Checking Your Soil's "Blood Work"


June 2016

Medical doctors routinely order blood tests to track a patient’s health, to look for any impending issues, or to diagnosis a health problem. Blood calcium scores a bit above normal? It could be a parathyroid problem. Hemoglobin on the low side? It could be a red flag for anemia that you should monitor.

Soil and water tests are similar to blood work, and every bit as important. Let’s review the most common tests used by turf and crop managers, and point out some “red warning flags” you’ll want to be aware of.

The Soil & Water Test Trio

The three tests that growers turn to most often are the standard soil test, the saturated paste extract test, and the irrigation water test. These tests show the soil or water pH level, and much more.

The standard soil test is the “go-to test” for almost all native soils except for extremely sandy soils. It shows the percent of organic matter in the soil, and all the micros and other elements (calcium, magnesium, iron, manganese, copper, etc.) that are on the soil colloid. What it does not show is whether these elements are available for plant uptake.

To determine the availability of those nutrients for uptake, you can refer to a nutrient availability chart such as the one below. Just use the pH determined by your soil test as your reference point.

Nutrient Availability at Various pH Levels

The chart indicates that most nutrients have the greatest degree of availability when the soil pH is between 6.3 and 6.5. As a general rule, if a soil’s pH is 5.5 or lower, plants lose their ability to capture N-P-K, whereas if the soil pH is above 7.0, plants’ uptake of micronutrients is severely reduced.

For sandy soils, sand-based golf greens, and soilless greenhouse media, the saturated paste extract test (also called the saturated media extract (SME) test, is really good. The paste extract procedure uses deionized water to wash the nutrients from the soil, and consequently the test results show which nutrients are available for plant uptake — and which are not.

As just one example, a standard test may suggest that a soil has adequate levels of phosphorus (P). However, a saturated paste test of the same soil may indicate no P or that very little P is actually available. That’s because phosphorus — the “energy molecule” — is subject to being bound up in the soil at certain pH levels, and because of the very nature of phosphorous. (see the peculiar shape of the phosphorus bar in the nutrient availability chart above).

The irrigation water test is critically important, because you are probably using more water than any other input in your operation. It’s a good idea to test your water quarterly or more often.

If your water is high in sodium, it’s like holding a salt shaker over your landscape. The results won’t be pretty unless you actively remediate the problem. You can call me or any other Growth Products advisor to set up a complete program to remediate or prevent saline soils.

In the meantime, remember that Essential Plus 1-0-1 and BioNutrients are exceptional sources of humic acids and other organic materials that will help restore and restructure damaged soils. Also, Sodium KnockOut is a great way to reduce sodium levels in soils or bicarbonate accumulations from irrigation water. Finally, always rely on low-sodium fertilizers such as Growth Products’ The Classic 18-3-6, 14-7-14 All Purpose, and Nitro 30 SRN, which have some of the lowest salt indexes in the industry.

Water pH is also immensely important, but we’re out of room here. Give us a call at (800) 648-7626 or email us at questions@growthproducts.com if you want to talk about that, or look for our next newsletter!