While citrus may be more sensitive to biuret toxicity through foliar application, isn't soil uptake an issue as well? At least that is what is presented in Vol. II of the Citrus Industry.

Quote:

The toxicity of biuret (NH2CONHCONH2 · H2O) to citrus has been investigated by Jones (1954), Impey and Jones (1960b), Haas and Brusca (1954a), Iwasaki and Shichijo (1962), and others. Biuret is formed when urea is heated. Its toxicity to pineapple plants was reported by Sanford et al. (1954). The yellow-tip mottling effects produced on citrus leaves by biuret are illustrated in figure 3-38. Biuret causes permanent injury and the leaves fall prematurely. Injury can result from either foliar or soil application of urea containing biuret in amounts varying from 0.5 to 2.5 per cent or more. This compound accumulates, as such, in the apex of citrus leaves and appears not to be metabolized, according to Impey and Jones (1960b). They found somewhat less protein in the injured leaf tips and an increase in several amino acids, especially glycine and serine. The biuret problem has been largely overcome by the production of urea containing < 0.25 per cent of this compound and by using urea (in spray formulations) at rates not exceeding 7.5 pounds to 100 gallons of water.

Kent

P.S. I'm on vacation, showing friends from Colorado around the Bay Area. Later this weekend I'll finish uploading photos of my trees. I didn't get that done before a trip to Arizona last week.

Most of the trees have responded positively to the increased application of my soluble fertilizer. Unfortunately the Page seems to be losing the battle with some form of stem rot.