Is urea a good fertilizer for citrus?
Chicken poop? Last year I put on too much chicken poop, as fertilizer, around my citrus. I remember posting, last year, and complaining, "I have beautiful dark green leaves on each tree, but no flowers on some as I usually get. No fruit on one tree all year long."
I do believe that tree had a bit too much nitrogen from the chicken poop, since it has very rarely missed a season of fruit and also... right now that same tree is completely covered in beautiful, fragrant blossoms.
Probably not. Urea is high in Nitrogen which citrus likes, but it tends to drive the soil PH the wrong way. You are better off with sulfate of ammonia. Still very high in nitrogen, but will tend to acidify the soil.
Urea is commonly used in citrus fertilizers. Citrus, like all other plants, CANNOT absorb or use it, at all, from the soil. Rather, it must be broken down by ammonifying bacteria to become ammonium, and then if your soil pH is high enough, it may further break down to become nitrate, by nitrifying bacteria. At least in Florida soils, urea has little or no effect on soil pH. Because of the need for bacterial break-down, it only becomes available to the plant as a source of N after a period of time -- perhaps weeks, and in the mean time, it is highly water-soluble. So if you get a big rain or over-irrigate, you can wash it deeper than your tree's root system before it has done any good. For that reason, we avoid using it during our rainy season. But in drier weather, it's fine.
Urea applications to the foliage ARE directly absorbed, and leaf tissue contains urease, the enzyme that breaks down urea, so that's a quick, reliable way to increase useable N in the tree.
One other thing to consider -- urea, especially the cheap stuff, often contains biuret as a contaminant. Citrus trees are more sensitive than most species to this poisonous substance, so if you do use urea, be sure it is a hiqh-quality fertilizer-grade material; NOT cattle feed grade.
Crop sensitivity to biuret levels in Urea depends upon factors such as plant species, soil properties, method and timing of fertiliser application.
A general guideline for the safe use of Urea applied to the soil would permit a maximum of at least 2% biuret. Many crops grown in New Zealand have a biuret tolerance level in the range of 4-5% in Urea.
At risk crops in New Zealand include citrus, new grass and possibly potatoes. It is likely effects may occur with levels >2.5% biuret. The risk to new grass appears greatest when Urea is sown with the seed, a practice which is not recommended.
The risk of effects of biuret to plants could be expected in contained growth systems such as indoor tomatoes and grapes, possibly hydroponic growing and pot plants. No information can be found of the effects from biuret in these situations.
Biuret is not retained in soil and leaches easily and is broken down by soil microorganisms relatively quickly.
Foliar application of Urea solutions containing biuret can cause injury symptoms on some plant species. The tolerance level for biuret concentration in Urea used for foliar spray is much lower than for soil application. At risk crops in New Zealand include avocado and citrus.
A safety guideline of 0.25% biuret in the product as applied for foliar application on many crops is widely accepted.
Unless the biuret level exceeds 2.5% there is unlikely to be any danger when Urea is applied to pastures.
Urea should not be applied with grass seed.
When Urea is applied as a foliar fertiliser the biuret level should not exceed 0.25% concentration.
Urea used for spraying should have a low biuret content (less than 0.4%), as higher levels cause leaf burn. Biuret is not a problem when urea is applied to the ground. http://www.agric.nsw.gov.au/reader/citrus/h2311.htm
Note that the above article gives maximum biuret percentages for "most crops," whereas citrus is among the very most sensitive of crops to the material.