Cooperative Extension Service
West Lafayette, IN 47907
Soils can be thought of as storehouses for plant nutrients. Many nutrients, such as calcium and magnesium, may be supplied to plants solely from reserves held in the soil. Others like potassium are added regularly to soils as fertilizer for the purpose of being withdrawn as needed by crops. The relative ability of soils to store one particular group of nutrients, the cations, is referred to as cation exchange capacity or CEC.
Soils are composed of a mixture of sand, silt, clay and organic matter. Both the clay and organic matter particles have a net negative charge. Thus, these negatively-charged soil particles will attract and hold positively-charged particles, much like the opposite poles of a magnet attract each other. By the same token, they will repel other negatively-charged particles, as like poles of a magnet repel each other.
Elements having an electrical charge are called ions. Positively-charged ions are cations; negatively-charged ones are anions.
The most common soil cations (including their chemical symbol and charge) are: calcium (Ca++), magnesium (Mg++), potassium (K+), ammonium (NH4+), hydrogen (H+) and sodium (Na+). Notice that some cations have more than one positive charge.
Common soil anions (with their symbol and charge) include: chlorine (Cl-), nitrate (NO3-), sulfate (S04=) and phosphate (PO43-). Note also that anions can have more than one negative charge and may be combinations of elements with oxygen.
Cations held on the clay and organic matter particles in soils can be replaced by other cations; thus, they are exchangeable. For instance, potassium can be replaced by cations such as calcium or hydrogen, and vice versa.
The total number of cations a soil can hold--or its total negative charge--is the soil's cation exchange capacity. The higher the CEC, the higher the negative charge and the more cations that can be held.
CEC is measured in millequivalents per 100 grams of soil (meq/100g). A meq is the number of ions which total a specific quantity of electrical charges. In the case of potassium (K+), for example, a meq of K ions is approximately 6 x 1020 positive charges. With calcium, on the other hand, a meq of Ca++ is also 6 x 1020 positive charges, but only ions because each Ca ion has two positive charges.
Following are the common soil nutrient cations and the amounts in pounds per acre that equal 1 meq/100g:
Calcium (Ca++) - 400 lb./acre Magnesium (Mg++) - 240 lb./acre Potassium (K+) 780 lb./acre Ammonium (NH4+) - 360 lb./acre
Since a soil's CEC comes from the clay and organic matter present, it can be estimated from soil texture and color. Table 1 lists some soil groups based on color and texture, representative soil series in each group, and common CEC value measures on these soils.
CEC in Soil groups Examples meg/100g ----------------------------------------------- Light colored sands Plainfield 3-5 Bloomfield Dark colored sands Maumee 10-20 Gilford Light colored loams and Clermont-Miami 10-20 silt loams Miami Dark colored loams and Sidell 15-25 silt loams Gennesee Dark colored silty clay Pewamo 30-40 loams and silty clays Hoytville Organic soils Carlisle muck 50-100 -------------------------------------------------
Cation exchange capacity is usually measured in soil testing labs by one of two methods. The direct method is to replace the normal mixture of cations on the exchange sites with a single cation such as ammonium (NH4+), to replace that exchangeable NH4+ with another cation, and then to measure the amount of NH4+ exchanged (which was how much the soil had held).
More commonly. the soil testing labs estimate CEC by summing the calcium, magnesium and potassium measured in the soil testing procedure with an estimate of exchangeable hydrogen obtained from the buffer pH. Generally, CEC values arrived at by this summation method will be slightly lower than those obtained by direct measures.
Cations on the soil's exchange sites serve as a source of resupply for those in soil water which were removed by plant roots or lost through leaching. The higher the CEC, the more cations which can be supplied. This is called the soil's buffer capacity.
Cations can be classified as either acidic (acid- forming) or basic. The common acidic cations are hydrogen and aluminum; common basic ones are calcium, magnesium, potassium and sodium. The proportion of acids and bases on the CEC is called the percent base saturation and can be calculated as follows:
Total meq of bases on exchange sites Pct. base =(i.e., meq Ca++ meq Mg++ + meq K+) saturation ------------------------------- x 100 Cation exchange capacity
The concept of base saturation is important, because the relative proportion of acids and bases on the exchange sites determines a soil's pH. As the number of Ca++ and Mg++ions decreases and the number of H+ and Al+++ions increases, the pH drops. Adding limestone replaces acidic hydrogen and aluminum cations with basic calcium and magnesium cations, which increases the base saturation and raises the pH.
In the case of Midwestern soils, the real mix of cations found on the exchange sites can vary markedly. On most, however, Ca++ and Mg++ are the dominant basic cations and are in greater concentrations than K+. Normally, very little sodium is found in Midwestern soils.
Recommended liming and fertilization practices will vary for soils with widely differing cation exchange capacities. For instance, soils having a high CEC and high buffer capacity change pH much more slowly under normal management than low-CEC soils. Therefore, high-CEC soils generally do not need to be limed as frequently as low-CEC soils; but when they do become acid and require liming, higher lime rates are needed to reach optimum pH.
CEC can also influence when and how often nitrogen and potassium fertilizers can be applied. On low-CEC soils (less than 5 meg/20000g), for example, some leaching of cations can occur. Fall applications of ammonium N and potassium on these soils could result in some leaching below the root zone, particularly in the case of sandy soils with low-CEC subsoils. Thus, spring fertilizer application may mean improved production efficiency. Also, multi-year potash applications are not recommended on low-CEC soils.
Higher-CEC soils (greater than 10 meg/100g), on the other hand, experience little cation leaching, thus making fall application of N and K a realistic alternative. Applying potassium for two crops can also be done effectively on these soils. Thus, other factors such as drainage will have a greater effect on the fertility management practices used on high- CEC soils.
The cation exchange capacity of a soil determines the number of positively-charged ions cations-that the soil can hold. This, in turn, can have a significant effect on the fertility management of the soil.
Cooperative Extension work in Agriculture and Home Economics, State of Indiana, Purdue University and U.S. Department of Agriculture cooperating: H.A. Wadsworth, Director, West Lafayette, IN. Issued in furtherance of the acts of May 8 and June 30, 1914. The Cooperative Extension Service of Purdue University is an equal opportunity/equal access institution.
I recently met with a client to update her will, and her big question was whether she still needs a trust for her daughter. Her child has graduated college, is on her second well-paying job, got married and is now a new mom. Her daughter has been maturing into a responsible young adult. But there’s another factor that weighs heavily on my client’s mind – her son-in-law and the potential for divorce.
My clients don’t want money they’ve worked hard for to pass down to their son’s or daughter’s ex-spouse, if the unfortunate reality of divorce happens.
With the current federal estate tax exemption in 2021 at $11.7 million per person or $23.4 million for married couples, setting up a trust to save taxes upon death is not as much of a driving force as it used to be. Even if the estate tax limit is cut in half, most people will still be protected, as far as taxes go.
The larger question becomes how well they think their children will handle receiving a large sum of money. As they watch their children mature, in most cases my clients eventually feel their child is up to the task. Yet they still want a trust because they worry about their adult child losing thousands, if not millions, of dollars of their inheritance as a result of a failed marriage. By establishing a trust as part of their will, these clients can help protect their child’s assets in a divorce settlement.
Let’s examine how this works. In many cases, if a child receives an inheritance and combines it with assets they own jointly with their spouse – such as a bank account, car or house – depending upon the state in which they live, the inheritance may become subject to marital property division if the adult child and spouse later divorce.
But if the child’s inheritance remains in a trust account, or they use trust funds to pay for assets only in their name, the inherited wealth can further be protected from a divorce. This gives the adult child their own assets to fall back on in the event of a divorce.
One of my clients left his daughter’s inheritance in a trust after her first divorce because he was afraid his hard-earned dollars might end up squandered if she remarried. It turns out my client was spot on – she married again; it did not work out, but her second ex-husband never got a dime from her trust.
Trusts can be complex and involve extra administrative work and costs, which may cost more compared with leaving assets outright to your children. In addition, a person or company must be named as a trustee to oversee these funds throughout the trust’s existence. But many people are willing to pay these costs to protect their child’s wealth.
How do parents decide whether to leave assets in trust for their children because of the possibility of a failed marriage? Here are three scenarios to consider:
I encourage my clients to think about estate plans as five-year plans: Review your wills, trusts and other documents every five years. It isn’t necessary to constantly change these documents, but reviewing them periodically helps a person to carefully evaluate relationships, finances and the emotional dynamics of their families. In addition, an estate lawyer can modify or delete the trust during your life, as your family circumstances change.