The residual effect of gypsum on subsoil conditioning, nutrition and productivity of sugarcane crops

Although the benefits of gypsum for subsoil conditioning are known, there is still a lack of information regarding the duration of its effects on soil chemical attributes and sugarcane productivity. Therefore, the objective of this work was to evaluate the residual effect of gypsum doses on soil chemical attributes, root density and productivity in seven sugarcane crops (ratoon). The experiment was conducted in an experimental area located at Embrapa Cerrados, in Planaltina, DF, Brazil. The experimental design consisted of four gypsum doses (0, 0.5, 5 and 10 t ha-1) distributed in randomized blocks with four replications. Gypsum was applied only one time to the soil surface after sugarcane planting in July 2009. After 13 and 87 months of gypsum application under sugarcane cultivation, the soil was collected from layers up to 120 and 200 cm deep, respectively. For evaluation of the soil chemical attributes: sulfate (S-SO42-), calcium (Ca2+), magnesium (Mg2+) and aluminum saturation (m) were assessed. Also, the root dry mass density was evaluated after the first and seventh sugarcane crops, in September 2010 and 2016, respectively. Furthermore, the variables leaf macronutrient concentrations (N, P, K, S, Ca and Mg), stalk yield and total reducing sugars (TRS) were analyzed in all seven crops/ratoons (first is the main crop and other six are ratoons). The application of 5 t ha-1 gypsum increased SO42- and Ca2+ and reduced the aluminum saturation after 13 and 87 months, with higher intensities in the subsurface layers of the soil. As a consequence of this chemical conditioning of the subsurface soil layers, the root dry mass density was increased by 18 and 37% in the 0-120 and 0-200 layers, respectively, after the first (main) and seventh sugarcane crops (ratoons) in relation to the absence of gypsum application. Furthermore, treatments with 5 and 10 t ha-1 of gypsum increased the leaf contents of S, Ca and N in relation to treatments with 0 and 0.5 t ha-1 of gypsum. As a consequence of the increased root growth and better nutrition of sugarcane, the use of gypsum provided a long residual effect, observed in the increase of stalk and sugar yields.