Nitrogen fertilizer use in the northern Great Plains as a general practice began about 10 to 15 years after the end of World War II. Industrial plants erected to produce ammonium nitrate for use as an explosive during the war became surplus property, and subsequently were transferred to private industry. After that, it didn't take long to determine from research that commercially-prepared nitrate and ammonium nitrogen were a lower-priced source of this essential element than that fixed symbiotically, and that nutrition of food did not differ due to nitrogen source-- at is, inorganic or organic.

Research with nitrogen fertilizers in North Dakota began in 1948 when Dr. E. B. Norum¹/ applied the "unheard of rates of 10 and 20 pounds nitrogen (N)" (his own words) to wheat grown on Fargo clay cropped to small grain the previous year. Trials with fertilizer applied to small grains at rates higher than 20 pounds N per acre were first conducted in 1955 by Dr. J. C.Zubriski ²/. Research which led to development of the nitrogen soil test now used in much of the North American Great Plains began in 1958³/ . (The test measures the soil nitrate-nitrogen content to two-feet depth or deeper.) Simultaneously in these same trials, pre-plant soil water content and growing season rainfall were measured and their contribution to grain yield response to nitrogen were evaluated. Also incorporated to these trials were methods of application of nitrogen.

Over the years, research expanded into other facets, including sources of fertilizer nitrogen, methods of application including foliar, placement relative to the seed, and timing of application, that is, fall or spring. The results of these trials, from various locations in the northern Great Plains, are published and have been widely publicized and form the basis for the nitrogen recommendations issued to the agricultural community. The results apply as well to the realm of the no-till system as other management systems.

Customarily, in soil fertility trials with small grains conducted before 1969, little attention was directed to plant performance during the intervening period of planting (emergence) and the harvest. Essentially the only part receiving attention was the grain. In 1969^4/ , plant yield component measurements (heads/unit area, kernels/head, and kernel weight) as affected by fertilizer nitrogen were begun when semidwarf hard red spring wheats were introduced.

In 1979, with the impetus generated by the AgRISTARS program (Agriculture and Resources Inventory Surveys Through Aerospace Remote Sensing), attention was focused on development of a crop calendar, the appearance, development, and growth of various plant parts from emergence to maturity, and, as well, greater detail on the components of yield. Attention also was directed to measurements of concentration and content of nitrogen in various plant parts⁵/. Of primary interest is the nitrogen content of spring wheat by plant development stage as depicted in Figure 3. These data suggest the possibility of applying fertilizer nitrogen after emergence to enhance grain yield. Studies were begun in 1987 to make this evaluation.

In the presentation to be made, the results of field and greenhouse studies begun in 1987 will be discussed. Variables in the studies were fertilizer nitrogen rates and application at several plant development stages. In as much as the laboratory analyses are not completed at this time, no data will be included in this report.