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Fluid Journal : Fluid Journal 2005-2007
Winter 2005 Fluid Journal 2 levels in the grain (by fertilizing) can be very difficult, requiring considerable knowledge of the specific nutrient's role in seed storage. The nutrient elements in the grain that are most likely to be altered by fertiliza- tion are those that are elemental components of the major storage products: starch, protein, or oil. Of these three storage products, only protein contains mineral nutrients, including N (approximately 12%) and sulfur (S) (approximately 1%). As a result, N and S are the mineral nutrient elements in corn grain that are most likely to be modu- lated through fertilization. In addition to directly affecting the level of a grain quality component, fertilizer or mineral nutrients can also indirectly alter grain quality by changing the plant's metabo- lism or physiology. While the possibili- ties for enhancement in grain quality through altered plant metabolism are innumerable, it is very difficult to describe and predict physiological processes with certainty, which makes managing them with fertilizer nearly impossible. Thus, we will not discuss this concept further, even though we are well aware that optimizing plant growth through proper nutrition can improve many aspects of grain quality. What we will discuss are some of our program's research results evaluating fertilizer N rates needed to optimize grain yield and grain protein concentration in corn grain. We will also examine how genetic differences in grain protein level alter the N rate/protein percentage relation- ship. N response Yield vs. protein. Our N response trials were conducted in Illinois over the last four years. While the data produced showed that grain yield and grain protein increased simultaneously as the N rate went from deficient to sufficient, it also demonstrated that the N rate needed to maximize grain protein was higher than that needed to optimize grain yield. For this data, the response function of grain yield to fertilizer rate is clearly quadratic, with an optimal N rate of about 150 lbs/A of N. Conversely, the grain protein response function to increasing N supply was much more linear, with more than 150 lbs/A of N being needed to achieve maximum protein percentage (Figure 1). A similar generalized response in yield and protein to increasing N supply has also been noted for wheat and other small grains. Hybrid effect. While grain yield response to N supply was basically similar for all the hybrids evaluated, the ability to modulate a hybrid's grain protein concentration with the N supply was highly genotype dependent. This dependency is illustrated in Figure 2 where grain protein concentration of an Figure 1. Generalized effect of fertilizer N rate on yield and protein percentage of corn grain, 2000-2003. Figure 2. Response of an ultra-high grain protein hybrid and ultra-low grain protein hybrid to incremental increases of N supply, 2000-2003.
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