Nitrogen

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Effects of cropping management on nitrous oxide emissions. The nitrous oxide emissions paired with a star were significantly higher among the cropping systems. Graph from Kong, 2007.

The Agricultural Sustainability Institute at UC Davis is partnering with many institutions and researchers over the course of the next two years to complete the California Nitrogen Assessment. The assessment will provide valuable insight for stakeholders into the balance between the benefits of agricultural nitrogen to society, and the effects of surplus nitrogen in the environment.

The impact of nitrogen on the environment has been a key area of research at Russell Ranch (see our list of publications related to nitrogen). In one study at Russell Ranch, the nitrous oxide emissions from the conventional corn-tomato rotation were greater than the emissions from the organic and low-input systems. The study grew cover crop in greenhouses in a 15N atmosphere and then incorporated the cover crop, or

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Total denitrification after irrigation or simulated rainfall. The organic system had cover crop and manure incorporated in the spring and had high ammonium content at the April sampling. Both systems were sprinker irrigated in October to simulate rainfall and the conventional system had ammonium nitrate applied five days before sampling. Graph from Burger, 2005.

15N-labeled fertilizer, in a microplot in each plot. The conventional system resulted in a greater amount of 15N derived from the fertilizer than the organic and low-input systems and also shorter mean resident times of the fertilizer in one soil fraction. These results indicate that the conventional system may have more rapid N cycling and greater N loss to the environment compared with the organic and low-input systems.

Another study at Russell Ranch showed that higher emissions of nitrous oxide occurred when high soil moisture content (above 60% water-filled pore space) coincided with fertilization and high soil nitrogen content. These results suggest irrigation management could control the duration of elevated N2O flux, although inorganic N concentrations should be kept low during the rainy season.