Assessment of Mixed Amendments of CaCO3/Na2SO4 Ratio on the pH Buffer Capacity and Exchangeable Sodium Percentage of Soils with Contrasting Properties

Reusing the by-products from wood pulp processing can promote the efficient use of resources. In this sense, the objective of this research was to determine the agronomic efficiency of CaCO3 and Na2SO4 by-products from wood pulp processing to establish criteria for their use and avoid undesirable side effects when applying these materials to the soil. Six treatments in proportions of 1; 0.9; 0.75; 0.5, 0.25, and 0, of CaCO3/Na2SO4, respectively, were incubated at a constant temperature and humidity for 15 days. The first proportion consisted of 100% CaCO3, while M1 mixed 90% CaCO3 and 10% Na2SO4, M2: 75% CaCO3 and 25% Na2SO4, M3: 50% CaCO3 and 50% Na2SO4, M4: 25% CaCO3 and 75% Na2SO4, with the last proportion comprised of 100% Na2SO4. Samples of 40 g from two soil series, Licantén (Inceptisol) and San José (Andisol), were used. The rates applied for each treatment were 0, 1, 2, 4, and 8 g of material per kg of dry soil. At the end of the incubation period, pH in water, pH in CaCl2, exchange bases (Ca2+, Mg2+, K+ and Na+) and extractable sulfur were determined. The results showed that the San José soil had a pH buffering capacity three times higher than that of the Licantén soil. The linear increase in pH was thus explained by the soil type in relation to the applied rate of CaCO3. The analysis of the increase in the exchangeable Na percentage (ESP) showed that the soils increased up to about 70% of their ESP with the highest added rate of Na2SO4. The application of a mixture of 25% Na2SO4 and 75% CaCO3 resulted in an increase in the ESP close to 15%; therefore, it is not recommended to use mixtures with a Na2SO4 content higher than 25% in these soils. Finally, we affirm that for M2 the maximum recommended dose for application should be 4 Mg ha−1, i.e., 3 g of material per kg of soil.