Nitrogen inputs are essential for optimum corn production. This essential nutrient can be supplied from: 1) soil organic matter, 2) a previous legume crop, 3) livestock manure, and, 4) commercial fertilizers. Nitrogen in soils is a complex and dynamic system. Management of this essential nutrient is not easy and there are direct environmental implications in the management decisions.
Management of nitrogen in soils has changed dramatically over the years. So, this might be a good time to reflect on these changes starting in the mid 1960’s and continuing to the present (a period of about 50 years). Farmers today are taking a hard look at rate of nitrogen used, the source of nitrogen used, and the time of application because of environmental and economic concerns. Higher prices for nitrogen and lower prices for a bushel of corn have forced corn producers to take a closer look at nitrogen management. There is increasing awareness of the fate of nitrogen in the environment as well. This concern for the environment has been one of the factors that have stimulated the Discovery Farms initiative.
In the mid 1960’s, the major challenge was to select a rate for application and apply before planting in the fall or spring. Anhydrous ammonia was the nitrogen source of choice. Initially, nitrogen rate was determined for the desired yield by multiplying this yield by 1.25 and then subtracting the various nitrogen credits. A soil test designed to measure carryover nitrate-nitrogen had been developed but was not routinely used by farmers and ag-professionals. Compared to other inputs for corn at the time, nitrogen fertilizer was not expensive often overshadowed by other concerns.
The soil test for nitrate nitrogen was first offered in the early 1960’s. Moving through the years, the test for nitrate-nitrogen was refined and with the help of commercial soil testing laboratories, was more widely accepted. Tests were developed for soil samples collected either in the spring or fall. Acceptance of this test by farmers increased substantially starting in the late 1990’s.
Beginning in 2006, there was a major change in the concept used to arrive at rate suggestions throughout the Corn Belt. The use of a “yield goal” or “expected yield” was discarded and replaced by a calculation of the ratio of the price of a pound of nitrogen fertilizer divided by the value of a bushel of corn. At first, adoption was limited but has gained acceptance as the price of nitrogen fertilizer has increased. Nitrogen credits including a measurement of carryover nitrate-nitrogen are still used.
This change in suggested nitrogen rate has been accompanied by a change in the source if fertilizer nitrogen. In the 1960’s, anhydrous ammonia was the most popular. Although sales of fertilizer nitrogen in Minnesota have remained relatively constant in recent years, use of anhydrous ammonia is declining while sales of urea and liquid nitrogen are increasing.
Some of this switch can be attributed to time of application. Because of the desire to improve efficiency in the use of fertilizer nitrogen, there has been a major shift in timing from a single application to a split application using a sidedress application. Driven primarily by speed of application, urea or liquid nitrogen is used for this second application. Use of the sidedress application is a closer match to the rapid uptake of nitrogen by corn. With this synchrony, the nitrogen applied in the fertilizer stays in the soil for a shorter period of time and, thus, is not subject to as much potential loss. Potential negative effects on environmental quality are reduced. We’ve moved away from the day when numerous tanks of anhydrous ammonia traveled the roads in the fall – especially in parts of Minnesota where soils are sandy. This has been a positive change.
Genetic improvement has helped to increase the efficiency of use of fertilizer nitrogen. Research has shown that modern hybrids, compared to those from the 1960’s can produce more grain from each pound of nitrogen. This has positive benefits for the profits of the corn producer. In addition, the impact on environmental quality has been positive. Over the years, changes have been subtle – not dramatic. They show that the corn producer and those who advise him have accepted technology in a very positive way.