9.4: Besides Organic Matter Management

Although enhanced soil organic matter management practices go a long way towards helping all aspects of soil health, as we discussed at the beginning of this chapter, other practices are needed to maintain an enhanced physical and chemical environment. Plants thrive when roots can actively explore a large area, get all the oxygen and water needed, and maintain a healthy mix of organisms. Although the soil’s physical environment is strongly influenced by organic matter, the practices and equipment used, from tillage to planting to cultivation to harvest, have a major impact. If a soil is too wet, whether it has poor internal drainage or receives too much water, some remedies are needed to grow high-yielding and healthy crops. Also, erosion, whether by wind or water, is an environmental hazard that needs to be kept as low as possible. Practices for management of soil physical properties are discussed in chapters 14 – 17.

Many of the practices that build up and maintain soil organic matter enrich the soil with nutrients or make it easier to manage nutrients in ways that satisfy crop needs and are also environmentally sound. For example, a legume cover crop increases a soil’s active organic matter and reduces erosion, but it also adds nitrogen that can be used to nourish the next crop. Cover crops and deep-rooted rotation crops help to cycle nitrate, potassium, calcium and magnesium that might be lost to leaching below crop roots. Importing mulches or manures onto the farm also adds nutrients along with organic materials. However, specific nutrient management practices are needed, such as testing manure to check its nutrient content before applying additional nutrient sources.

Other examples of nutrient management practices not directly related to organic matter management include applying nutrients timed to plant needs, liming acidic soils and interpreting soil tests to decide on the appropriate amounts of nutrients to apply (see chapters 18 – 21). Development of farm nutrient management plans and watershed partnerships improve soil while also protecting the local environment. And as discussed above, it is possible to overload soils with nutrients by bringing large quantities of organic materials such as manures or composts from off the farm for routine annual applications.

Also, when considering “carbon farming” (working to increase soil organic matter levels and carbon storage) as a way to reduce atmospheric carbon dioxide concentrations, the existing carbon status of the soil needs to be considered. The potential for storing additional carbon is low if large amounts of organic materials have been routinely applied and the soil is already near its carbon saturation point (e.g., some concentrated livestock operations or organic vegetable farms that applied a lot of compost). This implies that when additional organic matter is applied to the soil, little will be stored and more will be lost to the atmosphere as carbon dioxide. Conversely, carbon farming will be more effective with soils that are low in carbon due to past intensive management without replenishment with organics (like a typical cash grain farm). They are generally well below their maximum capacity to store organic matter and therefore will more effectively store the applied carbon.