The Haney Test or Soil Health Test is an integrated approach to soil testing using chemical and
biological soil test data. It is designed to mimic nature’s approach to soil nutrient availability as
best we can in the lab. The Haney Test is designed to work with any soil under any
management scenario because the program asks simple, universally applicable questions.
Each soil sample received in the lab is dried at 50o C, ground to pass a 2 mm sieve and weighed into two 50 ml Erlenmeyer flasks (4 g each) and one 50 ml plastic beaker (40 g) that is perforated to allow water infiltration. The 40 g soil sample is analyzed with a 24 hour incubation test at 24oC. This sample is wetted through capillary action by adding 20 ml of DI water to an 8 oz. glass jar and then capped. At the end of 24 hour incubation, the gas inside the jar is analyzed using an infrared gas analyzer (IRGA) Li-Cor 840A (LI-COR Biosciences, Lincoln NE) for CO2-C. The two 4 g samples are extracted with 40 ml of DI water and 40 ml of H3A, respectively. The samples are shaken for 10 minutes, centrifuged for 5 minutes, and filtered through Whatman 2V filter paper. The water and H3A extracts are analyzed on a Lachat 8000 flow injection analyzer (Hach Company, Loveland CO) for NO3-N, NH4-N, and PO4-P. The water extract is also analyzed on a Teledyne-Tekmar Torch C:N analyzer for water-extractable organic C and total N. The H3A extract is also analyzed on a Thermo Scientific ICP-OES instrument for P, K, Mg, Ca, Na, Zn, Fe, Mn, Cu, S and Al.
The methods use nature’s biology and chemistry, in that, the soil analysis is performed using a soil microbial biomass indicator, a soil water extract (nature’s solvent), and H3A extractant, which mimics organic acids produced by living plant roots to temporarily change the soil pH thereby increasing nutrient availability. These organic acids are then broken down by soil microbes since they are an excellent carbon source, which returns the soil pH to its natural, ambient level. The Haney Test doesn’t measure just one thing to arrive at the plant available NPK, we use an integrated approach. For example, if the soil respiration number is 80 ppm CO2 and the organic C: organic N ratio from the soil water extract is above 20:1 we credit no N or P mineralization, as the C:N ratio decreases we credit more release from the organic N and P pools based on CO2 and the lower C:N ratio. For soil with high CO2, low C:N and a high soil health score, we add an additional calculation from the organic N pool, however, we do not credit more N release than we can measure from the organic N and organic P pools.
Total N: This number is the total N from the water extract from your soil (in ppm). It contains both inorganic N and organic N sources from your soil.
Inorganic N: This is the combined amount of plant available forms of inorganic N (NO3-N plus NH4-N). NO3-N is the form of N that is easily lost from soil through surface runoff, subsurface leaching, erosion, and in water logged conditions it can revert back to a gas. NH4-H is usually quickly converted to NO3-N by soil microbes but is less susceptible to leaching. The majority of inorganic soil N is in the NO3-N form. If the NO3-N levels are high (above 50 lb/ac), then we would use grasses to convert this easily lost form of N back to the organic form.
Organic N: Organic N is the total water extractable N minus the total water extractable inorganic N in ppm. This form of N should be easily broken down by soil microbes and released to the growing plant providing minimal chance of loss since the N is bound in large organic molecules. This pool represents the amount of potentially mineralizable N in your soil.
This lists the same type of results as nitrogen but for inorganic P and organic P.
Soil Respiration 1-day CO2-C: This result is one of the most important numbers in this soil test procedure. This number in ppm is the amount of CO2-C released in 24 hours from soil microbes after your soil has been dried and rewetted (as occurs naturally in the field). This is a measure of the microbial biomass in the soil and is related to soil fertility and the potential for microbial activity. In most cases, the higher the number, the more fertile the soil.
Microbes exist in soil in great abundance. They are highly adaptable to their environment and their composition, adaptability, and structure are a result of the environment they inhabit. They have adapted to the temperature, moisture levels, soil structure, crop and management inputs, as well as soil nutrient content. In short, they are a product of their environment. If this were not true they most likely would have died out long ago, but they didn’t. Since soil microbes are highly adaptive and are driven by their need to reproduce and by their need for acquiring C, N, and P in a ratio of 100: 10: 1 (C:N: P), it is safe to assume that soil microbes are a dependable indicator of soil health. It is clear that carbon is the driver of the soil nutrientmicrobial recycling system. This consistent need sets the stage for a standardized, universal measurement of soil microbial biomass through their respiration activity. Since most soil microbes take in oxygen and release CO2, we can couple this mechanism to their activity. It follows that soil microbial activity is a response to the level of soil quality/fertility in which they find themselves.
Water extractable organic C (WEOC): This number (in ppm) is the amount of organic C extracted from your soil with water. This C pool is roughly 80 times smaller than the total soil organic C pool (% Organic Matter) and reflects the energy source feeding soil microbes. A soil with 3% soil organic matter when measured with the same method (combustion) at a 0-3 inch sampling depth produces a 20,000 ppm C concentration. When we analyze the water extract from the same soil, that number typically ranges from 100-300 ppm C. The water extractable organic C reflects the quality of the C in your soil and is highly related to the microbial activity. On the other hand, % SOM is about the quantity of organic C. In other words, soil organic matter is the house that microbes live in, but what we are measuring is the food they eat (WEOC and WEON).
Water extractable organic N (WEON): This number is the amount of the total water extractable N minus the inorganic N (NH4-N + NO3-N). This N pool is highly related to the water extractable organic C pool and will be easily broken down by soil microbes and released to the soil in inorganic N forms that are readily plant available.
Organic C: Organic N: This number is the ratio of organic C from the water extract to the amount of organic N in the water extract. This C:N ratio is a critical component of the nutrient cycle. Soil organic C and soil organic N are highly related to each other as well as the water extractable organic C and organic N pools. Therefore, we use the organic C:N ratio of the water extract since this is the ratio the soil microbes have readily available to them and is a more sensitive indicator than the soil C:N ratio. A soil C:N ratio above 20:1 generally indicates that no net N and P mineralization will occur, meaning the N and P are “tied up” within the microbial cell until the ratio drops below 20:1. As the ratio decreases, more N and P are released to the soil solution which can be taken up by growing plants. We apply this same mechanism to the water extract, as the C:N falls; we credit more N and P mineralization on a sliding scale. We like to see this number between 8:1 and 15:1.
Soil Health Calculation: This number is calculated as 1-day CO2-C/10 plus WEOC/50 plus WEON/10 to include a weighted contribution of water extractable organic C and organic N. It represents the overall health of your soil system. It combines 5 independent measurements of your soil’s biological properties. The calculation looks at the balance of soil C and N and their relationship to microbial activity. This soil health calculation number can vary from 0 to more than 50. We like to see this number above 7 and increase over time. This number indicates your current soil health and what it needs to reach its highest sustainable state. Keeping track of this soil health number will allow you to gauge the effects of your management practices over the years.
Cover Crop Mix: This is a suggested cover crop planting mix based on your soil test data. This is a recommendation of what you can do to increase your soil health number, but it is not what you have to do. It is designed to provide your soil with a multi-species cover crop to help you improve soil health and thus improve the fertility of your soil.
These numbers represent the amount of N, P2O5, and K2O present in your soil in lb/ac. The numbers include the inorganic NH4-N, NO3-N, and PO4-P from the H3A extractant, as well as the amount of N and P that the soil microbes will provide based on soil microbial respiration, the organic C: organic N ratio, and the N and P from the organic pools.
Nutrient value per acre: Current fertilizer prices are multiplied by the nutrients present in your soil. This is the value in dollars of nutrients currently in your soil.
NO3-N Only (traditional evaluation) lbs per acre: This value represents the amount of N in your soil when testing for only nitrate, similar to common soil tests.
Haney Test N Evaluation lbs per acre: This is the amount of available nitrogen measured using the Haney Test and is the same as the available N value on the report.
Nitrogen Difference lbs per acre: This number represents the difference in the amount of nitrogen we found using the Haney Test compared to the NO3-N only approach.
Nitrogen savings per acre: This value represents the amount of nitrogen saved in dollars per acre when using the Haney Test compared to traditional testing measuring only NO3-N.
Fertilizer Recommendations: This table provides recommended values for various plant essential nutrients in lbs per acre that your soil needs to produce your stated yield goal for a specific crop. You must provide a crop and yield goal for each sample in order to get recs.
Additional information is available on the website at www.wardlab.com and new information may be added as it becomes available. Any questions regarding soil health testing may be directed to firstname.lastname@example.org.
Listed here are general guidelines to sample for the Haney Test or Soil Health Test:
If combining Haney analysis with PLFA, please refer to the PLFA sample submittal instructions and follow those guidelines for submitting one sample for both tests.
Additional information is available on the website at www.wardlab.com and new information may be added as it becomes available. Any questions regarding biological/soil health testing may be directed to email@example.com.
|1:1 Soil pH:||The pH of the soil using a 1:1 ratio of soil and water. We may have to add lime to adjust pH if the value is below 5.5 for most crops.|
|1:1 Soluble Salts (EC):||A measure of the electrical conductivity of the soil based on the amount of soluble salts at a 1:1 ratio of soil and water expressed as mmho/cm.|
|Organic Matter:||This is the total soil organic matter expressed as percent loss on ignition (%LOI).|
|Soil Respiration/One Day C/Microbial Activity:||This number is ppm CO2-C released in 24 hours by soil microbes after soil has been dried and rewetted. This is a measure of microbial activity in the soil and is highly related to the fertility of the soil. In general the higher the number the better. This value can range anywhere from about 0 to over 400, but we typically don’t see values higher than 200 for most soils and management scenarios. The rankings would be as follows:
0-15 Very Low
30-50 Slightly below average
50-70 Slightly above average
100+ Very High
Notice that we do not list a true average because these rankings are on a sliding scale, which is dependent on soil types and climate. Sandier soils or dryer climates tend to score poorer. Therefore, we need to focus on the relative differences between samples and track change in time as a response to management rather than be entirely focused on one number.
|Total Nitrogen:||The total water extractable N (WEN) from your soil expressed in ppm.|
|Organic Nitrogen:||Organic N is the total water extractable N (WEN) minus inorganic N (NO3 and NH4) in ppm. The organic N pool is replenished by fresh plant residues, manure, composts, and dying soil microbes.|
|Total Organic Carbon:||The total water extractable organic C (WEOC) from your soil expressed in ppm. This pool of carbon is roughly 80 times smaller than total soil organic C pool (% organic matter) and reflects the energy/food source that is driving your soil
|Nitrate-N:||The amount of NO3-N extracted from your soil using H3A extractant expressed in ppm N.|
|Ammonium-N:||The amount of NH4-N extracted from your soil using H3A extractant expressed in ppm N.|
|Inorganic Nitrogen:||This is a sum of the NO3-N and NH4-N expressed in ppm N.|
|Inorganic Phosphorus:||The amount of P in your soil extracted with H3A and measured as orthophosphate (PO4-P) expressed in ppm P.|
|Total Phosphorus:||Total P is the amount of elemental P in your soil extracted with H3A and analyzed on ICAP in ppm P|
|Organic Phosphorus:||Organic P is the total P minus inorganic P expressed in ppm P. This represents P that is not currently plant available but may become available through microbial activity.|
|ICAP Potassium:||Is the total elemental K in your soil expressed as ppm K|
|ICAP Calcium:||Is the total elemental Ca in your soil expressed as ppm Ca|
|ICAP Aluminum:||Is the total elemental Al in your soil expressed as ppm Al.|
|ICAP Iron:||Is the total elemental Fe in your soil expressed as ppm Fe.|
|Organic C:Organic N:||This is the ratio of organic C to organic N in your soil based on a water extraction. This number is used in conjunction with the Soil Respiration CO2-C number to estimate potential N and P mineralization. It is also used in the soil health calculation. This number is a very sensitive indicator of the health of your soil and has a significant impact on the activity of soil microbes. We like to see number below 20. When the value is above 20, we will suggest a higher percentage of legumes in the system to help build organic N and lower the ratio over time. Ideally, we want to see this value between 8 and 15 and we consider it to be perfect between 10 and 12.|
|N – Mineralization:||The amount of N being released through mineralization expressed in ppm N. The Nmin estimates how much N will be immediately available to the crop based on microbial activity and the organic C:organic N value. When the organic C:organic N value is above 20, N will remain tied up in the bacterial biomass and won’t be released until the cell dies.|
|Organic N Release:||The total amount of N being released through microbial activity from the organic N pool expressed as ppm N. It is the sum of MAC WEON, which is the fraction of the organic N pool acted upon by the microbes over 24 hours, and N mineralization. This value typically increases as the soil system gets healthier.|
|Organic N Reserve:||The amount of N left in the organic N pool in ppm N following the release by microbes. The organic N reserve or organic N pool is replenished by fresh plant residues, manure, composts, and dying soil microbes.|
|P – Mineralization:||The amount of P that will be released through mineralization of organic P by soil microbes depending on their activity and the organic C:organic N ratio expressed in ppm P.|
|Organic P Reserve:||Organic P reserve is the amount of P that remains in the organic P pool following the release by microbes expressed in ppm P.|
|% P Saturation Al/Fe:||% P saturation is the amount of P divided by the amount of Fe and Al extracted from your soil. Number below 5 may indicate the need for P fertilizer.|
|Soil Health Calculation:||This number is calculated as 1-day CO2-C divided by organic C:N ratio plus a weighted organic carbon and organic N addition. It summarizes the overall health of your system based on the indicators measured in the test. The score typically ranges anywhere from about 0-30. We like to see this number above 7 in most situations, but not all soils have the same potential when it comes to the soil health score. The best way to get started is to establish a baseline of where your farm is right now. Then find one or two soils in the area (neighbor or down the road) that you think are in poor soil health based on your own observations or definitions. Then find a soil that you define as being in the best health. Try to look beyond yield when defining soil health, so this might be a fencerow or a tree line or a well-managed perineal pasture. The goal is to establish your own range based on your area’s general climate and soil types. This will also tell you where you have progressed from if you have been trying different tactics aimed at improving soil health, but it will also allow you to set some goals and realistic expectations. Again, not every soil has the same potential. Keeping track of this number will allow you to gauge the effects of your management practices over the years.|
|Cover Crop Mix:||This is a suggested cover crop planting mix recommendation based on your soil test data, the soil health score, and the organic C:N ratio. It is designed to provide your soil with a mixed species cover crop to help you balance the C:N ratio and feed the soil microbes to improve your soil health.|
|Nitrogen, lbs N/acre:||Pounds of plant available N per acre in soil. This value includes the inorganic N measured as nitrate and ammonium and the amount of N expected to be released from the organic N pool by microbial activity.|
|Phosphorus, lbs P2O5/acre:||Pounds of plant available P2O5 per acre. This value includes the inorganic P measured as orthophosphate and the amount of P expected to be released from the organic P pool by microbial activity|
|Potassium, lbs K2O/acre:||Pounds of plant available K2O per acre|
|Nutrient Value, $/acre:||Is the estimated value of the plant available NPK in your soil based on common fertilizer prices.|
|Traditional N Evaluation:||This number reflects the amount of N in lbs per acre that would have been measured using a more traditional soil test where NO3-N was the only test used for N evaluation.|
|Haney Test N Evaluation:||This number is the same as plant available N in lbs per acre and represents the amount of N measured with the Haney Test methods. It includes NO3-N, NH4-N, and the organic N release.|
|Lbs N difference:||Is the difference in the amount of N in lbs per acre between the Haney Test and a traditional soil test using NO3-N. This value typically increases with positive gains in soil health.|
|N Savings:||Is the amount of money saved on N application per acre based on the difference of N measured using the Haney Test and current N prices.|
PDF of information below: Haney Test Interpretation Guide
The Haney Soil Health Test offers a more comprehensive look at the nutrient needs and overall health of your soil system. However, it is not a complete evaluation of your soil’s health due to its lack in the direct measuring of some of the other soil health indicators such as bulk density, water infiltration rates or water holding capacity. Some of the items measured by the Haney Soil Health Test are similar to traditional tests. Soil pH and organic matter, for example, are evaluated in the same way as the more traditional soil tests many of you have used in the past. In addition, plant available nutrients such as NPK are evaluated with the same instrumentation. The Haney Test, however, uses different soil extracts, namely H3A and H2O, to determine what quantity of these nutrients are available to the crop and accessible to the microbes. Nitrate, for example, is soluble and there is little difference between various extracts. Other nutrient levels, however, will vary from traditional tests that use different extracts due to the unique ability of each extract to effectively pull nutrients out of the soil. We are currently working on a guide to help producers correlate values from the H3A and H2O extracts of the Haney Test to those of more traditional extracts such as Mehlich III, Bray P1, Ammonium Acetate, DTPA and others.
The Haney Test differs from traditional soil tests in that it also evaluates some soil health indicators such as soil respiration, the water-soluble fractions of organic carbon and organic nitrogen and the ratio between them. Finally, a soil health score is calculated based on a combination of these different soil health indicators. Below is a guideline for understanding and interpreting some of these different values.
The respiration test is aimed at measuring the amount of CO2-C a soil can produce over a 24hr incubation period following a significant drying and rewetting event. In other words, how much does your soil breathe when conditions are optimal? Most microbes produce CO2 through aerobic respiration just as we do and the more CO2 a soil produces the more life it contains or the higher the microbial biomass. This is important because it relates to a soil’s potential for microbial activity, which is tied to many functions of a healthy soil such as nutrient cycling, soil aggregate and organic matter formation, disease suppression and stimulation of plant growth.
Soil respiration readings can fall anywhere from near zero to 1000 ppm of CO2-C. However, most agricultural soils are currently degraded and do not read above 200 ppm. In general, the higher the number the better, but this can have an effect on subsequent management decisions. For example, a soil with a very low score may exhibit symptoms of slow residue breakdown. On the other hand, residue may cycle very quickly in a soil with a high score. Therefore, residue management strategies and the soil respiration score one might strive for are going to be dependent on the type of production system you find yourself in.
Below is a table showing the rankings as they relate to soil respiration. These rankings are based on my own observations and the observations shared with me by others. While I feel that these descriptions fit a lot of different production scenarios, they will not necessarily fit each unique situation. In any case, however, soil respiration is considered a strong indicator of overall soil biological function.
Soil Respiration Ranking Table:
|CO2-C in ppm||Ranking||Implications|
|0-10||Very Low||Very little potential for microbial activity; slow nutrient cycling and residue decomposition; high carbon residue may last >2-3 yrs. with limited moisture; Nearly no N credit given; Additional N may be required due to microbial immobilization|
|11-20||Low||Minimal potential for nutrient cycling; residue management can still be a problem; Very little to no N credit given|
|21-30||Below Average||Some potential for nutrient cycling; residue management can still be a problem with prolonged use of high carbon crops; Little N credit given|
|31-50||Slightly Below Average||Low to moderate potential for microbial activity; Some N credit may be given|
|51-70||Slightly Below Average||Moderate potential for microbial activity; Moderate N credit may be given; May be able to start reducing some N fertilizer application|
|71-100||Above Average||Good potential for microbial activity; Moderate N credit may be given depending on size of organic N pool; Can typically reduce N application rates|
|101-200||High||High potential for microbial activity; more carbon inputs may be needed to sustain microbial biomass; moderate to high N credit from available organic N pools may be given; N fertilizer reduction can be substantial|
|>201||Very High||High to very high potential for microbial activity; residue decomposition may be <1 yr.; keeping the soil covered could be a problem in some systems; high potential for N mineralization and N credits from available organic N pools may be given; N fertilizer reduction can be substantial|
You will notice that no ‘true’ average is given in the table above because the rankings are on a sliding scale and are somewhat dependent on soil type and climate region. Soil and farm management does, however, influence soil respiration scores regardless of what type of soil and climate one has to work with, but much like yield potential, we must work within reasonable expectations for a given area. In general, cold or arid climates and/or sandy or extremely high clay soils will not usually perform as well as regions with abundant moisture and/or a longer growing season. For example, a soil that has a respiration reading of 50 from New Mexico might be interpreted as above average or even high for that region. Whereas a soil that scores the same from central Iowa might be interpreted as below average for that region. A soil that scores below 10 or above 200 is considered to be very low or very high, respectively, regardless of these other aforementioned factors.
Soil respiration values can change with the growing season and environmental conditions. The variability or swings in respiration values are typically greater in poor to marginal soils due to these soils having less ability to buffer against disturbance and times of fewer carbon inputs such as fallow periods. On the other hand, soils that are healthier often exhibit the ability to sustain a higher microbial biomass or respiration value during times of drought or extreme temperature. In other words, a healthy soil becomes more resilient to environmental conditions and disturbance. In either case, it is important to sample at the same general time each year or at least under the same general soil conditions, especially when tracking change in soil respiration over time as indicator of overall progress.
Water Extractable Organic Carbon:
The water extractable organic carbon or WEOC is a measure of the organic carbon or food that is most readily available to the microbes. The WEOC is a smaller fraction of the total soil organic matter (SOM). The size of this pool can reflect the quality, rather than just the quantity, of the organic matter present in your soil system. Generally, the higher the number the better because there is more food or energy available to drive the microbial system. However, we want there to be a good balance with organic nitrogen as you will see covered in the sections below. There is not necessarily a direct relationship to organic matter content. We see soils with 2% SOM have over 400 ppm of WEOC and soils with 4% SOM have less than 200 ppm WEOC. However, it is more difficult to sustain a larger pool of WEOC without a moderate to high level of SOM.
Most agronomic soils that we have tested so far fall in the range of 50 to 800 ppm with a majority of those soils falling between 100 and 300 ppm. Typically native and perennial systems have higher WEOC values compared to row crop systems. This does not mean, however, that row crop systems cannot achieve higher values for WEOC. Inputs such as manure, compost or cover crops can increase carbon loading and cycling leading to higher WEOC levels.
WEOC values also fluctuate throughout the year. Typically, in late winter and early spring we see values climb as freezing and thawing events help with mechanical breakdown residues and the release of carbon from soil aggregates. There is less microbial activity this time of year across many regions due to colder soil temperatures and the carbon is allowed to build up in the system. As soil temperatures rise in the spring we usually see a dip in WEOC values because microbes are utilizing this food source faster than it is being resupplied to the soil. As we move into the growing season plant roots begin to leak more carbon into the system and we see a slow increase in WEOC until soils reach an equilibrium between carbon supply from the growing plants and past crop residues and microbial consumption. When annual crops reach maturity in late summer to early fall there is a large carbon influx from the roots due to root sloughing and the eventual breakdown of the root system. The WEOC values will then slowly decline as soils cool or moisture becomes more limited and the microbial activity slows to start the cycle over again through winter. Exactly when and how long each of these phases will last depends on your current soil health level, growing season, overall climate and production system. Furthermore, this cycle is more pronounced in conventional row crop systems.
Microbially Active Carbon (%MAC):
Microbially active carbon or %MAC is how much of the WEOC pool was acted upon by the microbes measured as soil respiration. If this value is below 25% this tells you that WEOC is probably not the factor limiting your soil respiration. Perhaps it is the soil’s overall fertility, prolonged cold temps or drought that is limiting microbial biomass. On the other hand, if the %MAC value is above 80% this might tell you that WEOC could become limiting to microbial respiration soon and your management focus should be on introducing more carbon into the system. Ideally, I like to see a %MAC value between 50 and 75% for most production systems. This generally tells you that the soil has a good balance of fertility and WEOC to support microbial biomass, but you are not limited by your WEOC pool. This value, however, should be taken into context and we still need to look at the respiration and WEOC individually to gain a better understanding of the overall status of your soil.
Water Extractable Organic Nitrogen:
The water extractable organic nitrogen or WEON represents the pool of organic N that is available to the microbes. Think of organic N as amino acids and proteins, which are linked to the carbon or food that the microbes are eating. Much in the same way we measure protein in the foodstuff for livestock, the Haney Test is measuring the amount of protein available to the microbes. Feeding the microbes an N rich food source, such as manure or a low C:N ratio cover crop, allows them to better carry out many important functions in the soil that can benefit the crop and your pocketbook. One of these functions is N mineralization or the conversion of organic N into plant available forms such as nitrate and ammonium. In a healthy soil with greater biological function this can lead to a reduced need for synthetic N fertilizer.
We have found soils to contain anywhere from 5 to 100 ppm WEON with a majority of soils falling between 10 and 30 ppm. Remember that 30 ppm is equivalent to nearly 60 lbs of N to the acre at a 6-inch sample depth. As with the WEOC, the higher the value the better in most situations, but we do not want to disrupt the balance between WEOC and WEON.
Organic C to Organic N Ratio:
This is the balance between the WEOC and WEON and it is expressed as the C:N ratio on the Haney Test report. Organic C and organic N are intimately tied together, and both are required to help get the optimal function out of your soil system. A soil that has very high WEOC with little WEON has a lot of energy present for the microbes, but the quality or nutrition of that food is low. Think of an energy drink or feeding wheat straw to cattle. On the other hand, a soil with very low WEOC and high WEON has a lot of N available to the microbes but very little energy value to help carry out important functions. Think of a multivitamin or feeding only a mineral supplement to cattle. All living things require a balance of energy and nutrition.
It is very important to note that there are a lot of different C:N ratios discussed in agriculture. This particular C:N ratio is that of the water extract performed as part of the Haney Test. This ratio is not the same as the total C:N ratio of your soil or the manure or cover crop you are using or even the C:N ratio of the organic matter in your soil. Decomposition and breakdown by microbes reduces the C:N ratio of the starting material. For example, corn stover has a C:N ratio of nearly 60:1. On the other hand, SOM has a C:N ratio between 10:1 and 12:1. If the corn stover is going to become part of the soil organic matter the microbes have to break it down to a ratio of nearly 10:1. They achieve this by converting carbon in the corn stover into microbial biomass and by releasing most of the carbon as CO2 (remember soil respiration). The water extract on the Haney Test is measuring part of this transitional process between the initial breakdown of residues and the product of more stable SOM. The higher the starting C:N ratio generally the longer it takes to accomplish this goal. This is one reason why high carbon crop residue lasts longer in your fields than low carbon residue. We can use lower C:N ratio inputs such as manure and legume/brassica cover crops to help speed this process or we can use higher C:N ratio inputs to slow this process. We will discuss this more in another section below.
Below is a table showing the rankings as they relate to the C:N ratio. The management needs listed are not the only solutions used in correcting for or maintaining the desired C:N ratio, but these are some of the more popular methods when overall soil health is the goal in mind.
Organic C:N Ratio Ranking Table:
|Ratio Result||Ranking||N Implications||Management Needs|
|>20:1||Poor; Too much organic C and/or not enough organic N||N tie up by microbes: No N credit given from WEON pool||Increase legumes in rotation or covers; reduce high carbon inputs; graze longer to reduce carbon|
|Between 15:1 – 20:1||Marginal||Some N tie up; Slower mineralization; Lower N credit from WEON||Increase legumes in rotation or covers; reduce high carbon inputs; graze longer to reduce carbon|
|Between 8:1 – 15:1||Good||Less N tie up; greater potential for N mineralization; higher credit from WEON||Make slight adjustments if near the boundaries to keep within this range|
|Between 10:1 – 12:1||Ideal||Greatest potential for N mineralization from WEON pool; good balance of available energy and N for microbes||Increase intensity to drive both WEOC and WEON up together to help increase biological processes|
|<8:1||Poor; Too little organic C and/or too much organic N||Limited energy for microbial activity; N credit may still be high if soil respiration and WEON are also high||Increase carbon inputs; graze shorter to retain carbon|
Organic N to Inorganic N Ratio:
Nitrogen in your soil is found in either the organic or inorganic form. Inorganic N is usually referred to as plant available N and is often in the form of nitrate and ammonium. On the other hand, organically bound N is typically only discussed within the collective context of soil organic matter. While it is true that organic matter contains a relatively large amount of organic N at nearly 1000 lbs for every 1% SOM, most of this N is relatively stable and hard to access by soil microbes, especially within a time frame that is helpful to the growing crop. More importantly, if we mine N from the SOM we must destroy the SOM. This is like trying to remove all the nails and screws that hold together your house, and to be successful, we must destroy much of the house. There is, however, a source of organic N that is in transition between plant and animal residues and stable SOM and that is the pool measured by the water extract on the Haney Test.
Most agriculture systems are out of balance when it comes to the relative amount of organic and inorganic N present in the soil. Agricultural practices have focused on large additions of inorganic N as fertilizers to increase production and yield. While this system has undoubtedly worked to boost crop yields, it has come with many costs to both your soils and the environment, not to mention your pocketbook. Overall, it is not a very efficient system and a lot of the N applied never makes it into the crop. I am not, however, saying that we should collectively stop applying N fertilizer, but there is a better way to utilize what you are paying for in fertilizer and reduce the overall need for large N fertilizer applications.
Soil systems that are highly dependent on N fertilizer additions will often exhibit a ratio below 1 between organic and inorganic N. This means that much of the N present in the soil exists as nitrate and ammonium. Microbes can utilize these sources of N, but this often results in N immobilization or tie up that is taking N from your growing crop. Soil management systems that focus on soil health and holistic management start to build an organic N pool that is greater than the residual inorganic N left in the soil. This is often done by varying crop rotations and the use of cover crops. In these systems, we start to see ratios climb above 2 and 3. I like to see the ratio above 5 and the higher the number the better. Remember that organic N, when balanced with organic C, is what helps fuel the biological system, which will in turn help feed the plants leading to a more efficient use of N.
Organic N Release:
The organic N release is the overall N credit given to your soil based on the parameters listed above. If the C:N ratio is balanced, then the amount of credit given will be dependent on the soil respiration score and the size of the WEON pool. The higher the respiration the more microbes present in the soil and the greater the potential for activity and N mineralization. Furthermore, the higher the WEON the greater the potential for release because there is more N for the microbes to access. The organic N release credit on the Haney Test, however, will never be greater than the amount of N measured in the WEON pool regardless of the C:N ratio or the respiration score. This credit is subtracted from the recommended N needed to produce the next crop based on the crop and yield goals provided by the producer.
The organic N release value is expressed in ppm, but this value can be converted to a credit shown in lbs per acre using the following equation:
Sample depth in inches * 0.3 * ppm value for organic N release = lbs of N released per A
For example, a sample of a depth of 0-6 inches and an organic N release value of 30 ppm would be calculated as 6*0.3*30 = 54 lbs of N per A credit from the WEON pool. An 8-inch sample with the same 30 ppm value would equal 72 lbs of N per A. Therefore, the Haney Test is measuring another N credit from your soil that the more conventional tests utilizing only nitrate or ammonium do not account for. In some cases, especially with soils that are deemed as unhealthy, this credit is minimal and may not have an impact on the amount of N fertilizer required. However, in very healthy and highly functioning biologically active soils this credit can have a real impact on crop production and reduced N fertility needs. In other words, some of the time, effort and money spent on making your soil better is paying you back with savings on N fertilizer.
You can see the difference between a conventional test that typically only measures nitrate as an N soil credit and the total N credits provided by the Haney Test by looking at the ‘Traditional N Evaluation’, ‘Haney Test N Evaluation’ and the ‘Lbs of N Difference’ values on the second page of the PDF report.
Organic N Reserve:
The organic N reserve is how much of the measured WEON pool is left following the credit given for organic N release. Don’t panic if you see a value of ‘0’ here. This simply tells you that you maximized your N credit from the WEON pool. A ‘0’ does tell us, however, that if you were able to increase the size of your WEON pool, that you would likely get a larger credit. On the other hand, if you have a number other than ‘0’ left in your reserve, then this tells you that if you had a larger microbial biomass (soil respiration) or a more balanced C:N ratio that you could likely get a higher credit on the release.
The soil is constantly refilling this pool with organic N by the continued breakdown and cycling of plant and animal residues. Remember, however, that you can help this process based on your management decisions and the constant addition fresh residues. It is a systems approach to building soil.
Soil Health Score:
The soil health score is a summary of the soil respiration, WEOC and WEON measured by the Haney Test and represents the current health level of your soil based on these indicators. The score is aimed at providing a producer a quick reference regarding the health of their soil compared to other soils under different types of management. The score can range anywhere from 0 to 50, but most soils do not score higher than 30. In general, the higher the score the better. We like to see the score above 7, but 7 is simply a starting point. To get a better understanding of what your score is telling you we have to make comparisons between different land managements, soil types and climatic regions.
Much like soil respiration, land management has a profound effect on the soil health score, but it is still somewhat limited by regional constraints. Using the same example from New Mexico and Iowa above, it would be unfair to say that a soil scoring a 7 from both regions would in fact mean that both producers are performing equally well in regards to soil health using this test. A soil in New Mexico likely has a much lower soil health score potential due to environmental factors and differences in soil type whereas the soil in Iowa may have a much greater potential under the same management. The best way to determine your own potential is to find a soil in your immediate area that you believe is the poorest and one that you deem as the best. I would encourage you to look beyond yield when determining the poorest and the best soils because yield is not necessarily a strong indicator of soil health. Rather I would focus on management and ecosystem type. Perhaps a soil that is tilled too often or has a very narrow crop rotation would be classified as poor and a soil that is relatively undisturbed or native with a lot of diversity would be deemed as good. Running a test or two from these soils along with your fields of interest will help provide you potential ranges on the bottom and top end for your region. Hopefully, your soil will fall closer to the top end, but if it doesn’t, it allows you to set some management goals with realistic expectations when it comes to what you can achieve on your own farms using the Haney Test.
Cover Crop Recommendation:
The cover crop recommendation is a very general guideline for helping you balance your soil system based on some of the various numbers on the Haney Test. It is nearly impossible to provide anyone with a specific cover crop recommendation due to the large number of variables that must be considered, such as the equipment and seed available, crop rotation, climate, etc. However, we can give some suggestions for the producer starting out and wanting to know where to begin.
The percentage of grass to legumes/brassicas is based on two factors. First is the C:N ratio. If the ratio is below 8:1, then we are going to suggest a higher percentage of grasses to help increase the amount of carbon going into the system. On the other hand, if the ratio is above 20:1, then we are going to suggest a higher percentage of legumes to help provide you with the organic N needed to help you start the residue decomposition and nutrient cycling processes. If your C:N ratio falls in the desired range, then we base the mix of grasses to legumes from the soil health score. The number one factor going into the soil health score is soil respiration. Remember that respiration is an indicator of living microbial biomass. Therefore, if you have a high soil health score you likely have a high respiration value, meaning more microbes to feed and your soil’s need for additional carbon inputs is greater. This leads to a higher amount of grass being recommended in the mix. If your soil health score and respiration is relatively low, but you are still balanced for C:N, then we want to add more legumes and brassicas because you have less microbes available to breakdown residue.
The best analogy that I have been able to come up with is that building a biologically active and highly functioning soil is similar to building a good fire. If you are just starting out, you have to make sure that you have the right type and balance of fuel. In addition, you must be careful not to put too much fuel on the fire at the very beginning or you will smother the fire. In other words, too much high carbon residue is hard to breakdown quickly early on in your soil health journey and we don’t want to bury your soil, microbes and growing crop in too much residue. So, the answer is to start with crops or covers that have a relatively low C:N ratio and try not to produce a cover that is 8 feet tall. I need to mention, however, additional management decisions such as grazing can affect your approach on this as well because you can use the livestock as a wonderful tool to help manage your residue. Back to the fire. As your fire slowly builds or as your soils start to increase microbial biomass so does the demand for fuel or carbon. Now you can start increasing the amount of high carbon crops that are being introduced to the system and you can start trying to grow more biomass or letting covers get closer to maturity if time allows. Use your own observations to determine if residues are sticking around too long or disappearing before your eyes and make adjustments as necessary to your mix. Once the system is really ramped up and you have a raging fire on your hands, you might find it difficult to keep residue around as long as you wish it did. This isn’t all bad, however, as you now know that your biological system is really working for you. You are now cycling nutrients, building and rebuilding soil aggregates, infiltrating and holding more water, getting better root growth and a more efficient use of your nutrients all at a lower cost in time and money.
Additional information is available on the website at www.wardlab.com and new information may be added as it becomes available. Any questions regarding soil health testing may be directed to firstname.lastname@example.org.