Soil Nutrients

A high level introduction to soil, agronomy, and nutrients.

Note: This content is largely copied from the work I did for The Growing Group. At that time, I spent many weeks studying and simplifying the dynamics of soil and how nutirents are delivered into plants and crops. This is a single (albeit long) article which introduces some of the main topics that factor into soil health.

Phosphate

Phosphate is essentially a rock that is mined throughout the world, which contains a macro-nutrient used by plants – Phosphorus. Phosphorus plays a role in many of the complex functions of a plant. When adequate supplies of Phosphorus are available within the plant it can promote or enhance the following benefits:

  • Early root formation and growth
  • Greater flowering and seed production
  • Fruit, vegetable, and grain quality
  • Better growth in cold temperatures
  • Water use efficiency
  • Early maturation of fruit and grain

Phosphorous is a highly reactive element. The majority of Phosphorous in most soil is in essentially insoluble forms and unavailable to plants. In most situations there is very little soluble Phosphorus in the soil at any point in time. It has been estimated that at any point in time, the solution/available forms of Phosphorus in many soils may only amount to from 0.01 to 0.06 ppm (0.02-0.12 lb P/acre). This Phosphorus will typically move no more than about one tenth of an inch in the soil. Roots quickly deplete the 0.10 inch cylinder of soil around each root and must continually grow into new areas of the soil to maintain adequate Phosphorus intake. Phosphorus is held within the soil in 3 different “Pools”:

The Solution Pool

This is the primary pool in which phosphorus is available to the plant, and is stored in the soil solution

The Active Pool

This is the pool that feeds the Solution Pool, or conversely may withdraw phosphate from the Solution Pool if the quantities of phosphorus in the Solution Pool are extremely concentrated. In this pool the phosphorus is adsorbed to particles in the soil, ready to feed the Solution Pool. It can also provide phosphorus in small amounts to the plant roots.

The Fixed Pool

The Fixed Pool contains very insoluble phosphate that may remain unavailable to plants for many years. Conversion into the the Active Pool occurs very slowly. Within the Solution Pool plants will take up nearly all Phosphorus as either Primary orthophosphate anion or Secondary orthophosphate anion.

Primary orthophosphate is taken up about 10 times as readily as the secondary orthophosphate form. All Phosphorus sources applied to the soil must be converted to the orthophosphate forms before a plant can utilize them. However, applying these forms of Phosphorus to the soil does not guarantee that they will remain in that form for very long. Because phosphorous is highly reactive, it is readily converted to other, less soluble forms. The particular forms that are created depend on other soil factors such as the soil pH, temperature, moisture, other elements, and others. This is one reason all aspects of the soil must be optimized before plants will perform at their best.