The area cultivated with sunflower had great expansion recently in Paraguay, but still does not have a phosphorus fertilization recommendation for the main production regions. The objective of this work was to elaborate a first recommendation of phosphorus fertilization for sunflower under no-till in Paraguay. Two experiments were carried out in Misiones and Itapúa in the harvest 2006/2007, in a Latossolo and an Argissolo. For determination of the chemical attributes ten sub-samples were made, composing a soil sample per plot, collected in the 0-10 cm depth. Grain yield and the soil critical phosphorus (P) content were determined. The experimental design was in random blocks, with four repetitions. The treatments consisted of doses of P (0, 40, 80, 120, 160 and 200 kg ha-1 of P2O5), with triple superphosphate as source. For sunflower crop, the P critical content for the Latossolo (soils from 410 to 600 g clay kg-1, class 1) was 14.4 mg dm-3 and for the Argissolo (soils from 210 to 400 g clay kg-1, class 2), was 15.5 mg dm-3. Doses of P2O5 between 40 kg ha-1 and 80 kg ha-1 were enough to overcome 2.000 kg ha-1 of grains yield; being the largest doses for the soil with higher clay and low phosphorus content.
fertilization; no-till; critical content
