Comparative analysis of marine and agricultural gypsum as nutrient sources: feasibility of marine gypsum as a substitute for acid sandy soils and sodic soil recovery.

Abstract

To minimize the environmental impact of sea salt production and promote agricultural sustainability, studies on the reuse of marine gypsum have piqued interest in semi-arid regions. This study aimed to (a) verify the characteristics of marine gypsum, (b) analyze its agronomic potential for replacing agricultural gypsum as a nutrient source in acidic sandy soils, and (c) assess its effectiveness in recreating sodic soils. The study comprised two experiments: acidic sandy soil (Red Latosol) and sodic clayey soil (Fluvic Neosol). Both experiments employed a completely randomized design with 14 treatments and three replications. The treatments included as follows: (1) soil without any additional treatment (Control-C); (2) agricultural gypsum (AG) (40 mesh-0.42 mm)-reference treatment; (3) 12 treatments involving marine gypsum (MG), with variations in recommended doses (50%, 100%, and 200%) and particle sizes (1.19, 0.84, 0.59, and 0.42 mm, corresponding to 16, 20, 30, and 40 mesh, respectively). MG exhibited higher levels of Ca²⁺, Mg²⁺, and S-SO₄^-2 and lower levels of Cd, Cr, Pb, and Ni, with a predominant mineralogy of gypsum. In sandy, acidic soils, adding marine gypsum (MG) increased the electrical conductivity (EC), Ca²⁺, Mg²⁺, K⁺, Na⁺, and S-SO₄^-2, especially in the first leaches. Thus, MG is recommended at a dose of 100%, with a granulometry of 0.59 or 0.42 mm, as it proves as efficient as agricultural gypsum in providing calcium and sulfur to the soil and facilitating the vertical translocation of cations and anions. Both gypsum types were essential to increasing base saturation in this soil type. However, high MG doses may induce deficiencies in Mg²⁺ and K⁺ due to leaching stimulation. In sodic soils, MG doses exceeding 50% of the recommended dose were more efficient than agricultural gypsum in lowering pH, increasing Mg²⁺ and K⁺ contents, and reducing exchangeable Na⁺ content in the soil. Thus, we recommend a 100% MG dose with a particle size of 0.42 mm. We conclude that marine gypsum should replace agricultural gypsum as a source of nutrients in acidic sandy soil and for the recovery of sodic soil.