Citrus demands for nitrogen are greatest from bloom through June, making spring the best time to apply supplemental nitrogen fertilizer to navel oranges. Growers typically apply between 1/10 and 1/4 of their annual nitrogen requirement foliarly, in pre-bloom and post-bloom low-biuret urea sprays.
Cooperative Extension Farm Advisor Craig Kallsen has been researching the amount of nitrogen a mature navel orange grove requires. Evidence suggests that nitrogen levels will depend on a variety of factors such as tree health, variety, productivity, irrigation scheduling and efficiency, and how fertilizer is being applied. Nitrogen requirements in mature commercial groves can be calculated best on a ‘per acre’ basis instead of ‘per tree’.
Navel orange trees demonstrate a significant response to nitrogen levels. A considerable amount of research shows that nitrogen levels between 2.4 and 2.6% provide a good balance between yield, size and fruit quality.
Excessive levels of nitrogen can have direct effects on size and quality and can also contribute to water contamination. Nitrogen levels above 2.6% present a greater risk for issues such as staining, crease, puff and decreased fruit size. At the same time, nitrogen deficiencies at levels below 2.0% will result in considerable yield losses in oranges.
Additional nitrogen can be stored in significant amounts within the tree, especially the leaves. Growers should also be aware of the nitrogen content in their irrigation water as well as nitrogen stored in soils.
Read Kallsen’s entire post here.