Soil quality and grain yield: A win–win combination in clayey tropical oxisols

[Display omitted] •Long-term field experiments studying P fertilizer strategies and soil quality.•Chemical and biological indicators integrated into a soil quality index (SQIFERTBIO).•P fertilization increased crop yield, soil quality and scores of soil functions (SF).•SQIFERTBIO and SF can be used to improve crop yields and land management decisions. Relationships between a soil quality index (SQIFERTBIO) and soil functions with both relative cumulative grain yields (RCY) and soil organic carbon (SOC), were evaluated in a tropical clayey Cerrado Oxisol. Soil quality (SQ) was quantified integrating chemical (FERT) and biological (BIO) indicators in a weighted-additive soil quality index combining three soil functions and respective indicators: (F1) nutrient cycling (based on the activities of soil enzymes β-glucosidase and arylsulfatase), (F2) nutrient storage (SOC and cation exchange capacity, CEC) and (F3) nutrient supply (Ca+2, Mg+2, K+, P, pH, H + Al; Al+3, sum of bases (SB) and base saturation (%BS)). The contribution of each indicator for the related soil function was scored using standardized scoring functions (SSF) that transform the indicator value on a scale between 0 and 1. Soil samples (0 to 10 cm depth) were collected in 2013 and 2015 from 21 treatments from three long-term field experiments, with different P fertilizer management strategies. P-fertilization resulted in higher cumulative crop yields that in turn were associated with better SQIFERTBIO and soil functions scores. Through linear regression analyses, critical limits (CLs) to interpret the individual scores of the SQI and of the soil functions, based on RCY and SOC were defined. The proposed SQI was positively associated with RCY (p