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The nutrient elements Calcium and Magnesium are the two most abundant nutrients within the soil. They have the most influence on the pH reading. These are the two elements that are present in all liming materials. Their presence or absence determines to a very large extent, what the soils pH reading will be. When both of these elements are at low levels in a soil, the pH reading will usually be low. The soil is then said to be acid and needs limestone. When these elements are at high levels, the soil pH will be high and soils are said to be Alkaline.

Sometimes Calcium can be high and Magnesium can be low and the soil will still have a high pH. Sometimes the Magnesium can be high and the Calcium can be low and the soil will also have a high pH. Limestone may still be needed in these situations because of the soils need for either Calcium and/or Magnesium. The ph is not necessarily the reason for apply limestone to a soil. The need for Calcium or magnesium is the reason for the lime application.

There are other things that can affect the soil pH reading. Things like carbonates, bicarbonates, Sodium levels, Iron levels, Aluminum levels, or Organic matter or Humus levels do play a role in determining pH. But Calcium and Magnesium are the most important and play the largest role in determining pH of a soil. Because of this fact, having both Calcium and Magnesium at the proper levels and balance for a particular soil is critically important. They are first and foremost in the production of healthy plants which will and does equate to healthy animals. It is not the pH reading itself that is so important, but rather the amounts of the elements that drastically affect the pH that is important.

Calcium is present in the soil in a soluble or an exchangeable form and is part of the soil mineral complex. Soluble and exchangeable calcium are the main forms that can move to the plant root and be absorbed.

Calcium is the dominant exchangeable cation in most soils. Calcium is held more tightly on soil exchange sites than either Magnesium or Potassium, the next two most plentiful exchangeable nutrients. The soluble Calcium is the form from which plants feed directly. While there is a relationship between exchangeable and soluble calcium levels for a particular soil, the relation is not the same for all soils.

Calcium is rarely found to be deficient in plant tissue regardless of the soil level. Calcium's greatest significance in plants and soils is providing the proper "balance" and "conditions" for
levels of the other nutrients within the soil and plant to be "ideal". Calcium is applied to soils to help develop "conditions" that improve soil and plant life. These "conditions" are optimum:

"Availability" of all nutrients
Microbial activity
Soil pH
Soil structure in clay and clay loam soils
Transport of nutrients within plants
Mineralization of soil organic matter
Protein production and nodulation for legumes
Depression of aluminum and iron
Nitrogen utilization

Calcium plays a major role in managing the Chemical, Biological and the Physical conditions of all soils. Managing a soil, then, involves managing the soils Calcium level and balance. When this is done correctly, soils can become very productive, producing healthy crops and healthy livestock.

MAGNESIUM

Magnesium found in soils is either in an exchangeable, non-exchangeable or soluble form. The largest amount is in the non-exchangeable form and is in the clay minerals of the soil. The soluble and the exchangeable forms provide the plants with the Magnesium needed for growth and production.

Exchangeable Magnesium is almost always present in soils in smaller amounts than Calcium. Magnesium uptake by plants is usually low in acid soils (low pH). It is also negatively affected by very high Potassium levels. Magnesium availability depends on adequate soil moisture especially if the Magnesium levels are low.

Magnesium is needed by plants to form chlorophyll which is the substance that makes plants green. Without chlorophyll, plants are unable to convert sunlight and carbon dioxide into various materials for the plant to grow and produce. Excess Magnesium can cause clay soils to become very tight and poorly drained. This doesn't happen in sandy soils.

PHOSPHORUS

Phosphorus is found in soils in four general forms:
Phosphorus as ions and compounds in solution,
Phosphorus adsorbed on the surface of soil particles,
Phosphorus minerals,
Phosphorus as a component of soil organic matter (Organic Phosphorus).

Phosphorus is usually very low in the soil solution. Most other major elements are at much higher concentrations than Phosphorus. A lot of Phosphorus may be present as soluble Organic Compounds in soils that are high in Humus or organic matter. There is rarely a lot of leaching of phosphorus from soils because most of the Phosphorus is not soluble and not present in the soil solution.

The three main soil phosphate fractions are:

Phosphate in soil solution,
Phosphorus held on surface of soil particles and is not soluble.
Phosphate as insoluble and unavailable compounds.

When soil pH rises to above 7, phosphorus becomes insoluble and much less available to plant root systems. The best availability is when soil pH is between 6.0 and 7.0.

As soil pH drops to low levels (5.5 and less), iron and aluminum fix the phosphorus in very unavailable forms.

Potassium found in soils is usually in one of four forms:
Soluble potassium,
Exchangeable potassium,
Non-exchangeable potassium,
Mineral potassium

Potassium moves from one category to another whenever potassium is added or removed from the soil. Conversion of potassium from the mineral form to one of the other forms requires a lot of time-months to years. The soluble potassium in the soil is the primary source from which the plant root system receives its potassium. Potassium may not move readily back into soluble form from non-exchangeable positions even though it is held less tightly on soil particles than other cations such as calcium and magnesium.

Exchangeable potassium is one of the major elements that is held on the soil colloids-mainly clay and humus particles. The amount of exchangeable potassium in a soil will vary considerably but ranges from 60 to 1000 lbs/acre. The ideal level would be around 200 to 600 lbs/acre for most soils growing good crops.

Non-exchangeable potassium is held between the soil clay plates and is not readily accessible by the soil solution nor the plant root system. When soils begin to get low in potassium, it will move from the non-exchangeable sites to a more accessible site on the clay colloid and become exchangeable. When potassium is added to a soil, some of it becomes non-exchangeable because it attaches between the clay plates of the soil.

Mineral potassium is slowly released from the mineral compounds that are present in all soils. They are from the soils parent material. The rate of release depends on the soil type and the microbial activity of a soil.

Some potassium may become fixed within a soil. That is it may become lodged in vacant spaces in between certain types of clay particles in the soil. The higher the clay content and the more weathered the clay is, the more fixation that may occur. Once fixed within the clay lattice network of a soil, it may be many years before it can again become plant available as either exchangeable or soluble potassium. This can account for many soils always being deficient in potassium. Fixed potassium is safe from leaching but it is also "safe" from plant root uptake.

When it again becomes soluble or exchangeable is when it becomes plant available.

Potassium is needed by plants for sturdy stalks and stems and helps plants resist lodging. Disease resistance is often associated with adequate potassium. Shortages of potassium reduce the rate of metabolism of carbohydrates and slow down the synthesis of protein with the plant.

Potassium functions in the control and regulation of the various minerals used by plants. It also activates plant enzymes. It plays a major role in translocation of sugars and carbohydrates from the leaves to roots and seeds of all plants. Plant leaves contain the largest portion of plant potassium. This accounts for the lower soil levels of potassium following hay and silage crops.

Sulfur is used by plants at nearly the same rate as phosphorus. It is, unlike phosphorus, highly soluble and, therefore, subject to leaching. Sulfur is used in the formation of all plant proteins, especially legumes. The nodules, nitrogen fixing sites on the root system of legume plants, show an increase in size and number when growing in soils that are well supplied with sulfur. When plants exhibit low sulfur content, the upper or younger leaves lose their green color and become yellowish.

Sulfur is present in soils in both the soluble form and in an organic form. The latter becomes soluble after action by soil bacteria which take the sulfur through many steps in becoming soluble and available to the root system. It is the sulfate form of sulfur that plants are able to utilize. Rainfall can add significant amounts of sulfur to soils. The soil organic matter holds a large amount of sulfur and it is released by the actions of the soil bacteria and soil fungi.

Sulfur or sulfate can range widely in various soil types. An ideal level would be 15 to 40 ppm soluble sulfur. Higher levels can be found without any detrimental effects on growing crops.

BORON

Boron is present in the soil in a rage of 20 to 500 ppm. Most soil boron is not plant available.

The available Boron fraction of the total boron may be in the range of .2 to 5 ppm. Sandy soils tend to be very low in boron because boron is soluble and subject to leaching. Soils with high clay contents and high humus or organic matter levels tend to have higher boron levels. Much of soil applied boron is held in the organic matter of the soil and some is in the soluble stage.

Boron does not move around the plant once it is stabilized. Boron will not move to newer leaves or shoots from older ones. Boron is used by plants to help translocate sugars. This will affect quality of the crop being grown whether it is hay, grass, or grain.

There is a relationship between potassium and boron in soils. Where there are high soil potassium levels and low soil boron levels, plants will not be able to uptake adequate amounts of boron. Where potassium levels are high and boron levels are also high, plants will take up large amounts of boron. Adequate soil calcium levels aids in the uptake of boron.

Iron is found in many forms in soils-iron oxides, iron hydroxides, iron silicate minerals, iron complexed by organic materials, and adsorbed iron. Certain iron minerals give soils their characteristic red color or yellow color. Some iron may be found as soluble iron compounds which are organic materials. Soils that are deficient in iron will have plants that lackchlorophyll production. It is the chlorophyll that gives plants their green color. The iron deficiency always begins in the newest leaves of the plant. Most soils do not have a true iron deficiency, but have a deficiency of available iron due to high pH, high levels of calcium, high bicarbonates, high manganese levels or soil compaction.

Manganese is present in soils as:
Solution manganese,
Exchangeable manganese,
Organically complexed manganese,
Mineral manganese

Manganese ranges in soils from 1/10 ppm to over 1000 ppm. Its availability depends on soil pH with very low pH creating possible manganese toxicity. Other factors affecting availability include organic matter content, microbial activity and soil moisture. Soils with adequate aeration and little or no compaction will have good availability of manganese. Deficiencies of manganese occur first in the younger leaves as chlorosis or yellowing of the leaves. High pH readings can cause manganese to be unavailable to plants.

Copper is found in several forms in soils:
Exchangeable copper,
Organic copper compounds,
Soluble copper,
Mineral copper

Most copper is complexed with organic materials and is available in this form. Exchangeable copper is less available to plants because it is held very tightly to the soil colloids. Mineral copper is not very available to plants. Copper that is in the soil solution is soluble and plant available. However, there is very little copper in this form within soils.

As soil pH increases, the amount of soil solution copper decreases. All forms of copper become less available as soil pH increases. Copper held on soil colloids is held very tightly unless the soil pH is very low. Sandy soils are low in copper as are very high organic soils such as peat and muck soils.

Plants utilize copper in the metabolism of carbohydrates and also nitrogen. Copper is not very mobile within plants although it can be moved from older to younger leaves. It is more mobile in plants that have very adequate supply of copper. It plays a role in the enzyme system of plants and it is used in the production of plant hormones. It is also used in the synthesis of nitrogen. It has a beneficial affect on flavor in most plants.

Zinc is found in soils as:
Exchangeable zinc,
Mineral zinc,
Organic zinc

Zinc is found in a range of 2 to 300 ppm. An ideal range may 2 to 10 ppm. The availability of exchangeable zinc may be lowered by high pH. Over liming a soil will definitely lower zinc availability. Zinc interacts with soil organic mater and both soluble and insoluble complexes are formed. High soil organic matter levels will increase zinc availability but high phosphorus levels will decrease its availability even when fairly large amounts of zinc are in the soil. Cold soils will have low zinc availability and young, newly emerged plants may exhibit zinc deficiencies until the soil warms and they grow bigger root systems to find more zinc. Poorly drained soils with high pH will decrease zinc mobility and availability especially for young plants.

Plants will use zinc in very small amounts and it is not very mobile within the plant. It is seed in protein synthesis and plays a larger role in disease prevention. Low protein levels are a result of low zinc or poor zinc utilization. It is related to seed formation and plant hormone production in all plants. It is used in DNA and RNA synthesis.

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