Tilth

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Tilth is how good soil is for growing plants. Good tilth means soil particles are put together into stable clumps (aggregates), the soil feels spongy, and there are enough air spaces and moisture for roots to grow.

What affects tilth
- The way soil sticks together, how much water it holds, how well air can move through it, and the activity of living organisms in the soil.
- Tilth can change quickly with weather, moisture, how the soil is tilled, and what organic matter or fertilizers are added.

Tillage and tilth
- Tillage is the mechanical turning or mixing of soil to improve tilth and boost crop production.
- But long-term, especially with heavy plowing, tillage can harm tilth by breaking down soil carbon, making the soil dense and less porous.

What good tilth looks like
- The soil is moist but not waterlogged, airy, and easy for roots to penetrate.
- Roots grow where there is enough oxygen, water, and nutrients.
- Good tilth supports a balance of air, water movement, and nutrient supply.

Ways to improve tilth
- Tillage, adding organic matter, fertilizing, and irrigation can help, but doing these too much can hurt tilth.
- Crop rotation and cover crops rebuild the soil’s carbon sponge, which strengthens tilth. A combination of practices usually works best.

The balance of strength and friability
- Healthy tilth has aggregates that are strong enough to hold together but easy to break up with light tilling.
- If the aggregates are too strong, the soil forms hard clods and becomes less workable.
- Proper management improves soil structure, porosity, and tilth over time.

Soil structure and pore spaces
- Soils with good tilth have a range of pore sizes.
- Large pores drain quickly and allow air to move in during wet times, helping roots breathe and preventing problems from excess water.
- Small pores hold water for dry periods, helping crops cope with drought.
- Subsoil is important for deep roots and moisture access, but heavy equipment and wet conditions can compact it and reduce tilth.

The soil biota and organic matter
- Tilth is kept alive by the interaction of plant roots, microorganisms, earthworms, and other organisms.
- Root exudates feed bacteria and fungi, which help form a stable soil carbon sponge that binds particles into aggregates.
- These natural processes can be disrupted by excessive tillage, but they are essential for long-lasting tilth.

Crop rotation and cover crops
- Rotation helps restore tilth by adding organic matter and feeding soil life.
- Perennial crops with deep roots (like alfalfa) create channels for water and roots and add organic matter year after year.
- Grass and legume sods, as well as some dense-rooted cover crops, contribute organic matter and support soil organisms that stabilize aggregates.

Soil types and management
- Sandy soils have fewer small pores and tend to be drought-prone; adding organic matter greatly increases their water and nutrient holding capacity.
- Clay soils have fewer large pores and can compact easily; they need organic matter to improve porosity. In clay, adding up to about 25% organic matter can help.
- When tilling, a common guideline is to mix in organic material—e.g., if tilling 8 inches deep, add about 2 inches of organic matter.

In short, tilth is built by natural soil processes aided by mindful management: moderate tillage, ample organic matter, smart irrigation, and, especially, crop rotation and cover crops that keep soil life active and aggregates stable.