Although the State of Parana, Brazil, has adopted crop rotation and no-till (NT) systems, fertilizer application is still based on recommendations developed more than 30 years ago for monocropping under conventional tillage because fertilizer recommendations developed specifically for crop rotation under NT are lacking. The objective of our study was to consolidate P calibration and evaluate crop responses to P fertilization so as to propose a system of technical recommendations for P fertilization for soybean, maize, wheat, and barley grown in a crop rotation system in Oxisols under long-term (>30 years) NT systems in the high yield potential South-Central region of Parana. Three calibration trials were conducted from 2008 to 2013, consisting of P broadcast application rates of up to 640 kg ha-1 P2O5. Forty-four P fertilization trials were carried out over the 2011-2012/13 growing seasons to evaluate yield response to P fertilization rates in Oxisols with different levels of P availability. Relative crop yield [RR = (yield without P/maximum yield) × 100] and soil P availability (Mehlich-1) were compared to obtain P critical levels and generate soil P availability classes based on crop response. For soils in the Low and Medium availability classes, recommended P fertilizer application rates were based on the yield response curve following the nutrient sufficiency approach. For soils in the High and Very High availability classes, P fertilizer recommendations were based on P removal through grain harvest. The winter cereal crops were more demanding to achieve maximum yields - the soil critical P level for the crop rotation system was determined at 8 mg dm-3 based on the requirement of these crops, considering the 0-20 cm soil layer. The recommended P fertilization rates for soybean, maize, wheat, and barley in Oxisols under long-term NT developed in our study are higher than the current P fertilization rates used in Parana, which is explained in part by the high crop yields and high P adsorption capacity of soils in the region. Although the nutrient sufficiency approach was used to determine P fertilization rates in the soils below the critical level, it is estimated that the P rates recommended for the crops will raise soil P availability above the critical level after a full crop-rotation cycle (3 years).
calibration; critical level; phosphorus; Mehlich-1
