Without question, food production for an ever expanding world population has been the catalyst for development, application and adoption of new technologies. It’s crystal clear that food and fiber production from American agriculture to serve the expanding population could not have been achieved with the technologies of the 1960’s and 1970’s.

The necessity to produce more food per unit of land frequently translates to the need for the use of fertilizers to avoid depletion of nutrients in our soils while, at the same time, ensuring the production of high-yielding, high quality crops. What is the value of fertilizer in modern crop production? A difficult question to answer. Yet Drs. Stuart, Dibb, Johnston, and Smyth, writing in the January/February 2005 issue of Agronomy Journal, have provided an estimate of this value based on the results of various long term studies with a variety of crops in both temperate and tropical environments.

A survey of plant scientists with national academic reputations was one approach used to arrive at an answer to this question. Results of this survey led to the conclusion that the yield of the U.S. corn crop would be reduced by about 40% if use of fertilizer nitrogen was eliminated. Likewise, yield reductions of 19% for barley and 16% for wheat would be the consequence of eliminating the use of fertilizer nitrogen.

These survey results match conclusions reached from a close examination of the data base used to develop the current guidelines for fertilizer nitrogen for corn used throughout the Corn Belt. That extension research effort showed that fertilizer nitrogen was responsible for 50% to 60% of yield when corn follows corn in a rotation.

Compared to past years, corn is also using nitrogen fertilizer more efficiently. When plagued by weeds and insects, efficiency was about 1.25 lb. N to produce a bushel of corn. Now that these pests are no longer a major problem, and combined with improved hybrids, that efficiency has improved to 0.6 to 0.7 lb. N to produce a bushel of corn in a corn-soybean rotation.

Nitrogen, of course, is not the only nutrient needed for optimum crop production. The Magruder Plots in Oklahoma have demonstrated, since the late 1800’s, the importance of the combination of nitrogen and phosphate fertilizers for the production of winter wheat. The yield attributed to the use of those two nutrients since 1968 is summarized in the following table.

The results of a 40 year study conducted in Kansas show that the portion of corn yield that can be attributed to fertilizer nitrogen changes with the rate of nitrogen applied. Again, the yield, due to the use of fertilizer, increased when phosphate was added to the fertilizer program (see the following table).

Data from 1961 through 2000

For several years, there have been various attempts to estimate the proportion of U.S. Crop production that can be attributed to the use of commercial plant nutrients. These estimates usually range from 30% to 50% for major grain crops. It is a challenge to arrive at these estimates and assumptions are always required regardless of the approach used. Methods used to arrive at these estimates are further complicated by factors such as variable levels of soil fertility, climatic conditions, crop rotations, and changes in production practices that change efficiency of nutrient use. Nevertheless, the data that have been summarized support the frequently cited percentages of 30% to 50%. As research based nutrient management practices improve, these estimates will be conservative in the future.

The previous discussion has focused on nutrients supplied in commercial fertilizer. There is no intent to ignore the importance of manure in U.S. crop production. On a national scale, there are estimates that N from manure accounts for 6% of total nitrogen inputs for the national corn crop. The same estimates produce of value of about 30% of phosphorus removed comes from manure. Obviously, these values will vary with many factors such as geography or proximity to livestock.

In modern production agriculture in Minnesota, there’s no doubt that the majority of the money spent for annual inputs is used for the purchase of plant nutrients. Naturally, this is a concern. The expenditure, however, is justified. When Best Management Practices are used the return is positive with no negative impact on the quality of the environment.

A NEW CAREER

I believe that most readers of this newsletter realize that I started a new career called retirement on January 1, 2007. After nearly 38 years of being paid by the University of Nebraska and University of Minnesota, it was time to pass the enjoyment of working in production agriculture to someone else. Hopefully, an active search process will find an individual who enjoys working with people in agriculture as much as I have.

When I left Graduate School to become an agronomist with the University of Nebraska, I had no idea where that road would go. Actually, the combination of production research and Extension was an excellent fit and, looking back, I couldn’t have asked for anything better.

Throughout the years, I’ve tried to base educational programs on facts supported by good research. Of course, there can always be some debate over how these facts were interpreted. There has been no effort to base educational programs on regulations. Also, there has been no effort to use “the sky is falling” approach to education.

Every year, I’ve thoroughly enjoyed working with farmers and the Ag professionals who work with them. I’m absolutely convinced that there’s no finer group of people to work with.

There aren’t enough words to thank all who have helped along the way – the farmers who gave permission to conduct research trials in their fields – support staff and students who worked hard to bring the trials to completion – Extension and Research colleagues throughout the state and the region who made the working environment enjoyable.

There are no plans to disappear. There are unfinished projects. There are winter meetings – I plan to stay connected to agriculture. So, call (507) 263-9127 if you wish. I look forward to conversations with many of you.

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