Soil Samples Ameriturf
The Importance of Soil Sampling
Posted in Best Turf Management Practices, General by Curtis Williams
By DALE MILLER, National Agronomist
With 2023 playing season just around the corner for most of us – and already there for Florida and the deep south – it’s time to start planning for the warm season and taking advantage of warmer temperatures and spring transition to summer.
Soil sampling is a key part of that plan and is best done this time of year.
As most are applying fertility only as needed for carbohydrate management this time of year, the soils will level out and be at baseline levels.
That is a great time to pull samples, as little or no influence on the content gives a much more accurate account of what is in place in the soils and solution on a normal, typical, unamended basis.
As all sampling in labs is based on certain lab standards, a few things should be kept in mind as you pull them and send them in to the lab for analysis.
Labs base their reports on samples taken 6 inches deep typically. The reason for this is that lab standards normally report on an acre by 6-inch-deep basis which is approximately 2,000,000 lbs. We will not be going to get into a lot of discussion on the reasoning but it is a lab standard and worth understanding going into sampling.
Different labs also use different extractants as well. We prefer samples to be run through Logan Labs as the results of samples and known extractants are very important to maintain consistently.
If all reporting, then is reported as pounds per acre 6 inches then the only thing you need to do to convert to parts per million (PPM) is divide by 2. The opposite if parts per million are reported. You would multiply by 2 to get to pounds per acre of each element (P, K, Mg, Micros, Ca) in the soil.
Remember that there are three key parts to a sample/analysis.
• Chemically extracted, soluble paste extraction and water sample.
• Chemical extraction uses various acids to extract nutrients from the soil that is intended to simulate what happens in the soil (sort of).
• The common extractant is Mehlich 3 solution which has a pH of 2.3 that does a great and very consistent job of extracting elements in soils.
• Reported in ppm or in pounds per acre.
• The other sample pulled is the soluble paste extraction which uses water from the site sampled or de-ionized water from the lab.
It is suggested to send enough water from the site, about half a gallon or so with the samples to allow the lab to use your water to run the paste extraction.
• The samples are saturated with the water, let sit for 24 hours then the solution is vacuumed out of the soil and analyzed for soluble elements.
The last thing in sampling every year is your water.
As water is typically the biggest contributor of nutrients in your soil, especially on golf courses where you irrigate frequently, it’s always advisable to send in at least one water sample a year to determine its content.
Water quality changes and you may be in an area where your water quality is getting worse every year.
The old saying goes “As your water is, your soil will be.” That continues to ring true in low or high EC/TDS water. Water will be reported in EC/TDS (Electro Conductivity, Total Dissolved Salts) with pH shown, soluble elements and a few other areas of value when looking at analysis and planning programs.
Remember in sampling, nothing is perfect and that this is simply a baseline, a starting point to making recommendations and planning your annual fertility program.
The combination of chemical analysis, paste extraction and water sample gives you several parameters to evaluate and suggest programs from the soils/water standpoint.
Then there is your grass type, climate, play levels, budget and all the field concerns that drive the rest of your planning for annual fertility, chemical inputs.
We would suggest pulling samples at a 4-inch depth as opposed to pulling the standard 6 inch samples and then labeling the sample bag/form as such. The lab will adjust calculations based on the change. The reason for this is in Turf, we really can’t influence deeper than 4 inches and more likely the top 2 inches.
For understanding this and actually seeing this, on courses that have a few years in operation or more, mark 2-inch lines on your sampling probe.
Take 6-inch-deep samples but split these into the 0–2 inch, 2-4 inch and 4-6 inch depth. Put each in separate bags and label as such for example
• G1, 0-2 inch
• G1, 2-4 inch
• G1, 4-6 inch
If you have never done this, prepare yourself for something very interesting that seems to never get attention. The three samples will have noticeable differences with lower and lower nutrient totals, OM, etc as you go deeper.
Going back to the reason discussed – that we only impact the surface 2 inches – will become very evident.
If you want to confirm this in your applications, feel free to do this following big granular applications during the year if you make them. You will not see the soils change at depth at all.
Common sense will tell you that there is nothing making it down to the 2 inch plus level, for sure not the 4 inch plus level, even in sand soils.
As a matter of fact, do a pre-app sample, do a sample a couple weeks after the application is made then another a couple months later. Sit and ponder the values you are seeing in the reports.
For those of you with poor water quality and salt concerns, this is a very important and highly recommended sampling method that you should consider seriously, especially during the summer when rain is low, and ET is high. You will be amazed at what the results will be.
While you’re at it, if you own a moisture device or a soil EC device, take those measurements at the same levels mentioned and ponder those results as well. If you have never done this, prepare yourself. Your opinion on changing the soil or level of influence of your fertility applications and your water inputs will be impacted.
From all the above, plus your comments and input, a solid fertility program can be drawn up that will prove very successful.
Take out as much of the guess work as you can and work on set standards and your conditions will improve and remain much more consistent.
Science + Management = Control