THE answer to the question, Why do farmers plough? should not be difficult to arrive at. Ploughing is almost universal. Farmers like to plough. If they did not get pleasure from seeing the soil turn turtle, knowing the while that by ploughing they dispose of rubbish that would later interfere with planting and cultivation, less ploughing might be done. Yet farmers are encouraged to plough. Deep ploughing is approved; or, in lieu of deep ploughing, farmers are advised to cut deep into the subsoil in every furrow. Such advice comes from farmers' papers, bulletins, officials whose business it is to advise farmers, and a long list of other sources from which farmers commonly welcome suggestions and information. There should be clear-cut scientific reasons to justify a practice so unanimously approved and recommended.

If there are such reasons I have failed to find them in more than twenty-five years of search. As early as 1912, when my fellow students and I were taking courses in soil management and farm machinery, we brought up the subject, asking our professors why ploughing, rather than a method of surface incorporation, should be the generally accepted practice in breaking the soil. A number of answers were offered, none, however, of a scientific nature; in the end some embarrassed lecturers had to admit they knew no really scientific reasons for ploughing. They suggested that the most important justifications for the practice might be that it " turned over a new leaf " for the farmer by the complete burial of preceding crop residues, thus leaving the land free from obstructions to future movements of planting and cultivating machinery.

Our experience was not unique. The editor of one of the leading American farm papers has this to say in a letter written to me on August 5th, 1937:

" It is a subject I became interested in about eighteen years ago. I made a two-thousand-mile trip among soil specialists and farmers and everywhere asked the question: Why do you plough? I was rather amazed at the unsatisfactory answers I received. Apparently farmers do not really know. When I summed up the answers it seemed that they had only one good reason for ploughing, and that was to get rid of weeds.⁽¹⁾"

In all truth, the ultimate scientific reason for the use of the plough has yet to be advanced. My own position, however, has already been advanced in earlier pages of this book. If I were advising farmers on the subject of ploughing, my categorical statement would be Don't— and for that position there is really scientific warrant. A brief review of the reasons frequently given for ploughing will give opportunity to point out the error involved in each.

An administrative officer in the department of agriculture of one of the New England states suggests in a letter that ploughing is designed to allow oxygen to reach the roots of plants; he suggests, too, that ploughed soil will not dry out so rapidly as unbroken soil. His reasons seem to cancel each other, indicating that he had not considered these two suggested effects simultaneously. Letting air into the soil is an efficient way of drying it out, particularly that portion which is disturbed. Since the roots of crops must develop first in this inverted (and necessarily dried) section of soil, it seems that my correspondent really gave a good reason for not ploughing.

This idea—that it is necessary to let oxygen into the soil has been in circulation for many years. It seems that those who pass it on do not pause to examine its implications. In a world organized as this one is, air is all pervading, except where something else fills the space. There is considerable space throughout all soils from the surface down to the level of ground water. Part of it is filled with capillary water, which clings to the rock fragments themselves; but since the spaces are too large for capillary water to fill them completely, air must fill the rest. When the water table ⁽²⁾ rises, this air is forced out of the soil; when it recedes again, the air re-enters.

It might be objected that more oxygen is required in the soil than can enter the undisturbed mass. Perhaps. In that case we should study the undisturbed forest floor. The surface of the soil where the giant sequoias grow was suitable for their needs a thousand years before the mouldboard plough was invented. It is not thinkable that such giants could have developed in the absence of an optimum amount of oxygen in the soil. It must be, then, that growing plants do not require more oxygen in the soil than naturally enters it in the absence of water. There may be extreme situations, for example where the soil has been excessively compacted by the trampling of animals or people, requiring special treatment. It is not clear, however, that ploughing would be the right treatment. The freezing and thawing of soil in winter usually assists a well-tramped path to grow up in vegetation the following season, unless the use of the path is continued.

Ordinarily it is permissible, in the United States, to quote freely the publications of the government and of the various state institutions. The information they carry is designed for public use, and wide distribution is desirable. Ohio State University's Agricultural Extension Bulletin No. 80 is the only exception to this rule I have seen. It was copyrighted in 1928 and reprinted in June, 1940, still retaining the copyright. The reprinting of this bulletin justifies the assumption that its contents are still considered correct. Significantly, along with other government and state publications as well as the books on soils of the last decade or two, it takes for granted that the farmer knows why he ploughs. The letterpress then proceeds to describe " good " ploughing as the complete burial of all " trash "—so complete that none is exposed even between the furrow slices. This, therefore, may be taken as the more or less official point of view.

Various books on agricultural subjects published about 1910 do give what may be considered hypothetical reasons for ploughing. Most of them are vague enough to, be interpreted in a number of ways. Here is a list:-

(a) Soil structure is made either more open or more compact.

(b) Retention and movement of water are affected.

(c) Aeration is altered.

(d) Absorption and retention of heat are influenced.

(e) The growth of organisms is either promoted or retarded.

(f) The composition of the soil solution is affected.

(g) The penetration of plant roots is influenced.

This list was compiled from a single paragraph of a well-known American soil text-book which was written in 1909. Though the authors did not realize it at the time, it is a bit of literary skating around a highly dangerous subject. The intent, apparently, was not so much to give information as to indicate in what various categories the student might expect to find it. The implied assumption is that ploughing improves the soil as environment for plant roots. The practice could scarcely be justified otherwise. Just how this improvement is accomplished is left wholly to the bewildered student's imagination. And while he is trying to rationalize this puzzle he is likely to conclude that, if ploughing really does improve the soil as a site for plants, the vegetation growing so lush on unploughed land must be to some extent underprivileged. Of course, even an astute student may miss that angle. It is obvious that most of us did.

Assuming ploughed land to be better for plant growth, we should find grass growing more freely on ploughed land than on similar unploughed land nearby. Weeds, too, should show preference for ploughed land. Spontaneous growth should take over and develop more rankly after land has been ploughed than before. Is this so? Observation is that, until ploughed land has subsided again to its former state of firmness, plants develop in it quite tardily, if at all. When dry weather follows the ploughing, it may be weeks or even months before either natural vegetation or a planted crop will make normal growth. The fact is that " bare " land, which is notably liable to be eroded more readily than soil in any other condition, consists almost wholly of land that has been disturbed recently by plough or cultivating implement. The only other bare land is that which has been denuded of top soil by erosion or other forces. There is significance in the fact that erosion and run-off are worst on bare land, and that bare land is defined above.

Take a casual glance at the landscape. Not only does the unploughed land continue to support its growth well while the ploughed land is recovering its ability to promote growth, but even the margins of the ploughed field itself continue to support their growth. Such evidence causes the argument that ploughing produces a better environment for plant roots to backfire. The loosening up, pulverizing, and inversion process seems a first-rate way to make good soil incapable of performing its normal functions in plant growth. The explosive separation of the soil mass wrecks temporarily all capillary connections, the organic matter sandwiched in further extends the period of sterility of the soil because of dryness. Therefore, it is not strange that ploughed soil is bare. Before it is ploughed, grass, weeds, and other vegetation grow normally because there is unbroken capillary contact from particle to particle, extending from the water table to the surface. After ploughing, this source of water is completely cut off until the organic matter at the ploughsole has decayed. Hence the soil simply takes time off from its business of growing things until its normal water supply is restored. There is no mystery about it. It is only the working out of natural law. Wishful thinking is peculiarly ineffective in preventing this undesired outcome of ploughing.

Another objectionable feature of ploughing is the merciless trowelling administered by the mouldboard to that portion of the furrow slice which is brought from the ploughsole and ex-posed to wind and sunshine. The effect is not noticeable, and probably not damaging, if the soil to the full depth of ploughing is dry enough to crumble; but in these days, when all soils seem to become more troublesome to handle, it is seldom that spring ploughing can be done early enough, if the farmer waits for the wet spots to dry out to a sufficient depth. Too often in his haste to get the year's work started, he rushes into the ploughing while the soil glistens as it leaves the mouldboard. Some men even plough when water follows them in the furrow. Such management of the soil certainly is playing fast and loose with resources which the soil might contribute to crop growth.

Ploughing done when the furrow slice is plastic creates clods; every clod is so much soil mustered out of service for the season. The tremendous pressure necessary to separate the furrow slice from its base compresses effectively any soil that is moist enough to be plastic; and a moderate amount of clay in plastic soil serves to harden the mass upon drying so that adobe-like clods result. Smoothing implements may reduce the size of these lumps, hut as clods they are likely to remain aloof from the rest of the soil throughout most of the growing season.

Such evidence of damage done by the mouldboard has passed unnoticed by farmers as well as by most other people. Several reasons may be given to account for the public's blindness to obvious faults of the mouldboard plough.

To begin with, conditions such as modern farmers face were remote indeed before the plough was first used with a crude mouldboard attachment. The land that had been cleared of trees was often not very well subdued, for it was a hopeless task to try to keep the soil free from competing weeds and shrubs while a crop was growing. The forest was for ever trying to recover the lost ground, and the only really effective tools farmers had against encroaching saplings, perennial weeds, and other unwanted growth were crude hoes, mattocks and spades. Such ploughs as they had threw the soil both to the right and to the left. They did not cover rubbish very well, much less uproot permanently the wild growth which cumbered the ground. To-day the " bull tongue " plough of the South of the United States of America is of somewhat the same design as most of the ploughs which preceded the mouldboard.

Into such an environment the mouldboard was introduced. It was a godsend. Pulled by an ox, or even by men, this plough would actually lift and invert the soil. This made it possible, by careful work, to eliminate completely the perennial weeds and some of the smaller shrubs. And, what was more important, the farmer who previously could manage only a small amount of arable land could now raise food on much more. Such an invention at a time when actual starvation might seem close at hand captured the imagination of rural people everywhere. It was electric in its effects upon contemporary thought. The population now could eat regularly and well, provided enough farmers could have mouldboard ploughs.

Inventions did not occur often in those far-off days. New aids to living were rare indeed. The mouldboard plough, destined to revolutionize the living conditions of world populations, marked the beginning of a new era. So completely did it fill the greatest material need of a poorly nourished mankind that it was accorded a place in people's thoughts such as is usually reserved only for saints and priests. The plough had saved humanity almost literally.

When we come to the eighteenth century we find that in England and America alike, the farmer had more trouble keeping unwanted things from growing than in getting his crops to grow. For him, then, the use of the plough was excellent strategy, because temporarily, at least, conditions were created which made it impossible for the weeds to grow. This gave the farmer time to get his root and grain crops started before the wild vegetation recovered from the setback caused by the ploughing. Once his crops were well started, the incomparable richness of the soil kept them well ahead of the weeds. Now that the richness has completely disappeared from most land in the United States, our proper strategy may well be the exact opposite of what was advantageous then. His ploughing, even though it covered a lot of organic matter, could not create for him the sandwich, organic matter profile (OMP), for there was too great a depth of organic matter inherent in the soil.

The crude mouldboards of the eighteenth century could not be favourably compared with the burnished products of to-day's factories. Hammered out by hand at forges erected at or near the ore mines, they could become smooth only through much use. They were designed by guess after many trials and did not become stabilized to dependable shape until a century later. Despite its shortcomings — much easier to appraise from our perspective than from that of the contemporary farmer—the plough was, even in this crude state, the greatest invention of the age. It dispelled hunger as the first oil lamp dispelled darkness. Aladdin's lamp could not have been more wonderful.

When in the middle of the nineteenth century the first experiment station was established at Rothamsted, England, no one seems to have raised a question whether the neat work done by the mouldboard plough might be responsible for the trouble farmers were beginning to experience in growing their crops. The men of science who manned that first station, as well as those in charge of the state experiment stations later established in the United States, inherited an unquestioning reverence for the plough. The doctrine of the Divine Right of Ploughs passed down from generation to generation, so that the possibility that the plough might account for the waning fertility of the soil never seriously occurred to anybody along the line. For decades, to my own personal knowledge, men have sensed that the ploughing in of a layer of organic matter at the ploughsole must of necessity interfere with capillary movement; but the subconscious feeling that The Plough Can Do No Wrong apparently prevented anybody from doing anything about it. The result is that, although we have had experiment stations in America for more than three-quarters of a century, not one of them conducted tests, before 1937, designed to compare directly the effects of ploughing, on the one hand, with the surface incorporation of all organic matter on the other. Failure to do this has definitely handicapped the development of basic soil information which might easily have prevented the debacle toward which American soils have been drifting.

The failure to harmonize the implications of ordinary observations with really scientific information may be the result of historical lag, or an attitude of mind, or mere carelessness, or, finally, a combination of all three. If we consider the published recognition given to the importance of organic material in the soil surface, especially since the opening of the present century, it is difficult to avoid assessing blame, on the score of carelessness, against those who did not look beyond their immediate data to the established data gained from ploughing. This is almost implicit in the following:

The Yearbook of the United States Department of Agriculture for 1903 carries this statement on page 284: " Decayed organic matter, by itself or in combination with mineral soil, absorbs moisture much more rapidly than soil containing little or no organic matter; hence, the greater the amount of leaf mold and other litter, the more rapidly will the rain be absorbed. Rapidity of absorption is also influenced by the degree of looseness of the mineral soil. In the forest the mulch of leaves and litter keeps the mineral soil loose and in the best condition for rapid absorption."

If such a statement seems sufficiently old for its validity to be questioned, compare it with the following, taken from pages 609 to 610 of the Yearbook of the same department for the year 1938: " Forest litter—the carpet of dead leaves, twigs, limbs, and logs on the forest floor —serves in several ways. Water falling as rain on bare soil dislodges silt and clay particles by its impact. These are taken into suspension and carried into the tiny pores and channels between the soil particles as the water makes its way downward. Very shortly the filtering action of the soil causes the openings to be clogged by the particles; water can no longer move downward through the soil, so it flows over the surface carrying with it the dislodged silt and clay; and erosion is actively under way. A protective layer of litter prevents this chain of events by absorbing the impact of the falling drops of water. After the litter becomes soaked, excess water trickles gently into the soil surface, no soil particles are dislodged, the water remains clear, pores and channels remain open, and surface flow is eliminated except in periods of protracted heavy rains."

I can detect no significant difference in the meaning of the two quotations. The latter gives a more intimate picture of the processes involved, but it fully confirms the less graphic description in the earlier statement. Moreover, every intelligently conducted experiment so far undertaken in this direction confirms the truth presented.

A paragraph from a letter dated February, 1940, should be interesting in this connection: " The Department of Agriculture has long been interested in developing new methods of soil treatment which will maintain and build up the organic matter content of the soil. Studies carried out by the Soil Conservation Service at a number of locations have already produced unusually outstanding results along this line. At Statesville, North Carolina, for example, it has been found that several inches of pine needles spread over the soil surface reduced the loss of soil by erosion to a point almost beyond measurement. There was also a considerable increase in the organic matter content of the soil and indications point to a worthwhile increase in crop yields. In Nebraska subsurface tillage, which leaves straw and other litter undisturbed on the soil surface, has proved remarkably effective in reducing soil and water losses and in preliminary experiments has led to a material increase in the yield of several crops tested." This was signed by the Assistant to the Secretary of the United States Department of Agriculture. It may be said that my letter, to which this was the reply, had mentioned and asked for comment on the fact that the mouldboard plough had never been put to test for validation. No mention of the matter was made in the official reply.

The fact that no advance whatever is apparent, when the statement of 1903 is compared with those of 1938 and 1940, indicates that effort to implement the earlier findings into general farm practice has been neglected. The statements from the year-books refer to forest soils, of course; but that fact must not obscure the larger fact that the findings discussed concern principles of universal application. Principles which are valid in the forest are valid in the field, always; so it seems that researches into the importance of organic matter on the surface of crop land should have been started as soon as the earlier announcement had been made. If any such work was begun earlier than 1937, I have been unable to find any record of it.

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