Biologicals Boost Plant Nutrition
Microbes have many soil functions. A healthy diverse microbial system improves soil structure, improves water drainage, stores more soil water, and consumes parasites and pathogens; releasing soil nutrients. Generally, about 50% of applied fertilizer gets into the plant, as it is first recycled through soil microbes. Microbes process nutrients to make them plant available.
Nutrient efficiency on N is only 40-65%, on phosphorus (P) 15-25%, and on potassium (K) around 30-50%. Farmers operating cost for fertilizer is around 36% for growing corn and only about half or less of applied fertilizer is efficiently used. Soil biology and soil microbes improve nutrient efficiency so nutrients are absorbed and used better by the plant.
Rhizobium bacteria are a type microbe that create plant useable N from the atmosphere. Legumes, clovers, and soybeans use Rhizobium bacteria to grow N to make soybean seed. Atmospheric N gas has two N atoms attached together by three strong bonds and is converted to ammonia which is one N atom bonded to 3 hydrogen (H) bonds. That takes a lot of energy. Lighting is a natural process to break the triple N bond. Lightning contributes about 9# of N/acre/year.
Commercial fertilizer creates synthetic N by heating up natural gas N to 700-900F under intense pressure of 150-250 atmospheres. This requires a lot of energy. Microbes do it for free but require food from plant roots to have energy to break the triple N bond down to ammonia.
Biologically active soils have protozoa and nematodes that eat the N rich bacteria and actinomycetes, making N available to crops. Some free-living bacteria release 20-100# N to grain crops. These free-living bacteria are not associated directly with legumes or clovers but live within .5 inch of roots. They tie up a lot of N, but in biologically active soils the N is more efficiently recycled. As much as 40%-60% of all plant available N comes directly from pseudomonas bacteria that live inside the plant in a process called rhizophagy. Nitrogen fertilizer makes up only a small part of the plants available N, and most of that N has to go through a microbe first.
Plants also use microbes to make all three major nutrients: N-P-K plant available. Microbes mine the soil, taking locked up N-P-K in soil minerals. This requires energy and the plant roots supply this in the form of sugars that are secreted into the soil by the root. If the plant get too much nutrients short-term from fertilizer, the plant root gets lazy and stops secreting sugars. This may become a problem if the fertilizer runs out. The plant suffers until it can grow more microbes.
Microbes also secrete hormones that increase plant root mass. Since a root can explore only 1% of the soil volume, the more roots; the more nutrients those root hairs can extract. Associating with mycorrhizae fungi (MF), the MF can explore 50X-700X more root volume than the root hairs. The MF bring back P, water, and micro-nutrients in the soil to the plant.
In addition, biologically active soils break down crop residues efficiently. Every 40 (200) bushel of corn produces 1 (5) ton of crop residue that contains 17# (85#) of N, 4# (20#) of P, and 34# (170#) of K. Crop residue has to have soil microbes and soil biology to break down and recycle those nutrients. If the ground is frozen or too dry, the soil biology does not work. If using biologicals, its best to apply them after harvest ASAP. If it is too dry or the ground is frozen, save your money. Residue breakdown biologicals should contain more than just bacteria. They need MF who are good at breaking down lignin, beneficial protozoa, and other benefical microbes to work properly.
Dave Stark is often asked if biologicals need to be applied every year. The answer is probably. Too often flooding, freezing, and drought reduce microbial populations; especially in conventional tilled fields. Soil microbes that need oxygen like protozoa, amoeba, fungi, and nematodes which consume the bacteria often decline, so the farmer loses microbial balance. About 6-10% of all microbes are associated with either one type of plant or even one crop (e.g. corn) variety. Right now, scientist do not know which microbes associate with each crop varieity, so wide biological diversity is the best.