When other ions combine they may precipitate or fall out of solution and thus become unavailable to the plant. Many of the micronutrients form complex combinations with phosphorous and calcium and precipitate out of the soil solution so the nutrients cannot be easily taken up by the plant. The pH, which means potential hydrogen, is a measurement of acidity or alkalinity. The pH greatly affects chemical reactions. The effect of pH varies with the ion, the types of ions in the soil, and the type of soil.
Water is required for nutrient movement into and throughout the roots.
Oxygen is required in the soil for respiration to occur to produce energy for growth and the movement of mineral ions into the root cells across their membranes. This is an active absorption process utilizing energy from respiration. Oxygen is not transported to roots from the shoot. Without adequate oxygen from the soil environment there is no energy produced for nutrient absorption. This also stops active absorption in which water flows into the cell due to the higher concentration of nutrients that were actively absorbed.