Home Systems biology Biological Absorption of Nutrients – Ohio Ag Net

Biological Absorption of Nutrients – Ohio Ag Net


By James Hoorman, Hoorman Soil Health Services, adapted from “Solubility versus Biology” by Lawrence Mayhew.

Regenerative farming practices focus on absorbing nutrients from soils through the soil’s natural biological cycles. This ecological farming approach uses microbes and carbon compounds to produce crops naturally rather than relying entirely on highly soluble “salty” nutrient inputs for plant nutrition.

Jim Hoorman, Hoorman Soil Health Services

Prior to commercial synthetic fertilizers, historically, soil microbes supplied approximately 80% of soil nitrogen (N) through the efficient process of microbial nitrogen fixation. However, soil compaction and excessive use of nitrogen fertilizers negatively impact nitrogen-fixing microbes. For the first time, the total fixed N provided by microbes is lower than the amount of synthetic N applied from fertilizers. Excess salt-based or soluble fertilizer upsets the natural balance of the soil.

Soil microbes interact with plant roots and soil minerals to release plant nutrients from soil minerals. Biological release of plant nutrients has much greater potential for plant mineral uptake than relying entirely on soluble nutrients from fertilizers. Plants have devised complex systems of breaking down minerals into nutrients and then using active transport mechanisms to move them through their roots. Active transport, biological activity and complex organic substances are essential components for efficient uptake of nutrients by plants. There are many natural organic ways to effectively, cost-effectively and environmentally-friendly absorb plant nutrients without using soluble or salty fertilizers. Currently, our understanding of these biological processes is just beginning to flourish.

To be highly water soluble, fertilizers must readily dissociate in water into highly charged positive ions (cations) and negatively charged ions (anions) called salts. “Salts” are the simplest, but most wasteful and environmentally harmful soluble fertilizers. Fertilizers are rated by their salt index, which ranks the potential to damage seeds and germinating plants. The salt index of a fertilizer is directly related to its solubility in water. So-called plant root “burn” is caused by soil dehydration, a natural soil response to counter high salt inputs. Other soil responses to highly soluble fertilizers are the “leaching” and “binding” of nutrients by soil colloids. The soil tries to buffer or keep these soluble salty nutrients at low concentrations so the soil biology can survive.

The soil is a living system sensitive to the supply of highly soluble salts. In low-input agriculture (sustainable, organic, organic, regenerative), highly soluble soil inputs are used sparingly. Salt disturbance is handled primarily by water, which surrounds and neutralizes high cation and anion fertilizers. These salts can cause a plant root to desiccate or dry out because water is retained and the plant is not available.

Soil water contains both dissolved and undissolved substances. The part of the soil water containing dissolved substances is called the soil solution. The total dissolved nitrogen in the soil solution per acre is in the range of about 0.4 to 1.5 pounds per acre. For dissolved phosphorus, the range would be 0.001 to 0.003 pounds in an acre! Just a trace. Most soil nutrients are soluble at very low concentrations to maintain healthy soil.

In countries where crops are fertilized with synthetic nitrogen fertilizers, the efficiency of nitrogen use is very low. In the United States, approximately 54% of all nitrogen fertilizer applied to corn crops is wasted. In biological systems, nitrogen is used efficiently by both microbes and plants. Approximately 1# of total elemental N grows 1 bushel of corn or 150# of total N to grow 150 bushels of corn/acre. There is only about 1# N/Acre naturally in the soil solution at a time. N uptake by maize is enormous as the maize begins to pollinate to kernel fill. Soil microbes use biological N fixation to convert atmospheric N into plant-available forms of N (50% of total N) to feed our crops. Soil compaction and poor soil structure deprive soil microbes of needed oxygen and nitrogen, thereby destroying the ability to reduce nitrogen inputs. Soil compaction also promotes many crop diseases. When highly soluble salt fertilizers are applied to soil, the soil system must achieve chemical and biochemical equilibrium. The leaching, denitrification and fixation of salts in soil colloids is a natural biological reaction. If you’ve ever tried drinking a glass of water containing a teaspoon of dissolved table salt, you know what I mean. If you don’t vomit, at least you will have an upset stomach and will be extremely thirsty for a long time. Heavy use of saline fertilizers means that soils will leach or use large amounts of water to compensate for high salt inputs. Using regenerative practices (cover crops, direct seeding, manure, compost, humates) improves soil life and improves nutrient efficiency.