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

Authors: LI, SAMEI - Chinese Academy Of Sciences; Banuelos, Gary; MIN, JU - Chinese Academy Of Sciences; SHI, WEIMING - Chinese Academy Of Sciences

Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2015
Publication Date: 5/10/2015
Citation: Li, S., Banuelos, G.S., Min, J., Shi, W. 2015. Effect of continuous application of inorganic nitrogen fertilizer on selenium concentration in vegetables grown in the Taihu Lake Region of China. Plant and Soil. 393:351-360. doi: 10.1007/s11104-015-2496-3.

Interpretive Summary: Selenium is an essential trace element in humans and other animals. Consequently, the daily intake of Se by humans has attracted much attention worldwide, especially in Se sensitive regions around the world, i.e., China. Vegetable production and consumption is vital for covering part of the Se requirements of the Chinese people. To sustain China's growing need for more food extensive production of polytunnel-grown greenhouse vegetables has rapidly increased in recent years in China. In this type of production, excessive use of N fertilizer is a common field management practice to improve yields, however, a lower Se content in vegetable tissue may be a consequence. In the present study, we conducted a consecutive long-term N fertilization field experiment in the Taihu Lake region of China to determine the influence of N fertilization on Se content in soil and in tomatoes and cucumbers grown in polytunnel greenhouse vegetable systems. The yield data indicated that conventional N fertilizer treatments produced twice as much vegetable than control treatment (only manure as source of nitrogen) but vegetable Se concentrations were significantly lower. The negative effect of continuous N fertilization on vegetable Se concentration was a consequent of excessive accumulation of soil nitrate. The lower Se content in vegetables was also a result of decreases in available soil extractable Se concentration after long-term N fertilization. Moreover, excessive N fertilization resulted in a decrease of pH. Generally, Se availability decreases with decreasing soil pH, due to the formation of less available selenium complexes. These results indicated that the long-term N fertilization inputs could eventually decrease vegetable Se content over time in typical intensive polytunnel vegetable cultivation systems and contribute to a reduced Se intake by inhabitants in selenium sensitive regions, i.e., Taihu Lake, China.

Technical Abstract: Selenium is an essential trace element in humans and other animals. Selenium enters the food chain primarily through plants and consequently, the consumption of Se-containing plants is necessary for maintaining adequate Se nutrition levels in humans and animals in Se-sensitive regions of the world, i.e., China. Excessive use of N fertilizer in intensive agricultural areas of China is a common field management practice to improve crop production, however, a lower Se content in crops may be a consequence. To evaluate nitrogen’s impact on selenium accumulation in vegetables, a six-year microplot field experiment was established in a polytunnel greenhouse vegetable system in Taihu Lake region of China with cucumbers and tomatoes and two different N sources; fertilizer (870 kg N ha-1 ) and manure (234 kg N ha-1 ). After each harvest, soil and vegetable samples were collected, and analyzed for soil NO3-N, Olsen-P, extractable S and Se, and vegetable Se. Six years of continuous N fertilization resulted in a significant accumulation of NO3-N, Olsen-P and extractable S in the soil over the course of the experiment. Soil phosphate extractable Se and Se concentrations in vegetables from fertilized plots were significantly lower than those grown in control plots. The phosphate extractable Se had a good negative correlation coefficient R2 to soil NO3-N, Olsen-P and extractable S (Fig.4) at 0.8922, 0.8053 and 0.9975, respectively, in N fertilizer treatment. Soil acidification was observed in the N fertilization plots. Generally, Se availability decreases with decreasing soil pH, due to the formation of less available ferric-iron-selenite complex. When NO3-N concentration increased to greater than 300 mg kg-1, vegetable Se content was negatively correlated to soils NO3-N. The mechanism of excessive N fertilization on vegetable Se contents was likely the result of soil nitrate’s competitive or antagonistic effect on Se uptake by vegetable grown in an intensive polytunnel vegetable cultivation system. These results indicate that the long-term N fertilization could eventually decrease vegetable Se content over time in an intensive polytunnel vegetable cultivation system and contribute to a reduced Se intake by Chinese inhabitants in the Taihu Lake region.