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

Abstract

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. 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. 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. 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.