4.3 Soil and sustainability  (Page 6/8)

Agriculture and food capacity

Soils on arable lands globally are a resource to society with potential use for food production. Production is ultimately limited by soil type, climate, hydrology, and land management. The native soil type is what has been provided by the land, from centuries or millennia of soil development, typically under mostly natural conditions under native plant vegetation. The effect of human populations may have been to drain land for cultivation (affecting hydrology), to modify the landscape, build structures, and to remove native vegetation. Some modifications have aided with food production. Others have had unintended consequences of causing land degradation, such as salinization, topsoil erosion, compaction, pollution, desertification, or depletion of soil nutrients.

Some of these issues are of serious concern in developing countries where oversight and regulations protecting the land may not be in place. For instance, overgrazing and rapid deforestation of the land, and generally poor land management, can lower the organic matter content of surface soils, thus lowering fertility and increasing the likelihood of topsoil erosion due to removal of the protective vegetative covering. As the world's population continues to increase, we will need to find ways to continually increase (or more effectively utilize) food production capacity from an essentially fixed amount of arable land worldwide. As population density has increased, crop yields and the numbers of acres in production have been continually increasing, with technological advances and more land in agriculture. This is not a sustainable trend, though, since the land area on earth is finite. In fact, some prime farmland is even being removed from production in developed countries as urbanization and land development occur on the ever-expanding edges of population centers. Efforts will need to be made to preserve enough high yield farmland to be sustainable for future generations.

Soil compaction, tillage, and sustainable practices

In modern agricultural practices, heavy machinery is used to prepare the seedbed, for planting, to control weeds, and to harvest the crop. The use of heavy equipment has many advantages in saving time and labor, but can cause compaction of soil and disruption of the natural soil biota. Much compaction is reversible and some is unavoidable with modern practices; however, serious compaction issues can occur with excessive passage of equipment during times when the soil has a high water content. The problem with soil compaction is that increased soil density limits root penetration depth and may inhibit proper plant growth.

Current practices generally encourage minimal tillage or no tillage in order to reduce the number of trips across the field. With proper planning, this can simultaneously limit compaction, protect soil biota, reduce costs (if performed correctly), promote water infiltration, and help to prevent topsoil erosion (see below). Tillage of fields does help to break up clods that were previously compacted, so best practices may vary at sites with different soil textures and composition. Crop rotation can also help to reduce bulk density with planting of crops with different root depth penetration. Another aspect of soil tillage is that it may lead to more rapid decomposition of organic matter due to greater soil aeration. Over large areas of farmland, this has the unintended consequence of releasing more carbon and nitrous oxides (greenhouse gases) into the atmosphere, thereby contributing to global warming effects. In no-till farming, carbon can actually become sequestered into the soil. Thus, no-till farming may be advantageous to sustainability issues on the local scale and the global scale.