Assessment of management-induced changes in soil quality is important to sustaining high crop yield. A large diversity of cultivated soils necessitate identification development of an appropriate soil quality index (SQI) based on relative soil properties and crop yield. Whereas numerous attempts have been made to estimate SQI for major soils across the World, there is no standard method established and thus, a strong need exists for developing a user-friendly and credible SQI through comparison of various available methods.

As Mohammadjavad says, it's horses for courses. pH at the extremes, available P and exchangeable cations, organic matter, salinity ... and don't forget how useful foliar analysis is as a diagnostic tool.