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Fluid Journal : Fluid Journal 2005-2007
Winter 2005 Is Fertilizing For Grain Quality Different From Fertilizing For Yield? Dr. Fred Below, Juliann Seebauer, and Martin Uribelarrea Summary: Fertilizer recommendation systems for grain crops typically have been developed for maximum grain yield, without really knowing if these systems lead to optimal grain quality. Using corn as our example species we will review how fertilizer mineral nutrients might alter grain quality, and present some of our research results examining the nitrogen (N) levels needed to optimize grain protein concentration. Nitrogen-rate trials conducted at various sites across Illinois over the past few years invariably have shown that the amount of N fertilizer needed for optimal grain protein is higher than that needed to maximize grain yield. We also have demonstrated that genetics (i.e. hybrid makeup) plays a major role in our ability to modulate corn grain protein with N fertility, and we suspect this is also true for other quality components and other fertilizer nutrients. The inevitable improvement in grain quality using biotechnology could have important ramifications in future nutrient needs. Illinois studies show that N rate needed to maximize grain protein is higher than that needed to optimize grain yield. Fluid Journal 1 Farmers usually apply fertilizers in hopes of obtaining maximum yield and profit, with little regard to their possible impact on grain quality. This view, however, could change in the future as more and more farmers grow specialty crops designed to contain a specific grain quality component. Grain quality itself is a fairly vague and encompassing term usually used to refer to the major seed storage products such as starch, protein, and oil. Grain quality, however, can also refer to a wide array of other grain factors such as the metabolites (i.e. sugars, amino acids, fatty acids), vitamins, or mineral nutrients found in crop seeds, many of which may have high economic values, depending on their end use. Mineral nutrients Because of the many components and/or definitions of grain quality, there are also multiple ways by which grain quality could be altered by mineral nutrient fertility. One obvious example is where an increase in the supply of a particular mineral nutrient leads to an increase in that nutrient in the seed. For this quality component, the inherent level (and range) of a particular nutrient in the seed largely determines its ability to be positively altered by increasing its availability through fertilization. An example of the variable levels and ranges of mineral nutrients found in corn grain is shown in Table 1. By inference, grain nutrients present in low amounts, and with small ranges (i.e. Ca and Fe), would not be expected to be easily alterable through fertiliza- tion, while the opposite should be true for elements present in large amounts and with high ranges (i.e. N and phosphorus (P)). Using this approach, if the level of a particular seed nutrient is not at its maximum, then it can generally be increased with fertilizer additions. Scientific literature is replete with examples showing where fertilizer additions positively increased the level of a particular quality component in the grain. Alternatively, we suspect there are even more unpublished studies where fertilizer additions had no effect on the concentration of a given grain quality component, presumably because the level of that component was already at its maximum range. Further complicating this approach are instances where it is disadvanta- geous for a fertilizer to increase the mineral nutrient level in the grain. An example would be phytate (the major storage form for P in the seed), which can be high in the manures of corn-fed animals, leading to P runoff and degradation of water supplies. Thus, even though mineral nutrients them- selves are important components of grain quality, positively altering their Table 1. The average concentration and range in some mineral nutrient elements in corn grain. Mineral Mean% Range% N 1.29 1.02 - 1.50 P 0.38 0.22 - 0.54 K 0.48 0.31 - 0.62 S 0.10 0.09 - 0.14 Mg 0.14 0.09 - 0.22 Ca 0.03 0.01 - 0.04 Fe 0.003 0.001 - 0.09 Adapted from Heckman et al. 2003
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