Beneficial elements

This chapter focuses on the role played by beneficial elements such as sodium (Na), silicon (Si), cobalt (Co), selenium (Se), and aluminum (Al). Sodium can stimulate growth of plants, particularly some C4 plants by aiding the movement of substrates between the mesophyll and the bundle sheath. It can also replace K to some extent in its role as osmoticum, and the application of Na fertilizers to sugar beet results in an increase in the leaf area index early in the growing season, thus increasing light interception and improving water use efficiency of leaves under conditions of moderate drought stress. Silicon plays an important role in cell wall stability by bridging between polyuronides and stimulating lignin synthesis. It can improve plant and leaf erectness, water use, and protect plants from pests and diseases. Silicon is also effective in alleviating toxicity of other metals such as Fe, Al, Cd, and Zn, which can be attributed to the interaction between Si and metals in the apoplasm or symplasm. Cobalt is essential for N2 fixing plants because it is part of the coenzyme cobalamin (vitamin B12), which is important in nodule metabolism. The chemistry of Se is similar to that of S and can replace S, to some extent, in proteins, particularly in Se hyperaccumulating plants. Selenium is essential for animals; therefore Se fertilization may be beneficial for human and animal health in areas with Se-deficient soils. Aluminum is beneficial to some plants, such as tea, and may alleviate proton toxicity and increase the activity of antioxidant enzymes.