Soil Testing: Interpreting the Results

Colorado State University soil testing results

Published May 25, 2013, in the Wyoming Tribune Eagle, “Did Barb’s soil pass the test? The results are in on a soil sample the columnist had analyzed by CSU.”

By Barb Gorges

The other day, my soil test results came in by email from Colorado State University’s Soil, Water and Plant Testing Laboratory.

As I opened the attachment, I felt a little trepidation, not unlike anticipating getting my cholesterol numbers from the health fair. Both tests document my progress in healthy living–or making healthy soil–within the limits of genetics–or bedrock.

pH balance

My front lawn’s pH was high at 7.4, but my vegetable garden was 7.2, within the preferred range of 6 to 7.2.

So I have alkaline soil—typical for this region. Most plants will still grow fine, except for acid-loving species. Because acidification treatments cost money and are not long lasting, we Westerners should instead take advantage of alkaline-loving plants.

Soil texture

Local gardeners often talk about Cheyenne’s clay soil texture so I was surprised my vegetable garden tested as sandy loam and the front yard as sandy clay loam.

“Loam” describes the perfect combination of sand, silt and clay particles for horticulture and agriculture: just enough sand for good drainage, just enough silt and clay to hold water and nutrients.

The modifier “sandy” means water will drain more quickly. This explains why I needed to water the veggies every morning last summer. With “clay” in the lawn’s soil texture description, it means it holds water well, but percolation is slower. That means when you water, apply it slowly.

Organic material

In my vegetable garden, organic material tested at 3.9 percent. This isn’t bad for an area that was first cultivated a year ago and amended with leaf compost.

The recommendation is to increase this category to 5 percent over the next two or three years by adding 2 to 3 inches of plant-based compost or 1 inch of animal-based compost in spring or fall, incorporating it into the top 6 to 8 inches of soil.

The front lawn, which I would love to convert to flower garden, came in at 4 percent. Though I can improve that, less may actually be better for native, drought-resistant plants I would choose.

Why organic matter?

Without it, soil would be nothing but weathered rock. Yes, you get many nutrients from minerals, but organic material feeds the soil microorganisms which feed your plants. The process also improves soil structure, which improves water permeability and absorption (think lower water bill). There can be as many as a billion microorganisms in a quarter teaspoon of topsoil. They are the real engines of plant growth.

Remember where organic material comes from? Plant and animal matter. It’s a cycle as old as life.

Fertilizer history

Sometime during the 20^th century, chemists determined plants could grow with nutrients from chemically processed mineral salts.

Today, it is common knowledge that highly processed fertilizers don’t feed microorganisms the way organic (plant and animal-based) fertilizers do. And sometimes they leave behind a buildup of salty residue that is hard on plants.

Unfortunately, the big fertilizer companies have become so influential that it is not always easy to pursue what we now call organic gardening and farming—back to the future, as I think of it, since organic growers use Grandpa’s pre-chemical farming knowledge augmented by new discoveries about organic materials.

Fertilizers

The vegetation of natural landscapes is the result of perfect nutrient cycling. However, gardens and lawns are more intensively grown and the natural nutrient cycle often needs our help.

We have a tendency to over-fertilize, which pollutes groundwater and surface water with the excess, and wastes our money.

As I read labels on various bags and bottles, I realized perhaps the reason we over-fertilize because many of us have trouble understanding the labels. And so we calculate fertilizer amounts as best we can–and then throwing in a little extra for good luck.

Actually, we should err on the side of less. It’s surprising we don’t kill everything growing in our yards with our generosity.

I confess to being stingy. In the days I only grew perennial flowers, I never fertilized with anything other than decomposing leaf mulch. Mark uses Revive, an organic fertilizer, on our lawn.

But now, thanks to my soil test, I have actual numbers to strike a balance between stingy and overgenerous.

 N is for Nitrate (Nitrogen)

Both my lawn and vegetable garden were low in nitrogen. Nitrogen is one of the three major nutrients, the one responsible for stems and leaves. But if you put too much on in one year, it interferes with producing flower and fruit buds and the excess disappears before the next growing season.

 P is for Phosphorus

Surprisingly, in my vegetable garden, this came in high. But the lawn needs some. Phosphorus gives plants strong roots, resistance to disease and good fruit development.

 K is for Potassium

Again, the vegetable garden came in high, and the anaylsis recommends adding a bit to the front yard–if I convert it to flowers. Plants need potassium for successful blooming—for flowers and fruiting vegetables like tomatoes.

Other results

Electrical conductivity: In both areas of my yard, electrical conductivity was low, a good thing, meaning no salty, plant-killing soil.

Lime: Rated medium, OK for growing plants.

Why a local store sells lime is beyond me. With very, very few exceptions, adding lime to Wyoming soils will only increase alkalinity, perhaps to toxic levels.

Micronutrients: Zinc, iron, manganese, copper and boron are all necessary for healthy plants but, as in my yard, they are seldom deficient here.

Recommended fertilizers

All processed fertilizers, whether they are chemically manufactured or lightly processed organic—meaning carbon-based, not necessarily organic as in growing method—have their N-P-K percentages listed on the label. The plants don’t care where these nutrients come from. But organic-based fertilizers release nutrients more slowly, provide some of that all important organic material, and they are safer around children and pets.

Needing just nitrogen for the vegetable garden, the soil test results recommended urea or ammonium sulfate, or one of three more organic choices: blood meal, corn gluten meal or alfalfa meal pellets—for that final item, think rabbit food.

The lawn needs three times as much nitrogen and phosphorus, by weight, as it does potassium. None of the “balanced” fertilizers containing all three really came close to these proportions, so I also looked at the individual recommendations for phosphorus and potassium. For phosphorus it was either bone meal (organic) or triplesuperphosphate (chemical). For potassium, potassium chloride or composted manure.

Shopping

Chemical fertilizers are available at garden centers all around town. Some of the organics are common as well, such as bone meal. Grant Farms has a good selection of fertilizers from organic materials.

For corn gluten, cottonseed meal and alfalfa pellets, check A & C Feed.

Calculations

My soil test result sheets explained how to figure out how much of the unconventional fertilizers I needed—after all, alfalfa pellets don’t come with nitrogen-phosphorus-potassium analysis.

Note: Here’s the formula cited by CSU’s lab, using nitrogen as the example: “…take the amount of N needed (my soil test results recommended 0.3 lbs. per 100 square feet) and divide by the % N in the fertilizer. For example, if your fertilizer contains 30% N, take 0.30 lbs (N needed) divided by 0.30 (N in the fertilizer) to get 1 lb of the 30% N fertilizer that is needed to apply per 100 sq. ft. For rates per 1000 sq. ft. multiply the quantities by 10.”

Essentially, for my 100 square foot garden I only need a pound of 30 percent nitrogen fertilizer—15 pounds of alfalfa pellets that will provide organic material as well. Perhaps my leaf compost can substitute for some of that.

Spreading

I think I can spread fertilizer over my tiny garden evenly by hand before digging it in, but the lawn, if I don’t convert it to garden this year, needs one of those spreaders for which you can adjust the rate.

On the other hand, a mature lawn doesn’t need fertilizing until late summer, so I can put that off for now. But when we mow we should start leaving our clippings on the lawn to decompose. They will not become thatch—other issues cause thatch build-up.

 The next test

In four or five years we can do another soil test and see how we’ve progressed toward our goals.

Caveats

Always read fertilizer directions thoroughly—and follow them for best results, and for your own health.

Think twice about using manure. If it’s fresh, it may burn plants. Avoid pig, dog or cat manure because their diseases can last years in soil and travel via vegetables to humans. And if manure from herbivores isn’t composted at high enough temperatures, it may carry viable weed seeds.

Be aware of how much salt comes with the fertilizer of your choice.

Organic materials from your own yard—unless sprayed with pesticides or diseased—are not yard waste. They’re treasure.

There are many fertilizer sources I haven’t discussed that are worth looking into, such as fish emulsion and cover crops that become green manure, among others.

 Resources

If you have questions on how to improve soil, it may be worth consulting an expert, especially at one of the local agencies that offer free advice.

You can also find out from them how to get your soil tested.

Also, check their websites or offices for bulletins with garden advice tailored to our area.

 Free Local Gardening Advice

**Laramie County Conservation District, 11221 U.S. Hwy 30, 772-2600, http://www.lccdnet.org.

**Laramie County Cooperative Extension, 310 W. 19^th, 1^st Floor, 633-4383, http://www.wyomingextension.org/publications/.

**Cheyenne Botanic Gardens, 710 S. Lions Park Dr., 637-6458, http://botanic.org/ (gardening advice specifically for Cheyenne).

Soil Testing: Preparing the Samples

Colorado State University’s soil testing application and instructions

Published April 21, 2013, in the Wyoming Tribune Eagle, “Get the dirt on soil: Maximize your lawn and garden success by finding the exact concoction of nutrients they need—with a little help from CSU.”

By Barb Gorges

You might be used to putting fertilizer on your lawn and in your garden.

But do you really know what nutrients they need and how much?

Yes, the major nutrients, nitrogen, phosphorus and potassium, the three big numbers you see on fertilizer bags, are important.

But the balance may not be right for your soil. You could be adding too much of a good thing.

Besides the fact that you might be wasting your money, consider the bigger picture.

If the concoction of fertilizer has more nitrogen than your lawn needs, the excess washes into the ground water, polluting someone’s future drinking water.

Excess phosphorus washes into local streams and ponds causing algal blooms, possibly suffocating other aquatic life.

Unlike your plants’ other needs of water and light, it’s not always obvious when your plants need more or less food. In extreme cases, you’ll see yellowed leaves or stunted growth in malnourished plants.

And too much nitrogen, for example, could spur the plant into producing an overabundance of leaves but no blossoms—no flowers, no fruit.

To get ahead of these issues before the growing season, you may want to test your soil.

Luckily, sampling is fairly easy. Unlike my Soils 101 class back in college, I don’t have to dig a 5-foot pit to find out what my soil is made of. This time, I only had to send in samples from the top 6 inches of the areas I wanted the lab to examine.

What a soil test tells you

Soil texture will tell you something about its fertility.

Is your soil sandy? If so, water (and dissolved nutrients) will percolate through it quickly.

Is your soil clayey like so much of Cheyenne’s? Water moves through it slowly. The lab can recommend how much water and what rate you should apply it to your garden or lawn.

Testing for electrical conductivity sounds odd, but that’s the way to find out how salty your soil is, which can affect the availability of nutrients to plants. Some soils are naturally salty, but often here they become that way because too much fertilizer has been added over time, or the irrigation water is salty–comparatively speaking.

Knowing a soil’s pH will help you understand how easily some nutrients can be taken up by plants. It will also tell you what plants may not grow well.

The Cheyenne area typically has alkaline soil. That is why soil amendment advice for the acidic soils of the eastern U.S., such as adding lime or wood ash, can be counterproductive here. Acid-loving plants, such as blueberries and rhododendron, will not grow here unless you plant them in a container in which you can acidify the soil.

The percentage of organic matter in your soil should match your garden plans. It is possible to add too much compost or manure for the plants you want to grow.

Get a soil-testing kit

Home testing kits sold in stores are not usually designed for our alkaline soils and also, the information will not be precise enough.

Colorado State University’s Soil, Water and Plant Testing Laboratory in Fort Collins is one of the few remaining labs of this kind at land grant universities. Being in our neighborhood, the folks at the CSU lab will understand our soils better than those farther away.

The standard test costs $31. See the accompanying information on how to get a sampling bottle, directions and submission form.

Follow the directions

Whatever lab you use, follow their directions.

CSU’s indicated that to get a balanced sample, I needed to collect the same amount of soil at each level—I needed to dig a perfect cylinder 6 inches deep. And dig one of these perfect cylinders 5 to 15 times in random places in my garden or lawn.

How do you get a cylinder of soil? The right tool for the job is a soil probe.

I went out to the Laramie County Conservation District office and asked Jim Cochran, district manager, if he had one I could borrow. He did. And you can borrow one, too.

A soil probe is a nifty little tool, a stainless steel pipe about an inch in diameter and three or four feet long, with a crossbar handle. You punch it into the ground 6 inches and pull out your sample, which you then dump out the side vent.

Well, almost. In my vegetable garden I had trouble keeping the soil in the tube until I was ready to dump it in my plastic dishpan. Maybe the soil needed to be just a little moister. I also tried twirling the probe to keep in the dirt.

Twirling didn’t get me more than an inch into one spot in my front lawn, even after making sure I was between blades of grass. I hit solid clay near the house—probably left by the builders 50 years ago. I had to get husband Mark to help. And then, I needed a sharp tool to dig the clay out of the probe.

I decided to sample both the vegetable garden and the front lawn areas. I took enough sub-samples of the lawn to make two cups’ worth and then mixed them together in a dishpan, doing the same in a separate dishpan for the vegetable garden sub-samples.

The directions said to break up clods and remove organic matter. I picked out as many roots as I could, and a few worms. I spread the dirt (excuse me, soil) out in the bottom of the pans and by the next day both samples were dry enough. Don’t use the oven—it will stink up the house and distort your nitrogen readings.

An important part of the testing is filling out the paperwork. The lab wants to know what’s been growing in the tested area, what fertilizers have been used and how much it is irrigated, so they can understand any anomalies they find. They also want to know what you plan to grow so they can make recommendations.

There is no good or bad soil. It just depends on what you want to grow and whether your soil currently is capable.

In a way, my perennial flower bed performs its own suitability exam. I plant a new type of perennial and if it doesn’t thrive–which could be due to incompatible amounts of light and water as well as incompatible soil–I know I should remember that experience and try something else the next year.

But now that I’m growing vegetables, which can deplete the soil, and we have a lawn that isn’t quite thick enough to shade out the dandelions, I’m curious to see what a soil test can tell me.

In next month’s column we’ll look at the soil testing results and find out what they mean.

 Where to get a CSU soil sampling bottle, directions and submission form

**Laramie County Conservation District, 11221 U.S. Hwy 30 (nearly 10 miles east of downtown, west of I-80 Exit 370), 772-2600.

**Laramie County Cooperative Extension, 310 W. 19^th, 1^st Floor, 633-4383.

**www.soiltestinglab.colostate.edu (put soil sample in Zip-loc-type bag and print and fill out the submission form)

**Soil, Water and Plant Testing Laboratory, Ft. Collins, Colo., 970-491-5061.