New Methodologies for the Surface Application of Limestone and Gypsum in Different Crop Systems

Abstract

To address the problems of soil acidity (pH values below 4.4) in surface and subsurface soil layers and improve soil chemical fertility, this study evaluated three methodologies for surface application of limestone (LS) (ensuring that calcium (Ca)2+ occupied 70%, 60% or 50% of cation exchange capacity (CEC) at a depth of 0.0–0.2 m) and gypsum (GP, phosphogypsum) (ensuring that Ca2+ occupied 60%, 50% or 40% of effective cation exchange capacity (ECEC) at a depth of 0.2–0.4 m). LS and GP were applied in a conventional pasture system (CPS), no-till system (NTS), and agropastoral system (APS) in an Arenic Hapludult in Brazil. Surface application of LS and GP using these three methodologies corrected surface and subsurface acidity and improved soil chemical fertility. Specifically, Ca2+ content increased in the CPS, NTS, and APS at a depth of 0.0–0.2 m and in the CPS and APS at a depth of 0.2–0.4 m; sulfur (S)-SO42− content and Ca2+/ECEC increased in the CPS, NTS, and APS at a depth of 0.2–0.4 m; base saturation (BS) increased and aluminum (Al)3+ content decreased in the NTS and APS at depths of 0.0–0.2 m and 0.2–0.4 m; and pH, magnesium (Mg)2+ content, CEC, Ca2+/CEC, and Mg2+/CEC increased and total acidity decreased in the NTS and APS at a depth of 0.0–0.2 m.

Review of the State of Impurity Occurrences and Impurity Removal Technology in Phosphogypsum

“…Calcium sulfate itself is an excellent cementing material and is rich in calcium and sulfur resources, which can be used as an artificial building material [ 5 , 6 , 7 , 8 , 9 , 10 ], a subgrade material [ 11 , 12 , 13 , 14 ], a backfill material [ 15 ], a ceramic material [ 16 ], and in the synthesis of new materials (such as nano-hydroxyapatite [ 17 , 18 , 19 , 20 ], nano-calcium carbonate [ 21 , 22 ], and calcium sulfate whisker [ 23 , 24 , 25 ]). It can also be used as a cement retarder [ 26 , 27 , 28 ], a water purification agent for adsorption of heavy metals [ 29 , 30 , 31 , 32 , 33 , 34 ], a soil conditioner [ 35 , 36 , 37 , 38 , 39 , 40 ], a slow-release nitrogen fertilizer [ 41 , 42 ], an agent in the coproduction of sulfuric acid for cement making [ 43 , 44 ], an asphalt improver [ 45 , 46 , 47 , 48 ], a plastic filler [ 49 , 50 , 51 ], an agent in carbon dioxide mineralization sequestration […”