Soil Testing and Sampling Procedures

Topic #2: Soil Testing and Sampling Procedures – [Oct. 14, 2011] Ms. Janet Fallon, Certified Crop Advisor; works at Dairy One Forage Lab / Agro-One Soils Lab in Ithaca, NY. — This was part of a 12-part “Soil and Nutrient Management for Berry Crops” webinar series, a project that was funded by NE SARE (Northeast Sustainable Research and Education Program), and which was organized by Marvin Pritts (Professor of Horticulture at Cornell Univ.) and Cathy Heidenreich (Extension Berry Specialist at Cornell Univ.). 

● Establishing a Sampling Schedule    ● Using the Proper Sampling Tools    ● Sampling Technique    ● Soil Test Options

Key Points:

  • Getting your soil pH at the proper level is probably the most important thing for optimum crop performance;
  • For blueberries and cranberries, you want to have loamy sand, pH between 4.2 and 4.8, organic matter greater than 4%, and low phosphorus.
  • Blueberries and cranberries thrive in soils with low CEC (Cation Exchange Capacity) (values < 18).
  • Establish a Sampling Schedule (before crop establishment); How Often? Every 2 to 3 years or as needed for troubleshooting; When? Fall is the most reliable time of the year (soil pH determination is more reliable when soil is moist when it is sampled, and, by sampling in the fall, you are allowing time to apply needed sulfur and fertilizer before spring, so the sulfur has more time to react with the soil)
  • Use the right sampling tool: Use a stainless steel probe or auger (to avoid iron contamination from rust), and use a clean plastic pail for mixing (zinc contamination can be a problem when using galvanized pails or sampling tools); Shovels or spades are “OK” for occasional use (they are slower and tougher to get a good sample); ‘Automatic’ samplers are gaining in popularity (especially with crop advisors) with precision agriculture advances; most consistent in untilled/no-till sites and for deep sampling; hand probes are best for shallow samples
  • Can use a lubricant to prevent plugging of your soil probe (WD-40, PAM, Dove Dish Soap, Silicone), unless you are worried about or wanting to test for a micronutrient deficiency such as Fe, ZN, Mn or Cu – research shows it’s okay otherwise.

Sampling Area:

  • Take sub-samples using a zig-zag pattern in each management area; 8 to 10 subsamples if < 2 acres, and 10 to 20 subsamples if > 2 acres; “More subsamples is always going to be better!”
  • Avoid unusual areas (unless sampling separately for troubleshooting or extra information)
  • Take separate samples from areas within the bed that vary widely in color, slope, soil texture, drainage, productivity or crop history.
  • Sample each ‘management area’ separately, or any single area where you suspect a nutrient imbalance.
  • Use a foliar tissue analysis, too, in conjunction with soil sampling, when troubleshooting!
  • Sampling to the proper depth is very important (surface to 8” depth is adequate for most berry crops, including cranberries)
  • Avoid sampling under extremely wet soil conditions.  Wet samples usually leak in transit, and some nutrients may undergo rapid biological transformations in very wet soils.  Also, it is hard to mix subsamples together when they are very wet, so allow your sub-samples to air-dry first (in a thin layer on a clean surface) so that you can mix them better.

Preparing Samples for Shipment:

  • If air-drying a wet sample: Do not use heat but a fan is ok to assist in drying
  • Grid sampling can be a good tool but can be very expensive when done properly
  • Complete the required information on the sample box or bag before filling it, and make sure it matches the information on the sample information sheet, and keep a copy for your own records.
  • Place about ¾ to 1 pint of the mixed sample in the sample box and then close it securely.
  • Avoid commercial paper bags or boxes (may contain boron—resulting in an artificially high measurement; may alter the results, especially if the sample is wet) – use the box or bag from the lab!
  • ‘Directed sampling’ based on topography (or troubleshooting) may be more meaningful
  • Remove large stones and break up large clods before mixing the sample thoroughly.

Handy website for discovering ‘general’ soil type info for an area: USDA/NRCS Web Soil Survey.

Different soil test methods used by some labs will extract different amounts of some nutrients (such as phosphorus or potassium), so you shouldn’t compare the raw numbers of test results from labs that have used different testing methods, or even from different labs that are using the same test, because of slight procedural differences and/or natural variability that can occur.

Summary:

  • Soil testing is required for optimum yield and quality of berries
  • Sample technique is key
    • establish a sampling schedule
    • use the right sample tools
    • sample at the correct depth
    • take enough sub-samples
    • air-dry, mix & ship to lab in box/bag from the lab
  • Select the appropriate service
    • routine or diagnostic
    • Morgan, or Modified Morgan, or Mehlich 3
    • Use the correct sufficiency ranges for the lab and services selected
  • Follow up every 2 to 3 years with soil testing and plant tissue analysis