Erner et al (2001) published a review paper about the most significant effects of potassium (nitrate) on citrus tree growth and productivity. The paper discusses K requirement and K effects on growth and yield, external and internal fruit quality, when applied to the soil or in a foliar spray. Growers should take into account that the differences in crop performance are related to the counter ion of the main K-sources used (i.e. nitrate, sulphate and chloride ions). For citrus trees grown in arid zones, potassium nitrate was found to be the preferred K-source. Most of the articles, referred to in the review paper by Erner et al (2001), can be found in this PNA library database as well.
Erner, Y., Y. Kaplan, B. Artzi, and M. Hamou. 2001. Potassium Affects Citrus Tree Performance. The Volcani Center, Institute of Horticulture, Department of Fruit Trees, PO Box, 6.