After obtaining the results of the soil test from a reputable lab — often the Cooperative Extension Service in your state or the Soil Food Web laboratories (www.soilfoodweb.com) — people are eager to tear open the envelope and begin reading. It’s here, though, where the confusion begins.

I always ask the audience another question: “If the soil test tells you to spread 20 pounds of product per 1,000 square feet, how many of you know how to do that?” In a room of 100 people, I usually get two or three people to raise their hands. That means that most folks are pointing down limestone and fertilizer — or worse yet, herbicides, insecticides and fungicides — as part of a giant guess.

The first step, therefore, in working with your soil test is to learn how to spread the required amount of nutrients on your lawn. The second is to understand the nuances of lawn soil that the soil testing service may not even understand.

A drop spreader works with a rotary auger at the base of the hopper that extends for the length of the hopper. The product essentially falls onto the ground directly below the spreader, therefore taking longer to cover an entire lawn than it does with the whirlybird model. Drop spreaders have their place, however, because many products such as weedkillers should only hit the lawn and not the flower garden. Drop spreaders are far more accurate and effective in tight spaces.

Both types of spreaders have dials that regulate the flow of product from the hopper. Most dials have numbers or letters, and these are often published on the back of fertilizer bags as a reference setting for that particular product. One stern piece of advice: Please IGNORE these numbers and letters.

Dials on spreaders can’t gauge how fast you walk or how high the humidity is that day, and both factors influence how fast a product comes out of the hopper. Spreader dials also have no way of knowing whether you have clay soil or sandy soil. Any fertilizer or pesticide application based on the blanket application rate on the back of a bag cannot possibly be accurate for your particular lawn.

Instead, you need to learn to operate the lawn spreader based on some old-fashioned math. Say, for example, the soil test tells you to spread 20 pounds of limestone per 1,000 square feet. The correct way to spread this is to pour a pound of the lime into the hopper, set your dial at a low setting, and then begin walking until the pound is applied. Then measure the area you just covered. If you blanketed 100 square feet with the pound of lime, then you would be spreading 10 pounds per 1,000 square feet. Based on the recommendation from the soil test you would need to cover the area twice, which is always a good idea anyway. Walk in the perpendicular direction during your second pass over the lawn.

If the limestone is 70 percent calcium by weight, then 20 pounds of limestone would contain 14 pounds of calcium. Many times, the soil test will specify an exact weight of calcium to add per 1,000 square feet. The same holds true for other nutrients such as nitrogen, phosphorus and potassium. If the fertilizer bag says the product contains 5 percent nitrogen, 1 percent phosphorus and 3 percent potassium — meaning a 5-1-3 designation on the front of the bag — that means that in a 40-pound bag you would be buying two pounds of nitrogen, 0.4 pounds of phosphorus and 1.5 pounds of potassium.

If your soil test tells you to apply one pound of nitrogen per 1,000 square feet, which is the maximum amount of nitrogen to ever apply all at once, then you would need to apply half the bag to get the necessary nitrogen. Here, though, you need to ask even more questions before getting started:

THE MYSTERY RATIO — Here’s something you won’t hear from most soil testing agencies outside of the Soil Food Web: The relationship between calcium and magnesium is among the most important in lawn care.

For years, especially in the East where soils are inherently acidic, folks have applied limestone to raise the pH. That limestone is often dolomitic, meaning it contains a high percentage of the heavy metal magnesium. Although soil does need magnesium to grow grass, too much magnesium will leave the soil overly compacted. The result is often a high percentage of weeds.

If your soil test result from the Cooperative Extension Service tells you to add limestone at a specific rate, you’ll almost always be better off adding high-calcium or calcitic limestone rather than dolomitic limestone. In soil, the ideal ratio is seven times more calcium than magnesium. Since calcium moves through the soil slowly, it’s almost impossible to add too much unless you’re rototilling it into the root zone of the grass.

Even though most soil scientists and laboratories still don’t know much about this “mystery” calcium-magnesium ratio in gardening, history provides ample evidence that calcium is often a deciding factor. Benjamin Franklin carted in copious amounts of gypsum to his Philadelphia farm and, by acclaim, had the best gardens of anyone in the colonies. Gypsum contains high levels of calcium. Amateur soil scientist Jay L. McCaman also reports in his book Weeds and Why They Grow that more than 90 percent of common lawn weeds appear as a result of not enough calcium in relation to magnesium.

So the next time you go shopping for limestone to “sweeten” your soil, read the back of the bag carefully. Products like Mir-a-cal from Jonathan Green and calcitic lime from Encap are starting to show up on store shelves.