University of Wisconsin–Madison Soil and Forage Lab

This lab uses:

• Phosphorus: Bray P1. Made for acid to neutral soils. It reads low on high-lime soils.
• Potassium: Bray P1. Made for acid to neutral soils. It reads low on high-lime soils.

Labs pull nutrients out of soil with different chemicals, and each one gives a different number for the same soil. 20 ppm on one test and 20 ppm on another don’t mean the same thing, so check which test your report used before you compare it to a chart.

• Basic test. pH, phosphorus and potassium, usually with calcium and magnesium. Enough for most gardens and lawns.
• Organic matter. How much organic matter the soil holds, which sets how much nitrogen it releases.
• Salts. Soluble salts (EC), and sodium where salt or poor drainage is a problem.
• Micronutrients. Zinc, iron, manganese and copper, sometimes boron.
• Texture. Sand, silt and clay, which sets how fast water drains and how much the soil holds.
• CEC. Cation exchange capacity: how many nutrients the soil can hold on to.
• Lead and metals. Lead and other metals, worth testing in old yards and near old buildings.

• The Lawn and Garden test covers pH, organic matter, phosphorus and potassium, with lime and fertilizer advice.
• Phosphorus and potassium both come from the Bray-1 extract.
• Drop samples at the lab or ship them. After-hours drop boxes are outside the door.

Sources: [1] [2] [3]

• Plant or turf disease, nematodes and insects

The lab’s site doesn’t say whether it takes samples from other states. Ask before sending one.

• Take 10 or more small cores across the area and mix them in a clean bucket. One spot tells you about one spot.
• Sample gardens and lawns about 6 inches deep, below any mulch or thatch.
• Keep beds that are grown differently, like a lawn and a vegetable garden, as separate samples.
• Wait a couple of months after fertilizing or liming, so the test reads the soil and not the last bag.
• Use the same lab and the same tests each time, so the numbers compare from year to year.

Your county Wisconsin Extension office can help you take the sample and read the report.

Once the report comes back, type the numbers into the soil test calculator to see what to add for your bed or lawn. The soil test guide walks through each line of the report.

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