Rangeland Pitting

When rain falls faster than hard bare ground can take it in, it slides away across the surface in a thin film, called sheet runoff, carrying loose soil with it. Rangeland pitting breaks that surface into thousands of shallow overlapping hollows cut along the level, each holding a share of the water where it landed until it soaks in. The hollows also catch drifting seed and shelter it from the wind.

The pits are made in one pass by an implement towed behind a tractor, so the ground must be even and open enough to drive across. It suits slopes below about 2 percent, with modified designs used up to about 5 percent; steeper or broken ground erodes under the disturbance instead. Soil decides the outcome more than rainfall does. Sandy ground receiving roughly 200 to 750 mm (8 to 30 in) of rain a year responds well; cracking clay swells shut, and a hard bare crust sheds water off the shoulder before it reaches a basin. The basins must be cut and mounded rather than pressed in, and every pass must follow the level: pits running across a grade join up and concentrate the water the practice exists to spread.

The pit is scaffolding; the grass is the product. A pass over ground with no surviving perennial roots and no seed sown into it just makes holes, so sowing the fresh basins is the other half of the job. The young stand then needs stock kept off it, two or more growing seasons for warm-season grasses, because animals walking the treated ground flatten the basins and the treatment is lost. Fencing and a grazing rotation make that rest possible. The water-holding effect closes on its own as the basins silt in and the surface reforms, somewhere between four and thirteen years, so it buys a window for establishment rather than standing permanently. Where erosion has already cut into the ground, replanting the bare patch or trapping sediment below it does work pitting cannot.