E. The plant root rhizosphere is the site of the soil plant interaction. All biochemical action is dependent on or related to the presence of enzymes. The variety of living organisms will determine the enzymes' presence and the intensity of biological process. G. Many aerobic microorganisms produce antibiotics that inhibit the spread of pathogens. The availability of phosphate to plant roots in a biologically balanced soil system is entirely different than chemical laboratory availability.
Rock phosphates come available slowly, but steadily in an organic system.
Most laboratory available phosphate can be fixed as inert iron or aluminum compounds at low pH and as inert calcium compounds at high pH. I. Water soluble potash in a soil goes easily where water moves - upward into the plant or downward away from it. Forage crops may absorb 5 to 6 times more potash than normal, being harmful to consuming livestock. Humus is the regulator to hold, to absorb, to avoid leaching or luxury consumption, yet hold the potash ready when the need arises. In stable humus we find practically no free ammonia, only a limited amount of nitrate, but a large amount of organic nitrogen. This organic nitrogen is contained in the proteins, amino acids, and other compounds of the life of microorganisms in soil or compost.