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Introduction to Soil Testing- What is It?

How to collect Soil Samples

Selecting a Soil Test Laboratory

__Testing Methods__

pH Tests

pH-Soil solution pH

Buffer pH

Phosphorous Tests including Sufficiency Ranges

Bray 1 (Weak Bray)

Bray 2 (Strong Bray)

Olsen

Mehlich 1

Mehlich 3

Morgan

Modified Morgan

Basic Cations/Nutrients Tests (Potassium, Calcium and Magnesium,

*also includes Sodium*) including Sufficiency Ranges

Ammonium Acetate

Mehlich 3

Mehlich 1

Morgan

Modified Morgan

Micro-nutrient Tests including Sufficiency Ranges

DTPA

Mehlich 3

Mehlich 1

Morgan

Modified Morgan

Other Tests (Boron, Salinity, Bulk Density, Texture/Structure- Sand silt and clay, Saturated Paste, Cation Exchange Capacity-CEC, Organic Matter, Sulfur, and Soil Carbonate content.

Miscellaneous Tests

*Test methods that are listed in all categories (Mehlich 1 and 3, Morgan and Modified Morgan) are considered "universal" tests as they can extract all nutrients- major, secondary and micro. Susceptible to the "Jack of all trades, Master of none" argument.

**THE CONDENSED VERSION**FOR USING SOIL TESTS**A SIMPLE METHOD for Determining Fertilizer Rates and Nutrient Levels to Achieve Optimal Nutrient Levels for Phosphorous and Potassium**

__Quick Digest 8 Step:__

Identify the Test method used by the Soil Test Laboratory.

In Most cases it will be Mehlich 3. Use the Mehlich 3 Sufficiency Ranges. If your CEC is Below 4, use the "Sand" ranges where noted.

Mehlich 3 Sufficiency Ranges for P and K:

P: 26-54

K: 75-176, 50-116 for sands

If Mehlich 3 wasn't used, Ammonium Acetate was most likely used for Potassium. Use the Ammonium Acetate Sufficiency Ranges. Bray 1 and/or Bray 2 was likely used to measure P if your pH is below 7. If your pH is above 7, Olsen was probably used for P. Use the appropriate (Bray 1 or 2, or Olsen) Sufficiency Ranges to be found in the thread that follows.

Ammonium Acetate Sufficiency Ranges for K

K: 100-235, 75-175 for sands

P Sufficiency Ranges

__Bray 1__(Bray P1, Bray 1-P, Weak Bray)

Sufficiency Range (ppm): 15-30

__Bray 2__(Bray P2, Bray 2-P, Strong Bray)

Sufficiency Range (ppm): 40-60

__Olsen__

Sufficiency Range (ppm): 12-28

Nitrogen is the driving force in the turf's usage of nutrients. For every unit of N the plant uses, it will use a proportionate amount of P and K. The following calculations will be based on ppm of elemental P and K with conversion to weights of P2O5 and K2O

For every pound of N applied to the lawn:

Cool season grasses will use approximately 0.3 lbs of P2O5 (or 3 ppm of P) and between .5 and .75 lbs of K2O (or 9-14 ppm of K).

Warm season grasses will use approximately .3 lbs of P2O5 (or 3 ppm of P) and .75 and 1 lbs of K2O(or 13-18 ppm of K).

1. Determine the Total pound of N you will be applying for the growing season.

2. Multiply the Total number of lbs of N by 3 to determine the total amount of P the turf will be expected to use for the season as ppm.

3. Multiply the Total number of lbs of N by 9 (for cool season turf) or 13 (for warm season turf) to determine the total amount of K the turf will be expected to use for the season as ppm.

4. Compare your soil test ppm for P and K to the appropriate sufficiency range.

5. a) If your soil test ppm value for P falls within the range, an adjustment value is 0, no adjustment.

5. b) If your soil test ppm value for P is below the sufficiency range, select a ppm value somewhere in the middle of the sufficiency range. Subtract the test report ppm value for P from your selected mid-range sufficiency range value. This value will be the P "addition" adjustment.

5. c) If your soil test ppm value for P is above the sufficiency range, select a ppm value somewhere in the middle of the sufficiency range. Subtract your selected mid-range sufficiency range value for P from the test report ppm value for P. This value will be the P "subtraction" adjustment.

6. a) If your soil test ppm value for K falls within the range, an adjustment value is 0, no adjustment.

b) If your soil test ppm value for K is below the sufficiency range, select a ppm value somewhere in the middle of the sufficiency range. Subtract the test report ppm value for K from your selected mid-range sufficiency range value. This value will be the K "addition" adjustment.

c) If your soil test ppm value for K is above the sufficiency range, select a ppm value somewhere in the middle of the sufficiency range. Subtract your selected mid-range sufficiency range value for K from the test report ppm value for K. This value will be the K "subtraction" adjustment.

7. Add the value calculated in step 2 to the value calculated in step 5 b (if applicable) or subtract the value calculated in step 5 c (if applicable) from the value calculated in step 2. If the result is zero or a negative number, the soil contains sufficient P and no P application is needed for the season. If the result is a positive number, then divide by 9. The result will be the total pounds of P2O5 fertilizer that needs to be applied for season to meet turf requirements and soil reserves. Do not apply more than 1lb/M of P2O5 within a 30 day period.

8. Add the value calculated in step 3 to the value calculated in step 6 b (if applicable) or subtract the value calculated in step 6 c (if applicable) from the value calculated in step 3. If the result is zero or a negative number, the soil contains sufficient K and no K application is needed for the season. If the result is a positive number, then divide by 18. The result will be the total pounds of K2O fertilizer that needs to be applied for the season to meet turf requirements and soil reserves. Do not apply more than 1lb/M of K20 within a 30 day period.

**A more detailed, somewhat redundant, explaination. (The "Original Condensed/Simplified" version):**Soil testing was originally aimed at helping farmers improve crop yields. 70+ years or so ago when soil tests were being developed, farmers, by necessity, applied/fertilized all of the nutrients needed for that growing season prior to planting that year's crop. It was the only time the soil was available and the fertilizer could be tilled in to distribute it throughout the soil. One and done. Through studies, agronomists developed a data base that become the nutrient level ranges within which crops performed well. Regional testing by local University agronomists could narrow the spread of these ranges based on soil and climatic conditions particular to a region or State, but adjustments were still necessary to find the optimal nutrient level (defined as a point where further additions showed no further improvement) for each nutrient for a particular field and crop. Turf specialists have built on this model to develop turf grass sufficiency range levels.

The take away: range levels are intended to reflect the amount of nutrients needed to supply a crop/turf grass with sufficient nutrients for the WHOLE growing season.

Sufficient means acceptable, but not necessarily optimal. Optimal, the point at which increased amounts do not improve performance, can be defined as ensuring that the turf has all of the nutrients it needs for the level of performance we subjectively desire. How can we fertilize for optimal, avoid deficient, avoid excessive and be good stewards of the environment?

The Rational:

During my research, I kept coming across a turf grass fertilization method called the Minimum Level of Sustainable Nutrients (MLSN). Minimum? Sustainable? No thanks and I blew it off. A couple of years ago, I revisited the MLSN method (http://files.asianturfgrass.com/mlsn_cheat_sheet_us.pdf) and some tweaks suggested by a number of other specialists (like https://turf.unl.edu/NebGuides/g2265.pdf and more recently http://www.turfhacker.com/2018/03/mlsn-math-step-by-step.html) in depth.

It's simple and logical. It just makes sense.

Before we proceed with the Simplified method, we need to address a couple of points, including the not so simple issue of soil pH. Because pH has a massive influence on plant/turf nutrient availability, if it is or even CAN be modified, it should be the first thing adjusted. Generally, turf will perform well in a pH of 5.5 to 7.5 Even pH soil levels up to 8 can produce great turf. Nutrients are most available when soil pH is between 6 and 7. Refer to the in-depth guide below for guidance in making pH adjustments.

In order to keep the simplified method simple, it will address only those nutrients where optimal levels are most likely to have the greatest impact on turf performance. NP&K are used by all turf plants in far greater quantities than any other nutrient. Due to shear volume of usage, NP&K have the greatest influence on turf performance. That is why they are labeled the primary or major nutrients. More often than not, poor turf grass performance is due to shortages in one or more of the primary nutrients. Consequently, in the majority of cases, applying and maintaining sufficient quantities of the primary nutrients for the quantity of N applied will improve turf performance as well as provide the turf with the optimal amounts of major nutrients needed to achieve maximum turf grass performance.

As long as a soil test reports some value for the trace/micro/minor nutrients, leave them be for now. Do not adjust them unless there is some persistent visual indicator (deformed turf plants or unusual leaf color) that further researching indicates might be micro nutrient related. Even then I would confirm a micro deficiency with a tissue test prior to making any addition. Turf grasses are very efficient at extracting sufficient micros. In 17,000 soil tests, PACE turf never found a soil with detrimentally insufficient micro levels. If they are high, there isn't much of anything that can be done to lower the levels. Fortunately turf grasses are fairly tolerant to higher levels. Refer to the in-depth guide below for guidance in modifying micro/trace nutrients.

Ditto for making adjustments to improve soil tilth or for adjusting nutrient balance ratios, Those are items that will require referring to the in-depth portion of this guide for modification and don't qualify as simple.

Same for Ca and Mg. They are not included in the Simplified Method.

Ca and Mg are not commonly deficient but if they are, you will need to refer to the in-depth guide. Their correction can become a bit complicated as often the correction of another soil characteristic may involve adding Ca and/or Mg to the soil (pH as an example). In any case, they are not part of the simplified method.

Back to the simplified method:

That leaves us with N, P, K and S. These are the nutrients of greatest plant demand, most likely to deplete and be in need of replacement, and which are commonly contained within readily available fertilizers. We will also consider S, and Fe shortages as those nutrients are often contained in NP and K fertilizers and can influence which N, P or K fertilizers are selected, bought and applied. However, targeting and modifying for specific values for S or Fe, does not qualify as simple. Refer to the in-depth guide for guidance.

In a nut shell: Nitrogen is our primary turf grass growth regulator. Nitrogen applications increase the rate of growth, color, turf lushness and determine turf plant demand for the other primary, secondary and micro nutrients. Turf grass will use about 0.1 - 0.15 lbs of phosphorous and between .5 and 1 lb. of potassium for every pound of nitrogen that is applied (Note: Research has shown a direct relation between turf tissue N values and P and K values; those studies are the basis for these calculations and have proven to correlate quite well). The turf will draw these nutrients from what is already in the soil, from applied fertilizer or some combination of the two. Based on that relationship, If we apply 1#/M of nitrogen on May 30, September 1, October 1, November 1 and on December 1 (the winterizer) for a KBG lawn, that is a total of 5#/M of nitrogen for the season. Therefore, the turf should consume about .5#/M of phosphorous for the season (5#/M of N X 0.1 = 0.5#/M of phosphorous) and 2.5#/M of potassium (5#/M of N X 0.5 = 2.5#K/M). Those are the amounts that should be supplied over the season through fertilization to meet turf demand.

How will that result in optimum levels? What if those applied amounts aren't enough to be optimal for my turf? What if those applied amounts are more than needed?

This is where the results of the soil test are employed. A soil test reports the amount of each nutrient already present in the soil that is/will be AVAILABLE for the growing season (it is

__not__a measurement of the

__total amount__of a nutrient in the soil,

__again, I repeat, it is the quantity of nutrient__) to the turf for the growing season. As some soil specialists suggest, think of these soil test values as being stored in the soil. A "bank account", an insurance policy, or a rainy day fund from which withdrawals or deposits can be made. If the soil test nutrient values fall within the recommended sufficiency ranges (or at least above MLSN minimums) we are good to go. If the 0.5#/M of P or the 2.5#/M of K that we applied turns out to be insufficient for the turf grass demands, the turf will withdraw any shortage out of the soil "bank." In other words, the optimal value is always available to the plant. If the 0.5#/M of P or the 2.5#/M of K that we applied turns out to be more than what the turf grass needed, the excess amount will be stored/deposited in the soil "bank". Either way, a subsequent soil test will reveal if nutrients were taken out of the soil or deposited in the soil and we can make adjustments in next year's fertilizer application to keep the soil "bank" sufficient (within the ranges) to supply optimal nutrient levels to the turf and avoid any deficiency or excesses by staying within sufficiency ranges.

**available****The EASY, SIMPLE Method, How to use:**

1. The Soil Test

2. Determine the test extraction method used. In this case it is Mehlich 3

3. Pull the Sufficiency range values for the test method from the in depth guide.

In this situation:

With a CEC of >16, this is not likely a sand, so we will not use "sand" values. If CEC is less than 6ish, then you the "sand" sufficiency ranges.Mehlich III (M3)

Ranges (ppm)

P: 26-54

Ca: 500-750

Mg: 70-140, 60-120 for sands

K: 75-176, 50-116 for sands

Na: unreported/N.A.

S: 15-40

Fe: 50-100

Cu: 0.4-2.5

Zn: 1-2

Mn: 4-8, 8-16 for pH >7

B: unreported/N.A. (update: per PACE and R. Carrow: 0.4/0.5- 1.5)

4. Compare the ppm values for each nutrient on the soil test report to the sufficiency ranges. Make note of all nutrients falling outside (above or below) range. If after achieving optimal P and K levels, the turf is still performing poorly, you will want to do further investigation of each deficient nutrient to eliminate it as the source of the issue. But:

__Our goal is to determine the amount of fertilizer necessary to obtain optimal available primary nutrient levels and turf growth.__

**Period,**so we limit our focus to:P: 26-54 Soil test reported value: 23, just slightly short of range--adjust.

K: 75-176, 50-116 for sands Soil test reported value: 80, within range, but at lower end. adjust?

S: 15-40 Soil test reported value: 9, low, adjust.

Fe: 50-100 Soil test reported value: 225, high, but not likely to be detrimental and no adjustment needed.

*TMI: For reference when reading the paragraphs below: 1# of P2O5 = .44# of P (or lbs of P times conversion factor of 2.3 = lbs of P2O5, example: 0.5 lbs of P times 2.3 = 1.15 lbs of P2O5) and 1# of K2O = .83# of K (or lbs of K times conversion factor of 1.2 = lbs of K2O, Example 2.5 lbs of K times 1.2 = 3 lbs of K2O).*

In addition, theoretically, the application of 1#/M of P2O5 will raise soil P test levels by 9 ppm and adding 1#/M of K2O will raise soil K test levels by 18 ppm.

The inverse is also true. Removing 1#/M of P2O5 from the soil will theoretically lower soil P levels by 9 ppm and removing 1#/M of K2O will lower soil K levels by 18 ppm.

In addition, theoretically, the application of 1#/M of P2O5 will raise soil P test levels by 9 ppm and adding 1#/M of K2O will raise soil K test levels by 18 ppm.

The inverse is also true. Removing 1#/M of P2O5 from the soil will theoretically lower soil P levels by 9 ppm and removing 1#/M of K2O will lower soil K levels by 18 ppm.

For a total annual application of 5#/M of N, We need to supply the turf grass with 0.5#/M of P and 2.5#/M of K. They don't sell elemental P or K fertilizer. Fertilizer manufacturers sell in P2O5 and K2O equivalents. Therefor, we will need to apply 1.15/M of P2O5 equivalent fertilizer ( 0.5#/M of elemental P is the equivalent of 1.15#/M of P2O5, see above for formula) and 3#/M of K2O equivalent fertilizer (2.5#/M of elemental K is the equivalent of 3#/M of K2O, see above for formula). We could just apply a straight nitrogen fertilizer and just let the turf get its 0.5# of P or 1.15 lbs of P2O5 and its 2.5# of K or 3# of K2O from the soil, but that would lower the soil's P levels by 21 ppm (9 ppm X 2.3# of P2O5, see formula above) and the soil K levels by 54 ppm (see formula above). This would be fine if our P and K soil levels were excessively high and we wanted to lower them back into range, but our P and K levels are already on the lower end of the ranges and we do not want to drain the "bank", empty the rainy day fund, and have no insurance policy. In fact, as our P and K levels are on the low side, we want more insurance in this case.

Therefore, we will supply the turf with the 1.15#/M of the P2O5 it will use for growth this season PLUS we will apply an additional 1#/M of P2O5 to "bank" in the soil for additional insurance by adding 9 ppm to the rainy day fund. (Eventually, and there is no hurry, it would be good to raise soil P ppm levels in the mid to high 30s. over the next couple of years) That's 2.15#/M of P2O5 in total that we will apply this season. That can be broken up and applied however we like: into 5 applications of .43#/M of P2O5 or two applications of 1.1#.M (the general rule is no more than 1# per app within 30 days for any amendment, but an extra .1 is no problem). We will also supply the turf with the 3# of K2O it will use for growth this season PLUS we will apply another 1# of K2O to bank in the soil. (Eventually, and again, there is no hurry, it would be good to have soil K ppm levels at 100-120.) That could be applied in 4 equal applications of 1# of K2O.

To improve the S levels, we will look for sulfate content fertilizers like ammonium sulfate, potassium sulfate or sulfur coated urea.

Fe is high, so no modification is required. If it was low, we would look for an N,P or K fertilizer fortified with some iron content or consider the addition of iron from another source (FAS, or Iron sulfate for example).

To a great degree the source (whether a complete fertilizer, a TNPK, separate applications of SOP or TSP, and N or some combination of synthetics and organics) of the P and K and the rates (spoon feeding or max rates) and timing of application is not important as long as the total amount calculated gets applied during the growing season.

That's it. It really is much simpler in practice than it sounds. With a little practice, you can do it in your head.