Soil Fertility

Soil fertility is a key component in growing healthy plants.  There are many different factors which affect soil fertility and as a result, the soil makeup is constantly changing.   There are at least 16 nutrients which are necessary for plants to grow and complete their life cycles.  Of those 16, non-mineral elements are used in the largest amounts and are found in air and water.  Those non-minerals are carbon, hydrogen and oxygen.   Plants rely on the sun’s energy to convert carbon dioxide (carbon and oxygen) and water (hydrogen and oxygen) into food.  This process is known as photosynthesis.   The rest of the elements (minerals) are known as macro-nutrients and micro-nutrients and can be either found in the soil or added as fertilizer or lime. 

The 3 primary macro-nutrients are nitrogen (N), phosphorous (P) and potassium (K).   These are most commonly supplied as fertilizers and come in different ratios to accommodate different needs.  The three secondary macro-nutrients, calcium, sulfur and magnesium, are needed in smaller quantities than the primary nutrients.  Sulfur can usually be supplied through fertilizers and calcium and magnesium are usually present in lime and gypsum.  Lime and gypsum are typically used to effect changes in soil pH or as buffering agents to neutralize acidity. 

There are seven micronutrients; boron, copper, chlorine, iron, manganese, molybdenum and zinc.  While these nutrients are found in even smaller quantities, they are just as important to the functioning of plants as the primary and secondary nutrients.   Deficiencies in micronutrients affect plant growth, vigor and production.

Nutrients take different forms; liquids, solids or gases.  These elements react with each other differently and these reactions in turn, affect the absorption of the nutrients by the plants.  Plants utilize certain nutrients in certain forms, but to speak in detail about this now is well beyond the scope of this article.  Other factors affecting nutrient uptake include soil pH, microbial activity and the condition of the soil, such as aeration, temperature and moisture. 

Soil pH affects microbial activity, which is needed to convert nitrogen and sulfur into useable forms for the plants.   Using lime will raise the pH of the soil.  Ideally, soil pH should be 6.0–6.5.   At this pH, microbial activity increases and nutrients are more readily absorbed by the plants.  (If using artificial medium, i.e. peat moss, pH should be one point lower because there are no soil components to act as an exchange site for the elements.)

Soil type affects the absorption of nutrients by plants as well.  In general, the macro and micro nutrients are dissolved in water and taken up by the plants’ roots.  Soil type varies with the makeup, or texture, of the soil.  That is, the proportions in the soil of clay, silt, sand and organic matter.  Soils with higher amounts of sand have increased drainage.  This drainage causes a washing away, or leaching, of the nutrients in the soil, creating a lack of nutrients for the plants.   Ideal soil types would have equal proportions of clay, silt, sand and organic matter.

As you can see there are many factors affecting soil fertility.  It is very important to feed your plants on a regular basis.  Just as people need food, so do your plants.  With the proper nutrition, your plants will thrive and flourish.