By Scout Nelson
The University of Nebraska–Lincoln (UNL) is addressing a long-standing misconception about nitrogen fertilizer needs for corn. Many believe UNL recommends applying 1.2 pounds of nitrogen (N) fertilizer per bushel of corn yield, but this is not true. In fact, UNL has never made such a recommendation.
This misunderstanding began in 1973 when USDA soil scientist George Stanford published research in the Journal of Environmental Quality titled “Rationale for Optimum Nitrogen Fertilization in Corn Production.” Stanford found that corn requires about 1.2 pounds of total nitrogen per bushel of yield, but this figure represents total nitrogen uptake, not the amount of fertilizer needed.
Stanford explained nitrogen use with the equation Nf = Ny - Ns, where Nf is the fertilizer need, Ny is total crop nitrogen requirement, and Ns is nitrogen supplied by the soil. Because soil contributes nitrogen through natural processes, fertilizer needs are always less than total crop nitrogen requirements.
Nitrogen supplied by soil comes from several sources, including mineralization of soil organic matter, residual inorganic nitrogen, irrigation water, manure, and legume nitrogen credits. These natural contributions mean fertilizer applications should always be lower than the total crop requirement of 1.2 pounds per bushel.
Over the years, many nitrogen rate prediction equations, including those used by UNL, have started with the physiological requirement of 1.2 pounds per bushel to calculate total need. However, experts stress this is not a fertilizer recommendation. Some suggest using lower starting factors like 1.0 or 0.9 to improve predictions, but this ignores the biological basis of the 1.2 figure.
UNL research over the past three decades shows that weather patterns greatly influence nitrogen needs. Modern sensor-based in-season nitrogen management often provides more precise application rates than prediction equations alone, allowing for adjustments as weather changes.
The key takeaway is that corn’s physiological nitrogen requirement remains 1.2 pounds per bushel, but actual fertilizer applications must subtract the nitrogen already available from the soil to ensure efficient and environmentally sound nutrient management.
Photo Credit:gettyimages-awakr10
Categories: Kansas, Crops, Corn