Healthy Soil is the Foundation for Food

According to M. Jill Clapperton PhD, Principal Scientist, Rhizoterra Inc. Copyright Rhizoterra Inc 2014.

So why do we treat soil like dirt? We cause soil and nutrients to wash away in rainstorms or with irrigation, blow away in the wind, and burn up the organic matter with tillage. How much soil can we lose before we say enough? When is it too late to start creating healthy productive soil? We have choices.

When we are standing on the ground, we are really standing on the roof top of another world. Living in the soil are plant roots, viruses, bacteria, fungi, algae, protozoa, mites, nematodes, worms, ants, maggots and other insects and insect larvae (grubs), and larger animals: the soil biota.

Indeed, the number of living organisms below ground is considered to be far greater than that above ground. Together with climate, these organisms are responsible for the decay of organic matter and cycling of both macro- and micro-nutrients back into forms that plants can use. The activities of the soil biota stabilize soil aggregates, building a better soil habitat and improving soil structure, tilth and productivity, and hence the primary productivity of the ecosystem that they inhabit. Not only that- plants are adapted to take-up and use nutrients made available through biological processes easily and efficiently.

Soil fertility is largely dependent on the processing of organic substrates – root exudates, and residues or soil organic matter (SOM)- through the soil food-web. There are three primary carbon (C) sources: root exudates, litter or residues, and soil organic matter (SOM). These C sources vary in their availability and accessibility to soil organisms, and thus, increase the C flow and biodiversity within the food web. The bacteria can immediately use the C that leaks from the roots, protozoa and nematodes eat the bacteria that are attracted to the roots, and the mites and collembola chew on the dead and dying roots and shoots.

Building soil organic matter begins in the soil. Carbon from roots is retained and forms more stable soil aggregates than shoot derived C (Gale et al. 2000). Roots normally account for only 10-20% of the total plant weight, and contribute 12% of soil organic C, 31% soluble organic C, and feeds 52% of the microbial biomass (Liang et al. 2002). The amount of carbon from corn roots and corn root exudates can be as much at 1.5-3.5 times higher than the organic C contribution from corn stover (Allmaras et al. 2004; Wilts et al. 2004). Soil structure defines the amount of access these organisms have to their preferred C sources.

People need infrastructure (roads, running water, electricity, and communication networks) to work effectively and efficiently. Soil biota require belowground infrastructure or a suitable soil habitat, with a stable soil pore network so they can move easily from one resource to another. Earthworms and some insect larvae have the ability to burrow, most of the other organisms that live in the soil need good soil structure in order to do their job. Soil biota need an adequate amount of quality organic matter (as an essential food source), with enough clean air and water to live and reproduce.

In order to really recycle nutrients you need below ground predator/prey relationships, and this also requires a continuous soil pore network super highway – or- great soil structure. Microorganisms are the primary producers in soil, and they can out compete the plant for nutrients every time. Predators like protozoa and nematodes keep the populations of bacteria in check, and concentrate the nitrogen from eating the bacteria in an organic form that plants can use- in the rhizosphere! The predators need to use the soil pore network to reach their prey. The really interesting thing about the activities of the soil biota is that every organism is trying to modify the soil structure so they have a unique advantage over the competition. Together (if we let them) they will build a really awesome well structured soil.

In agriculture, we modify the soil habitat with tillage and crop rotation practices and so influence the ability of the soil ecosystem to provide essential services such as decomposition, nutrient cycling, and pest management (depending on our practices we can either help or hinder soil ecosystem functions). This in turn, can affect the nutrient quality of the food and forages we produce, and ultimately human and animal health.

Mixed forages (if you have livestock or access to livestock), companions, living mulchs, covers, and green- or brown- manure plantings are all soil health primers. In the rotation they can enhance soil structural stability, increase soil organic matter - to depth (providing a diverse source of root exudates) and increase the number, diversity andactivity of most soil organisms.

The take home message is that for healthy productive soils we need lots of biologicalactivity to transform or mineralize the organic nutrients into the inorganic nutrients that the plant and the soil microbes use, predator- prey relationships have an important role to play in feeding the plant, and we can speed-up the rate at which the soil biota create well structured soils by reducing soil tillage and using mixed species forages or soil health primers in rotation.

Its all about a win for the plant and a win for the soil biota. A better soil structure means more roots, healthier plants, more roots again, and more root exudates from more root surface area (are you starting to see the cyclical pattern?). Together this means more biological activity in the rooting zone (rhizosphere), more predator/prey activity recycling nutrients near the root, less disease (healthier plant) and the cycle keeps spiraling in a beneficial way. “But Rome was not built in a day”- and neither was your soil. Annual tillage collapses the soil lattice structure with its maze of soil pores, and big iron recycles all the soil biological activity, cuts up the carbon and micronutrient trading network of the mycorrhizal fungi, and selects for only the organisms that can function in a dysfunctional system.

Soil is the foundation of agriculture so allowing it to erode will have a direct impact on the productivity of the soil, that means more inputs, a higher cost of production, and less net return. The scenario is the same for both the upstream and downstream farmer. There are no reasons for allowing soil erosion.

Healthy soil means healthy food, and better nutrition for us all, including our livestock. Feed your soil so it can feed the plants. That means looking at the quality of organic matter not just the quantity, and understanding more about how you can actively build organic matter in your soil type and climate. It would always be a good idea to study soil health, not in isolation, but in the context of agroecosystem health, knowing that one size fits no one. The good news is that the processes behind creating healthy soils are universal and can be adapted to where ever you live. There will be different players in the soil health “theatre” for every different agroecosystem, but they will all be working towards the same goal- creating a better habitat.

When you have soil health, you have agroecosystem health, and a better bottom line.

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