Fertility trials and nutrient critical levels have been the traditional method to improve a producer's fertility program. These are limited by the sensitivity of small replication field trials and the site specific applicability of critical levels. An alternative method is regression analysis of field yields versus soil and tissue nutrient levels, to identify nutrients that possibly limit yield. Field yields were normalized by year and long-term field yields to allow multi-year comparisons. This method has been applied to commercial farms resulting in yield correlations with nutrients and planting environment.