WHY SOIL ORGANIC MATTER IS SO IMPORTANT
WHY SOIL ORGANIC MATTER IS SO IMPORTANT 
A fertile and healthy soil is the basis for healthy plants, animals, and humans. And soil organic matter is the very foundation for healthy and productive soils. Understanding the role of organic matter in maintain-ing a healthy soil is essential for developing ecologically sound agricultural practices. But how can organic matter, which only makes up a small percentage of most soils, be so important that we devote the three chapters in this section to discuss it? The reason is that organic matter positively influences, or modifies the effect of, essentially all soil properties. That is the reason it’s so important to our understanding of soil health and how to manage soils better. Organic matter is essentially the heart of the story, but certainly not the only part. In addition to functioning in a large number of key roles that promote soil processes and crop growth, soil organic matter is a critical part of a number of global and regional cycles. It’s true that you can grow plants on soils with little organic matter. In fact, you don’t have to have any soil at all. (Although gravel and sand hydroponic systems without soil can grow excellent crops, large-scale sys-tems of this type are usually neither economically nor ecologically sound.) It’s also true that there are other important issues aside from organic matter when con-sidering the quality of a soil. However, as soil organic matter decreases, it becomes increasingly difficult to grow plants, because problems with fertility, water availability, compaction, erosion, parasites, diseases, and insects become more common. Ever higher levels of inputs—fertilizers, irrigation water, pesticides, and machinery—are required to maintain yields in the face of organic matter depletion. But if attention is paid to proper organic matter management, the soil can support a good crop without the need for expensive fixes. The organic matter content of agricultural topsoil is usually in the range of 1–6%. A study of soils in Michigan demonstrated potential crop-yield increases of about 12% for every 1% organic matter. In a Maryland experiment, researchers saw an increase of approxi-mately 80 bushels of corn per acre when organic matter increased from 0.8% to 2%. The enormous influence of organic matter on so many of the soil’s properties— biological, chemical, and physical—makes it of critical importance to healthy soils (figure 2.3). Part of the explanation for this influence is the small particle size of the well-decomposed portion of organic matter—the humus. Its large surface area–to–volume ratio means that humus is in contact with a considerable portion of the soil. The intimate contact of humus with the rest of the soil allows many reactions, such as the release of available nutrients into the soil water, to occur rapidly. However, the many roles of living organisms make soil life an essential part of the organic matter story.
A fertile and healthy soil is the basis for healthy plants, animals, and humans. And soil organic matter is the very foundation for healthy and productive soils. Understanding the role of organic matter in maintain-ing a healthy soil is essential for developing ecologically sound agricultural practices. But how can organic matter, which only makes up a small percentage of most soils, be so important that we devote the three chapters in this section to discuss it? The reason is that organic matter positively influences, or modifies the effect of, essentially all soil properties. That is the reason it’s so important to our understanding of soil health and how to manage soils better. Organic matter is essentially the heart of the story, but certainly not the only part. In addition to functioning in a large number of key roles that promote soil processes and crop growth, soil organic matter is a critical part of a number of global and regional cycles. It’s true that you can grow plants on soils with little organic matter. In fact, you don’t have to have any soil at all. (Although gravel and sand hydroponic systems without soil can grow excellent crops, large-scale sys-tems of this type are usually neither economically nor ecologically sound.) It’s also true that there are other important issues aside from organic matter when con-sidering the quality of a soil. However, as soil organic matter decreases, it becomes increasingly difficult to grow plants, because problems with fertility, water availability, compaction, erosion, parasites, diseases, and insects become more common. Ever higher levels of inputs—fertilizers, irrigation water, pesticides, and machinery—are required to maintain yields in the face of organic matter depletion. But if attention is paid to proper organic matter management, the soil can support a good crop without the need for expensive fixes. The organic matter content of agricultural topsoil is usually in the range of 1–6%. A study of soils in Michigan demonstrated potential crop-yield increases of about 12% for every 1% organic matter. In a Maryland experiment, researchers saw an increase of approxi-mately 80 bushels of corn per acre when organic matter increased from 0.8% to 2%. The enormous influence of organic matter on so many of the soil’s properties— biological, chemical, and physical—makes it of critical importance to healthy soils (figure 2.3). Part of the explanation for this influence is the small particle size of the well-decomposed portion of organic matter—the humus. Its large surface area–to–volume ratio means that humus is in contact with a considerable portion of the soil. The intimate contact of humus with the rest of the soil allows many reactions, such as the release of available nutrients into the soil water, to occur rapidly. However, the many roles of living organisms make soil life an essential part of the organic matter story.
