Fertilizing one-year old trees – be careful!

Posted by Brent Holtz  /   March 15, 2010  /   Posted in Almond  /   8 Comments

Nitrogen is the most important element we can apply to our tree fruit crops. Almond growth and productivity depend on the availability and uptake of nitrogen. Most fertilizer recommendations are based on making nitrogen available to our trees so that a nitrogen shortage does not limit tree growth or productivity.

Young almond trees don’t require as much nitrogen as older trees. I like Wilbur Reil’s rule of “one ounce of actual nitrogen per year of age of tree”. That rate can be applied several times per season, but never more than that at any one application. Thus, a first leaf (first year in your orchard) almond tree should not receive more than one ounce of actual nitrogen per any application. A five year old almond tree should not receive more than 5 ounces of actual nitrogen per one single application. The University of California only recommends one ounce of actual nitrogen per one year old tree over the course of the season, but I have been told by many growers and PCAs that this rate is not enough for the growth they desire. So, if you want to put out five ounces of actual nitrogen per one year old tree, do so in five applications and not all at once!

I have seen many trees burned by nitrogen, especially if liquid fertilizers like UN-32 (urea ammonium nitrate 32 %) or CAN 17 (a clear solution of calcium nitrate and ammonium nitrate) are used in single applications. These liquid fertilizers are very effective and easy to use but it doesn’t take much to burn young trees. I do not recommend using these liquid fertilizers on first leaf trees–I prefer to see triple 15-15-15 (15% Nitrogen – 15% Phosphorous – 15 % Potassium) fertilizers used on first leaf trees. I like to see these granular fertilizers placed at least 18 inches from the trunk. With micro-sprinkler and drip irrigation systems liquid nitrogen fertilizers can be used very efficiently and easily by growers. But be careful, I know several farm managers that will not allow more than 10 gallons of UN-32 per acre per application on mature almond trees. UN-32 contains 3.54 pounds of actual nitrogen per gallon, if you put out 10 gallons of UN-32 per acre you added 35.4 lbs of nitrogen per acre. If you have 120 trees per acre and do the math you come up with 4.72 ounces of actual nitrogen per tree–almost 5 ounces! I recommend not applying higher rates than this per application. I have seen nitrogen burn occur more often during hot summer temperatures when trees have elevated transpiration rates and obviously faster nitrogen uptake rates than what would have occurred at a cooler time of the year.

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About Brent Holtz

Brent Holtz is a University of California Cooperative Extension pomology farm advisor for San Joaquin County.

8 Comments

  1. Anonymous April 15, 2011 2:59 pm Reply

    I thought UN-32 is a slow-release fertilizer or is it not?

  2. The Almond Doctor April 15, 2011 3:14 pm Reply

    UN-32 or UAN-32 is an abbreviation for the fertilizer urea ammonium nitrate that contains 32% nitrogen. There are other blends that contain less nitrogen.

    It is not considered a slow release unless it is specified as slow release. Slow release urea fertilizers will be granular (pellets) as they typically are composed of water insoluble urea and some type of polymer casing/shell. This prevents the rapid release of nitrogen since some nitrogen is “washed off” with each wetting cycle. Most slow releases have a quick release component as well in order to get some nitrogen into the plant quickly. These fertilizers cost about $5-$8 more than regular fertilizer equivalents per 50 pound bag.

    All liquid and most granular fertilizer are not considered slow release fertilizers. These fertilizers will move into the rootzone quickly, usually with an irrigation. Since urea and ammonium have to be converted to nitrate by the soil microbial community before becoming available to the plant, uptake may not be immediate. In cooler temperatures this may be a day or so, but as the soil warms up, this process occurs more quickly. So, in cooler temps, applying urea may have a delayed affect, but its not truly a slow release fertilizer.

    I hope this is clear. Please let me know if it is not.

  3. Nick July 18, 2011 5:28 pm Reply

    Hello, I think i might be experiencing an excess nitrogen problem in my first leaf almond orchard. The symptoms are defoliation starting at the trunk working out towards the tips of the scaffolds. I was appling 1.5 gallons of can-17 per acre per irrigation (which doesn’t seen all that high) but through a one gallon per hour dripper located at each tree. I pulled petial tissue samples and found that I was still low on nitrogen at this point I switched to UN-32 and applied 3 gallond per acre, this is when the problem occured. I think the fact that my water and fertilizer is so concentrated is why I might be having a problem. At first I thought I might be over watering now after reading your article I think I over fertalized. Will these trees push out of this? what can I do from this point forward?

  4. The Almond Doctor July 18, 2011 6:19 pm Reply

    Nick: Sorry to hear about the problem. Quick rundown of your application – each gallon of UN-32 contains 3.4 pounds of nitrogen, or roughly 55 ounces. Multiply this by 3, 165 ounces applied per acre. This rate is too high for first leaf orchards, especially during times of high evapo-transpiration rates (Remember, no more than 1 ounce of actual nitrogen per tree!). My guess is that you are correct in your assumption that the leaf die-back is associated with too much nitrogen.

    Now the good news: the trees will grow out of the problem. Once the leaves drop, the vegetative buds will push and the trees will green up and put on new growth. Although the damage may have set the trees back a few weeks, there is no need to feel that the orchard is seriously damaged – just try and reduce the chances of this happening again by fertilizing with low rates of nitrogen more frequently. Using around 2-3 gallons/acre of CAN-17, or 1-1.5 gallons/acre of UAN-32 should be the maximum amount of nitrogen applied to these young trees.

    If the trees do not push out of this in a few weeks, give me a call/email so we can discuss other possible causes of the problem.

  5. john March 2, 2012 8:14 pm Reply

    What would you recomend applying through a double line drip system if granular was out of the equation on first leaf trees? My concern is that the drip line is up on top of the berm and closer than 18 inches to the tree.

  6. The Almond Doctor March 2, 2012 9:06 pm Reply

    John, Liquid fertilizers can be used and injected through the system…just use low rates. I would start off with around 0.25 ozs/tree, or in a 110 tree planting, 28 ounces of actual N per acre (1.75 pounds/acre). Once the trees increase in size, the rate can be increased. This does not need to be applied until well after leaf out – wait until the tree has a couple of inches of growth before considering the application.

    Preliminary studies suggest that spoon feeding low amounts of N multiple times a year will increase tree vigor, provide some level of vigor control, and decrease the risk of over application.

  7. david March 5, 2013 7:56 pm Reply

    I am new to this game and I got a soil sample and I am looks at applying 15x15x15 to the trees. You indicated I should apply the 15x15x15 at least 18″ from the trees and not more then 1 ounce of nitrogen per tree. So how do I figure out how many pound of triple 15 to use pre tree?

    • David Doll March 6, 2013 4:01 am Reply

      Hello David!
      Plan to apply the fertilizer somewhere around 12-18″ inches from the trunk. Apply no more than an ounce of actual N at any one given time. About 4 ounces of N made every 5-6 weeks from mid-April through August will provide maximal growth.

      To determine the amount of N to apply, divide the number of ounces wanted (1) by the percentage of nitrogen within the fertilizer (15% in 15-15-15 (the first number is the percentage of N, second phosphorous, third potassium – N-P-K)). So 1.00 divided by .15 = 6.66 ounces. So 6.66 ounces of triple 15 will be needed for each application in order to apply one ounce of N.

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