By Blake Jackson
Yield goals have long been associated with nitrogen (N) recommendations for corn, but they can also influence suggested rates of phosphorus (P) and potassium (K).
According to Dr. John H. Grove of the University of Kentucky, this practice deserves closer examination because higher yield goals can lead to substantially higher fertilizer recommendations without clear evidence of additional yield benefits.
Grove compared soil samples analyzed by the University of Kentucky and a private laboratory using the same Mehlich 3 extraction method.
The results for soil-test P and K were nearly identical, indicating that differences in fertilizer recommendations were not caused by differences in laboratory measurements.
The key difference appeared when yield goals were considered. When comparing corn yield goals of 200 and 250 bushels per acre, the higher target produced fertilizer recommendations that averaged about 32 pounds more P2O5 and 80 pounds more K2O per acre.
Grove questions whether increasing fertilizer rates based on yield expectations is justified when critical soil-test levels generally remain similar regardless of potential yield.
University recommendations focus on maintaining adequate soil nutrient levels and replacing nutrients removed by harvested crops. In contrast, some private laboratory recommendations appear to use yield goals to increase maintenance applications, potentially resulting in fertilizer rates beyond what is needed to maintain critical soil-test levels.
For producers, those differences can have a meaningful financial impact. In one comparison, the private laboratory recommended 98 additional pounds of P2O5 and 182 additional pounds of K2O per acre compared with University of Kentucky recommendations. At the fertilizer prices cited in the article, that difference represented nearly $145 per acre.
Higher fertilizer applications do not automatically translate into higher yields. Excess nutrients can also create economic losses and increase the risk of nutrient movement through runoff, erosion, or other processes.
The findings raise an important question for corn growers: Are yield-goal-based P and K recommendations delivering enough additional crop production to justify their added cost? Producers may benefit from evaluating fertilizer recommendations against soil-test levels, crop nutrient removal, local research, and expected return on investment.
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Categories: Kentucky, Crops, Corn