Acidez e disponibilidade de fósforo e potássio do solo e resposta de arroz irrigado e soja após aplicação de gesso agrícola em terras baixas

Studies that evaluate the crop responses to the soil modifications intermediated by gypsum application are relatively abundant, but most of them are performed in highlands. Such studies are still scarce in lowlands. In addition, many studies are focused in direct soil modifications (i.e. calcium and sulfur addition) of gypsum application, ignoring the indirect soil modifications, as acidity and phosphorus (P) and potassium (K) availability. The objective of our study was to evaluate soil acidity and P and K availability, as well as crop (irrigated rice and soybean) yields, as a function of different rates of gypsum application in lowland. The experiments were conducted in a Planosol (Triunfo, Rio Grande do Sul, Brazil). The treatments consisted of six gypsum rates (0.00, 0.25, 0,50, 1.00, 2.00 and 4.00 t ha-1) and the experimental design was a randomized blocks with four replications. The soil was sampled after crop harvests, in the 0–5, 5–10, 10–20 and 20–40 cm layers. The soil pH (in water), the potential acidity (H+Al) and the available P (Mehlich 1) were not affected by gypsum application. After the irrigated rice cropping and in the soil layer of 0–5 cm, the available K (Mehlich 1) contents was higher with the gypsum application of 0.25 to 1.00 t ha-1, and the lowest content was observed in the absence of gypsum (0.00 t ha-1). After the soybean cropping, the available K content was not affected by gypsum application. The gypsum application did not impact irrigated rice and soybean yields in the evaluated season, which did not present water deficit.