Soil Health and Soil Management

What soil health means

Soil health is the soil’s ability to keep working as a living system: holding water and nutrients, supporting roots and soil life, and resisting erosion and compaction. A healthy soil isn’t defined by one number. It shows up as crumbly structure, earthworms, fast water infiltration after rain, and crops that hold on longer in a dry spell.

The USDA Natural Resources Conservation Service sums up soil health management in five principles that most agronomists would recognize:

• Disturb the soil as little as possible.
• Keep the surface covered with crops or residue.
• Grow a diversity of plants through rotations and cover crop mixes.
• Keep living roots in the ground for as much of the year as possible.
• Integrate livestock where it makes sense.

Our guide on how to improve soil health on a farm turns these into practical steps.

Soil testing basics

A standard soil test measures pH, the main nutrients (phosphorus, potassium and often magnesium, calcium and sulfur), organic matter and cation exchange capacity, which is the soil’s ability to hold nutrients. Add electrical conductivity if salinity is a concern. Most farms test each field every two to four years, more often on high-value crops or where a problem is being corrected.

How you sample matters more than which lab you use. Take 15 to 20 cores across each management zone, at the same depth each time (commonly about 6 inches or 15 cm for cropland), mix them in a clean bucket and send a subsample. Sample at the same time of year so results are comparable. Keep cores from areas that are obviously different, such as a low wet patch or an old fence line, in a separate bag. Our overview of soil testing instruments covers what labs and field kits each measure.

Soil acidity and salinity

Acidity

Most field crops do best with a soil pH between about 6 and 7, though some, such as blueberries and potatoes, prefer more acidic ground. Soils turn more acidic over time through rainfall, crop removal and nitrogen fertilizer. Low pH locks up phosphorus, releases aluminum that damages roots, and slows the bacteria that fix nitrogen in legumes. Agricultural lime is the standard fix; the rate depends on the soil’s buffer capacity, which a lab test measures. Lime moves slowly, so apply it months ahead of the crop that needs it. Our article on neutralizing acidic soil with lime goes through rates and timing.

Salinity

Salty soils draw water away from roots, so crops wilt even when the ground is wet. Salinity builds up where irrigation water carries salts, drainage is poor, or a shallow water table brings salts to the surface. The usual answers are better drainage, leaching salts below the root zone with good-quality water, and choosing tolerant crops. Gypsum helps on sodic soils, where sodium has broken down soil structure. See our guide to reducing soil salinity.

Structure, organic matter and tillage

Soil organic matter is a small share of most soils by weight, but it does a lot of work: it binds particles into aggregates, holds water and nutrients, and feeds soil life. It builds slowly, through roots, residues, cover crops, manure and compost, and it is lost faster when soil is tilled often or left bare.

Tillage is the biggest lever most farms have. Reduced tillage and no-till protect structure and organic matter and cut erosion, though they can mean cooler, wetter seedbeds in spring and a heavier reliance on herbicides for weed control. Compaction from heavy machinery on wet soil is the other common problem; controlled traffic and staying off wet fields prevent most of it. Our comparison of till and no-till farming weighs the trade-offs, and the piece on soil organic carbon explains how to raise it.

Mapping soil across a field

One soil test per field gives an average, and averages hide the problems. Satellite data helps show where a field varies, which makes it possible to sample and treat zones differently. With Farmonaut satellite crop monitoring, each field report includes soil acidity, salinity and organic matter, and the field’s 16 satellite views include soil organic carbon, radar soil moisture, elevation and slope at 10-meter resolution. Use those maps to place your sampling zones, then let the lab results set lime and fertilizer rates.

Crop health maps from past seasons are useful here as well. A patch that has been weak in the same place for several years usually points to something in the soil, such as low pH, compaction, poor drainage or salt, and is worth its own sample bag. A patch that moves from year to year is more likely to be weather, pests or management.