When conventional tillage is replaced by no-tillage (NT) changes occur in the dynamics of soil nutrients and acidity, which may influence the soil-plant relationships and consequently, the criteria for soil fertility management. This study determined the criteria for liming as well as the soil critical levels for P and K in a crop rotation of soybean, maize, wheat, barley, and white oat, widely used in the South-Central region of the State of Parana, in Southern Brazil. The study involved 13 field experiments on Hapludox soils under long-term no-tillage (>15 years) in Guarapuava, Pinhão and Candói; five of the experiments were related to liming and eight to P and K fertilization. In soil samples from the layers 0-0.10 and 0.10-0.20 m, of the liming studies, CaCl2-pH and base saturation (V%) were quantified and available P and K (Mehlich-1) in the samples from the fertilization. The quadrant method was used to determine the liming criteria; the critical levels for pH and base saturation were based on values that ensured relative crop yields above 90 % and never below 80 %. The ratio between the soil P and K levels and the relative crop yields could be represented by the Mitscherlich equation, where the levels required for relative crop yields of 90 % represent the critical values. The results indicated that the critical levels of soil acidity and available P and K were higher in the 0-0.10 m than the 0-0.20 m layer. Soybean was most sensitive to soil acidity, while the winter cereals were most demanding in P and K. Based on the most restrictive crop in the rotation and 0-0.20 m soil layer as reference, the critical levels for liming were CaCl2-pH of 4.9 and base saturation of 60 %, while the critical levels of fertilization were 8.0 mg dm-3 for P and 0.30 cmol c dm-3 for K for Oxisoils under long-term no-tillage, in the South-Central Region of Paraná.
soil acidity; grain crops; calibration; soil fertility; tropical soils
