Chapter 3. Various Soil Tests Pro & Con

The pH test is not the only one. Your soil's structure, organic composition, mineral (nutrient) content—all can be tested by vari­ous methods, with home kits or professional equipment. My prin­cipal objection to the use of most "all-purpose" home garden soil test kits is that the readings they give mean very little unless interpreted by someone who is experienced in the techniques of testing.

I often encounter the effects of a delayed action fuse of Christmas-gift soil test kits—usually in late March or early April. Up to that time, bad weather has prevented the gardener from trying out his gift kit, but as the soil thaws he rushes eagerly forth to do battle with his soil problems. Soon he is in a state of desperation because his soil seems to have gone to pieces over the winter. His tests show excesses or shortages of nitrogen, phosphorus, potash, iron—almost everything—and some of the readings run right off the chart.

On questioning him, I find he has grown good plants in the past (that's natural, for soil test kits usually are given to better garden­ers), and he says he has never before noticed any serious deficiency symptoms. My advice to him is to sit down and drink a cup of coffee and forget soil tests until early June. Then test again, and the read­ings will be satisfactory. The reason for his "problem," as mentioned before, is simply that cold slows up or stops bacterial action, which throws the soil (and thus the tests) way out of kilter.

In my opinion, as far as chemical testing is concerned, gardeners should confine themselves to a simple acidity-alkalinity pH check. If the dollars spent for chemical toys such as "complete" soil test kits were spent on fertilizer instead, gardeners and gardens would be much better off. This is not meant to be a blanket condemnation of testing. A farmer who is growing hundreds of acres of corn or wheat often saves himself hundreds of dollars by acting on the results of a soil test. Usually, however, if he is not himself a university-trained man he has the help of his county agricultural extension agent who not only knows how to make actual tests, but to read them. He usually tests in fall at which time soil can best be checked for shortages of essential minerals as well as for pH. If lime is needed, ground limestone can be put on in fall and will have time to act so that an accurate reading can be taken the following spring to see if more is needed.

For home gardeners who still insist they want their soils tested, a list of state agencies is included in the Appendix.

TAKING A SOIL PROFILE

If you have serious soil drainage, compaction or structural prob­lems, it may pay you to take a soil profile. This is done simply by digging a pit into a "central" area of the garden to get an over-all idea of what lies underneath the topsoil. The pit ought to be at least two feet deep and wide enough so you can get down in it to "read" the soil profile.

At the top of the profile you will see the dark layer of topsoil (unless a building contractor got rid of clay from an excavation by spreading it over your lot, in which case a layer of hard, stiff, light-colored strata will overlay the darker topsoil). Sometimes, in semi-arid regions, topsoil may be lighter than layers underneath but this is rare in any soil where garden plants will grow.

The depth of the topsoil usually shows how deeply roots of grasses and shallow-rooted weeds have penetrated. In prairie soils where bluegrasses often penetrate as deep as two to three feet, a surface layer of that depth is often found. The darker color of the topsoil indicates where perishable plant tissue has decayed, leaving behind a residue of humus and carbon.

In the soil scientist's language, this upper layer is called the A horizon. In many soils, just below it is another darker layer, but separated from it, which is called the Ax horizon. In some soils, where organic matter is tightly held by the topsoil, no well-defined At hori­zon develops. In such cases the next lower layer is the B horizon or subsoil. The science of pedology makes a great deal of these hori­zons. From them, earth scientists can read the history of soil forma­tion. However, our interest is in checking depth and condition of the topsoil and the subsoil.

WASH TESTS

I am often asked whether a wash test cannot be used by the home gardener to see what materials make up a given soil. A direct yes or no answer is not possible. Light sandy soils containing little clay are easy to check in this way. The heavier the soil, however, the less accurate a wash test will be. The difficulty lies in breaking the bond between the acid clay particle and its cluster of alkaline particles. However, I find that if two tablespoonfuls of sodium nitrate are added to the soil sample, some of the electrical charge holding clay and lime together can be neutralized.

To make a wash test, use a half-gallon mason jar. If any other type of container is used, be sure it is round so the water and soil can be swirled around rapidly. Put half a cupful of soil into the jar and then half fill it with water. Pull down the top tightly and swirl the soil and water for half a minute. Allow this to settle and then swirl again. Repeat several times.

With each mixing, more and more coarse particles will drift to the bottom and more and more clay particles will drift to the top, with silt settling out between them. Some of the clay particles may not settle out for several days: they are so fine they form a colloidal solution in water.

Interesting information on a soil can be uncovered with the wash test. For example, a soil which one gardener complained was always cracking and was so high in clay he couldn't work it, produced an entirely different picture when washed. It contained only about IS per cent clay, but about 45 per cent silt. In this proportion, clay and silt particles intermeshed so completely that they worked like the cement in a concrete mixture. The addition of steamed cinders to this soil worked wonders with its texture.

In soil testing laboratories, where samples are dried and sieved into their component parts, a much more accurate reading is pos­sible, but these tests are not necessarily of more value than the simple home-made wash test which gives a pretty good idea of the proportions of various soil ingredients.

FERTILIZER ELEMENT TRIALS

Serious students of soils will want to find out how plants respond to various fertilizer elements. A lawn is the best place for such in­vestigations. Tests of chemicals are not difficult but do require the use of an accurate fertilizer spreader. The hopper is filled with a chemical that supplies only one fertilizer element and a strip of it is laid down across the lawn. Other single-element chemicals are ap­plied in the same way, until the entire lawn is covered with strips of various elements. Be sure to leave one or more grass strips untreated to serve as a check.

Next, apply strips of the same materials in the opposite direction, creating a checkerboard. This will give a reading both of single el­ements such as nitrogen, phosphorus, potash and others, as well as of any stepped-up effect when two are used in combination. Results of tests of this kind are often surprising. Certain treatments show little or no response while others will produce dark green islands of vigorous growth among the other tests. Usually the combination giving the best response is the one for your soil.

Fortunate owners of small greenhouses can run similar tests in­doors during the winter to give a clue to treatments for the entire garden the following spring.

TISSUE TESTS

The testing of plant tissues, particularly leaves, for nutrient levels is usually carried out for farm operations rather than for the home garden, but occasionally a friendly county agent can be found who knows the technique and will "read" your feeding efficiency. Foliage tissue tests are particularly valuable because they show the rate at which food is being taken up by the plant. Such tests can detect a nutrient deficiency long before the plant itself begins to show it. (See Appendix for a fuller discussion of this testing method.)

Chapter Digest

An answer is given to the controversial question of "to test or not to test" the soil; excluding pH tests made with inexpensive home kits, the answer is "don't bother." There are too many variables involved in testing for nutrients and other conditions, and a non-scientific gardener can easily misinterpret the test results. Professional testing, of course, is costly but can be relied upon. Soil profiles and wash tests are practical ways for the home gardener to find out about his soil makeup.