FAQ's

(Click on the Questions for Corresponding Answers)


1. Why do we need to get the soil tested?

Different plants have different soil pH and nutrient requirements. Testing is inexpensive when compared to investments in your plants, amendments, time and efforts. The fertilizer guidelines provided with the soil test results are based on research results that are environmentally-friendly soil fertility management practices.

A soil test will assess the levels of plant available nutrients (P, K, Ca, and Mg), soil pH and micronutrients (Al, Fe, cu, Mn, and Zn) that exist in the field, garden, lawn, etc. Recommendations will include the amounts of limestone and fertilizer, if necessary, to meet the requirements of the specific plant or crop being grown. If elevated or deficient nutrient levels are indicated, appropriate information will be included with your results to address the problem.

2. Who can benefit from soil testing?
Homeowners, Gardeners, Farmers , Fruit and vegetable growers, Greenhouse Growers, Nurserymen, Lawn Care Companies, Landscape Firms , Construction Firms, Groundskeepers, Environment planners, etc.
3. How do I get a soil test kit? How much are the soil test kits, and what do they include?

Standard Soil Fertility Test Kits are available at no cost. You can obtain a soil test kit from your local ISU Extension office, or you can request with an a SPAL Order Form from

Soil and Plant Nutrient Analysis Laboratory
G501 Agronomy Hall
Iowa State University
Ames, IA 50011

Each kits includes a soil mailing bag and a submission form that needs to be filled out and sent with the sample to generate proper recommendations for your field, lawn, or garden.

4. When/how often should I test my soil?

Samples can be collected any time of year when the ground is not frozen. Soils can be tested in the spring right before planting, but fall is an optimal time especially if a soil pH problem is suspected. Amendments such as limestone or sulfur can be added in the fall as can slow release, natural organic sources of phosphorus and potassium. This allows sufficient time for reactions to occur in the soil so the pH and fertility should be at or close to the target levels by spring.

A soil test should be performed about every three years to monitor soil pH and fertility levels. However, if a large correction in soil pH or fertility is called for by the initial soil test, it is a good idea to retest one year after amendments or fertilizer additions to evaluate if the situation has been corrected. Soil sampling during the same time every year is recommended for better comparison and monitoring of the soil test results from previous years. Seasonal temperature and soil moisture fluctuations impact soil test results.

5. How long are samples held before they are discarded?
Samples are held in storage for two weeks upon completion of testing.
6. Can SPAL test my soil for heavy metals?
We often test for heavy metals, including lead under our Research category. Please check the description of our heavy metals tests to ensure we can fulfill your request. Keep in mind that you will not receive any recommendations or test results interpretations if you choose to have your soil tested through Research. However, we are not a state certified environmental laboratory. Samples with direct regulatory and/or public policy implications should be submitted to a certified laboratory.

Note: We are actively working on getting certified in various analysis areas.

7. I have some environmental samples (some soil and plant material) that I want to have analyzed for pesticide residues. Can you help?
We do not currently offer analysis of herbicide, pesticides, and other organic chemicals in various materials. A complete list of our offered analyses can be found at Research Services.
8. Does your Laboratory perform particle size analysis?
The SPAL can provide soil characterization service in addition to its nutrient analysis service. Please contact the lab for submittal form.
9. I'm not a resident of Iowa State. Can I send you some soil so that I can get recommendation on the amount of lime and/or fertilizer I should spread on my land?
You can certainly submit soil samples from outside of Iowa State, but we cannot generate recommendations for you. Recommendations are generated via a computer program that takes into account the different soil types found throughout our state. Since our program does not contain information on out-of-state soils, we cannot generate recommendations for non-Iowa State soil. If you live outside of Iowa State and you want recommendations, it is better to send you soil to your local laboratory
10. I live abroad, and I'd like to have some soil analyzed by your laboratory. I'm not interested in receiving recommendations, just nutrient concentration figures. Is this possible?
Anyone, living in the United States or elsewhere in the world can submit soil or plant material for us to analyze. International submissions are treated as regulated samples, and we will issue you a permit to accompany your sample. Please call our office to make shipping and payment arrangements.
11. I'm not a farmer, but I do have a large garden in which I grow all kinds of flowers and vegetables. Can I get recommendations on my soil?
Absolutely! And your samples will be received and treated with just as much care and attention as our farmers' and growers' samples.
12. Is the lab a certified lab?
We are certified by Iowa Department of Agriculture and Land Stewardship to perform limestone analysis. The lab also participates in a national proficiency testing program called North American Proficiency Testing Program administered through Soil Science Society of America
13. What is the turn-around time for soil samples submitted for standard fertility test packages?
Turn around time is usually between 4 to 5 business days from the time we receive your samples. However, during the spring and fall seasons, which are our busiest time, it may be slightly longer. Turnaround may be delayed if a proper submittal form is not used, inadequate sample amount is enclosed, or if we did not receive appropriate payment
14. If I send you some soil or solution samples for nitrate and other analytes (not the soil fertility test packages) determination, how soon can you get the results to me?
Our turn-around time for processing soils range from 4-5 business days for samples that require recommendations, to 2-3 weeks for soil, plant tissue and solution samples that are submitted in large volumes (> 100 samples) and require many tests. Generally, spring and fall are our busiest seasons for handling farmers and growers samples. If needed during such times, you may arrange to pay a rush fee to expedite analysis of your samples. Solution samples < 100 samples are usually processed within 7 days.
15. Who do I contact regarding my soil test results and recommendations?
Your local Iowa State University Extension office will have valuable resources and expertise to handle your questions regarding your test results. They will contact the Soil and Plant Nutrient Analysis Lab if there are questions they cannot answer.
16. How do I convert pounds per acre to milligrams per kilogram; and pounds per acre to parts per million?
2 pound per acre is equal to 1 part per million is also equal to 1 milligram per kilogram.

2lbs/acre = 1ppm = 1mg/kg

17. Do I have to use the special soil sample bags?
The soil sample bags are preferred (particularly when sending in large groups of samples). Quart-sized zip-lock style bags can be used if necessary - but if you use them, be sure to double bag the samples to prevent the bags breaking open.
18. Where can I get the special soil sample bags?
The bags are distributed free of charge at the county extension offices. Clients planning to send 50 or more samples to the ISU SPAL should e-mail the lab and request bags directly from the us.
19. Can I drop off my sample(s) at the lab?
Yes. However, the lab can operate more efficiently when all samples are delivered to the lab at the same time daily; it allows us to group samples by analyses requested.
20. Can I send my sample in an envelope?
We do NOT recommend mailing samples in manila envelopes or bubblewrap lined envelopes as the heavy soil bags will frequently burst the envelopes open. Thick padded envelopes can be used, but boxes are preferred
21. Can I put the information sheet in my sample bag, stick a stamp on the bag & mail it?
Not recommended. The bags are not strong enough to stand up to the normal shipping conditions.
22. How do I package & ship/mail my sample(s)?
Put the bags in a sturdy cardboard box and fill the empty space with packing material so that the contents don't shift during shipment. Enclose your info sheet and payment in the box - if your samples are particularly moist, you might want to put the paperwork in a ziplock. Our wax-lined bags are water-resistant, not waterproof.
23. What form and test series do I use if I want to test for contaminants like lead or arsenic?
We do offer analyses for these kinds of contaminants. However, we are not a state certified lab and do not provide interpretations and recommendations. The State Hygienic Lab associated with the University of Iowa (click here) is an excellent resource for well water analysis and lead toxicity concerns.
24. What form and test series do I use if I want to test for soybean cyst nematodes or other pests?
We do not offer analyses for these kinds of pests. SCN soil samples and diseased plant tissue samples can be submitted to the Plant & Insect Diagnostic Clinic (PIDC) in the Plant Pathology Dept, located in another building here on campus. Their contact information can be found at (Click Here)
25. What form and test series do I use if I want to test for contaminants like motor oil or herbicide/pesticide residue?
We do not offer analyses for these kinds of contaminants. There are numerous labs in and around the state of Iowa that can perform some of the other non-fertility soil analyses such as chemical drift/carryover. A list of labs currently participating in the State of Iowa lab certification program is linked below. The list includes contact names, numbers, e-mails, and in some cases websites. You will need to check with the individual labs to see if they can perform your desired analysis. This list is not a complete list of soil analysis labs in Iowa, nor are all the labs located in Iowa. However, it can be a good starting point.
26. What form and test series do I use if I want to test for the levels of nutrients in my compost or forage?
We do offer analyses for compost and forage materials. However, we do not provide any interpretations or recommendations for the data.
27. Are there other tests the lab performs that are not listed on any of the forms?
The ISU SPAL offers other analyses, intended primarily for agronomists and other researchers who will interpret their own data. We do not offer interpretation of the data, nor do we make recommendations based on the data; we only report the data. Feel free to e-mail us at soiltest@iastate.edu with questions about analyses not covered by the above responses. If we cannot perform the analyses, we may be able to help you find an alternative lab.
28. Do you accept credit cards?
No, we do not accept credit cards.
29. Do you still have a question?
Contact us at soiltest@iastate.edu