After centuries of learning, agronomists—i.e., the managers of either agricultural or horticultural endeavors—are beginning to understand that plants don’t need us nearly as much as we need them. Our cultural practices are indispensable to our needs but not to the plants’. They don’t care how they look or if they produce enough to make someone a profit. Whether our crops are there for consumption, recreation, or aesthetics, the way we cultivate them is for our benefit only. Plants, and the ecosystem in which they grow, have plodded along just fine for millennia before the advent of agriculture and horticulture. Their natural system can function without fertilizer, pesticides, growth regulators, soil amendments, or other man-made inputs.
The plant growing system can be broken down into three main components, plants, biota, and nutrients. Each of the three is inexplicably complex but maintains a balance with the other two. Plants can and do regulate the kind and amount of nutrients available to them by releasing photosynthesized food through the root system. Those foods attract and proliferate specific groups and species of soil organisms that perform nutrient cycling and release what is essential for the plant. They also protect the plant from pathogens. Plant nutrients reside in both the organic and inorganic soil particles and are released through dissolution, assimilation, predation, and exudation. These processes of nutrient release for plants are incredibly complex and not fully understood but one thing we do understand is that without the biological component of the system, it wouldn’t happen. This has been evident for some time. Soils where the biological activity is waning require more plant available nutrients to maintain an equal amount of production. If soil organisms don’t have the resources they need they can’t release soil bound nutrients for the plant. But wait! Didn’t I just write that the plant releases nutrients through its roots (you might have asked)? Yes, but the plant is trying to select specific organisms from a less diverse biological pool. It’s analogous to finding a qualified employee for a technical job in a region where that kind of training is unavailable.
So we can supplant nature’s nutrient release system and bypass biological activity but that can (and often does) impact the protection against pathogens that organisms provide. It’s no secret that plants growing in a biologically active environment are less susceptible to pathogen infection and when infection does occur, it is typically less severe.
Biological activity also impacts nutrient reserves and retention in the soil. Organisms provide structure to the soil that benefits plants but also enables better nutrient release, retention, and availability. Passageways through the soil created by earthworms and soil aggregating fungi not only allow better root development but also improve the movement of air and water. A wave of plant available, soluble nutrients from a typical fertilizer application can reduce the intensity of biological activity and the level of functions it performs. Plants respond and that is all we humans look at and care about but over time, the plant growing system often shows symptoms of problems that are related to this reduction in biological activity. The correlation between plant health and soil health isn’t always direct. Soil organisms build and maintain soil structure that enables better root development and improve the movement of water and air through the soil. Biological activity is directly related to not only the movement of air and water but the holding capacity as well. Soils with insufficient pore space and inadequate levels of stable or labile humus (by-products of biological activity) often have problems with drainage—either too little or too much. Biological inadequacies can indirectly lead to problems for plants down the road.
When natural fertilizers are applied, they not only feed the plant but also provide resources for soil organisms. Ingredients to look for on the label include compost, animal and vegetable protein meals, natural minerals, and dehydrated manure. Fertilizers with a greater diversity of ingredients have the potential to feed a more diverse population of organisms, which give plants a better selection for their needs. Natural fertilizers are typically more expensive than their chemical cousins but if a value could be assigned to biological soil management, it would clearly be worth the extra expense.