N spray burn

[lebmung]

Tahiti lime burn

This is an accidental burn as I sprayed the near citrus with a nitrogen mixture spray ( urea ).
Only a couple of leaves got burnt. This still happen with UV protection.
The Tahiti lime had a massive infection with scales so I covered the plant in neem oil during the winter, like 3 months ago, and it still has a shiny oil on the leaves.
This is an example of incompatibility, I knew it so I tried to put them aside.

[Millet]

All urea contains an impurity called biuret.  Do you know what the content of the biuret that was in the urea you used? 

[lebmung]

All urea contains an impurity called biuret.  Do you know what the content of the biuret that was in the urea you used?

Yes, under 0.5%. The other citruses like shekuwasha, satsumas, keraji didn't have any burn. I still can see the urea on their leaves how it attracts water in a humid green house. Also double layer plastic with UV protection.
Mango seedlings got burnt as well. Mature mangoes didn't.

[Millet]

Urea residue on  a leaf will resolubleizes when the humidity raises.  For citrus growers this is a plus, because with each resoluble action more and more of the nutrient value of urea is given to the tree..

[Ilya11]

Biuret is formed from urea with storage, especially under higher summer temperatures.
Urea should  not be kept for  a long time.

[SeaWalnut]

Urea pellets or urine?
The urine i use to fertilise my trees,i mix it with a little gypsym to prevent burns ,but i dont fed it foliar
The gypsum binds the nitrogen from urea as nitrogen sulphate but it needs a lot of water to do so.
Ive read thats 200 litters of water needed to fix a kilogram of N from Urea with gypsum.
When it rains its most efficiently converted.
Gipsum its also used to recover burned patches of grass from dog urine wich its verry high in N.

[Millet]

What is considered low biuret urea by the University of California and the University of Florida is urea with a biuret contend of 0.25% biuret.

Time has passed to apply a winter prebloom foliar application of low-biuret urea. The most effective period for summer spray is between July 1 and July 26.  Use summer applications of low biuret urea: (1) If your goal is to increase fruit size, and (2) if your tree is carrying a heavy crop.  Spray either in the early morning or early evening.

[luak]

Millet, that low Biuret treatment I started in the beginning of December work out too good. Sprayed all my tree’s, small and larger have heavy bloom, most have small fruitlets. Never saw so many blooms . Hopefully they thinned themselves.
Have to give them 2 more sprays. It would make a nice display come fall.

[Millet]

Luak, sounds like your doing every think correctly.  As you wrote, your tree will adjust the initial crop load to keep what the it is capable to bring to harvest.  Your summer spray in July will help the tree to hold onto all the fruit, and to increase the fruits size. 

[lebmung]

Biuret is formed from urea with storage, especially under higher summer temperatures.
Urea should  not be kept for  a long time.

I keep my fertilizers under dry conditions with desiccants.
Like I said they other nearby citruses did't get any leaf burn. So I suspect an incapability between neem oil and urea. Which is not a thing, because a neem oil application during the winter would kill any larvae or scale insects left from the summer.

[lebmung]

What is considered low biuret urea by the University of California and the University of Florida is urea with a biuret contend of 0.25% biuret.

Time has passed to apply a winter prebloom foliar application of low-biuret urea. The most effective period for summer spray is between July 1 and July 26.  Use summer applications of low biuret urea: (1) If your goal is to increase fruit size, and (2) if your tree is carrying a heavy crop.  Spray either in the early morning or early evening.

I don't know any supplier of 0.25% maybe only order with chemical labs.
The spray was a pre bloom few weeks ago, and the leaf burn didn't appear right away it took about 2 weeks and hot weather. Next time I will wash away the neem oil with soap before urea spray.
My mango seedlings also got burns once the sun started to get strong.

[sunny]

Biuret is formed from urea with storage, especially under higher summer temperatures.
Urea should  not be kept for  a long time.

I have 1% low biuret urea for 3 years stored, 2-3 months ago i sprayed my dekopons, pomelo, finger limes with it according to millets recipe...it's sunny all day here like 10 hours a day sun, 33-35 celcius and no burn at all...instead the largest fingerlime is covered in flowers right now.

[Ilya11]

Biuret is formed from urea with storage, especially under higher summer temperatures.
Urea should  not be kept for  a long time.

I keep my fertilizers under dry conditions with desiccants.

Biuret is formed by decomposition of urea giving volatile  ammonia, water is not necessary for this reaction

[lebmung]

Ilya11: that is good to know.

I will make a test on a leaf, spray neem oil then spray urea. I am sure it will burn in few days if sun is present.

[Millet]

Ilya11, I have always read that biuret resulted from the high heat process during manufacturing.  Possible biuret build up from any other causes other than the manufacturing process I am unaware off.

[sea4]

I am under the understanding that biuret forms when urea is heated above it's melting point. Pure urea melts at 135C. So that leads me to believe that storage below 135C should be adequate. But I am not a chemist