There are at least 18 known elemental nutrients that are required for normal green plant growth. Three of these are the non-mineral nutrients, carbon, hydrogen and oxygen which are received through the air and the water. The 15 remaining nutrients are all minerals and fall into three groups called primary, secondary, and micronutrients and in varying amounts become necessary for healthy plant growth. It is interesting that many acknowledge the possibility of other elements that are essential to growth but the chemistry involved has not been discovered or is not presently known. Some of the elements include other trace minerals, vitamins, enzymes, amino acids and growth regulators.
Healthy soil is abundant with many different types of life forms, both alive and dead. In order to sustain these life forms it is critical that a sufficient supply of oxygen is maintained. A rich soil always contains insects, worms and bacteria or microbes which help to provide sufficient pore space in the soil which should be at least 25% occupied by air.
The ability of soil to hold air depends on particle size which are called separates. They can vary from the finest which are clays, through silt and sand all the way to gravel, the coarsest. The particle size of clay is 0.005 mm or less and when these fine particles are packed closely together they virtually eliminate any air space causing all life forms to disappear. It is important to note that air in the soil has a different composition than that above the ground, containing less oxygen and more carbon dioxide.
The similarity of the plants ability to use water is almost identical to the human body. Lets take a closer look at this comparison. Plants are composed of 70% to 90% water, making them a little higher than our human body water content. They are comprised of hundreds to thousands of individual cells that have a variety of functions, such as air conditioning (which is called transpiration), to feeder roots or enzyme factories, to propagation or the perpetuation of their existence.
Water is removed from soil in four ways. As mentioned plants transpire water in carrying on the life processes, water is carried away in the plant products, soil surfaces evaporate water, and the other side of the coin, gravity pulls the water to the subsoil and rock formations.
Agronomy is taught today in most of our universities as it was at the turn of the 20th century and we find ourselves almost at the start of the 21st century. Let me explain what I mean. Nutrient recognition is concentrated on the N, P, K, there is some recognition given of course, to the minor nutrients and their importance in specific areas. However, no real emphasis has been placed on the minor nutrients, vitamins, enzymes, amino acids and growth regulators by the universities. It is interesting to note that most agricultural colleges still treat our soils as though they are hydroponic media in the way they accept the fertilizer. The chemical reactions in soil are different than in soil, and the uptake of nutrients is affected by this. Additionally, no university has included the role of microorganisms in the uptake process. These microorganisms live in water and in soil.
Water is most commonly found in the pore space of the soil and often displaces the air. Sorption is the general term that covers both adsorption and absorption and in either one of these methods of sorption the water is not readily released. It is interesting to take the driest soil you can find and heat it in a test tube. You will find it releases a considerable amount of moisture. Dry soil is not really dry in the chemical sense.
The sorption of water in soils can be explained easier when you look at the chemical composition of a typical soil. There is basically nine elements that make up the great bulk of the earths soils: oxygen, silicon, aluminum, iron, calcium, magnesium, sodium, potassium and hydrogen. Note that in this group of elements, oxygen is the only element that contains strong electronegative charges, allowing strong polar or ionic bonds to form with each of these other elements in the soil.
In order to have a productive soil we must have percolation. This is the ability of a solid material to drain a liquid from the spaces between the solid particles. Soils with good percolation will drain the water from all but the small pores in the natural flow of the water. The flow of the water is an absolute necessity in order to grow anything successfully. It actually takes several hundred pounds of water for the typical food crop to make only one pound of food. There is a negative side to this high water flow because of the leaching effect of the water.
Water is, of course, the universal solvent. Because of its ability to dissolve so many different materials, we find it often leaches away the nutrients needed by the plants for growth. You must insure the replacement of these nutrients or a way to preserve them from this leaching process. We have found that the combination of certain long chain polymers that exhibit a strong attraction for these same nutrients can be extremely important in preventing this leaching action.
Because percolation is so important to our soils and the growth of our crops, we must make certain that our soils have the proper tilth. In years past, the farmer would go out to his fields and pick up a handful of soil and crush it in his hand to make sure it did not turn to powder but into small clumps. That told him he had good tilth. This gave him an indication that he had the proper pore space. True productive soil should have 50% pore space.
Leaching can also cause soils to become acidic, or sour, because of the combination of oxidation of organic matter along with the leaching. Salts of the alkali and alkaline earth metals are more soluble than the other salts of transition metals. For example, a soil containing calcium, magnesium, iron, and aluminum is likely to be slightly alkaline, or sweet, prior to leaching with water. If calcium or magnesium are removed in excess of the iron or aluminum, the soils become sour or acidic. This is why the old farmer would taste the soil to find out if it was sweet or sour.
Think of the water (along with the air) in the soil as the giver of all life. Nothing would grow without it because the plants couldnt reach the nutrients and the plant cells would shrivel and die. Undesirable minerals are actually leached away from the soil and of course the plants. This purification of soil from these contaminants is a true blessing to the farmer who understands the process. If the tilth of the soil is of proper size and texture and are maintained with a minimum amount of cultivation, you have the key to successful farming, as long as you maintain the proper level of water on the plants. Additionally, for higher yields and better plant health, the level of microorganisms and micronutrients in the soil is important. Ignoring any of the 3 major factors can be detrimental. These factors are: proper pore space in the soil; adequate amounts of water, sun, nutrients and micronutrients; and a thriving beneficial microbial count .