Crops take up nitrogen that is released to the soil as a direct result of several catalysts, including atmospheric deposition … soil organic matter mineralization … crop residue decomposition … and animal manure and/or inorganic fertilizer applications.

A deficiency in nitrogen causes severe damage to crop yields - and can even cause a catastrophic, total crop failure. However, an excess of nitrogen may lead to excessive vegetative growth, lodging, delayed maturity, increased disease susceptibility and low crop quality. Excesses also may contribute to acid rain, destruction of the ozone layer in the stratosphere, the greenhouse effect, an increase in chemical nutrients in surface waters, contamination of ground water, and fish and other marine-life kills, among other negative side effects.

It’s clear, then, that it’s important to growers - both from an economic and an environmental standpoint - to carefully control the nitrogen content of field soil. The ideal situation is to maintain adequate inorganic nitrogen during the growing season and to minimize the occurrence of inorganic nitrogen during the off-seasons, when nitrogen may be introduced into field soil via surface and groundwater.

The PSNT is different from routine soil tests in that nitrogen testing shows specifically when nitrogen fertilizer applications need to be adjusted to suit crop- and field-specific conditions.

The PSNT generally is most useful for confirming legume and manure nitrogen content and for determining the amount of nitrogen in a specific field. It’s especially important to do a PSNT when not enough hard data is available to determine nitrogen content using more standard techniques.

For example, a PSNT can answer a lot of questions when a grower doesn’t know the previous manure application rate or nutrient content of a particular field. It’s also useful when the stand density of a previous crop is unknown. (Stand density is an absolute measurement based on basal area, number of trees per acre or volume per acre. It reflects the degree of crowding of stems within a stand.) Another instance when PSNT is of particular value is when unusually cool weather conditions may have impacted nitrogen mineralization rates, or when excessive rainfall causes a dramatic loss of inorganic nitrogen - both of which conditions would be missed without the PSNT.

Soil samples for the PSNT generally are taken after planting, when the crop has begun its initial growth and is several inches above the ground. By this stage of the growing cycle most of the conversion of organic nitrogen sources to forms of nitrogen able to be utilized by plants has occurred.

PSNT core soil samples are collected to a specific depth, determined by the type of crop, and are collected randomly over the full field. Then, the cores are mixed to obtain a composite sub sample and are submitted to a soil-testing laboratory.

The United States Department of Agriculture (USDA), as well as local colleges and universities, will have charts and graphs for growers in all areas of the country to determine the ideal soil nitrogen content for their specific crops. The wise grower will have his or her soil undergo a PSNT to assure the best possible crop.

A soil test allows a land owner to balance the potential impact of harm from soil contamination against the cost of undertaking a cleanup operation with the advice of our soil testing lab. 

Soil testing is used as part of contaminated land rehabilitation projects to determine the presence and levels of harmful substances. A site is deemed to be contaminated when areas or the entire site has toxic chemicals in the ground that are harmful to humans or the environment at levels higher than those normally found in the region.  

Midwest Labs is able to test for the presence of heavy metals like arsenic, lead, mercury, and zinc, other toxic metals such as cobalt, beryllium, nickel, and chromium, carcinogenic solvents like toluene and benzene, oils, fuel additives, radioactives, cyanide, pesticides, poisons, and fertilizers. 

These substances can make their way into the ground from sites of heavy industry like smelters and factories, manufacturing plants, transit infrastructure like airports, docks, the roads, rail yards, and other vehicle depots, from leaking storage tanks and pipelines, runoff from agriculture, waste disposal sites and dumps, and even from commercial and residential sources.  

As well as direct exposure, contaminants can make their way into environments that have never directly housed toxic substances, by blowing onto the site from neighboring properties through the wind, or leeching into the local soil and groundwater through the underground aquifers. 

Once a soil test determines that toxic substances are present on a site, you need to consider how likely it is to affect those who come into contact with it. This depends very much on which substances are present and their quantities, where the site is, and what it shall be used for.  

Some contaminants can cause harm to humans simply by inhaling dust from the air, or by contact with the skin and mucus membranes such as the eyes and mouth. In other cases, drinking tainted water can cause health problems. Towns which have high levels of heavy metals in the environment show increased rates of birth defects, retardation of newborns, lower IQs, and increased rates of many types of cancer. 

In agricultural areas, plants and livestock can also be affected by these contaminants in the same way, and after being tainted, can pass on toxic substances to anything that eats them through several stages of the food chain.  

In residential areas where children are likely to be present, contaminated soil testing is crucial, as lower concentrations of toxins are considered acceptable when compared with zones near heavy industry like ports and rail yards.  

Moreover, children typically come into closer contact than adults with the dirtier parts of the environment by their nature, whether that means getting dirty while playing or ingesting dirt directly. 

Government guidelines for contaminated soil testing and management vary across different regions, however, they tend towards an approach of risk management: It is necessary that some areas become polluted for the wheels of industry to keep turning, so town planning focuses on concentrating heavy polluters with waste disposal, landfill, and high-risk operations like chemical factories, away from the residential and commercial districts. When soil tests show the presence of toxic substances, it does not always make sense to launch a clean up operation, at least until levels get so high as to violate EPA regulations.  

Instead, what action is to be taken depends on likely it is that the contamination will cause harm. The risk of damage to business and lives must be balanced against the potential impact of such harm occurring and the cost of remedy. 

Fortunately, there are many ways you can commence soil remediation following unwelcome test results, with potentially cheaper options available for sites that have a low risk of causing harm.  

Ideally, Midwest Labs will be able to advise you on which of these is the most appropriate for a given site.  

In extreme cases, it may be necessary to completely excavate the affected soil, and seal it in below ground pits or an alternative waste storage repository. This is the method used to decontaminate areas affected by radiation and radioactive fallout, such as nuclear test zones, and the aftermath of nuclear power plant accidents.  

Modern landfills are usually interleaved with layers of thick plastic membranes where there is a risk of contaminants reaching the groundwater, thus spreading.  

Agricultural soil affected by excessive fertilizers and pesticides can be reconditioned by flushing with large quantities of water, as the containments tend to be concentrated water-soluble salts. Some contaminants can be bound in place with the addition of cement, while other harmful substances can be broken down by burning, rinsing with biodegradable chemical solvents, or with the addition of microbial agents into the soil.

Depending on the levels and type of toxicity, a cleanup operation can involve relatively inexpensive remediation methods, such as simply rezoning and sealing affected land, or the introduction of suitable microbial agents into the soil to digest certain chemicals at one end of the scale, and at the other, total excavation and containment of affected topsoil, such as has been conducted in retired nuclear testing sites in the deserts of Australia and China. 

Before redeveloping any land after a significant period, you should consider contracting the services offered by leading soil testing company, Midwest Laboratories, in order to ascertain the presence or absence of any potentially harmful agents.  

Contaminated soil testing will reveal the presence of several types of contaminants, such as volatile compounds like acetone, benzene, chloroform, trichloroethylene, tetrachloroethylene, and toluene; other organic compounds like oils and petroleum products, PCBs, and gasoline additives; heavy metals such as arsenic, cadmium, lead, and mercury, and other toxic substances like barium and hydrogen cyanide. 

Other substances that are not strictly considered pollutants may also be found at excessive concentrations, like fertilizers, pesticides, and their metabolites. When found in sufficiently high concentrations, these can act as pollutants by changing the pH of the soil, reacting with nutrients, or rendering the ones present less readily available to plants.  

A comprehensive soil test from Midwest Labs will not only show which toxins are present, but with professional interpretation of the results, can also be used to predict what cleanup methods will be most effective. This will depend on various factors, especially the makeup and characteristics of the land, and which contaminants are present. 

For example, some contaminants will more readily adsorb to the surface of sand or clay particles, which is the way chemists describe one substance sticking to another.  

Removing them may require the introduction of a chemical agent, or might involve simply flushing sufficient water through the soil to gradually lower the level of contamination to acceptable levels.  

After any remedial action is taken, a soil test - or several if covering a large area - must be subsequently conducted to ensure that the cleanup has succeeded as planned. 

Midwest Labs can provide you instructions on how to properly collect samples for your initial test, analyze your samples with a battery of tests that will vary depending on your site, produce a detailed report based on the results, and more importantly, give you a professional interpretation of what those results actually indicate.  

From there, we can suggest a plan of action in consultation with our clients to return the land to its desired state.   

Whether that means making the land suitable for the crop or livestock of choice, getting contaminants down to safe, legal levels, or where the soil test indicates contamination is significant, but of only minor real concern, alternative measures to a full clean up, such as how to build over the affected land in such a way that it will not adversely affect human health or the environment.  

This calculation is based on the “rule of thumb” that organic matter contains 5% nitrogen. The rate at which organic matter will decompose and release nitrogen depends on many factors, but those of greatest effect are soil type, moisture and temperature. Because of this we adjust the ENR for geographical region (zones are listed on Midwest report), soil type (see Table 1 in the Midwest Laboratories, Inc. Agronomy Handbook), and crop (warm season vs. cool season).

Midwest uses ENR in computing nitrogen recommendations so that we do not over apply nor under apply nitrogen to our crops. Questions sometimes arise as to how to explain the use of the ENR to the farmer. Following is an example of how one may explain its use regarding a corn recommendation:

A 150-bushel corn crop will remove 150 lbs. per acre in the grain and 75 lbs. nitrogen per acre in the stover meaning the total crop need is 225 lbs. nitrogen per acre. If we assume we have an organic matter level which will result in an ENR of 65 lbs. nitrogen per acre, we then have to supply the crop an additional 160 lbs. per acre through fertilizer or other plant foods. Realize that the Midwest nitrogen recommendation has already been adjusted using the ENR.

Let’s further assume that we have a nitrate level in the surface soil sample of 30 lbs. nitrogen per acre. Our nitrogen requirements would not be 130 lbs. Remember that nitrogen applications of fertilizer are not 100% efficient. Nitrogen is subject to losses by volatilization, immobilization, denitrification, and leaching. We can normally assume an efficiency factor of 60% to 70% with a preplant application. With an assumption of 70% efficiency, we would have a recommendation of 185 lbs. for 150-bushel corn.

150 bu./A X 1.5 =            225 lbs. nitrogen needed
                                    -65 lbs. ENR
                                     —
                                   160
                                   -30 lbs. NO3-N
                                     —
                                   130
                                  x 70 % N efficiency factor
                                     —
                                   185 lbs. nitrogen recommendation

As you split your applications of nitrogen, you reduce your risk of loss and increase your efficiency. If you increase your efficiency factor to 90%, you would only need 145 lbs. nitrogen. This is where adjustments can be made in nitrogen recommendations which are received from the laboratory.

Another adjustment in making nitrogen recommendations would be credit for the previous crop (legume). Remember that this nitrogen is in the crop residue and roots. These must be decomposed before the nitrogen is available. If you are planting a cool season crop following a legume, no adjustment should be made as time has not permitted crop residue to be decomposed. For corn following soybeans we suggest a 20-lb. N credit and 50 lbs. for a good stand of alfalfa.

Midwest Laboratories offers four different soil testing packages, including a basic soil test, advanced soil test, complete soil test, and soil testing for homes and gardens. These packages include individual tests for the presence of quick and slow release phosphorous (P1 Weak Bray and P2 Strong Bray respectively); soil pH, which is a measure of relative acidity; levels of the available cations found in fertilizers which are essential for plant health (Exchangeable potassium, magnesium, calcium, hydrogen, and nitrates); soil nutrient retention potential (Cation Exchange Capacity); and levels of important trace elements such as copper, boron, iron, manganese, and zinc. Other tests include measures of organic matter and microbial activity, a Buffer Index report, and a measure of excess sodium and lime content.

One of the most important tests we perform is the soil pH test. pH is a measure of relative acidity running from 1 to 14, with 7 being considered neutral, lower numbers acidic, and higher numbers being alkaline. Microbial activity can occur in both acidic and alkaline soils, however, the best balance of desirable microbes is achieved in soil that is relatively neutral at around pH 7.

In chemical terms, soil with a low pH has an abundance of hydrogen (H+) ions, which carry a positive charge (cations). In acidic soils, sulfur, nitrogen, calcium, magnesium, and potassium, and phosphorous become unavailable in forms that plants can use. Soil with a pH of above 7 is alkaline, with an abundance of hydroxyl (OH-) ions. Alkaline soils tend to be deficient in important trace elements which plants need to remain healthy. Soil that is very acidic or alkaline can eventually be toxic to crops, and can cause the soil to change in such a way as to hinder crops in future years. Accordingly, we advise that you pay close attention to the pH levels of your farmland, and take preventative action before a problem develops, or appropriate corrective measures where needed.

A Cation Exchange Capacity test is a measure of the soil’s ability to retain nutrients as cations available for plant use over time. The levels of clay and other soil components will change this value. A higher value is desirable, indicating that soil nutrients will not simply be washed away during irrigation, but rather, will adsorb to clay and humus particles within the dirt. Fields determined to have a lower CEP are still useful, but may need to be monitored more closely to maintain optimal usefulness.

With proper care, it is possible to improve the overall health of a field over time by employing good farming practices such as planting alternating strips of crops, known as inter-cropping, and letting fields rest while growing nitrogen-fixing crops like legumes (peas and beans), referred to as crop rotation. Periodic soil testing will allow you to assess when the best time to take action is, and more importantly, how effective your existing regime has been.

Despite its ancient roots, agriculture has remained one of the most active scenes for new advances in science for thousands of years. Modern farmers are among the first to embrace new technologies when they first become available, and as our understanding of what soil testing and its results imply improves, so too can your response in dealing with nutrient deficiencies and chemical imbalances. Each field has a different history and characteristics, so with the health and fertility of any particular field changing across its breadth, seasonally, and over the course of years, care must be taken when collecting samples.

ENR - Estimated nitrogen release from the O.M. to the next crop. It is used as an adjustment on nitrogen recommendations. The amount used varies by geographic area and Cation Exchange Capacity.

ppm P1 - P2 - P1 is the standard Bray phosphorus extraction showing the most readily available P on pH’s 5.8 - 7.5.

P2 is a stronger extraction which picks up phosphorus loosely held in O.M. and Ca-P reserves. The difference between P1 and P2 is considered active reserve.

P1:P2 ratios greater than 1:3 indicate increasing amounts of free calcium and relate to unpredictable herbicide activities. (See Capsules #106 and #134).

ppm K - Uses a standard ammonium acetate extraction with a five minute agitation time. We find this procedure gives the most consistency over variations in environment, wet to dry and frozen samples.

K-ratings (H, M, L) reflect the relative availability of K and are related to C.E.C.

K2O recommendations will be increased on higher % Mg soils.

Soil pH - is the pH we use when referring to crop response (see Capsule #123) and general pH references. It relates to the concentration of hydrogen ions in the soil solution. More hydrogen relates to lower pH’s or more acid soils.

Some sources of hydrogen are O.M. decomposition, root absorption of cations (K, Ca, Mg, etc.), leaching of calcium and magnesium and fertilizers containing ammonia and ammonium sources of N.

Buffer pH - is only used for lime recommendations. It is an index of the lime requirement which measures a soil’s resistance to pH change. On soil reports, the M.E. of hydrogen and % hydrogen reflect the hydrogen concentration related to buffer pH.

C.E.C. - is a soil’s relative holding capacity for water, nutrients and chemicals. For a given area, the higher numbers are relatively heavier soils than small numbers (see Capsule #102). The concentration of cations or ppm of K, Ca, Mg, Na on western soils and hydrogen on buffer pH’s 7.0 and less are used in calculation of the C.E.C.

Percent Base Saturation - The percent saturation of each cation element represents the proportion of that element within a given soil system. A 70% base saturation calcium tells us that 70% or 7/10 of the cations in that soil system are calcium. The % saturation of all the measured cations add up to 100%.

It is not possible to create a perfect soil in the field. We can, however, use the information the laboratory can supply to make the proper decisions on the soil we have to work with (i.e., as percent saturation Mg increases, several conditions are indicated which should be checked out (see Capsule #104).

1. Because of the extreme weight difference per volume of soil and the shrink incurred when drying, an average conversion factor of .65 should be used to convert the ppm test readings to lbs/A. Organic Soils Weigh Less than Mineral Soils

2. Organic soils or peat “do not improve the amount of moisture available to the plant because of the higher wilting point and the marked decrease in volume weight of the soil.”

3. The Cation Exchange Capacity does not show that much difference from a mineral soil again because of the weight difference. The CEC of a muck may be five times greater than a loam soil but a fibrous peat will be about the same.

4. In most organic soils, the ideal water or soil pH range is 5.5 to 6.0. On organic soils, pH’s over 6.0 can reduce the availability of manganese, zinc, boron and phosphorus.

5. Organic soils contain large amounts of potential nitrogen. However, during a given growing season, only small amounts are mineralized into available “N”. How much is released in any year is governed by the nitrogen content itself, temperature, moisture, acidity and aeration, all of which affect soil microbiological activity. In the northern states, most organic soils respond to some nitrogen in the spring when soils are wet and cold.

6. Liming improves the availability of phosphorus in mineral soils but decreases its availability in organic soils that are low in iron and aluminum.

7. Organic soils contain low amounts of potassium. Unlike mineral soils, organic soils do not fix nor strongly adsorb potassium, so the nutrient is more mobile, especially if they receive excessive amounts of drainable water.

8. Salinity can be a problem, since organic soils often receive liberal rates of fertilizer. Critical salinity values are about twice those suggested for loam soils. Organic soils have some specific micronutrient problems. After testing and more specific information is in hand, your Midwest Laboratories representative will assist you in further interpretation.

2. Corn has approximately 20 days food reserve in the seed (2).

3. The seed’s food reserve provides energy and supports the plant through the three leaf stage or about ten days after emergence. Within this time:

a. When the shoot hits light, the secondary root system and growing point will be about 1-1/4 - 1-1/2″ below the soil surface.

b. At the growing point, the primary ear has been initiated. The number of rows and approximately the first 14 kernels of each row are also determined.

With these basic principles, let’s review some variations which can influence plant stands.
4. Planting too deep (4) places stress on seed food reserve and can relate to leafing out below the ground. If the shoot does emerge, this early stress may carry on to the harvest as a tall thin plant with a nubbin ear. Planting deeper does not move the secondary roots down; the mesocotyl (5) only becomes longer.

5. Planting too shallow (6) can move the secondary root system closer to the surface. Two primary concerns are:

1. The secondary root is closer to concentrations of surface incorporated chemicals.

2. If surface soils dry out, the young plant will show the classic stress symptoms of purple and/or yellowing. Planting in a depression when soils are mellow can result in the same symptoms and potential chemical stress as planting too shallow. If the depression is filled in by dragging, wind or water moving soil, it changes the relative position of the seed to the soil surface. As a result:

a. More stress is on the seed for reserve to push the shoot to the soil surface.

b. Visualize where chemicals are (herbicide or banded insecticides) in relation to the secondary root system which is 1-1/4 - 1-1/2″ below the shoot when it breaks the soils surface. The secondary root can be very close to herbicide and insecticide concentrations. Insecticides which are phytotoxic can increase the potential stress.

c. Under these conditions, you should expect to see hybrids react differently.