Interação do silicato de cálcio e magnésio granulado em mistura com adubos fosfatados solúveis

Abstract

The mixture of grained silicate with NPK fertilizer, still not evaluated agronomic. Reactions between the components can occur, affecting principally the silicon and phosphorus solubility. Thus, three experiments were set up to evaluate the interaction between Si e P in two soils, with maize and soybean crops. The first study consisted in incubation of silicate for 120 days using a Red Latosol and a Sandy soil. The soil was mixed with 0, 50, 100 and 200 mg kg-1 of Si and 100 mg kg-1 of P sources: monoammonium phosphate (MAP), triple super phosphate (TSP) and ordinary super phosphate (SSP) was added to plastic containers. After 60 and 120 days of incubation the soil was analyzed to determinate: pH (CaCl2), silicon, calcium, magnesium e phosphorus. The second study was conducted with Red Latosol soil. The treatments consisted of line, side and under the seeds applications, of different (N-P2O5-K2O) formulations at rate 800 kg ha-1. Those formulations were made from different phosphorus sources with different content of free acid (high free acid = 3,62% and low free acid = 1,85%). The NPK formulations were added with different rates of Si (0, 80, 160 e 320 kg ha-1 Si granulated). The cultivar of maize was seeded (P 30k75) and harvested after 60 days of seedling, dry and fresh matter was determined, and foliar contents of P and Si were evaluated. A soil sample was analyzed to determine Si, pH, Ca, Mg e P. In the third study, the soil, red latosol, was initially incubated for 30 days, to elevate the bases saturation to 40 and 60%. Later, simulating fertilization in line, 240 kg ha-1of P2O5 (SSP) was applied with high free acid and low free acid (5,94% e 3,12%, respectively), 0, 150, 300 and 600 kg ha-1 of commercial product Siligran AWM. Leaves were collected with 30 and 90 days after emergence to be analyzed for P, Ca, Mg, Si, N, K, S and micronutrients. After the harvest the number of nodules and pod per plant were counted and samples of soil were collected to determine P, Ca, Mg, Si, pH and micronutrients. The results showed that, the application of Si mixed to phosphates can not affect the P solubility in the clay and sandy soil, but silicon source can increase Si, Ca, Mg and the pH. Analyzing the mixture of silicate and formulation NPK in maize observed that availability of Si and P were not influence by the silicate and, as well dry matter and soil pH. The soybean crop was not influence by the silicate but the Si and pH in the soil were.