Optimizing nitrogen fertilizer-use recommendations for winter wheat in a Mediterranean-type environment using tissue nitrate testing

Although nitrogen (N) fertilizer use is essential for economic yields of modern field crops, whether rainfed or irrigated, the underlying concern is to maximize nutrient-use efficiency and avoid excessive N use that results in deterioration of water quality from the environmental standpoint as well in the interest as human and animal health. Soil testing for N forms and total plant N analysis can contribute to the efficient use of N, but both strategies have limitations. Accordingly, tissue testing of the growing crop has been promoted as an alternative approach. Although such tests have been widely used in the West to monitor the N status of crops, they are rarely used in developing countries. A 2-year field trial examined the potential of tissue testing of rainfed wheat in a typical Mediterranean environment in the Cukurova region of southern Turkey, because observations from wells in the region had suggested increasing and excessive nitrate levels, most probably from fertilizer N use. The trial, in essence, compared different levels of N fertilizer application based on farmers' traditional application in addition to considering soil mineral N with tissue N based on a color index to refine N application recommendations. The measurements were taken in conjunction with observations on wheat yields. The study showed that using the combined approach of soil and tissue nitrate resulted in lowering the N fertilizer recommendations without any lowering of crop yields, clear evidence that farmers had been using excessive amounts of fertilizer N in the absence of limited or no official guidelines. Thus, such tests should be promoted to replace traditional fertilizer application practices as a simple and easily used tool to improve N-use efficiency for the farmer, in addition to reducing negative environmental impacts of such use. The quick tests can help promote the awareness of the potential negative effects of overuse of N fertilizer.