How to Read a Soil Test

A soil test is a short list of decisions. Most of the page is background. Two or three lines change what you do before this crop goes in. Read those first.

pH first

pH is the gate. It is not a nutrient. It decides whether the nutrients already in the soil can move into the plant. Below the range the crop wants, phosphorus ties up. Molybdenum drops off. Above it, iron, manganese, and boron get scarce. You can add the bag the lab circled and still watch the crop stall.

If one number changes this season's plan, it is pH. Lime or sulfur is the application. Fertilizer is the second pass, after the pH can use it. Do not skip the lime because the nitrogen looked low. The nitrogen was never the lock.

Organic matter

Organic matter is the slow tank. It feeds the soil life, holds water, and releases a little nitrogen as it breaks down. It does not move in one season the way pH does. A low number tells you to keep cover on the beds and to add compost as a program, not as a rescue. A high number does not mean you skip fertility. It means the soil can hold what you add.

Do not chase organic matter with a single heavy compost dump to “fix the test.” Compost also carries phosphorus. On a bed that already tests high in phosphorus, that dump is the opposite of a fix.

NPK

Nitrogen on a standard test is a snapshot. It moves with rain, with the last crop, and with soil temperature. Do not build the season on that one line. Build it on what this crop will take off the bed. The soil tool does that from the crop mix and the bed-feet, then credits manure already deposited.

Phosphorus and potassium are stickier. They are the lines worth reading against a target. High phosphorus is common on beds that have taken compost and manure for years. Adding more because the bag is balanced is how you load a nutrient the crop cannot use. The balancer caps phosphate against removal for that reason. Potassium is the one that often still needs a bag on a sandy bed. Read it on its own. Do not let a blended fertilizer drag phosphorus along for the ride.

CEC

CEC is capacity. It is how many nutrient ions the soil can hold before they leach. A low CEC is a sandy bed. It needs smaller, more often. A high CEC is a clay or a high-organic bed. It holds a larger application. CEC does not tell you to add a nutrient. It tells you how to split the application you already decided on.

Treat CEC as background unless you are choosing between one feeding and three. It does not pick the bag.

The misread

The common misread is chasing one nutrient while pH locks the rest. The lab flags potassium. You buy potash. The pH is still sitting where phosphorus and the minors cannot move. The crop looks the same. You buy another bag.

The second misread is treating every line as an order. A test is not a shopping list. pH changes the application this season. Organic matter and CEC change how you apply it. NPK changes the bag, and only after pH is handled. Phosphorus is the line you refuse to overfill.