Frequently Asked Questions

Answers to Frequently Asked Questions (FAQ):

  1. Why use the LSU AgCenter Soil Testing and Plant Analysis Laboratory (STPAL)?
    The LSU AgCenter STPAL offers a variety of soil tests and plant tissue diagnostic tests to meet your planning needs for profitable production. Fees charged at STPAL are cheaper than any commercial laboratory on similar tests. The STPAL offers adequate fertilizer recommendations based on latest results of Louisiana-specific research. We do not recommend fertilization that wastes your money and may cause adverse environmental consequences. In addition, STPAL uses a modern quality assurance program to improve its analytical process for accuracy and efficiency. The STPAL is the only Louisiana laboratory that participates in the well-recognized North American Proficiency Test (NAPT) program and maintains an acceptable level of proficiency (View our NAPT performance).

  2. How do I take a soil sample?
    In general, soils that differ in appearance, crop growth or past treatment should be sampled separately, provided the area is of such size and nature that it can be fertilized separately. For each sample, collect soil from 10 or more places in each sampling area in a zigzag fashion so as to make a representative sample. Mix thoroughly before filling a sampling carton or container to be mailed to the Lab. One soil sample should represent 10 acres or less. Avoid sampling directly in the fertilized band. Proper sampling depth depends on the kind of crop you plan to grow. We recommend that for pasture, turf, established orchards and minimum tillage, you take top 2-3 inches of soil and for cultivated crops, you collect upper 5-6 inches of soil. Click here for an illustrated version of soil sampling.

  3. When and how often do I need to collect soil samples? You need to take soil samples every 2-3 years to ensure that you update field fertility conditions. We recommend that you collect and submit samples 3-5 months before your projected planting date to ensure that you have plenty time to plan your liming and fertilization program for the upcoming season.

  4. How much sample do I need to send to the Lab for testing?
    For soil samples, you need to send in between ½ to 1 pint of soil for each sample to the Lab for analysis. We need 4 oz. of water for the irrigation/aquaculture water test. If you are submitting a potting mix sample, at least 1 pint is needed.

  5. What happens if I do not have an LSU AgCenter sample carton/box?
    You can contact your parish extension office for sampling cartons. If you are not able to get the cartons, you can send in your sample in a heavy-duty plastic zippered bag.

  6. Do I need to state the specific crop to be grown for fertilizer recommendation?
    Yes. It is absolutely important to specify what crop you plan to grow so a correct recommendation can be generated for your sample. The back sheet of the Soil Test Request Form lists available crops.

  7. What condition of soil sample should I mail to the Lab?
    In general, you can send in any soil sample. If you send samples that are very wet, you may consider using a plastic bag rather than a carton to contain your sample. Very wet soil samples can damage cartons and cause a loss of your sample in delivery process before reaching the Lab.

  8. What form of payment should I use for tests?
    You can enclose a money order or check for payment made out to SPESS-STPAL. You may also use either a VISA or Master Card credit card. If you use a credit card we will need the name on the card, the address of the card holder, the credit card number, expire date, and the 3 digit CID number from the back of the card.

  9. Is it OK to submit the soil sample through nursery or hardware stores?
    Soil samples may be submitted through local nursery stores where they offer such service. For quicker turn-around, please drop your samples at your local parish agent's office or mail directly to the Lab. There have been instances in which the Lab never received clients’ samples mailed by stores.

  10. How do I convert fertilizer or lime rates for larger lands to small areas, single rows or potted plants?
    Fertilizer recommendations are usually given in pounds per acre and lime in tons per acre. For fertilizing small areas, single rows or potted plants, it is necessary to make conversion to suit your needs. You can click here to view conversion tables.

  11. Why do I need to run a plant diagnostic analysis?
    Plant analysis provides immediate diagnosis of nutrient deficiency, toxicity or imbalance. It serves as a supplemental tool to soil tests. It can monitor the effectiveness of your adopted fertilizer practices.

  12. How do I take a plant sample?
    Plant samples should be taken at early growth stages sensitive to nutrient requirements. Depending on crops, different parts of plant are taken for diagnostic analysis. General guidelines on what to sample are provided in Table 1 for field crops and Table 2 for vegetable crops. For crops you do not find in these tables, you may sample the youngest but fully mature leaves. Avoid soiled, diseased and insect-damaged or mechanically damaged plants and exclude dry and dead tissue. Please mail your plant samples in paper bags (no plastic bags) directly to the Lab.

  13. What types of water samples can I send to the Lab for analysis?
    We run water samples for agricultural and aquacultural applications.  
5/4/2005 11:45:59 AM
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