As crop yields and nutrient removal rates continue to increase, many growers wonder whether it’s time to top up fertilizer rates.
At the core of the discussion in Ontario is whether critical soil test values for corn and soybeans are still valid and whether they pack the nutrient punch needed to allow new hybrids and varieties to optimize yield potential.
At the recent Southwest Agricultural Conference, University of Guelph soil scientist Dr. Ivan O’Halloran told growers that although we now have higher-yielding crops that remove more nutrients, it doesn’t mean they need more fertilizer. The reality is they may just be more efficient in utilizing the available nutrients in the soil.
O’Halloran, who defines critical soil test values as the level where there is no longer a yield response to additional fertilizer, maintains critical soil test values for corn and soybeans are still valid. In fact, he says, they tend to error on the high side to compensate for field variability. In this interview, O’Halloran shares his thoughts on how growers can best manage and mitigate nutrient variability across fields. He also discusses the limitations of grid sampling and outlines his strategy for how growers can spend their fertilizer dollars wisely while maintaining fertility levels.