Organisms Liberate Nutrients for Plants

The activity of soil organisms is responsible for much of the liberation of nutrients to plants. A certain kind of bacteria is capable of producing nitrates from organic matter, and these nitrates supply the plant with the growth-element nitrogen. At the same time, other nutrients are made ready for the plant by many organisms, either as the direct result of decomposition or because solvents are produced to attack and free the nutrients from the more inert minerals. A small amount of nutrient will go directly into solution in water without the intervention of soil organisms.

The most active portion of the soil is the clay and humus, both of which are capable of absorbing and holding soluble nutrients carrying such elements as potassium, magnesium, phosphorus, and others that are supplied by fertilizers. These nutrients held by the clay and humus are prevented from loss by leaching and are gradually given up to the absorbing roots of a growing crop.

The plant roots make contact with the moist colloidal clay and humus, and through these surface contacts absorb both nutrients and moisture. The spongy crumb structure of soils, rich in humus with only a moderate amount of clay (a loam, sandy loam, or silt loam texture), is most favorable to profuse root development and efficient functioning of the roots.

The undisturbed soil before man arrives upon the scene to start cultivation is, therefore, a natural body formed by natural processes operating on natural materials over a long period of time to develop physical, chemical and biological properties that enable the enriched soil to support plants. The arrival of man with tillage tools is not always good, so far as soil properties are concerned, as evidenced by much once-good soil now in varying stages of deterioration.

Soil – A Physical System

As a physical system, soils must have good depth (10 or 12 feet) without obstructions in the profile, to allow crop roots not only to penetrate deeply but so that the roots can obtain air (oxygen), water and nutrients simultaneously from soil contact. By volume. the ideal soil is about 40 per cent rock (mineral) particles, 10 per cent organic matter and 30 per cent open space. The 50 percent open space should be approximately one-half occupied by water and one-half by air when the soil has all the crop water (capillary water) it is capable of holding. Good soil will hold about two inches of crop water for each foot of depth.

Soil – A Chemical System

As a chemical system the soil is a storehouse of nutrients, nitrogen, phosphorus, potassium, sulfur, calcium, magnesium, iron, copper, zinc, manganese, and boron that plants require for normal nutrition. A large portion of these nutrient elements in the top soil are in organic combination (with the humus) and are liberated as the organic matter rots. The chemical properties of the soil are most favorable to the plant when the reaction is about neutral, due to the combination of clay and humus with lime, and when the humus is regularly and liberally renewed.

Soil – A Biological System

As a biological system, the soil organisms (bacteria, fungi, and many animal organisms) are active in breaking down organic matter and in attacking inert minerals, causing solutions and oxidations that prepare the nutrients for absorption by plant roots. Some organisms can take nitrogen from the air where it is abundant and leave it in the soil in organic form where gradual liberation feeds the plant. This was the original source of all the nitrogen that the soil contains.

To the extent that man cooperates with nature to preserve the favorable properties of the soil developed through ages of activity, crop yields will be maintained at a satisfactory level. Legumes probably will be needed to renew the supply of nitrogen and humus, lime will be needed to correct the acidity of the soil (where rainfall is greater than 30 to 40 inches annually) and fertilizers are necessary to supplement the supply of available essential elements in the soil.

Crops cannot be continually removed with nothing put back, nor can the soil be left bare and subject to leaching and erosion that has destroyed the productivity of so much good land. Nature covers her fields with grass or timber, and man must recognize that a plant cover is one essential to the preservation of a productive soil. If he observes these fundamentals, he should be able to produce profitable harvests over the years to come and to maintain the soil in a high state of productivity for the generations that are to follow.

By R Stephenson

Related Articles Of Interest:

• Organic Soil and Analysis
• Know Your Garden Soil
• Soil Testing – What’s Your Soil Flavor?
• Applying Fertilizer