Custom Soil Audits for Complete Turfgrass Diagnostics

Soil Physical Properties

ISTRC's main objective is to provide turf superintendents with the necessary information to be proactive in regards to cultural practices that affect the understanding of sand-based greens, push-up greens, and athletic fields.

Soil Chemistry
AgSource Laboratories - Harris, the oldest and most experienced independent soil-testing laboratory, provides a full-range of turf-testing services. AgSource Laboratories - Harris has been conducting testing services for all 50 states and 38 foreign countries since 1958.
Soil Biology Biomass

Earth Fort Laboratories is the world's premier Laboratory offering comprehensive Soil Food Web Analysis. Our Lab, formerly the Oregon State University Soil Microbial Biomass Service, has over 20 years providing functional soil microbiology group profiles for land managers across many industries.


Custom Soil Audit Service

 Nutrient Deficiencies

Create Clarity As You Go: Build your Turf Health looking glass with a 1, 2, 3 process

Turfgrass Soil Analysis has never played a more important role in the management of turfgrass’ than it does today.  With tightening environmental regulations and ever present budgetary constraints, today's turfgrass managers have to look deeper and wider than ever before. THP's Custom Soil Audits open new windows into the turfgrass environment, which lead the way to new and exciting tools that fit acceptable resolves for today's evolving challenges. The need for an integrated analytical method has never been more relevant.

That's why, THP has partnered with 3 of the top laboratories in their respective fields to give you that complete window into the turfgrass ecosystem:
A BIO-GEO-CHEMICAL window, that supports all 3 legs of turfgrass ecology. 

More Than Just a Test: Data Driven Directions

 Nutrient Deficiencies

First, samples are collected and sent to Agsource Harris Laboratories in Lincoln, NE; one of only six accredited labs in North America. Once data is complete, a Comprehensive Soil Report is written by the staff of THP Co.; noting deficiencies, excesses, and suggesting proven methodologies to un-tie locked up nutrition and re-balance the soil chemistry for efficient nutrient use by the plant community. Our Soil Chemistry Service has twelve years of local knowledge to access as an archive.  

 ISTRC Soil Test Second, samples can be sent to I.S.T.R.C. laboratories for a complete diagnosis of physical properties, inch by inch of the profile, to discover where and what may be limiting turfgrass performance. The I.S.T.R.C. concept of developing a better understanding of the physical properties of sand-based greens, push-up greens, and athletic fields started in the spring of 1991. Working with hundreds of courses throughout the U.S., including 6 of the top 10, I.S.T.R.C. has built a strong database of information and knowledge. There is no doubt, the most important component to a strong management program is a strong foundation.

Third, we can look even deeper to see how microbiology if affecting your soil chemistry and potential for disease pressure with an Earth Fort Microbial Analysis. This test reveals your soil micro predator/prey relationships: The key to understanding total system health.

 Nematode Damage

For instance, normally nematodes do not kill turf. Instead they can cause grass to become  weak and thin, which increases damage from other stresses. Symptoms of nutrient deficiency and rapid wilting during dry weather, can be the result of a nematode infection. Evidenced  in the adjacent photo.

THP Custom Soil Audits are flexible and can be tailored to fit any need. They can become the most comprehensive soil testing service during 'stormy weather', or can be dialled down for routine maintenance during clear sailing. The quickest return to health and productivity, we feel, is achieved through expanding diagnostic capabilities into Physical Properties and Soil Microbiology, to improve perspective and help guide an even more accurate and efficient management direction.


When Mother Nature throws you a curve ball, rely on THP to get you back on track.



The Soil Audit Explanation: Step 1- Chemistry

 Cation Exchange Capacity

There are several key factors when reviewing soil audit results. The most important is the Cation Exchange Capacity, or C.E.C. – the “horsepower of the soil” so to speak. CEC, represents the soils ability to hold positively charged nutrients, displayed as a numerical scale referencing the total possible sites (soils are negatively charged). This information is found in the middle left box of page one, next to the Percentage Base Saturation box; which represents how many of those cation exchange sites are occupied by basic (positively charged) nutrients. The CEC reading, and a target range sheet (included for your review) go a long way to understanding deficiencies and excesses in the rootzone. Using the CEC from each sample, and comparing that samples ppm readings from above, against the target range sheet allows for qualified decisions to be made with regards to nutrient excesses, deficiencies and overall product choice and design of the fertility management program. This is where the discussion typically begins. The Target range sheet, was developed from Dr. Albrecht's information, and has proven to be an excellent predicator of nutrient requirements in golf greens, sportsfields, parks and overall turfgrass environments, grown in native or modified rootzones.

The Bases (Ca, Mg, K, Na and H) become the next part of the discussion. The better balance the bases have the more nutrient will be available to the plant. As a general rule, when reviewing soil chemistry, the following percentage should be used to compare results – Ca – 65-75%, Mg – 15-25%, K – 2-7%, Na - <5%, and H - < 5%, for this geographic area. If these balances are not present, the challenge of nutrient tie up is inevitable.

 Power of Hydrogen

pH: Due the relative acidic conditions of the West Coast most soil audit results have some pH challenges. As a general rule, 6.2-6.8 is the optimum for turfgrass growth – most of the required nutrients are available within this pH range. Over the years, I have found that even higher pH readings – the 6.5 -6.8 range is more advantageous; there is less Hydrogen present at a higher pH, while still allowing turfgrass nutrients to be available.

Examples of this theory: If 2-3-4 and 5-6-7 playfields both have pH values in the appropriate mid- 6.0's, then limited Hydrogen is present. As the pH drops the H content increases; say in sample 8-9-10, this corresponds to 14% of the Base Saturation being unavailable to the plant for nutrient uptake purposes. More Calcium will alter the pH and remove some of the H in this particular rootzone; it also creates more availability.

Organic matter is becoming increasingly important, in any discussion, with regards to overall plant health. Microbial function and activity is based on organic matter content. Too much or too little are the challenges. A straight sand rootzone may struggle to maintain nutrient balance, due to excessive flushing of nutrients; where a native soil (excessive amounts of OM/clay) may not drain and compact too easily. Once again balance is the key. Organic matter discussions are dealt with in more depth with the ISTRC Sampling Method, as they test the soil column in one inch intervals. These samples (the ones that were sent to Harris Labs) are taken at a 2-3 inch depth, but the organic matter has been mixed together from each of the levels. Thus, the OM reading (next to the CEC readings on the data sheets), becomes a slightly unreliable predicator of actual organic accumulation in the viable rootzone (that area where roots have the ability to gather nutrition for the turfgrass plant).

Ca/Mg ratio: Another “measuring stick” of soil nutrient balance. As two of the largest nutrients required for turfgrass nutrition (atomic weight speaking) the balance of these two nutrients are very important. Simply take the ppm readings of Ca and divide it into the ppm of Mg. Target range Ca/Mg ratio can be found on the target range sheet (at the bottom). In the range means more nutrient availability.

Specific Nutrients and Plant Requirements:

Hydrogen ions are of no value to the plant, but are often found in soil audit results on the West coast. This is due to the acidic conditions of the soils that are used as rootzones, and the climatic region we find ourselves in. Hydrogen flushing is a necessary evil, and is done by every informed turfgrass manager. The removal of H from the rootzone in this region, is the single largest contributing factor to better balance in the PBS (Percentage Base Saturation). Again Ca, Mg and K applications will replace the H ions in the rootzone; as their atomic weights are much larger than the atomic weight of H (1). Removal of H should become part of any fertility/nutrient schedule. This is another reason to over extend the recommended amount of Ca, K and Mg from the recommendations. Better balance is the result.

Sodium levels are sometimes of concern, in certain situations. Plants do not recognize nutritional elements, and practise luxury consumption (taking up whatever is free and available). In the absence of K plants will take up any Na, due to their similar atomic weights (Na++ is 22 and K+ is 19); this leads to desiccation and wilt in extreme cases. Due to low levels of K+ (as explained above) the sodium should be mentioned in all reports. In certain situations, typical water (irrigation) may contribute to higher than acceptable sodium readings. Also the origin of the rootzone material (distance from the ocean) could contribute to the sodium content. Over time, the massive amounts of rainfall/snow melt should flush the sodium in the rootzone down to an acceptable level. Ca applications will expedite this process, when there is a requirement for Ca. Appropriate amounts of K and good irrigation/rainfall water tend to alleviate the sodium situation.

Nitrogen has long been thought of as the “solve all” nutrient. If the field is weak, yellow, or thin – apply some N and it will fix everything. There is no doubt that N is one of the most important nutrients for turfgrass managers, but not the only one. N is responsible for the photosynthetic process (plant food creation) and chlorophyll production (with Mg), but as with anything too much of a good thing can also cause problems. Too much N leads to succulent growth, weak cell wall structure, stunted roots, and clipping accumulation. Balance and types of N play a huge role in the success of nutrient management. Discussions should be had with regards to release technology, and types of N matching up with times of year.

Phosphorous is responsible for running the energy cycle of the plant (the “gas” for the engine). New shoot and root growth rely on P for regeneration (a good principal for sportsfield management). The challenge with P is to keep it soluble in the rootzone as it is a negatively charged ion and has a tendency to tie up positively charge ions (all that were mentioned above). P applications should be done light and frequently. Also as some root zones indicate, through testing, there could be huge amounts tied up; this requires re-balance as well, and is often done by using Ca.

Potassium is the only free moving ion, in the rootzone, and for this reason it moves extremely well in the rootzone. This means that irrigation, spring melt or rain events will move the K ion through the rootzone, potentially away from its area of efficacy. Better (deeper and more mass) rooting through fertility management and cultural practices, will better use the K that is applied. K (potassium) is responsible for cell wall structure, protein formation, and the overall strength of the cells within the tissue (in conjunction with Ca). Applied light and frequently the advantages will be almost immediate. Most often there is not enough K in the ground to facilitate solid protein formation which in turn creates solid cell wall construction. As we look at each surface we can fine tune K recommendations for each field.

Calcium is extremely important for overall plant function; as a “general rule”, Spring and Fall applications are made. In certain instances, and especially in the presence of Hydrogen build up in the soil, Ca applications are advantageous throughout the growing season. By continuing to provide a constant source of Ca, the plants ability to stay healthy increases, all the while, re-balancing the overall soil chemistry. Ca is responsible for plant transpiration and respiration – two important plant functions, breathing and sweating. As sportsfield use increases and acceptable turfgrass growing weather decreases these plants will attempt to protect themselves, and by not being able to carry on simple plant processes such as transpiration and respiration stresses will appear – turf thinning, yellowing of the blade, reduction of rootmass (carbohydrate storage), winter hardiness will suffer and overall strength to support the use of the surface. Planning a solid Ca schedule throughout the Spring and Summer will ensure solid strength for the Fall and Winter. By removing the H ions from the rootzone before the onset of increased stress, will also allow for more nutrient uptake to the benefit of the plant (more K for cell wall structure, etc.)

Magnesium is the nutrient responsible for (in conjunction with Nitrogen) chlorophyll production. Mg can be considered a “colour” nutrient, if you desire. In the absence of, or deficient position of Mg, all the Nitrogen applied will not create chlorophyll. Chlorophyll is the molecule that absorbs sunlight and uses its energy to synthesise carbohydrates from CO2 and water (photosynthesis).


Minor nutrients (Iron, Boron, Manganese, Copper, Zinc, and Sulfur) are required for several processes within the plant. Protein synthesis and formation, cell wall connectivity, defence mechanisms, and plant strength are a few of the many processes that minor nutrients play a role in. In deficiency positions, many of these processes are stunted or do not occur at all. Adding a “complete” minor nutrient package to any fertility choice is an extremely prudent decision. For instance, As audit reports may show, Zinc, Boron and Manganese may be in a deficient position. While, Iron and Copper may be in excess and removal from any fertilizer until it is required would also be wise. These are all possibilities from a custom blending prospective.