Take Advantage of Phosphorus and Nitrogen Interactions to Boost Corn Yields

For corn farmers, it’s well known that phosphorus (P) and nitrogen (N) fertilizers are crucial for increasing yields. Farmers typically focus resources on nitrogen applications to their fields, but research findings show that applying both phosphorus and nitrogen together is far more effective – potentially increasing yields up to 225 percent.

Dr. Alan Schlegel, Agronomist-in-charge at the Southwest Research-Extension Center at Kansas State University, is one of the lead researchers of a 50-year study being conducted at the Southwest Research-Extension Center near Tribune. Per Schlegel, the interaction between phosphorus and nitrogen provides the highest yield benefit rather than applying one or the other.

“This interaction can help improve farmers’ profitability by increasing corn yields, improving nutrient efficiency and getting the maximum return on their crop investment,” he said.

Evaluating Appropriate Rates

The study at Kansas State University that yielded these results began in 1961 with the goal of determining optimal nitrogen rate and evaluating the interaction between nitrogen and phosphorus in irrigated corn.

The experiment was conducted on a Ulysses silt loam soil with inherently high soil test potassium – 30 years of no response to potassium fertilization. Researchers hand-applied all fertilizer in the spring prior to planting. The study compared nitrogen rates at 0, 40, 80, 120, 160 and 200 pounds per acre. At each nitrogen rate, phosphorus rates included 0 and 40 pounds of phosphorus per acre. To maintain consistency of results, researchers kept the nitrogen rates the same throughout the length of the study. They determined the optimal nitrogen rate was between 170 and 180 pounds per acre.

Researchers saw a change, however, in the yield response to phosphorus fertilizer over the course of the study. In 1991, they noticed a decrease in the phosphorus soil test levels in the 40 pounds per acre phosphorus plots, thus indicating P application rates were less than P removal rates.

For example, at 110 bushel per acre corn yield, a total of 42 pounds of phosphorus per acre would be removed – based on the removal rates in our Nutrient Removal Calculator. With corn yield greater than 110 bushel per acre, higher rates of phosphorus would be removed, therefore decreasing soil test phosphorus.

In response to this, starting in 1992, researchers added an 80 pounds per acre phosphorus rate each year to every nitrogen rate. Researchers documented a yield increase of 4 percent and a buildup of soil test phosphorus levels after the higher rate was applied.

The plots with only phosphorus applied showed a 20 percent yield bump over the untreated control plot. The plots with only nitrogen boosted yields by 103 percent over the control plots. However, the plots with both phosphorus and nitrogen applied together increased yields 225 percent.

“We expected a yield boost from the interaction of both nutrients,” Schlegel said. ”However, the size of the interaction was a little surprising.“

Improving Nutrient Use Efficiency

The interaction of phosphorus and nitrogen also improved the nitrogen nutrient use efficiency in corn. Schlegel reported a 25 percent greater apparent nitrogen fertilizer recovery rate at the 40 and 80 pounds per acre phosphorus rates compared to the 0 pounds per acre phosphorus rate.

To determine the nutrient use efficiency, researchers calculated an apparent nitrogen fertilizer recovery rate for corn plants. Schlegel explained the higher the apparent N recovery rate, the more efficiently the plant is using nutrients. For example, percent nitrogen fertilizer recovery can be calculated as follows:

Percent Fertilizer Recovery

= ((Total N taken up in fertilized plots) – (Total N taken up in control plots)) / (Rate of fertilizer applied)

Improved nutrient use efficiency shows the importance of phosphorus fertilizer to help farmers maximize their return on their crop nutrition investment and, thus, their profitability.

Farmers can use this research and other tools, such as the eKonomics Nutrient ROI Calculator 2.0, to estimate the most economical phosphorus rates to boost corn yields and increase the plant’s efficient use of nutrients.