Many herbs and spices are known to contain potent antioxidant compounds. However, it's not always clear how growing conditions affect the levels of antioxidants in plants. Researchers at Southwestern University in Texas wanted to find out the effects fertilization had on antioxidant levels in basil. They tested three varieties of basil ('Dark Opal', 'Genovese', and 'Sweet Thai'), applying various amounts of nitrogen fertilizer (0.5 mM to 5.0mM) to the plants during the growing season.
They measured the corresponding levels of antioxidant phenols and found antioxidant levels in basil were two to five times higher in the plants given the lowest amounts of nitrogen compared to the plants with the highest nitrogen doses. In general, the higher the levels of nitrogen added, the lower the antioxidant phenol levels in the basil leaves.
For more information on this research, go to: Journal of Agricultural and Food Chemistry.