Soil health is the latest catchword in sustainable agriculture. We keep hearing how farming practices such as cover crops, reduced tillage, and diverse rotations can improve soil health, but what does this mean? Why should we care if soil is healthy? In this article, we will look at some concrete outcomes of improving soil health and why it matters.
What is Soil Health?
Before we can get to what is healthy soil, let’s start with what is soil. Soil is made up of minerals, organic matter, water, air, and living organisms. It is both the food source for plant roots and soil organisms as well as the structure that they live in. Though it is often dismissed as just dirt, it actually contains a complex ecosystem of interconnected soil organisms that contribute to many of the soil characteristics that make land productive. For example, the water cycle, nitrogen cycle, and carbon cycle are all mediated by living organisms. Soil health is therefore a measure of a soil’s capacity to function, just as our health is measured by our body’s ability to function.
Why does it matter?
Plants rely on their soil organisms in the same way we depend on the microbes living in our intestines. They assist with digestion, provide nutrients we cannot access, and protect us from disease. When people have fewer or less diverse gut flora, they tend to get sick more easily or just don’t feel well. The same is true for plants growing in unhealthy soil; they just don’t grow well where we see compaction, reduced drainage, and nutrient run off.
Plants depend on soil to provide certain functions. A healthy soil has a stable soil structure, containing an abundance of diverse soil organisms, and keeping nutrients in place so that they are available for plants and soil organisms. A soil ecosystem with these attributes provides a better environment for root development, has improved water management and nutrient availability in both wet and dry conditions, and reduces soil pest and disease pressures.
Micro-organisms consume plant matter and other organisms. As they digest their food, they exude sticky carbon substances that stick soil particles together. This is how you get beautiful crumbly soil everyone wants. This structure increases the pore space in soil, which allows it to drain when it’s wet and stores water in the summer when it’s dry. Pore space also brings more air to the roots. Soil microbes subsist on dead plant matter and organisms, as well as carbon secreted by plant roots. When there isn’t a living root in the ground, or plant matter on the surface, the next best source of carbon for microbes are the exudates holding the soil particles together. Therefore it is important to make sure the microbiome is fed.
The soil beneath our feet is not just a structure to hold plants up. It is a complex ecosystem—an interconnected web of organisms and their physical environment. All of the various nutrient cycles, the water cycle, nitrogen cycle, and carbon cycle are all mediated by living organisms. The state of this ecosystem affects how well these other systems work.
How does this happen?
Plants and soil organisms alter their environment to make it more favorable for their growth. These processes are often described as building their house, storing food, and encouraging beneficial neighbors to live near them. When we have lots of different kinds of organisms in an ecosystem, they make it harder for pathogens and pests to establish themselves because they must compete with the current inhabitants. Pest predators will also be more abundant when they have a consistent supply of prey throughout the year; and remember, not all prey species are pests. Most insects and microbes are either beneficial or benign.
How do you get these benefits?
There are many opportunities to improve soil health, and thanks to PRN donors we can get the word out about these methods. Practices such as cover crops, reduced tillage, and diverse rotations improve soil health by feeding the soil biology and protecting the soil structure they’ve created. However, this is a dynamic system that can either help or hinder crop production. For example, under wet, warm conditions, some soil bacteria will convert anhydrous ammonium fertilizer to nitrate, which is water soluble and can be washed off the field. Soil ecology is always an active player in our cropping systems. The only choice is whether to work together or not.
The point of focusing on soil health instead of just nutrient pollution is that poor soil health results in a leaky system, which leads to nutrient pollution. Only so much progress can be made by changing how much and when fertilizer is applied, or trying to catch nutrients after they’ve left the field. To truly address nutrient pollution requires a systems change. When a field’s soil biology is healthy, it is much more forgiving of inevitable variations in weather and fertilizer practices. Investing in soil health can turn this leaky system where nutrients are lost into a tight system where plants and soil organisms trade nutrients with a handshake.
