identified.

The long term application of nitrogen (N) fertilizer has changed the global N biogeochemical cycle (Erisman et al, 2008). Understanding the fate of N fertilizer in soil and plant system (crop uptake, residual in soil, and loss) is important to increase N use efficiency and decrease its loss. Nitrification is very fast in upland soil. Therefore, the accumulation of nitrate in soil profile is one of important fate of N fertilizer after application. China has consumed about one thirds of the global N fertiliser now. Fruits and vegetables together in China have consumed at least 30% of N fertilizers. However, there are limited researches to study nitrate accumulation in soil profiles both at field and catchment scales, to evaluate their potential risk to the groundwater quality.