The term “till soil” can cause confusion because it refers to two distinct concepts: Glacial Till, a natural geological sediment, and tilled soil, the result of an intentional agricultural process. In geology, “till” is a noun describing sediment left behind by ice sheets. Conversely, in farming, “till” is used as a verb to describe the mechanical act of cultivating or disturbing soil for planting. This article clarifies both meanings, exploring the origin of the geological sediment and the consequences of the agricultural practice.
Glacial Till: The Geological Definition
Glacial Till is a geological sediment deposited directly by the ice of a glacier or ice sheet as it melts and retreats. This material is unsorted and unstratified, lacking the distinct layers or size separation seen in sediments carried by water or wind. It is a chaotic jumble of rock fragments ranging from the finest silts and clays to large boulders. The composition of Glacial Till reflects the bedrock the glacier passed over, as the ice erodes, grinds, and plucks material from the landscape beneath it. When the ice melts, this debris is deposited instantly, creating landforms like moraines.
Tilled Soil: The Agricultural Process
Tilled soil is the result of mechanically manipulating the upper layer of the earth using equipment such as plows, harrows, disks, or cultivators. This practice of tillage is fundamental in farming, primarily serving to prepare a suitable environment for planting seeds. The immediate goal is to loosen the soil, which facilitates easier root penetration and promotes seed-to-soil contact for germination. Tilling also serves as a method of weed control, as the mechanical disturbance either uproots or buries existing weeds. Farmers use tillage to incorporate soil amendments, such as fertilizers, manure, or compost, distributing these materials uniformly. This deliberate aeration is intended to improve water infiltration and gas exchange in the short term.
Structural Implications of Mechanical Tilling
While tilling offers immediate benefits for planting, the repeated mechanical action has several long-term consequences for soil structure and health. A significant issue is the degradation of soil aggregates—the small, stable clumps of soil particles held together by organic matter and microbial secretions. Tillage fractures these aggregates, pulverizing the soil and making it more susceptible to compaction. This breakdown increases the soil’s vulnerability to wind and water erosion, as there is less residue cover and the loosened particles are easily washed or blown away. Tilling also accelerates the loss of organic matter because the increased exposure to oxygen speeds up the decomposition rate by soil microbes. Repeatedly plowing to the same depth can also create a dense, compacted layer just below the tilled zone, known as a plow pan or hardpan, which severely restricts water movement and root growth.
Alternatives to Traditional Tillage
Concerns over soil degradation have led to the widespread adoption of conservation-focused alternatives that aim to minimize mechanical disturbance. The most intensive of these is “No-Till” farming, where crops are planted directly into the residue of the previous crop without any plowing or turning of the soil. Specialized equipment, like no-till drills, is used to open a narrow slit for the seed and fertilizer, significantly reducing soil disruption.
Minimum and Reduced Tillage
Another approach is “Minimum Tillage” or “Reduced Tillage,” which involves reducing the number of passes, the depth, or the intensity of cultivation compared to conventional methods. Techniques like strip-tillage only disturb a narrow band of soil where the seeds will be planted, leaving the rest of the area covered with residue.
Cover Crops and Manual Methods
The use of cover crops, such as non-cash crops like rye or vetch grown between main crops, helps suppress weeds, build organic matter, and protect the soil from erosion. This reduces the need for mechanical intervention. For smaller-scale gardening, tools like the broadfork can be used for manual aeration of the subsoil without inverting the soil layers, relieving compaction while preserving soil structure.