had soil test, it indicated relatively hi levels of P and K; soil report recommended nitrogen only fertlizer.

verything I find has at least some of the other nutrients.

what is source for nitrogen only, possibly organic?

thx. in advance for any help.

Dan

how old are these trees..

how big

what signs on the trees themselves... indicate any kind of problem???

ken

I use it for my nut trees, which are heavy N feeders once they come into production, but for almost nothing else. Guess if I were into the 'lawn' thing, I'd probably use it for fall fertilization. But, by & large, I don't see much need to fertilize ornamental trees in the landscape, and rarely find any need to do much in the way of 'feeding' for established fruit trees.

tj

tj

Dan

I'm sure you have plenty of NFTs (nitrogoen fixing trees) and shouldn't be worried about it.

The International Society of Arboriculture sells a great book on the subject: Tree and Shrub Fertilization: Proceedings from an International Conference on Tree and Shrub Fertilization. It contains several studies concerning methods, long term growth and health, etc. A lot of people believe adding N increases pest problems. There is a specific paper on the subject that reveals the exact opposite.

The studies all show the same thing - routine N surface applications in either the spring or late fall are very beneficial to trees. Slow release N is the safest to use but is more expensive. The other nutrients (primarily P and K) can be determined from a soil test. Soil tests for N are a snapshot in time and cannot be relied on routinely to determine N needs.

If the trees are in a lawn setting and haven't been planted in the last year, add N for a healthy tree.

If your soil has average pH (6-7) and an organic matter content of 4% or higher, that soil is able to contribute the equivalent of 1-2 pounds of nitrogen per 1000sf per year. That is sufficient to support the healthy growth of all woody plants. And if your trees are planted in the lawn or adjacent to it and your lawn is fertilized regularly, no other fertilizer for the tree is needed.

Excessive amounts of nitrogen can have detrimental impacts on tree health. It can negatively impact flowering and fruiting. Excess nitrogen increases water stress and reduces drought tolerance. It impacts the root system by delaying or reducing the carbon allocation and decreases root reactivity to damage or stress, including cold tolerance. And it can cause extension or elongation of nodes, resulting in a leggy, lanky growth habit.

And I'd not put too much stock in a single paper that disputes a correlation between excess nitrogen and pest problems. The succulent new growth that results from excessive or fast-acting nitrogen applications IS attractive to certain insects and the correlation is well studied and thoroughly documented.

As with any other type of fertilizer application, it is important to know your plant and your soil before applying. Look for signs that the plant is struggling or displaying nutrient deficiencies. Have your soil tested by a professional lab that measures both nitrogen and organic matter levels (home test kits don't cut it). And apply only as directed by the test. And avoid fertilizing routinely like most fertilizer manufacturers would like you to believe you need to do - trees are not lawns and if warranted, fertilizing every 3-5 years is typically all that is necessary to maintain their health and well-being.

Otherwise there is no need to apply nitrogen willingly or if a soil test shows low nitrogen (wheather by a lab or not) as there are too many variables that effect that level.

The general urban forest standards are still set by Miller and wrt this topic Harris, who wrote many of the questions on the ISA-Western chapter test and by Struve, whose work is cited by many municipalities in justifying their outlays. Here is what Struve says:

Although the logic behind early spring N fertilizer application is faulty for trees under clean cultivation, it may be an environmentally responsible practice for fertilizing trees growing in sod where grass clippings are not removed.

Recent concern about the effects of high N applications on plant health and environmental quality have caused a reevaluation of fertilizer practices (Miller 1998, 2000). High N applications reduce the concentration of defensive compounds, increasing the tree’s susceptibility to certain pests (Herms and Mattson 1992). However, high fertility increases growth rate and often results in nutrient loading. Nutrient loading is defined as an increase in the eedling’s nutrient concentration without a significant increase in dry weight (Malik and Timmer 1995). Nutrient-loading conifer seedlings increased planting stock quality; they established more rapidly on stressful sites than non-nutrient loaded seedlings (Malik and Timmer 1995, 1998; Paquin et al., 2000; Imo and Timmer 2001). Lower concentrations of defensive compounds caused by high fertility levels during production can be compensated for by pesticide applications, which act as surrogates for naturally produced defensive compounds. However, the use of pesticides in landscape sites is not as easily done as in the production environment. The benefits of nutrient-load nursery stock planted in stressful urban sites needs to be tested.

The reason for fertilization is to supply nutrients determined to be deficient to achieve a clearly defined objective (ANSI 1998). The objectives include correcting a visible nutrient deficiency; eliminating a deficiency not readily visible that was detected through soil or tissue analysis; increasing plant growth, flowering, or fruiting; or to increase plant vitality (Smiley et al. 2002). Further, the fertilizer should be applied in the manner most beneficial to the plant (ANSI 1998). Before a mineral nutrition program is prescribed, the objective of the mineral nutrition program must be stated. If the goal is to maximize growth in the nursery, then soil fertility should be maintained in the high range (Darrah 2000; Smiley et al. 2002). However, if maintenance of an acceptable aesthetic level is the goal, as in a landscape situation, then lower soil fertility levels are appropriate. In addition to meeting the aesthetic goal, low to moderate soil fertility would likely maintain natural plant defense mechanisms. The difficulty in meeting a fertilizer objective is that soil test calibrations [how much fertilizer needs to applied to effect
the desired response (adjusted for soil type, species, and geographic region)] for the different management objectives (maintain vigor of old trees, maximize growth of recently established plants, or achieve rapid growth during production) are lacking for most woody ornamental species (Darrah 2000). Current N application standards are 1.0 to 1.5 kg/100 m2 (2 to 3 lb/ 1,000 ft2) to maintain mature tree vitality and 1.0 to 2.0 kg/100 m2 (2 to 4 lb/1,000 ft2) to increase growth of established small trees and higher levels (Smiley et al. 2002). [footnotes omitted, emphases added]

Humans already fix as much N in a year as nature fixes. Urban eutrophication into receiving waters makes many urban streams the most polluted waterways in the country. Willy-nilly stating that one should apply N for a healthy tree is not only against proper arboricultural practices, it is irresponsible to the biosphere at large.

Dan