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

Abstract

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 < 0,001; R2 = 0,95) and SOC (p < 0,001; R2 = 0,88). Similar significant relationships were found between the three soil functions and RCY or SOC. Overall, the lower and upper limits of the interpretative classes for the SQIFERTBIO and soil functions scores (where the index scores are equivalent, respectively, to 40% and 80% of the optimal RCY or SOC) were 0.42 and 0.64. The combination of chemical and biological indicators in different soil functions and in the SQIFERTBIO proved to be a simple and useful strategy to assess SQ in tropical Oxisols, linking agronomic management practices to both SQ, yield benefits and SOC. These results will help extensionists, agronomists and soil scientists, when assisting farmers, in soil health assessments, by making easier to explain the importance of SQ for the economic performance of farms.