A bottom plow is used to slice, lift, and flip soil upside down, burying crop residue, weeds, and surface debris while creating a loose, well-drained seedbed for planting. It’s one of the oldest and most recognizable pieces of farm equipment, and it remains the go-to tool when a farmer needs to completely turn over a field. The term “bottom” refers to each individual plow unit (the cutting and turning assembly), so a “three-bottom plow” has three of these units working side by side.
How a Bottom Plow Works
The plow does its job through a curved metal plate called a moldboard. As the plow moves forward, a sharp edge at the front (the share) slices horizontally through the soil at a set depth. The moldboard then lifts that slice and rolls it over, sometimes flipping it a full 180 degrees. This action fractures compacted ground and creates a long, turned-over ribbon of soil called a furrow.
Several parts work together in each bottom. The share does the initial cutting. A piece called the shin helps guide the soil up onto the moldboard. The landside runs along the wall of the unplowed ground, keeping the plow stable and tracking straight. Some setups include a trash board, a smaller plate mounted above the moldboard that helps push surface material like stalks and straw down into the furrow so nothing is left sticking out.
Primary Uses on the Farm
The main reason farmers reach for a bottom plow is to prepare ground for planting. By inverting the top layer of soil, the plow accomplishes several things at once. It buries 80 to 90 percent of crop residue left on the surface after harvest, pushing old stalks, roots, and leaves underground where they decompose and add organic matter to the root zone. It buries weed seeds deep enough that most can’t germinate. And it breaks up compacted soil, improving drainage and giving new roots an easier path downward.
This type of plowing is also used to deal with heavy weed pressure or insect pest problems. Flipping the soil buries pests that overwinter near the surface and disrupts their life cycle. In fields with thick stands of weeds, a moldboard plow can roll under tall growth more effectively than lighter tillage tools. Farmers preparing vegetable ground, converting pasture to cropland, or breaking sod for the first time commonly use a bottom plow because no other implement turns the soil as completely.
One-Way vs. Rollover Plows
Bottom plows come in two basic configurations, and the choice between them depends on field shape and irrigation setup. A one-way plow turns all its furrows in the same direction. The farmer typically plows in a loop pattern, working from the outside of the field inward one year and reversing the pattern the next. This leaves a raised ridge along the starting line (called a back furrow) and a depression in the middle or at the edges (called a dead furrow). Finishing off dead furrows and headlands takes extra time and passes.
A rollover plow, also called a two-way or reversible plow, has two sets of bottoms mounted on a frame that rotates. At the end of each pass, the operator flips the frame so the plow turns soil in the opposite direction on the return trip. This means every furrow falls the same way, leaving the field flat with no dead furrows. Rollover plows are heavier and pull harder, but they save significant time in irregularly shaped or small fields. They’re practically required for fields with furrow or border irrigation, where a dead furrow in the middle of the field would disrupt water flow.
What Happens After Plowing
A bottom plow is a primary tillage tool, meaning it does the heavy, first-pass work. The rough, chunky surface it leaves behind isn’t ready for planting on its own. Farmers follow up with secondary tillage, typically a disk harrow to chop up clods, then a field cultivator or drag harrow to smooth and level the seedbed. This sequence of moldboard plow followed by disking and harrowing is what’s meant by “conventional tillage.”
Tradeoffs and Soil Health Concerns
For all its effectiveness at preparing a clean seedbed, moldboard plowing carries real costs to soil structure. Flipping the soil exposes organic matter that was protected inside soil aggregates, and microbes quickly break it down, releasing carbon dioxide. Research at Michigan State University’s long-term experiment station found that no-till fields accumulate more soil organic carbon than conventionally tilled fields over time. More striking, a single pass with a plow on soil that had never been farmed reduced soil aggregation to levels found on fields tilled for more than 50 years. Soil structure built up over years of rest or no-till management can be lost almost instantly.
Tilled fields also lose more greenhouse gases. When Conservation Reserve Program land (ground that had been resting under perennial cover) was converted back to cropland, conventional tillage released 100 percent more carbon dioxide and 20 percent more nitrous oxide than no-till conversion over the following six months. Plowing increases the risk of erosion too, because bare, loosened soil is far more vulnerable to wind and rain than ground protected by surface residue.
These findings have pushed many grain farmers toward no-till or reduced tillage systems. But the bottom plow hasn’t disappeared. It remains valuable in specific situations: breaking new ground, managing severe weed infestations, incorporating lime or manure, preparing vegetable fields that need a deep, loose seedbed, or dealing with compacted soil that lighter tools can’t fix. The key is understanding it as a powerful but disruptive tool, best used when the situation genuinely calls for complete soil inversion rather than as a default annual practice.