Tillage is an agricultural practice that involves mechanically disturbing the soil to prepare it for planting. This practice uses tools like plows, harrows, and cultivators to break up the soil, control weeds, and incorporate organic materials. Historically, the primary purpose of tillage has been to manage weeds that compete with crops for resources such as water, sunlight, and nutrients. It also creates a suitable seedbed, allowing for better seed placement and germination.
Soil Health Degradation
Tillage disrupts the natural structure of the soil, which is composed of aggregates—small clumps of soil particles held together by organic matter and microbial activity. The mechanical action of plows and other equipment breaks these aggregates apart, weakening the soil’s structure and making it more vulnerable to erosion.
This disruption accelerates surface runoff, leading to the loss of valuable topsoil through wind and water erosion. When soil particles are dislodged, they can be carried away by strong winds or washed away by rainfall, resulting in the loss of fertile topsoil that is rich in nutrients and organic matter. This process diminishes the soil’s ability to support healthy plant growth over time.
Tillage also accelerates the decomposition of organic matter within the soil. When soil is disturbed, more air is introduced, which speeds up the activity of microorganisms that break down organic materials. A rapid loss of organic carbon from the soil occurs. A reduction in soil organic matter lessens the soil’s capacity to retain water and nutrients, making it less resilient to drought and requiring more external inputs like fertilizers.
Impact on Soil Life
The physical disturbance caused by tillage has negative effects on the diverse community of organisms living within the soil. Beneficial microorganisms, such as bacteria and fungi, are susceptible to this disruption because tillage destroys their microhabitats and can directly harm them. These microbes are essential for various processes, including nutrient cycling, which makes nutrients available for plants.
Tillage also impacts macroorganisms like earthworms, which are important for improving soil aeration and structure through their burrowing activities. Studies have shown a decline in earthworm populations in soils that are regularly plowed, with deeper disturbance being more harmful. Their burrows enhance water infiltration and root penetration, and their castings contribute to soil fertility, but these benefits are diminished when their populations decline.
The loss of soil biodiversity due to tillage has broader implications for ecosystem health. When microbial communities and earthworm populations are reduced, the soil’s ability to perform natural functions, such as breaking down organic matter, suppressing disease, and maintaining a stable structure, is compromised. This reduction in biodiversity can lead to less resilient and less productive agricultural systems over time.
Contribution to Greenhouse Gas Emissions
Tillage plays a role in releasing greenhouse gases into the atmosphere, primarily carbon dioxide (CO2) and nitrous oxide (N2O). Disturbing the soil exposes previously sequestered organic carbon to oxygen, accelerating its decomposition, which leads to the release of CO2, a major greenhouse gas, into the atmosphere.
The exposure of soil carbon to oxygen promotes its loss. Long-term cultivation practices have been linked to historical carbon loss from soils, which contributes to atmospheric CO2 levels.
Tillage can also alter nitrogen cycles in the soil, increasing the emission of nitrous oxide (N2O). N2O is a potent greenhouse gas, with a global warming potential significantly higher than that of CO2, estimated to be around 298 times greater over a 100-year period.
Water Pollution and Runoff
Increased soil erosion resulting from tillage contributes to sediment runoff into nearby water bodies. When topsoil is dislodged and carried away by rain or irrigation, it can enter rivers, lakes, and streams, causing turbidity. This increased cloudiness of the water reduces light penetration, which can harm aquatic plant life and disrupt the food chain, negatively impacting fish and other aquatic organisms.
The degradation of soil structure and the reduction in organic matter also increase the likelihood of nutrient leaching and runoff. Fertilizers applied to tilled fields, especially nitrogen and phosphorus, are more susceptible to being washed away during rainfall events or leaching through the soil into groundwater. These excess nutrients can then flow into waterways.
The influx of nitrogen and phosphorus into aquatic ecosystems can lead to eutrophication, a process where excessive nutrient enrichment causes dense growth of algae and aquatic plants. When these large algal blooms die and decompose, they consume dissolved oxygen in the water, creating “dead zones” that lead to fish kills and a decrease in aquatic biodiversity. Some harmful algal blooms can also produce toxins that are dangerous to humans and wildlife.