Field diagnostics
Testing pH, organic matter, and drainage before you dig
This page explains how a representative soil sample is taken and what the main indicators measure. Results depend on each plot, so read them as a starting point for your own observation, not as a fixed target.
Sampling protocol
Four steps to a representative sample
A composite sample gathers several small cores from across a zone and mixes them, so that one lab result reflects the whole area rather than a single spot.
1. Identify the zone. Split the plot into areas with similar exposure, past use, and visible soil. Sample each zone separately. Note the location and the intended use of each area.
2. Collect sub-samples. Take 10 to 15 cores per zone in a zigzag pattern, at a uniform depth, usually the top 15 to 20 cm for garden beds. Keep the depth consistent between cores so the comparison holds.
3. Mix thoroughly. Combine the cores in a clean container, break up clumps, and remove stones, roots, and debris. Mixing is what turns separate cores into one composite sample.
4. Prepare for the lab. Air-dry the mixed sample away from direct sun, label it clearly, and send it to an accredited laboratory with the method and depth recorded.
Reading the results
What each indicator tells you
Soil pH
pH describes how acidic or alkaline the soil is. It affects how well nutrients are available to plants. Interpret it against the crops you intend to grow, not a single ideal value.
Cation exchange capacity
Cation exchange capacity indicates how well the soil holds nutrients such as calcium and potassium. It relates closely to clay and organic matter content, which vary widely across Breton soils.
Drainage and percolation
Percolation shows how quickly water moves through the soil. Slow drainage can point to compaction or heavy texture. Field observation, such as how a pit fills after rain, complements any measurement.