Effect of continuous application of inorganic nitrogen fertilizer on selenium concentration in vegetables grown in the Taihu Lake region of China

BACKGROUND AND AIMS: Vegetables provide an important source of selenium (Se) for many regions of China. Excess nitrogen (N) fertilizers are commonly used for vegetable production. In this regard, the effect of inorganic N-fertilizer application on the Se content in soils and plants was evaluated in vegetables produced in a polytunnel greenhouse vegetable system. METHODS: Vegetables were continuously cultivated for 6 years in a microplot field experiment and treated annually with conventional N fertilizer (870 kg ha⁻¹ inorganic fertilizer) and 0 kg N ha⁻¹ as control treatment in polytunnel greenhouse vegetable system in the Taihu Lake region of China. Both treatments included 234 kg ha⁻¹ N provided by manure. After each harvest, soil and vegetable samples were collected, and analyzed for soil NO₃-N, Olsen-P, Se, phosphate extractable S and Se and vegetable Se. RESULTS: Six years of continuous application of inorganic N-fertilizer resulted in a significant accumulation of NO₃-N, Olsen-P and extractable S in the soil over the course of the experiment. Soil NO₃-N concentration accumulated up to 600 mg kg⁻¹ with application of inorganic N-fertilizer, while soil phosphate extractable Se and vegetables Se concentration were significantly lower than that those grown in control treatments. The negative effect of continuous application of inorganic N-fertilizer on vegetable Se concentration may be a consequent of excessive accumulated soil NO₃-N. When NO₃-N concentration was greater than 300 mg kg⁻¹, vegetable Se concentration was negatively correlated with soil NO₃-N. CONCLUSIONS: The negative effect of continuous application of inorganic N-fertilizer on vegetable Se concentrations was likely the result of soil nitrate’s competitive or antagonistic effect on Se uptake by vegetables grown in an intensive polytunnel vegetable cultivation system.