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Fluid Journal : Fluid Journal 2002-2004
Drs. J.S. Schepers, S. Payton, D.D. Francis, and J. Shanahan Improving Nutrient Management Via Evolving Strategies and New Technologies Nebraska studies focus especially on nitrogen and its impact on the environment. Nitrogen (N) is the most abundant nutrient in plants, which explains why its management has important implications on productivity and profitability of production systems. The fact that aerobic N transformations in soil ultimately produce nitrate, which is soluble in water, makes nitrate a potential contaminant of surface and ground water. The reality of the situation is that emphasis placed on N management is typically related to the profitability of the fertilizer user unless other segments of society are negatively impacted. In the long run, suppliers and growers have a vested interest in doing what they can to promote the efficient use of N, and this includes the scientific community. For it is now clear that whenever soil N availability is not synchronized with crop use, environmental impact is possible. The purpose of this article is to discuss evolving nutrient management strategies and new technologies in light of the needs of corn in its different growth stages. Uptake patterns Problems with the occurrence of higher-than-acceptable concentrations Summary: Synchronizing soil nutrient availability with crop use is an ongoing process involving studies of nutrie nt uptake patterns and dev eloping new and better ways of monitoring plant nutrient status. of nitrate in groundwater during the '70s in Nebraska prompted many questions about synchronizing soil N availability with crop use. After going through a denial stage for a decade or so, irrigated corn producers in the Central Platte River Valley of Nebraska were finally forced by the Natural Resources District to implement selected management practices to protect groundwater resources. Although the need to improve synchronization between soil N availability and crop use emerged as an early priority, literature was not able to document if current N uptake patterns were applicable for modern hybrids. Unpublished data generated during the 1993 and 1994 growing seasons showed that N uptake patterns before silking for five modern hybrids were statistically similar to a common hybrid grown in the '60s. However, after silking the N uptake patterns followed divergent patterns. Francis et al. (1997) found that up to 7 percent of the N applied before silking and up to 10 percent after silking, was lost from the leaves as ammonia during reproductive growth. They also found that 89 percent of K uptake occurred before silking but only 41 percent of P uptake occurred during the same time (Table 1). Prior to silking, dry matter accumulation for irrigated corn amounted to 37 percent of the total dry matter accumulated at harvest. Only 58 percent of final N accumulation had occurred by silking. This fact means that there is an opportunity for improved N management both before and after silking. Cumulative N uptake starts slowly but then gradually increases until silking, at which time N accumulation falters for a few days before again increasing (Figure 1). Expressing the same data in terms of N uptake rates shows that uptake can reach 4 lbs/A/day shortly before silking (Figure 2). During the pollination process, daily N uptake declines to a very low rate until after anthesis when translocation of photosynthates to the ear shoot begins. The second phase of rapid N uptake reaches a peak rate at about the R2 growth stage. Shortly thereafter, senescence can be observed in some hybrids, especially when grown under N deficient conditions. The loss of volatile N from leaves is associated with the senescence process and represents a component that is not accounted for when measuring total N uptake at harvest. Early Spring 2003
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