Weeds -- Guardians of the Soil

by Joseph A. Cocannouer

5. Plant Roots

ONCE while sitting in on an agronomy class during iny first year at college (I wasn't permitted to enroll in tbe course owing to my not having the prerequisites), thc professor announced what he considered a new and very important discovery. "Imagine the young roots of alfalfa making ten times the growth of the stem during the first three weeks! Why, it's almost unbelievable -- "

Forgetting that I was merely a visitor, I bobbed up from my seat in the back of the room -- "It's that way with weeds, Professor! " I chirpcd right out. "The roots of most all weeds grow lots faster than the tops -- "

All eyes turned suddenly upon me -- and I wilted back onto my bench. The professor went on with his discussion of alfalfa seedlings, ignoring the profound wisdom I had so generously offered to his class.

But it struck me as being nigh to shocking for a teacher of agriculture just then to be discovering that the roots of plants grew more rapidly than the above-ground parts. I didn't know a thing about alfalfa at that time, but I was plenty familiar with the root habits and stem habits of sunflowers and lamb's quarter and cockleburs and a passel of other weeds. On our own farm I think we unconsciously meant weed roots whenever we thought of weed injury to our crops. The vegetative parts were royally disliked, needless to say, but largely because the green parts indicated what was taking place down in the soil. The various leaf changes meant specific root changes; appearance of flowering buds and later of flowers told us what kind of growth the roots were making. Every farm boy knew that, if the weeds were growing thick, like a jungle, most of the roots were feeding close to the surface of the ground. But if each weed had ample room for unrestricted growth, by the time the plants were a foot tall the roots were foraging far from home.

Those gluttonous roots! Mother could see them only as vile enemies of her potatoes and cabbages and sugar corn that must be taken from the soil completely. When we had not been able to eradicate the thistles and pigweeds. and sunflowers and such before they became large, we had to get out and pull the things on rainy days. We had to carry the weeds completely off the field, too, or if the field was large, we grudgingly allowed sufficient space for building weed piles. We never thought of employing the pulled weeds as a mulch on top of the ground where they could have helped to conserve moisture and keep the soil cool. We wouldn't even give the weeds a chance to decay and go back into the soil as fertilizer.

Luckily for our soil, only a small fraction of the weed roots could be extracted, even when the ground was slushy. Since weed eradication could receive only its allotted time, the weeds often passed beyond the pulling stage before we got round to them. Then they had to be cornknifed. "Can't go fishin' today -- got to cut poison nightshades and sunflowers outa our corn!"

"Mean yer knifin' 'em already?"

"Shore! Nightshades got buds!"

"Gee! Then that means their roots are powerful. Break too many cornroots to pull 'em -- "

"And Pap says it'll take me and Jim three, four days -- "

The redroot pigweed intrigued me particularly in those days. Not that I had any special admiration for the thing, but because on a plant growing alone the vegetative development used to be such a perfect indicator of what the roots were doing at every stage of growth. The black and shiny seeds of the redroot, produced by the thousands by every full-grown plant, have marvelous vitality. The husky red rootlets go galloping down into the ground immediately the seed germinates, and the subsequent roots don't stop foraging as long as there is life in the stem. At first this pigweed stem is delicate and innocent looking, but in a short time it takes on the rough, don't-touch-me appearance. By the time the greenish flower clusters appear in every branch axle, which is usually before the plant is a foot tall, the lateral roots, which spring from the strong taproot, have penetrated long distances in every direction. At this stage most of the feeder roots are diving into the subsoil for their food and water.

And by the time the main stalk with its rough flowering parts reaches two feet or so, an even larger proportion of the feeding roots are working in the lower soils. At this period, even if the soil is muddy, the weeds are so well anchored they are difficult to pull up. And what those weeds in all such situations are gathering up to be stored in the roots and stems and leaves! Nitrogen and phosphorus and potash and almost everything else needed in the plant-food line. Nature's soil improvers -- and we were treating them all the time as some of our worst enemies.

And what is true of the pigweed is also true of its usual companions: the sunflower, lamb's quarter, sow thistle, ragweed, ground cherry -- even the trifling cocklebur.

In classifying plant roots, botanists list first the strong or anchorage roots that hold the plant in the ground against the pull of the elements. These roots also support the plant so it can get the necessary sunlight, for the sun is the power plant that supplies the energy for the leaf laboratories. The anchorage roots have to be rigid, yet in a measure flexible to stand the severe strain that may be placed upon them. After the anchorage roots come the great mass of roots known as the food hunters. These roots range in size from slender threads to roots many inches in diameter. Normally the food-hunting roots prowl through all parts of the soil world.

A few domesticated crops, and practically all herbaceous wild plants that I have listed as valuable weeds, appear to have two distinct groups of feeding roots: those which secure their food entirely in the surface soil, seldom wandering far from the base of the mother plant, and which usually are vigorous only during early growth; and those rovers that go far for food and water. I have found these two types of roots on desert plants in Africa, on many tropical plants, and on temperate-zone wild annuals. On some common weeds, like the pigweed, ragweed, and sunflower, the two types of roots are at times very noticeable.

I had my first introduction to these two types of feeder roots when we were digging the well. Practically all weeds do have plenty of roots that feed in the surface soil, and until the deep feeders are well established in the lower soils the former will get their share of the food materials near the surface of the ground. Once the deep feeders are settled to their task of feeding down below, however, most of their feeding is done down there -- unless the subsoil is extremely weak. From then on, provided the weeds don't crowd each other, they will more than pay back to the cultivated crop all they robbed it of.

The reason those common wild plants known as field and garden weeds are persistently classed as pests is because they are judged entirely by what the surface-feeding roots appear to be doing. No thought is given to those deep feeders which are improving the soil by fiberizing it and thus enlarging the feeding zone for the cultivated crop -- to say nothing about those large quantities of rich food materials which they pump up to the surface from the lower regions.

The rover roots generally (except in grasslike plants) cannot themselves take up the food materials once they have reached them. This task of absorption must be carried on by the delicate, very tiny root hairs which protrude mostly from the smallest rover roots. These absorbing rootlets are very short-lived, and are developed right where they are to do their work. They have no openings whatever, but can absorb food-substances when the latter are dissolved in water. By providing no openings into the root hairs, Nature guards the plant against many undesirable substances, probably to the ultimate great benefit of the human race.

Since the root hairs are so frail, their ability to function efficiently depends on the condition of the soil world. Actually, it is possible for a soil to be rich in plant-food elements, yet give low production because some of the factors which encourage the growth of root hairs are lacking. The condition most likely to prevent the development of the short-lived feeding rootlets is lack of suitable soil fiber, which means a soil that is either too loose or too compact. Neither can feeding roots grow efficiently in a soil that is too wet, too dry, or too cold. In other words, a soil may be declared strong on chemical analysis, yet give low production because of improper physical condition. The soil may be locked so far as the feeding roots are concerned.

Where farmland is giving poor returns, in the great majority of cases it is the physical condition that needs most attention. The soil probably has all the minerals it needs, if not in the surface soil, then stored in the subsoil. A few lush crops of deep-rooted weeds, grown as a link in a rotation scheme, or as properly regulated companion crops, will go a long way toward righting the situation.

Before the root hairs can absorb any of the food substances, those substances must be dissolved in the soil water, and the water must be in the form of a thin film which surrounds or clings to the particles or granules of soil. Except in water plants, very little water can be taken in by the rootlets save from this delicate film. The root hair coils partially around the particle of soil which contains the food materials and which is enveloped in the water film, then "draws" into itself the film containing the materials in solution. The water stream then moves up through the roots and stems, climbing even to the tops of the tallest trees. Starting in the soil-world laboratory, going through many intricate processes while yet in the soil world and after leaving it, finally ending up in the leaf factory, this stream becomes the greatest watercourse in our Nature world. When the leaves have completed their part of the entire operation, the result is a finished food product without which there could be no human life -- nor any other life.

When no factors are missing in the soil-world laboratory, there is a reserve supply of food and water in the lower soil zones -- in the fiberized subsoil -- that can be called upon during periods of drought, or when the surface soil is being too heavily mined. But that condition obtains normally only when all major links in the fertility chain are functioning. Such soils will produce crops with far less water than will a soil that is out of balance. In a poor soil it takes a lot of water film to meet the meager food requirements of the plant. Crops dry up quickly on poor land, not only because they need moisture, but because, having been deprived of food, they lack the power of resistance.

And now the question: what is it about weeds that makes it possible for them to do all this soil-improving work not possible with most farm crops? If weeds are directed, or even if given a fair chance to go it alone, they will establish that reserve referred to above, through the fiberizing of the subsoil.

Most wild plants have been forced, through their struggle for existence across the ages, to develop roots which will forage deeply for food and water under adverse conditions. The larger portion of domesticated crops, by virtue of their having been more or less pampered by man, have lost most of the soil-diving ability possessed by their wild ancestors -- if they happened to come from wild ancestors. What has happened is that most crops have received their improvement above ground; their root systems have grown weaker with civilization. The root vegetables are exceptions, of course. As a rule crop roots are not fighters in soils where it requires a real struggle to make a go of it.

Aside from being husky divers, many wild plants have the ability to "eat" their way through compact soils because of special dissolving substances which they exude from their roots. The dissolving materials soften hard obstructions and thus aid root passage. But, so far as I have been able to discover, these dissolving materials are not harmful to the weed roots or to the roots of crops that may be growing with the weeds. Sweet clover is an excellent example of a weed that eats its way through hard soil. Just what weeds put out this dissolving substance is not definitely known so far as I am aware. Sunflowers and ragweeds I think do, and probably cockleburs. The chances are that all deep-diving weeds have some ability to eat their way through stiff soils.

And there always seems to be room in the weed-root tunnels for the roots of cultivated crops. I have found the roots of some garden vegetables following the roots of pigweeds and lamb's quarter down into the subsoil, though ordinarily these same vegetables are not deep feeders. Beans and sweet corn and onions like to send their feeders into the lower soils along with those of the weeds. In a clean onion field the onions feed very close to the surface. Many normally shallow-feeding crops will forage deeply in a soil if the soil conditions are made right for them.

It is hard to make farmers or gardeners see that the weed roots are not the water robbers they appear to be. If pusley or pigweeds or nightshades or ragweeds or what not are found in a garden or field when a drought strikes, the wild plants are blamed if the crop dries up. The fact is (unless the weed crop is very heavy), the weeds will not only feed in the lower soil zones themselves -- unless there is no subsoil -- but will also be the cause of an upward movement of capillary water along the outside of their roots. This will happen even if there is only a small amount of water stored below. The upward-moving moisture becomes immediately available to the crop roots that are feeding in the surface soil. Though the crop may dry up in the end, the chances are that the weeds prolonged its life considerably.

To repeat: a crop growing in a weedy field, provided the weed crop is reasonably thin, will go through droughts better than crops grown on clean land. Moisture comes up along the outside of the weed roots; many crop roots accompany the weed roots into the lower soils and thus secure extra moisture in that manner; and the weed growth checks evaporation from the surface soil.

Concerning weed roots as good soil fiberizers, a Kansas farmer reported to me what he considered a very important discovery on his part. He said he had several acres of extremely tight land with which he had been struggling for years. Finally, in disgust, he abandoned the fight -- turned the land over to cockleburs. Or rather, he turned a part of the field over to the burs, while he continued to farm the remainder.

"And you ought to see what the cockleburs have done to that abandoned part!" his neighbor told me. The farmer himself said he was waiting anxiously for the burs to take over the rest of the field as they had done on the first part. He had a mess of cockleburs, all right, on the abandoned area -- and last year made a good profit from corn produced with the help of the cockleburs. The cockleburs, with their deep-forage roots, opened up the tight land and fiberized it. The weeds, not being too thick, had done a good job.

One of Nature's valuable laws is that two unrelated root systems do better when growing together than when either is growing alone. There are, of course, occasional exceptions to this. The wild growth in forest or meadow shows the law wonderfully in operation. Nature keeps her soils in complete balance largely in this manner. Wherever one species of plant occupies an area alone, it will usually not long survive. My boyhood weed cove was an exception. Ordinarily the single species gives way to a mixed growth. And this mixed growth is likely to hold its own for a long stretch of years. This is Nature's system of crop rotation. But she needs to do much less rotating when the roots are dissimilar.

In maintaining her green carpet on the earth, Nature wastes nothing. For instance, some plants secrete strong substances from their roots (substances which are apparently not useful in the dissolving processes) which, if left in the soil, will prove injurious to some unrelated plants as well as to the plants exuding the materials. But many unrelated plants find these substances in no way harmful when contacted by their feeding roots. Actually, the substances may be taken up by these plants as food. Or if not as food, certainly with no ill effects. A few members of the sorghum family leave in the soil considerable toxic material. In the irrigated sections of the west it often takes two or three cropping seasons to eradicate this poison. However, when legumes are grown with the sorghum, the land rarely registers any lowering of production during the following season. The legumes seem to take care of the poison left by the sorghum.

And weeds -- every one of our soil improvers -- will also take care of those toxic materials. I remember a field of grain sorghum that was given little or no cultivation, with the result that the weed crop was more conspicuous than the sorghum, though there was an excellent crop of sorghum growing among the weeds. The land produced heavily the following year, a crop unrelated to sorghum, but an adjoining field that had been kept free from weeds on the same type of land did not do so well. The weeds strengthened the land and took care of the sorghum secretions at the same time.

Several years ago a friend told me about a case of tree planting which indicated how unrelated trees, when employed together in building a farm grove, can mean longer life for the grove than when only one species is planted on the land. It seemed that an "impractical" farmer had moved into the community from the city. In the eyes of the old settlers, this man did everything incorrectly -- and was too contrary to accept advice even when offered to him gratis.

One of this city man's worst sins of commission was that he planted a timber lot, using several types of trees carefully interspersed. I don't remember just what the trees were, other than that they were all hardwoods. The man who gave me the report said he was a boy when the grove was started. He was now past middle age, and the grove of mixed trees was still holding on well in his old neighborhood. All of the other groves had vanished almost completely. It would seem that the mixed grove survived because of the diversified root systems which had been able to work constructively together.

Now to summarize the values of deep-diving weed roots: (1) these roots are persistent explorers in a rich world which is to a large degree unknown to domestic crops -- until the weed roots build highways leading into it. Thereafter the crops are provided with a more extensive feeding zone. (2) The weed roots pump those "lost" food materials back to the surface soil; (3) the weed roots fiberize the subsoils and (4) help to build a storage reservoir down there for water; water moves up along the outside of the weed roots -- up to the surface soil and the thirsty crop roots which feed in the surface layer. That is why a crop on "controlled" weedy land can go through a drought better than a clean crop on similar land.

And yet we slaughter them! We destroy with poison the natural source of the essential soil fiber, and with our food-producing soils screaming for fiber and the food elements which the fiber carries with it. Aside from destroying the weeds, we also pour poison into the soil-world machinery. The claim by some spray promoters that the poisons, after the spray has been applied, will vanish into the air, certainly will not hold water in all situations, and probably not in many. A goodly portion of the poison will be in or on the bodies of the dead weeds, and cannot fail ultimately to reach the soil -- unless every sprig of the weeds is removed from the land. Even then it will not be possible to eradicate all of the poison. Perhaps a single spraying will do little or no harm; but the persistent use of "weed chemicals" is pretty sure to bring about a condition which may prove difficult to overcome once the soil has taken up any quantity of it beyond a still unknown danger point.

However, the greatest injury to result from the continuous use of weed sprays on cultivated land will in all likelihood prove to be the deprivation of the lower soils of their fiber content which some of our weeds are particularly capable of putting down there. Without this fiber the soil particles settle close together -- into a compact condition. Ultimately the heavier soils become so "run together" that the upward movement of capillary water is almost entirely cut off. And when this condition obtains, though the surface layer may be amply fertile, the soil world as a whole is in danger of being thrown out of balance, because it is not a completely normal feeding zone for most plants. And, of course, in such cases there is no emergency reservoir to call upon; growth even of crop roots is restricted; and that valuable storehouse of minerals and nitrogen in the subsoil remains locked up.

But even so, there are situations where weed chemicals would seem to have a constructive place. There are times, you know, when reputable physicians prescribe strychnine as a medicine. Using chemicals in eradicating poison ivy may well be compared with the doctor and his strychnine. Here is a place for it! And I can see cases where "noxious weeds" may need to receive the same treatment -- as an emergency. On the other hand, there is no sense in slaughtering the mockingbirds and cardinals and song sparrows and other songbirds -- simply because the crows pull up the young corn.

Occasionally a report comes in to me that some chemical weed killers actually enrich the soil; enhance crop production directly. Such is entirely possible, for it is not difficult to stimulate soil into false production. A few commercial fertilizers will do that, and weed sprays could do it if enough of the spray reached the soil. But stimulation is not fertilization.

Then again I have had reports to the effect that some crops on sprayed land did not seem to react favorably to the spray, while others did not appear to be affected either way. What, some wish to know, is the reason for this? Also, why do some crops seem to do very well on sprayed land during a part of their growing season, and do poorly at other periods of their growth? "They don't act that way when we cut the weeds -- "

As I have stated elsewhere in this book, there is much about the workings of the soil world that we do not yet understand. It goes without saying that we still have much to learn about the effects of many of our chemical compounds on cultivated soils. But there is one thing that we do know with certainty: anything that interferes with the constructive laws of Nature down there in the soil world is going to stir up trouble. Whether the poison goes down into the soil through the weed roots, whether it is carried into the soil through the dead bodies of the weeds when the latter decay, or whether the stuff is sprayed onto the soil directly -- there is bound to be some interference with the soil-world machinery. And it is entirely possible that a very small amount of some poisons will create far more havoc than is at present suspected of them.

Next: 6. Weeds as Mother Crops

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