Efeito do silicato de cálcio e magnésio em sistemas de sucessão de culturas

Abstract

Silicon (Si) can contribute to plant resistance to pests, diseases, and abiotic stresses, although its response varies according to the cultivated species and soil conditions. This study aimed to evaluate the residual effect of calcium and magnesium silicate and crop succession on Si in the soil and plants, on the development and productivity of corn, wheat, and soybean crops, on the insect population associated with these crops, and on soil microbial activity. The experiment was conducted in an area with clayey soil (37% clay) and a high initial Si content (11.53 mg kg⁻¹). The experimental design was a randomized block design in a factorial scheme (silicate application × agricultural seasons of the crop succession). Treatments included four successive cropping cycles after prior silicate application, in addition to two controls: one with dolomitic limestone to balance the calcium and magnesium supplied by the silicate source, and another without application. Calcium and magnesium silicate was applied at 8.2 t ha⁻¹, equivalent to 1.0 t ha⁻¹ of total Si, and dolomitic limestone at 7.0 t ha⁻¹, adjusted to maintain the balance between calcium and magnesium. The first sowing occurred 23 days after application (DAA), with soybean and corn. In the second season, at 184 DAA, corn and wheat were established; the third, at 321 DAA, included brachiaria and forage radish; and the fourth, at 391 DAA, consisted of soybean and corn. During the cycles, insect populations, Si contents in soil and leaves, and productivity indicators were evaluated. At the end of the experiment (541 DAA), soil microbial activities were assessed. Statistical analyses were performed by ANOVA, and means were compared using the Tukey and Scott–Knott tests at 5% and 10% probability. Insect populations were analyzed using a mixed generalized linear model. Silicate application increased Si availability in the soil, reaching levels of up to 15.18 mg kg⁻¹ in the MTB Si+ system (corn–wheat–brachiaria with Si application), with a more pronounced effect at 321 days after application. Soil Si content tended to be lower after forage radish cultivation compared with brachiaria; however, this effect was not confirmed by leaf Si content in subsequent crops in the succession. Soybean, as a preceding crop compared with corn, favored vegetative growth and the formation of reproductive structures in wheat, without, however, resulting in a significant increase in productivity. Insect population density varied according to sampling time, with no consistent effect of the treatments. Soil microbiological attributes, such as microbial respiration and microbial biomass carbon, showed no differences at 541 days after application. Despite the soil having a high Si content, the application of calcium and magnesium silicate was able to increase the levels of this element in the soil and plants in the long term, with a pronounced effect for approximately one year after application. However, no effects of Si and crop succession were observed on the reduction of insect populations or on soil microbial activity. Although there was no effect of Si on the productivity of corn, wheat, and soybean, some productivity indicators were positively affected by Si in soybean and wheat and by crop succession in wheat.