Nitrogen is a major structural component of many organic compounds found in plants including chlorophyll, proteins, nucleic acids and enzymes. Proper nitrogen nutrition is commonly associated with development of aboveground parts of the tree, including branch length and diameter growth, bud number and size, and foliage density and color. The most common visible symptom of nitrogen deficiency in Christmas trees is yellowing and stunting of needles. Because nitrogen is a mobile nutrient within the tree, older needles yellow first as nitrogen can move to the younger foliage.
Although nitrogen is a critical nutrient for Christmas trees, N recommendations are not based on soil testing. This is because nitrogen is a mobile nutrient in the soil, and levels can fluctuate widely with weather and soil conditions over a short time. Nitrogen rates primarily are determined by species and trees age in order to match soil supply with plant uptake Foliar testing is a useful tool to assess nitrogen levels. (examples)
Keeping nitrogen in the root zone:
As mentioned previously, nitrogen is mobile in soil and plants. Nitrogen is mobile in soils because soil microbes eventually convert the various forms of N found in soils to nitrite (NO2) and then nitrate. Both of these compounds are negatively charged and therefore cannot bind to soil organic matter or clay particles, which are also negatively charged. This inability of soils to bind nitrate-N means that excessive nitrogen in soils is subjected to leaching. Loss of nitrogen can be expensive but also can be detrimental to the environment. Excess nitrate is considered a groundwater pollutant. In surface water, excess nitrogen, along with phosphorus, can contribute to harmful algal blooms and oxygen depletion.
Management practices to minimize nitrogen loss are:
- Rate – Don’t over apply