Interpretation of Soil Test Results
Topic #3: Interpretation of Soil Test Results – [Nov. 4, 2011] Dr. Marvin Pritts, Cornell University, Professor & Chair, Dept of Horticulture (with a concentration in Small Fruit Production); Online Profile
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.).
Key Points and/or Points of Interest for Maine Cranberry Growers:
- Soil testing is a measure of plant-available nutrient levels (not the levels of nutrients that are in the soil)
- Recommendations from different soil-testing labs have different philosophies: Some want to build up the nutrient bank so there is never any risk of nutrients being limited; Others want to apply just enough to where the economic gain from additional amendment is equal to the cost of the added amendment. This would be the point where you first begin to see a ‘slow-down’ in terms of a plant’s response to having more nutrients added….the point just before a plateau, in other words. University labs tend to fall into this category of philosophy, versus labs that also sell fertilizers.
- Most response curves that have been obtained and studied have been done from agronomic crops but much less often for fruit crops!
- It is difficult to move nutrients into the root zone when perennial plants are already established.
- Cation Exchange Capacity (CEC) of Various Soil Types (ranges a lot depending on soil type): Sands = 2 to 10, Loams = 7 to 25, Clays = 20 to 40, and Humus = 200 to 400.
- Organic Matter %: Good to see organic matter % be at least 2%.
- Changes in pH: Significant time is required for lime or sulfur to affect soil pH (6 months to a year); depends on the particle size of the lime or S (smaller = faster), soil moisture (wetter = faster), temperature (warmer = faster), and aeration (higher aeration = faster).
Interpreting Soil Tests:
- Soil pH and Macronutrients (P, K, Ca, Mg) (easy to find & interpret on the test results) – Note: nitrogen recommendations are based on ‘ballpark standards’ rather than soil test findings.
- Micronutrients (harder to interpret; usually not used by labs for deciding upon recommendations [except for Boron] – mostly useful if trying to diagnose a problem)
- Boron is important for cell elongation (so helps with root growth and having a good root mass density) and in cranberries, the germination of pollen and the growth of the pollen tube are enhanced in the presence of boron. It is very mobile in the soil (and can be applied any time of the season), but à it is not very mobile in the plant (and neither is calcium).
- The best analysis in the world is useless without a good recommendation.
- Unfortunately, many analytical labs provide “general plant recommendations for field crops” without fine-tuning to the needs of specific crops. Dr. Pritts has often seen lab results for blueberry samples, for example, with recommendations that looked more relevant for corn!
- gypsum / calcium sulfate — does not raise your pH so a good choice if you are low in calcium.
- Magnesium sulfate — does not raise your pH and is a good choice if you are low in magnesium.
- Once plants are established, a foliar analysis will provide many more clues to help you diagnose nutrient problems.