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Spraying Urea?

Discussion in 'Sports Field Management' started by HobieDude, Jun 9, 2011.

  1. HobieDude

    HobieDude LawnSite Member
    from 7b
    Posts: 26

    We have been applying N to our bermuda football field using urea and ammonium sulfate alternately at rates of up to 1lb N/1000 sq. ft. Is there any advantage to dissolving urea in water and spraying the bermuda foliage? If so what is a safe rate to use without burning (especially in the hot weather we've been having)? thanks
  2. Blazerfb

    Blazerfb LawnSite Member
    Posts: 136

    I, too, would like to know the answer to this question.
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  3. waters lawn care

    waters lawn care LawnSite Member
    from alabama
    Posts: 128

    Posted via Mobile Device
  4. plainsane

    plainsane LawnSite Member
    from GA
    Posts: 5

    so foliar applied fertz have the draw back of increasing certain fungus growth (if already present) and significant increase in burn potential.

    some advantages are a lot less fertz used, increased carbohydrate production which leads to increase soil microbes (as the plant discharges excess carbs via the root) which in turn leads to a more healthy and robust root canopy.

    foliar applied fertz should be done with a flat fan tip and completed in 2 pass of opposing direction (unless you can prevent any overlap in spray on a single pass).

    here is how you calculate the concentration and application rates. this is a general rule of thumb BE SURE TO TEST ON A SMALL PATCH FIRST and wait at least 3 days as foliar burn from excessive nitrogen in the foliage will usually occur in that time frame.

    2lbs of urea + 2 lbs of water = 4 lbs
    2lbs of urea = .92 lbs of N
    .92 / .46 (46-0-0) = .23 so now you have a 23-0-0 concentration.

    i personally would dilute this further as you will have saltification issues around 60 degrees F (maybe add some iron chelates in liquid form) and account for that in the formula above. private message me and we can work through that if you like.

    so general rule of thumb is that bermuda will only absorb 20% of the N put out by urea due to leaching, microbes etc. and will absorb 80% of foliar applied nitrogen. from this point forward ill refer to oz=ounce as an ounce by WEIGHT, not volume (unless specified).
    so to get our N i break the montly feeding into 4 since urea is not going to stick around in the soil but for 3-7 days:
    16 oz / 4 = 4 oz (a week)
    4oz * .2 = .8 oz of N actually absorbed in first week.
    so since we want to put out around .8 oz of N we need to measure out:
    .8 oz N / .23 (our 23-0-0) = 3.478 oz BY WEIGHT of our solution from above, per 1000 ft.

    this is just a jump off spot. you will need to test a small patch first before spraying large areas, but this is how i calculated my dilution rate.

    this is the most important information, foliar applied nitrogen will have no effect (aka can not be absorbed) while the stomata are fully opened. they will constrict when the grass cools down aka, at dusk and early morning. here in atlanta i have observed no efficacy after 10 am...to be more precise, after the ambient temperature has increased by 12-15 degrees from the nightly low. i have had very little luck with late afternoon applications.

    i have now switched over to lessco 12-0-0 which contains 13% fe. i spray this every 4 weeks when i put out my pgr.
    i say this because i want to put the lessco application into perspective as my calculation from above is a little hotter than what i use currently.
    2.5 gallon = 28 pounds
    448 oz (28 lbs) / 320 oz (2.5 gallons) = 1.4 oz (by weight) per ounce (by volume)
    im using 4 oz (by volume) per 1000 ft. so that means:
    4 oz * 1.4 oz (by weight) * .12 (12-0-0) = .672 oz (by weight) of N per 1000 ft.
    but im just trying to balance color with growth surge and pgr degradation.

    lessco recommends all the way up to 9 oz per 1000ft which is higher than my first calculation.

    you may want this thread to bake for a minute, im sure there is a REAL turf manager on this forum somewhere that can show a fault in this post. im just a software engineer that wants to be a turf manager on the side so my education is limited and most likely incorrect in places (as with my assumption to divide the monthly fert rate by 4 to get what is taken up by the roots).

    but this is how i got to my mixture a few years ago, sorry i do not have my application logs from that time frame or i would pass that along to you, i lost it in a hard disk crash, but if you like i can share my google docs spreadsheet that i use for my nitrogen/primo/granular break down/tracking if you think that will help you. honestly, there is really nothing to it, and it doesnt provide a lot of help if you are not applying a pgr.
    Last edited: Aug 9, 2011
  5. HobieDude

    HobieDude LawnSite Member
    from 7b
    Posts: 26

    Thanks for your response. Why does it have to be so complicated? If I know that I want to put down 1/4 lb. N per 1,000 sq. feet on 100,000 sq. feet and my sprayer puts out 2 gallons per 1,000 then I would need to dissolve 50 lbs (46-0-0 urea) in 200 gallons of water.

    I found your observation about the stomata interesting. Are you saying that N is better absorbed when the stomata are closed and that I should spray in the mornings or evenings and not during the day when they are open?

    Thanks again for your reply.
  6. plainsane

    plainsane LawnSite Member
    from GA
    Posts: 5

    1. Yes stomata are more N will be absorbed.
    2. It's complicated because foliar applications are highly sensitive so you must be precise. If you notice with what I posted above...that 2lbs of nitrogen is going to treat WELL over 2000 feet.
    Bermuda will only take up about 20% of the urea you put out through the root. It's going to uptake about 80% of the foliar applied fert.

    See the reason for the formula. You must be highly precise when providing nutrients via the foliage...really anything via the foliage.

    You should how sensitive primo application is
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  7. HobieDude

    HobieDude LawnSite Member
    from 7b
    Posts: 26

    Yes, we've found that we can't put down much more than 1/4 lb. N foliarly without burning. We want to create alternate dark a light stripes every 5 yards on our bermuda football field. Mowing in one direction doesn't do it. We thought we'd apply liquid N and chelated iron to achieve this effect. Any thoughts?
  8. plainsane

    plainsane LawnSite Member
    from GA
    Posts: 5

    wow my enrish is rocking today. on my previous reply...
    #1 i should have said, yes more nitrogen is absorbed when the stomata are closed, they only vent gases and have a thick waxy lining to stop water absorption.

    as for "Why does it have to be so complicated?", sorry about that, i just like being as precise as i can be so using the method i described above has made it easy to adjust my concentrations to achieve more consistent results. just remember, if you are going to add iron to the mix, it will reduce your nitrogen concentration (not by much at all) but it can make a very subtle difference. plus, im a software engineer, we over complicate EVERYTHING.

    as for your strips, i do not think you will have the hard straight line you look to achieve, you will have some drift from the spray if you are at high enough pressures, the wind will carry it a little bit so you will have a scalloped line forming...but im not sure, that is just my personal opinion. if you can stop the drift, then it might work as foliar applied nitrogen will not travel past the stem and into the roots so it will not become systemic and travel through surrounding runners.

    you might want to cut back on the 1/4 lbs a little bit as it will reduce your growth surge...but you will have to play around with that concentration because i dont know what type of bermuda you have nor do i know your ph level. this is all trial and error...at my house i have 2 sentinel patches that i always test on (i alternate between the 2 to prevent previous tests from effecting the current, well as much as possible).

    the only way i know of to get the hard lines in the turf is by using a very heavy grove roller. they are crazy expensive unfortunately and my buddy uses one and his lawn and it looks AMAZING...the strips are so strong and pronounced and they will last all week as he uses a plant growth regulator to reduce growth activity.

    you also might want to investigate pgr's. they have become my version of rhinoplasty, im crazy addicted to what it does and how you can use it to strengthen grass and reduce clippings. its not for the faint at heart but well worth the time and effort to understand.

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