Changes in pH and Mehlich-3 Extractable Nutrients of Selected Soils From the Midwest and South USA As Influenced by Different Rates of Iron Calcium Silicate Slag.

Calcium silicate (CaSiO₃) slag is among the sources of silicon (Si) in crop production and commonly obtained as by-products in steel industry and production of elemental P. These slag by-products have high calcium carbonate equivalent (CCE) making them also suitable as liming material. In the USA, CaSiO₃ slag is commonly apply to soil cultivated for rice and sugarcane production at quantities ranging between 1 MT to as high as 6 MT ha^-1. With high application rates and high CCE value of CaSiO₃ slag, the solubility of essential nutrients such as P, Zn, Fe and Mn can be altered. This study was conducted to quantify the effect of different rates of iron and steel CaSiO₃ slag by-product (17% Si, 81% CCE) on soil pH and extractable elements of soils collected from the Midwest and South USA. Soils were acidic (pH 5.0) to slightly alkaline (pH 7.4) with wide ranges of Mehlich-3 (M3) extractable macro- and micro-nutrients. Bulk soil samples were processed and placed in 2-kg capacity pots where CaSiO₃ slag rates of 0, 1, 2, 4, 6 and 8 MT ha^-1 were thoroughly mixed with the top 15-cm surface of the potted soil. Soil samples were collected after allowing ryegrass to grow for 3 months. The pH of several soils increased linearly with increasing rates of CaSiO₃; these soils either had initially low pH or classified as coarse-textured soils. The highest change in pH before and after CaSiO₃ application was a unit of 1.05 for soils which received 8 MT CaSiO₃ ha^-1. Mehlich-3 extractable Mg, Mn, S, and Ca of all the soils increased with increasing rates of CaSiO₃ slag. This can be attributed to the large concentrations of these elements contain in the slag material. The steady decline of M3-extractable Fe and Ni (and Zn in some soils) may be related to the potential of CaSiO₃ slag to raise soil pH, hence decreasing the solubility of these metal cations. Our results show that both liming potential and composition of CaSiO₃ slag had significant effect on the amount of M3-extractable essential nutrients.