Soil Health Concepts Leading to On-Farm Prescription, Interpretation of the Haney Soil Health Tool and Phospholipid and Fatty Acid Analysis (PLFA)

As I previously discussed in the two previous articles on "Concepts to On-farm Prescription" articles, farmers need to add active carbon into their farming operation. Active carbon is produced by having a plant growing or present 365 and 24/7. That is, we need to have green plants present to intercept sun energy (photosynthesis) to transfer that sun energy to carbon in the form of sugars. These sugars are then translocated throughout the plant that ultimately leaks from the roots. These sugars are then consumed by soil biology. As carbon increases, soil biology increases. I also discussed in the last article that you need to protect carbon increases by minimizing disturbances such as tillage. Also, we need to leave the soil covered. All of these principles protect the food sources and habitat protected. Another principle of soil health is to add diversity. The additional diversity adds quantity and quality of soil biology. The last soil health principle is integrating livestock which brings manure, urine, and saliva to the crop field. These low carbon-nitrogen ratios additions also provide a short-term explosion of soil biology.

The foundation of improving soil health is to increase and protect carbon inputs while the soil biology consumes the active carbon and aggregates soil and cycles nutrients. Many farmers who practice the soil health principles see anecdotal benefits. I want to discuss in this article the interpretation of Soil Health Tool known as the Haney Test developed by Rick Haney, USDA-ARS and a biological soil health test known as Phospholipid and Fatty Acid Analysis (PLFA). I will hit the highlights of these two soil tests. I encourage readers to check out both tests on-line by typing the name of these tests to find out the steps of taking the tests and how they are performed in the lab. I concentrate on the highlights of some of the components and provide a practical discussion on how to interpret the tests.

I will be using the Soil Health Tool (Haney Test) version 4.7 in my description and interpretation. The test will provide available nitrogen (N), phosphate (P), potassium (K) amounts. This test will also provide organic nitrogen and phosphorus sources in addition to inorganic sources that normal soil tests provide. The test also provides potential savings in nutrients due to the organic sources. Farmers will need to test these amounts in plots to decide if these amounts (NPK) recommendations are practical for them. 

The section of the Haney tests that I want to focus on are the Soil Health components: CO₂-C (respiration); water extractable organic carbon (WEOC); water extractable nitrogen (WEON); the ratio of WEOC to WEON (WEOC: WEON); and Soil Health Calculation. These components are the results of farmers following the principles of soil health which will lead to better soil health functions. They are minimize disturbances, keep the soil covered, keep plants and roots growing, and add diversity. A fifth principle is integrate livestock.

The respiration test is a measurement of microbial activity in the soil and is related to soil fertility. In most cases the higher the number in respiration, the higher the fertility of the soil. Respiration measures the activity of soil microbes which provides consumers for the WEOC. Just raising WEOC does not improve soil function. However, we need consumers to decompose the WEOC to see soil function improvements such as better soil aggregation resulting in better soil structure and better nutrient storage and cycling. Again, by reviewing some of the findings in Tennessee from this test, we see respiration increasing around year three and certainly in year four. We usually see a dip in WEOC as these populations increase and digest the WEOC. In most cases we see an equilibrium and WEOC will then increase gradually along with steady increases in soil biology. What this means to farmers is they need to continue to tweak cover crop mixes and crop rotations to continue these increases. Remember the worst thing that can happen is to not have growing green plants. Carbon must be replaced annually. We have seen losses in soil aggregation in one year when plants are not present. I am going to make this plain and simple. You must have green plants and roots growing to increase carbon. You must increase carbon for soil functions to improve.

The first component I want to discuss is the water extractable carbon (WEOC). The WEOC is about 80 times less than total soil organic carbon (soil organic matter). Rick Haney explains that % of soil organic matter is the house where WEOC is the food. Farmers who practice the five soil health principles will increase carbon which in this test is food for microbes. We all know that food is essential for human existence. It is the same for soil biology. We in agriculture must produce food for soil biology to thrive and do their job in improving soil function. Where I have seen Soil Conservation Districts using this test, we normally see an explosion of WEOC in the first three years when adding cover crops and practicing the five principles of soil health. This carbon increase will show results in soil function such as better water cycling in the first three years, better water infiltration. Farmers normally experience substantial increases in water infiltration due to these increases in WEOC. One of the reasons for this is we get to approximately year three, we see an increase in CO₂-C or respiration, which correlates to better soil aggregation. 

The second component, respiration is the amount of CO2-C released in 24 hours from soil microbes after the soil sample is rewetted which occurs naturally in the field with a measurable rainfall event. To improve soil function such as water infiltration, carbon must be produced. As carbon is abundant and is diverse (from many plant sources), soil biology will thrive in both numbers and quality or diversity. About 95% of soil functions are influenced or affected by soil biology. So, it is a big deal to increase respiration as shown in the Haney test. We need consumers to eat, digest, and respire. Sometimes carbon levels are in equilibrium before we see gains. I speculate that is because soil biology is increasing and consuming the carbon. As the soil biology reaches an equilibrium, carbon continues to increase but probably on a less steep growth curve. As we reach year four and five, we see a lot of anecdotal improvements in soil such as infiltration, earthworm casts, more consistent yields, residue consumed more quickly. 

The third component of the Haney test is WEON, which is water extractable nitrogen. Nitrogen and carbon are separated in laboratory analysis, but in nature thy exist in a molecule together. Nitrogen is released as carbon is consumed and decomposed. The higher the quality the carbon, the more N is released. The difference between a early soil health system and one that is five years or more is nutrient cycling. As the system matures, that is carbon is increased and carbon sources are diverse, and soil biology is diverse and numerous nutrient cycling is more abundant. Nitrogen is much more available as organic N is mineralized to ammonium and nitrates both are plant available. Nitrogen is more available as a fourth component in the Haney test is measured and that is C:N ratio which is carbon to nitrogen ratio. 

As the system matures and soil biology readily breaks down carbon, nitrogen is released more readily due to a lower C:N ratio. Farmers will need to keep tweaking their cover crop mixes. May need to decrease C:N ratios early when beginning and increase it as soil biology increases. Farmers can increase C:N ratios by two ways. One is the mix itself. More grasses or higher percent of grass to legumes will add carbon to the system for soil biology to break down and release N. Another way is let the mix grow later to near head stage or bloom stage.

The last factor or component in the soil health portion of the soil health tool is soil health calculation. All of the above components are considered with equations to give a relative soil health calculation. This number is dependent on WEOC increasing with respiration and WEON being released due to C:N ratio.  For example, Farmer Adam has higher WEOC in year 2, but CO₂-C is low, and C:N ratio as 15 to 1 with relative low N released, soil calculation will be approximately 9. Farmer Allen has higher WEOC in year 3, and has higher CO₂-C. The higher respiration will break down carbon and release N more readily. The C:N ratio is lowered with more N released due to higher soil biology activity. The soil health calculation would be somewhere around 15-16. As all factors improve soil calculation will increase.

The Haney test provides cover crop recommendation as far as % grass to legumes to assist farmers in developing mixes. This is simply a guide to show if biology is low and need easily digestible carbon or that the population is growing and need more carbon. Early on, a recommendation may be 40% grass and 60% legumes (Low C:N). Then you might see 50% grass to 50% legumes. As the respiration numbers increase and C:N ratio reduces then grass recommendation will increase. I have seen recommendations as high as 90% grass and 10% legumes. These farms will show high soil health calculation, maybe as high as 20. So, your first year in cover, you will receive 40% grass and 60% legumes. This means farmers need a lower C:N ratio. As the system matures, the grass recommendation or a higher C:N ratio will be shown on the Haney Test.

 A screenshot below illustrates my explanation. Note the fourth row with high respiration and high organic C (WEOC) with a soil health calculation is 23.78. That soil is going to function at a higher level than the other rows shown on the spreadsheet. 

Note from the above screen shot that the last entry has higher respiration with higher WEOC, adequate N released with about the same C:N ratio, but a higher soil health calculation. Note, the lower percent of legumes and higher grass recommendation. This is a guide to add higher C:N ratio as soil biology increases in quantity and quality.

Coffee County Soil Conservation District in Tennessee received a grant from Tennessee Department of Agriculture to test many fields using the Haney Soil Health Tool. They also tested some soils that added livestock for short-term grazing. These fields showed much higher respiration rates. So, grazing can add low C:N ratio sources that will provide temporary increase in biology activity.

Bottom line to readers, we want carbon present, increasing to the point that soil biology explodes in populations. As carbon is decomposed and C:N is lowered and more N is released, soil function or soil health is improving. All of this depends on carbon being produced, keep plants growing, keeping the soil covered, minimize disturbances, protecting the carbon produced, and adding diversity.

Haney test shows components like carbon and how it relates to N and respiration. The respiration tells of activity but what activity? What about specific groups such as arbuscular mycorrhiza? We hear so much about the need to improve fungi in agricultural fields. Some of these trends can be shown with the next test that I will discuss.

The Phospholipid Test (PLFA) is a biological analysis that provides farmers information on microbial biomass and functional groups that are important in biological processes that improve soil function. My experiences come from interpreting PLFA from Ward Labs, Kearney, Nebraska. I am not promoting Ward Labs over other ones that provide soil test for PLFA. I am just familiar with their tests and interpretation (Wardlab.com, PLFA Information).

As already noted, soil biology is very complex and important to improving soil health. When soil organisms die, fatty acids are found in membranes. Soil sampling can capture these characteristics by extracting the PLFA. The PLFA results can estimate total soil microbial biomass and functional groups. As farmers follow the four and sometimes the five principles of soil health, soil carbon increases and the corresponding food web that thrives from carbon. 

Below is a chart showing total soil microbial biomass in ng/g of soil. Conventional tillage will have a lower total microbial biomass at approximately 1,200 ng/g. Whereas, long-term no-till with cover crops will exceed approximately 3,500 ng/g. Adding manure and integrating livestock can increase numbers by approximately 2,000 ng/g.

The second column below considers functional groups of soil biology. This is where diversity is important. As farmers can diversify crop rotations then this number will increase. I realize markets dictate crop rotations. Some farmers are establishing their own markets and diversify somewhat. However, if farmers cannot diversify their commodity crops, farmers can use a multi-species cover crop mix of five species or more to add diversity. Again, the number s below are for the Ward's version of PLFA. If other PLFA analysis are used, be sure and ask lab for interpretation. These are normally relative in comparison. The more diversity the better the soil is functioning. Diversity also provides a policing effect with the food web. that is as more diverse biology increases, problem or pest organisms are more readily controlled by the biology itself. For example, fungi can trap and be parasitic to root eating nematode.

Total Microbial Biomass

The importance of the total microbial biomass is to show populations. The greater the populations then the more consumers that the soil harbors. The test can correlate with the activity from the Soil Health Tool (Haney Test) of respiration. These show that as farmers increase soil carbon and protects those benefits by leaving the soil covered and minimizing tillage, populations will increase. Diversity is essential for quality and diversity of functional groups. Again, all of this carbon-based. We must have continuous plants/roots available to produce active carbon. 

Fungi: Bacteria is a ratio of fungi to bacteria. Agricultural fields are bacteria dominated. Farmers can change that by minimizing disturbances that will increase fungi populations. As farmers grow cover crops, fungi populations will continue to increase. Disturbance or lack of disturbance is the key. When tillage is reduced, fungi numbers will increase to break down more resistant carbon sch as cellulose. There are three broad groups of fungi. One is saprophytic. The second group is arbuscular mycorrhiza, and the third group is pathogenic. This test pertains to the first two groups. A way to counter pathogenic fungi, is to practice the four principles, especially minimizing disturbances and maximizing diversity. The literature talks about a goal for soil health should be approximately 1:1 ratio of Fungi: Bacteria. This test shows PLFA ratios of Fungi: Bacteria. Bacteria has higher concentrations of PLFA than Fungi. So a 0.3+ (see scale below) or higher is close to 1:1 ratio. Farmers will benefit by having 0.3+ because they will see corn stalks and other high residues breaking down more readily (due to saprophytic fungi). Arbuscular mycorrhiza fungi infect the carrier plant root. The fungi hyphae is like a extended root system that increases ability of roots by 10X. The hypae can reach areas of phosphorus, zinc and water that roots can never reach. Fungi Mycorrhiza also aggregates soil and helps to police the soil by being parasitic to some nematodes. Having higher fungi:bacteria is very positive for farmers.

Predator:Prey is simply a ratio of predators (protozoa) to bacteria. Protozoa feeds off bacteria. When they digest nutrients, they release them when they die. This is a key indicator of soil fertility. We need to increase predator numbers. Note that even as these ratios increase, they are still quite small due to the large numbers of bacteria compared to protozoa. Higher ratios are the goals of farmers improving their soil health.

Gram (+): Gram (-) is simply an indicator of when Gram (-) and when Gram (+) are dominate. Early season when soils are cool during a fallow period will show a greater preponderance of Gram (+). As the season proceeds, the numbers will be more balanced. Gram (-) will dominate during periods of drought or recent pesticide applications. Gram (+) representative group is actinomycetes which is a colony growing bacteria. They secrete an organic compound called geosmin. This is the sweet soil aroma we smell in healthy soils. The Gram (+) representative is rhizobia bacteria. This is the bacteria that infects roots of legumes. They fix nitrogen for plants with the trade off of carbon for energy from the plant's carbon to the bacteria. It is a nice symbiotic relationship that provides nutrients to plants. These functional groups are very important for soil function.

Research and farmers' experiences show that PLFA can be useful to show a farmer the status of their total microbial biomass and functional groups over time with different management. The last few years, the Coffee County Soil Conservation District took many samples on many fields under different management scenarios. A lot of data showed what we saw as anecdotal. The longer the system was in no-till with added multi-species the higher the PLFA as far as microbial biomass with higher fungi: bacteria, and higher predator: prey. The Haney test showed higher respiration with higher carbon at first with lower carbon once biology increased followed by higher carbon and then an equilibrium as soil biology (respiration increased. The Haney soil test soil calculation ranged from a 12 to a 24 over three years. Respiration went from 50 ppm to 350 ppm in three years. Carbon (WEOC) went from year 1 from 270 ppm to 120 ppm in year 2 to 100 ppm and back up to 175 ppm in year 3. This shows the major increases in soil biology consumed the active carbon and provided the better infiltration, more sustained yields, and much less weed pressures. The PLFA microbial biomass began in year 1 at 2,500 ng/g to 4,500 in year 3. Those fields with livestock had microbial biomass number of 6,500 ng/g. Again livestock or the additions of manure, urine ,and saliva do not raise total carbon, but it does add biological activity which quickens the process of carbon turnover and in improved soil function.

Robertson county has also done considerable testing and found similar results. These are not research plots but demonstration plots following the soil test recommendations with numerous management scenarios. They show trends. 

Haney Test in Coffee County on CO2-C and WEOC

I talked to Mr. Lance Gunderson of Ward labs about timing of sampling. The PLFA is a biological analysis, when you sample, do not leave on dashboard of truck for extended time. Sample and send or freeze and then send. Take samples for PLFA when corn is growing well. Biological conditions are ideal. I would recommend third week of May to mid-June in Tennessee. Other locations, I would recommend v-4 corn stage. For the Haney test, early harvest would be good time. The main thing is to be consistent. Keep in mind for PLFA, temperature is critical and could skew the data.

My purpose for writing this article is to show how to interpret these tools. They are tools are available to potentially inform farmers and conservationists trends of soil health. These results tend to correlate with other trends such as in-field infiltration tests, underwear being consumed in demonstrations, and shovel findings. The bottom line is if farmers increase carbon by keeping green plants growing, diversify by planting crop rotations and adding multi species cover crops, protect the benefits by keeping the soil covered, and minimizing disturbances, carbon will increase as well as soil biology. With that, we receive the benefits of those actions as seen with better soil function. Integrating livestock will increase these actions by adding bursts of soil biology.