Sampling Soil and Plant Tissue 


 
 
Goodfertility is IPM. The best defense against pest problems is to grow healthy, vigorous trees. The best way to keep trees growing at their greatest potential is to fertilize on the basis of soil and plant tissue analysis. The amount of fertilizer or lime needed for optimum nutrient levels in the tree will vary with different soils and sites, or even different land-use history. Too much of a nutrient is often as harmful to Christmas trees as too little. Your county extension agent can help choose which fertilizers to use by using representative soil and/or plant tissue samples. The North Carolina Department of Agriculture and Consumer Services provides soil and plant tissue analysis, as well as other diagnostic services to state residents. It is often the job of the scout to collect such samples.
    When to take soil samples. Site preparation is the first and one of the best opportunities to fix soil fertility problems. Soil samples should be taken before the first tree is ever set. Only before planting can fertilizers be incorporated into the soil. After planting, fertilizers can only be applied to the soil surface, and some nutrients, such as phosphorous, are very slow in reaching roots growing several inches below. Changing soil pH is also much slower when lime or materials cannot be incorporated into the soil.
    After the trees are in the ground, maintaining adequate soil fertility requires annual sampling until the nutrients in the soil and the pH are at their optimum levels. Once the optimum levels have been reached, sampling every other year should be enough to make certain that the optimum is maintained. Soil samples also may be needed to diagnose the cause of poor color or needle shedding, and as an aid in interpreting the results of tissue analysis.
    Do not take soil samples within 3 months of fertilizing as nutrient levels will reflect the fertilizer and not the true soil levels. In addition, the pH on the sample may not be accurate for up to a year after a lime application. Soil sampling is best done in the fall, when there is plenty of time to determine which fertilizers should be applied the following spring.
    How to take a soil sample. A soil sample is made up of many soil cores from five to ten different locations in each block. If a soil sample is not representative of the soil in the block, it will not accurately reflect the nutrients found in the soil. Most Fraser fir fields are on slopes where the soil characteristics such as color, amount of organic matter, or depth to the subsoil vary with the slope. It is important to know what variation is present. Initially, take enough soil samples in a field to represent the variation. For example, collect separate samples from the top, middle, and bottom of a slope. If test results are different, fertilize the sections differently. If they are the same, treat the entire block the same and only take one composite soil sample in the future.
    Always use a soil probe when taking soil cores. It provides the most accurate and quickest method of taking samples to a specific depth. Typically, the core is taken from the upper 4 inches of soil if no incorporation of nutrients is possible. A separate 4- to 8-inch sample may also be important when evaluating a new field or a nutrient problem. Always push the soil probe straight into the soil. If a rock is encountered, move to a new area. Remove any surface debris, such as dead needles, before placing the soil in a plastic bucket.

Using a Soil Probe

    Where to take soil samples. Take soil cores from around 10 to 15 trees per acre. If plant tissue samples are taken, take soil cores from around the same trees. Take four cores per tree, varying the position of the core between the row, middles, and dripline.
    Mix all cores from all locations in a bucket before placing a single sample in the soil sample box. Boxes and forms can be obtained from your local county center of the North Carolina Cooperative Extension Service.
    When to take plant tissue samples. Tissue samples provide information on more nutrients than the soil samples. Comparing the soil samples with the plant tissue sample can show if the tree is taking up the nutrients. Take the first tissue sample when the trees have been in the field for 3 years. Take a second tissue sample when the trees are a year from market to help fine-tune fertility recommendations and to make certain that color and needle retention will be good at harvest.
    Additional tissue samples should be taken to help diagnose the cause of color problems or poor growth in trees any time through the rotation or any time through the year. When diagnosing growth problems, always take two plant tissue samples -- one from the problem trees and a separate sample from good growing trees in the same block.
    Time of year to take plant tissue samples. Tissue samples taken when the trees are dormant reflect nutrient levels most accurately. Nutrient levels in actively
growing tissue may vary considerably from the established standards. Therefore, avoid sampling from bud break until bud set. Samples taken during the active growth period should only be used for problem trees, and the results should be compared to samples taken at the same time from healthy trees.
    How to take plant tissue samples. Sample from the same trees you have taken soil samples from. Plant tissue samples without a current soil sample are worthless. It is usually best to take samples from trees that are average in growth rather than from the best or the worst looking trees.
    Take two shoots from the most current growth. Samples should be from the upper third of the tree. Try to sample shoots from a uniform position on branches such as a branch terminal. The laboratory will need at least 40 inches of growth to run their tests.
    Local county extension agents can give you more information on taking soil and plant tissue samples and help you determine fertilizer needs from sample results. Your county agent can also help you take samples to diagnose problems where trees are not growing well.
 
 

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