Focus your fertilizer dollars on more than just nitrogen

Focus your fertilizer dollars on more than just nitrogen

Position fields for success by implementing a sound all-around fertility program.

As budgets tighten and farmers focus on the profitability of their operation, they often focus on the most limiting factor impacting their yield. For most producers, specifically corn producers in the Midwest, the most limiting factor is often nitrogen. However, focusing all of your fertilizer investment dollars only on nitrogen can have a negative impact on the profitability of your operation.

Robert Mullen, director of agronomy for the Potash Corporation of Saskatchewan, offers the following advice on how to position your fields for success by using a sound fertility program.


How nutrients work together to promote plant growth
Nitrogen is often the largest fertilizer input cost farmers face, as it serves several plant needs: it functions as the primary fuel for a plant, is required for production of both protein and chlorophyll, and improved nitrogen nutrition translates into high vegetative biomass production. Higher vegetative biomass production, or increased growth rate, also translates into higher water use.

While nitrogen is a vital component of nutrient management plans, it is important that these plans are well rounded and represent a balance of essential nutrients. In many cases, this means that farmers must avoid a sole focus on nitrogen and acknowledge the ways various nutrients work together to promote plant growth. For example, good potassium nutrition increases a plant's ability to utilize water effectively and effective water utilization is central to ensuring efficient nitrogen use. Potassium is often recognized for its independent ability to make plants more productive, but it is important to note that it can also make other nutrients more productive such as nitrogen.

Refuting the focus on the most limiting factor
In spring, many farmers only focus on nitrogen fertilization, specifically for non-legume crops like corn, because they're considering the concept of Liebig's Law of the Minimum. Liebig's Law explains the yield achievable is dictated by the availability of the most limiting nutrient, but this concept is all too often misunderstood when it is applied to nutrient management. Just because nitrogen is the most limiting factor, it does not mean this is the only nutrient that is below the critical level for optimal crop production.


The misperception of this theory often leads farmers to focus their input investments on a single nutrient, which costs money in the long run as maximum yields are not achieved. In most cases, there are other yield-limiting factors whose levels should also be addressed, such as potassium and phosphorus. Because of this, even if the most limiting factor is supplied to 100% sufficiency, if there are other yield-limiting factors that aren't also supplied to sufficiency, farmers will miss out on potential yields, and ultimately profits.

Nutrients don't act independently; adequate K may require more N
Another misperception is that yield is only impacted by the most limiting nutrient. However, even if you ignore the most limiting factor and increase another limiting factor to 100% sufficiency, achievable yield will still increase. These nutrients do not operate independently if you don't have adequate potassium it can actually require more nitrogen to be supplied. 

As shown in the below graph when potassium is not supplied to sufficiency, the corn yield does not quite reach a maximum. When adequate potassium is supplied, corn yield does reach its maximum and achieves that rate at a lower rate of nitrogen.

Bottom Line: When examining fertility programs, specifically when applying the concepts of Leibig's Law, farmers must look at the bigger picture of nutrient management. There are a number of nutrients necessary for successful growth, namely nitrogen, potassium and phosphorus, and farmers should make sure to evaluate the levels of each of these before finalizing nutrient management decisions.

For additional advice on nutrient management visit

Dr. Robert Mullen, director of agronomy with Potash Corporation of Saskatchewan is chief contributor to this website. It's an online resource that delivers easy-to-understand analyses of soil science data, agronomic information, research and best management practices to help farmers achieve greater financial success.

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