Controlling nitrogen over enrichment in agriculture
Tuijl, Martijn van
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Nitrogen is one of the key ingredients that organisms require to live. Farmers have been using nitrogen fertilizers to increase their crop yields. The overuse of nitrogen fertilizer has been damaging the ecosystems that are surrounding agricultural areas. If too much nitrogen leaks into the surrounding water ways algal blooms can become harmful problems, with significant damage to the aquatic ecosystem as a result. In the nearby terrestrial ecosystems, an increase in nitrogen is also problematic as plant species that thrive in those conditions outcompete those that are not able to take advantage of the increased nitrogen levels. In order to combat these problems a decrease in nitrogen fertilization is required. These strategies are dependent on the knowledge of plant nitrogen uptake, as plants can take up nitrogen in several different forms which are all dependent on different uptake mechanisms. Several studies have shown that often fertilizers are overused such that a decrease in application would not decrease the yield. In order for farmers to find out whether they have applied enough fertilizer they need to the ability to measure the nitrogen content in the crops that are growing in their fields. The measurement of sun induced fluorescence could allow farmers to do exactly that. By measuring the reflected light from the plants scientists have been able to accurately estimate the nitrogen content in plants at the canopy scale. If applied by farmers this would allow them to measure the nitrogen content of plants, potentially allowing them to only apply fertilizer when and where it is required. The other solutions proposed in this review are based on genetical engineering. Researchers found the zmm28 mutant in maize, called DP202216, to have a higher nitrogen uptake when compared to the wildtype maize strain. In this mutant a transcription factor called zmm28 is fused to a constitutive promoter. It remains unclear however what the molecular mechanism behind this increase is. Other researchers found an Arabidopsis thaliana mutant that reacts differently to nitrate deficiency stress then the wildtype. The wildtype shows reduced root growth under nitrate stress conditions, while the NAC075 mutant found by these researchers does not. In these mutants the nac075 gene is mutated such that the protein cannot leave the cells where it is produced. The underlying molecular mechanism has been uncovered which makes it an interesting target for research in other species. In order to actually lower the nitrogen input in the field a combination of several solutions might be the best option as they are not mutually exclusive. Using a transgenic crop similar to the mutants DP202216 or NAC075 could decrease the amount of nitrogen used in agriculture and thus reduce the severity of the problems that it causes. Farmers would also be able to measure the nitrogen content of these plants to even further decrease the amount of over fertilization.