7. Soil by Machine
WITH a good deal of truth it may be said that we have allowed our soils to degenerate chiefly because there have been too generous supplies of good soil everywhere over the face of the earth. The existence of these fertile areas, and particularly the discovery by Columbus, at an opportune time, of a few hundred million extra acres previously unheard of and unsuspected, served to make man's way easier. As long as this condition obtained, it was not imperative that man learn how to provide tillable soils where none existed.
It is now time, however, that the truth be realized. We can recreate soil wherever good soil formerly existed, and we can do so by machinery. Any exceptions to this categorical statement will be found to result from human mistakes, as, for example, land made untenable by the silting of the streams that naturally would drain it, or desert sands robbed of both their water-holding clay and the conveniently shallow water table. For the whole category of areas that have suffered merely water erosion, however severe, there is still the definite assurance that as good soil as ever existed upon them can be restored. Much the same can be said of areas damaged by wind erosion, or, by excessive cropping and grazing.
Nature did not put precisely the same kind of soil everywhere. There has been a great variety of difference in soils because of the complex forces by which they were created. That we need not go into here, except to say that the one thing all soils had in common was organic matter in or on the surface. We need not be interested in the slightest as to whether the soil was what the scientist calls a podzol, a prairie, a chernozem, or just plain dirt; the significant thing about each of these, in the virgin state, was the quantity of organic matter it contained, which implies also the conditions under which the moisture supply would permit the maintenance of a certain amount of organic matter in the soil.
It is not even necessary that soil be of brunette shade in order to produce well, although soils made productive by nature always reveal their quality through the presence in them of decaying organic matter, which is necessarily dark in colour. (The single exception to this statement -- if indeed it can be called an exception -- is the desert area to which irrigation water has to be supplied. Such soil is rich by reason of the suitable minerals which are brought up from the soil depths by water, which, on evaporation, leaves the minerals in abundance. The dependence of desert soil on irrigation really rules it out of this discussion.) Enough organic matter can be put into the surface at a single discing to make any ordinary soil productive almost immediately; yet the quantity of organic matter introduced at one time may be too little for its decay to influence the colour of the soil. This was true of the soil I farmed in 1940, with rye three to six feet tall disced in to serve as the organic source of nutrients for my crops. I could never detect any of the dark tint which is associated with organic decay, yet the crops behaved as if there was plenty of fertility in the soil.
The blackness of virgin soil is the result of a cumulative process more or less complex, since it involves repeated deposits annually of plant, and possibly animal, debris upon the soil surface -- to which must be added the destructive effect of an innumerable biologic population which lived and died in this environment and contributed in turn toward its enrichment. The effects of the resulting black deposit in and just under the surface -- not in an impassable layer several inches under the surface -- kept all the water absorbed by the soil in the same zone that plant roots would be searching for it. The supposition that for hundreds of years nothing had disturbed its surface does not satisfactorily account for the fertility of the soil. We have developed some useless theories in that field. Men have come to feel, for example, that centuries are necessary for the development of a productive soil. The satisfying truth is that a man with a team or a tractor and a good disc harrow can mix into the soil, in a matter of hours, sufficient organic material to accomplish results equal to what is accomplished by nature in decades.
In nature, long periods were occupied in developing the black OMP of the meadow or forest because the mixing in of organic matter was a task mainly for bugs and worms. The soil surface was their home environment. They worked slowly but painstakingly, and they developed that first essential of all life, the health of the land.
This has been true, necessarily, of the natural formation of soils everywhere. The grasses of the plains developed thicker, blacker layers of organic matter in the surface because they were annual plants. They died down each autumn. New growth came up each spring. The dead plants accumulated, and were mulled over by the living things of the soil surface. Only a few years of this process were necessary to develop the tough sod the settlers found when first they undertook the gigantic task of ploughing it. It is not surprising that in many instances ten-ox teams were necessary for the purpose.
The forest did not lay down organic layers as deep or as black. Why? Because the decay of leaves each year was more complete, and the material was re-used in tree growth. The farmer who cleared the land got merely the "crumbs" from the forest's "table." It could not be otherwise.
With the halo of mystery thus stripped from the mechanics of natural soil building, it no longer appears impossible for men to create their own soils as needed, and where needed. It has to be remembered, too, that when the soil of an old forest site has been restored to a condition as productive as the one which originally existed, there will not be the necessity of waiting for stumps and roots to rot out, as was once the case, before the land can be handled profitably. Many a farmer of another generation found that, by the time these interferences were out of the way, the soil was no longer productive. The modern farmer has a big advantage in that he can simply disc in a crop of green manure whenever he chooses and withdraw a good portion of the decay products in the first year's production. And the process lends itself to infinite repetition.
Historically, we are told, soils are very different in their origins. So different, in fact, that their adaptation to specific crops is affected. The more correct view is that these idiosyncracies of soils were developed only after the original organic profile had been destroyed and most of the organic matter used up. On good virgin land, the chief production limitations are due to climatic factors rather than to the peculiarities of soil origins. My experience in growing sweet potatoes is a case in point: the plants had completed their growth in two months, rather than four, on land near Lake Erie quite outside their normal habitat. The presence of sufficient organic matter in the soil, a plentiful supply of water in the organic matter, and the prevalence of hot, sunny weather all combined to overcome any adverse factors. I had been told by a Virginian, a local buyer for a chain-store organization, that sweet potatoes could not be grown successfully in this locality. I was disinclined to believe him. When the crop matured, he bought part of it, paying about 25 cents a bushel above the prevailing market price for the best southern-grown roots.
Personally, I doubt whether one type of soil is any better suited than another to a given crop, provided each soil is supplied with an abundance of organic matter in the surface. Note the fact that a liberal quantity of organic matter is stipulated, and that it must be in the surface. If two soils so treated are subjected to similar climatic conditions, however different they may be in origin, their respective crops will be too little different to indicate a substantial superiority for either. In other words, sweet potatoes -- definitely preferring sandy soils -- will produce heavily on tight clays, provided first the clays have been richly endowed with a supply of organic matter in the surface. I have already produced parsnips in heavy clay so treated; the yield figured 1,220 bushels to the acre. Parsnips ordinarily are grown in sandy loam.
I am not prepared to say that the mere discing of organic matter into the soil surface is the complete remedy for all adverse soil conditions. There are too many unusual conditions of which I have too little knowledge. My acquaintance with soils is not broad enough to justify a complete generalization for all soils. However, unless we are prepared to question the universal application of theories and principles that have been proved by generations of use in other fields, we must admit the widespread applicability of this idea of surface mixed organic matter as a remedy for many, if not all, of our soil troubles. Also, the fact that all applicable experiment station results support the idea gives additional weight to the contention I have advanced.
We do not have any implement that is well suited to the incorporation of organic matter into soil surfaces under all conditions. The disc harrow is a good one to use under a great variety of conditions, but even it has its limitations. It cannot be used in soil that is very stony, even though it would successfully follow the plough in such case. It is difficult to manage on side hills. Unless special techniques in its management are used, the disc harrow does not leave a smooth surface. Some of these difficulties could be overcome by the use of power lifting devices, but such devices are of no use to farmers who have only horses. Yet, until somebody invents a better implement, the disc harrow is the one tool that can be substituted for the plough in the successful preparation of land (not in sod) for cropping. Its use for this purpose, however, is so different from its traditional role of smoothing up after the plough that a few hints should help the farmer who wants to try it. Such a routine as the following will work best:
- Be sure the discs are sharp and free from rust. Have the entire implement in good working order, all grease cups or other oiling arrangements fully supplied with lubricant. This last is especially important, for the disc harrow was not designed for heavy work like land breaking. Work of this kind will subject it to very unusual strains, so it should be kept perfectly lubricated all of the time.
- Use only the front section of the implement as long as you are trying to cut into the soil. Detach the rear section after reaching the field, for it will be useful in the final work of smoothing up. If it is allowed to follow along while the front section is trying for depth, its weight will tend to keep the front section from running deep enough.
- Weight the front section heavily. Here is where some of the extra strain comes in. The plough is so designed that it naturally seeks a certain sub-surface level and therefore does not require weighting. The only force that urges the disc harrow into the ground is gravity. Weight adds to this force.
- Set the discs to cut in -- how much is difficult to say -- but try adjustments at different angles to see what the effect is. Do not be surprised, though, if, on the first trip over a field, you cannot see that the discs have cut in consistently. Usually they will have cut in slightly, even though the dirt is not thrown up sufficiently to be seen.
- One important procedure to observe in putting in a tall, strawy crop, like rye, is to lay it all down in one direction, then cut across it at an angle. This serves to cut the straw into lengths that can be worked into the soil easily. For this work, of course, the discs need to be sharp. Also, there are limits to the amount of rye that can be managed by the disc harrow, however sharp the discs may be. Experience is the best guide here; no rules can be laid down.
- It may be that a clay soil in a very dry condition will not yield at all to the discs. In that case, it probably will help to run over the field once anyway. This will ride down the green manure crop so that it will lie closer to the surface. Some improvement in moisture content of the surface soil should result. Later, say in a week, a second attempt to cut into the surface is likely to be successful. Failing this, wait for rain.
- Farmers who have always used double disc-harrows may need to be told that when the front section alone is used it should always be lapped half way each time in order to leave the land smooth. This is very important if the discs are cutting in, less so, of course, when they are not.
- Following the routine outlined below will make it possible for the operator to do a smooth job, or at least a smoother job would result than if this method were not followed. You may be able to work out a better plan for your own situation. This is offered as a suggestion, assuming a square or rectangular field:
Decide first which way you wish to make all turns. With some outfits, left turns can be made better; with others, the turn is easier to the right. Since all turns are to be the same, it is necessary to determine this in advance.
Start along one side of the field and follow the boundary to the limits of the field. Turn along the border and follow it about four or five widths of the harrow; then torn and follow a line parallel to the first direction to the opposite limits; return to the beginning.
Repeat by lapping the harrow a half width toward the middle of the field as you follow the earlier track. At the ends no lapping is possible, since in going one direction the previous cut of the implement is to your right, or in going the opposite direction it is to your left. At the ends you must make this change of sides.
In the above three paragraphs you have the simple directions for what may be called a "spiral" discing routine. If you begin by crossing one end of the field, then your progress is very gradually toward the opposite end, by these crosswise trips that inch over one half the width of£ the implement each time.
Also, after about ten times around the "spiral," you begin to catch up with the forward side of the original first-round track. At this point you may wonder what to do. The answer is to continue just as you began, lapping one half width all the time, until you reach the opposite end of the field with the forward track. Then you will have double disced the first ten rounds and the last ten rounds, while all between will have been quadruple disced. In other words, most of the surface will have been stirred four times with the discs, but the end strips will have been stirred only twice.
It could be that, by the time you have gone over the entire field once in this fashion, it will be in proper condition for the final smoothing. However, I have usually found that, in order to prepare land sufficiently well to make the use of cultivating equipment possible, it is necessary to repeat this process exactly as indicated, except that the disc is run crosswise the direction taken by the original work. Of course, if the routine just described was preceded by the operator's going once over the area and riding down the green manure crop, the quadruple discing operation will have reduced this material to six-inch lengths. In that case, it is likely that once or twice over with the reassembled harrow may serve to complete the seedbed sufficiently to make planting possible. Do not expect it to look as smooth as it would if the land had been ploughed, even after you have done all the smoothing possible. And there may be at best some rubbish visible here and there. Neither the lack of perfect smoothness nor an occasional bit of trash will be fatal to the use of ordinary equipment; though in planting it probably will be necessary to delay the work occasionally long enough to remove from planter shoes accumulations of the rubbish. A little patience in this respect will be richly rewarded later, for you will find that the crop will be much less subject to drought damage, will require absolutely no nitrogen fertilizer, and will yield out of all proportion to customary standards. This will apply, regardless of the kind of crop grown.
You may or may not have to smooth the final work of the disc with a drag. Certainly you will not have clods to contend with. Compacting is likely to be important if the weather is dry. However, the disc harrow may be used for this purpose, not as effectively as a regular roller or corrugated compacting implement, but with the discs set straight and heavily weighted it does a fair job.
One caution should be given concerning cultivation. I came near ruining one corn crop because I failed to discover that there was enough uncut straw in the surface to lift slightly almost every hill of corn as the cultivator passed. The rye on this field had been six feet tall. It had proved impossible to work it in at all, and much of it lay there, not even cut into sections. If you should have that same condition to contend with, delay the first cultivation until the straw has had time to disintegrate sufficiently that it cannot interfere. This will not require long, providing a little rain falls. If the weather is dry following the planting of the corn, two or three weeks may be required. Success in this respect is wholly a matter of careful observation and management.
Of course, if you encounter such conditions as have just been described, you cannot hope to plant the area by means of ordinary equipment. It was to make planting possible in such a surface that I devised the pressure marker. Planting after this rig was used had to be done by hand, but the manner in which the crops grew fully justified the hand method. It can readily be seen that, if the planter can expect several times the customary yield per acre from soil so recreated, he is justified in conceding something to painstaking care. Again, if it is possible, by renewing the soil with green manures, to cut the usual acreage to one-fifth, one-third or one-half, the concession is scarcely a concession at all.
Eventually, it is to be hoped, suitable implements will be devised and put on the market. Meanwhile, I anticipate modifying to some extent the plans I followed in 1939 and 1940. Instead of growing green manure in quantities sufficient to make incorporation impossible with the disc harrow, I hope to spend more than one season in getting the land ready for crops; then, after working a two-to three-foot rye crop in early in spring, some summer crop will be seeded to be put in later -- to be followed by rye again. This would involve two green manure crops each year. Not many such short crops would be required, it would seem, to make the soil begin to look black again. And, treasonable as it may seem, I hope that while this routine is in progress each crop will be accompanied by the germination of multitudes of weed seeds. Discing in immature weed plants with each green manure crop may be an excellent way to reduce weed growth. More is said about this in a later chapter.
It might easily be that some land would be so refractory to discing that the first crop of green manure could not be worked in at all. This event need not stop your efforts. Do not plough it in. Or, if you do plough it in, plough the land again immediately, and a little deeper. If you do plough twice, you will have created a superior soil situation by that means, for the second ploughing will have returned to the root zone your mass of green manure. In this position the disc harrow will be able to reach and cut it. To your delight you will discover that no clods form in connection with the work, so the follow-up operations usually necessary can be cut quite short.
Double ploughing is not a new device. Friends of mine recall that the farmers of a previous generation often ploughed down clover in the autumn, then ploughed the land again in spring for potato growing. Apparently the method worked well. However, much decay of the clover must have occurred during the winter, and the leaching away of much of the products would have been inevitable. Moreover, the decay of this material made it possible for the farmer to do a much neater job of ploughing in spring than might have been possible had the land been ploughed twice in quick succession. Many a farmer who decides to plough down a heavy green manure crop and follow up immediately with a second and slightly deeper ploughing will be thoroughly disgusted with the idea before he has gone many furrows. The appearance of the resulting surface will be disheartening to farmers who have always taken pride in the neatness of their ploughing.
The trouble here is not the appearance of the surface but our notion of what constitutes beauty. Few people realize how thoroughly we have become enslaved by the idea that nothing effective can be done toward preparing land to grow crops until the land has first been ploughed. Ploughing has been accepted as axiomatic -- a necessary prelude to every other operation. Even though the work of the plough has been for many years associated with the deterioration of our land, we still have not awakened to the fact that, to solve the problem, we must cease ploughing; or, if we wish to continue to use the plough, we must do the work in a different way. The methods we use, whatever they be, must produce a surface that is filled with debris that will rot. Let the surface of the soil wear a "beard" of exposed material, if need be. That condition will eventually become beauty in the soil. "Handsome is as handsome does" is not a new saying. It is particularly applicable here, for debris-filled soil alone is capable of the highest quality yields. The ancestry of a soil is a very minor matter in comparison with the present ability of that soil to supply to hungry roots a soil solution enriched by abundance of decay products.
An alternative to double ploughing land that cannot be managed by discing is to leave the area wholly undisturbed. This may seem an acknowledgment of failure, but the matter should not be prejudged. Much will happen to an intractable soil while the crop it has produced is decaying. The decay of a green manure crop, in place, will of itself serve to start a heavy soil surface on its way toward granulation. When granulation has proceeded sufficiently, a clay soil can be worked like sand. Moreover, if the crop in question produces seeds -- which any annual crop will do -- it will reseed itself naturally; and, without any work whatever, the farmer will have a second, volunteer crop of green manure to reckon with. This second crop will be very easily managed when the time comes to disc it in.
It has to be admitted frankly that the preceding paragraph is a deduction from the known effects of the practices described. For this reason, the conclusion may be considered vulnerable. My best suggestion is that anyone who is inclined to doubt the feasibility of the plan advanced should try it on an area of supposedly unmanageable clay. I have seen clay become so friable, under conditions that were comparable to those suggested here, that it could be raked about like sugar. The same clay, before treatment, was so solid that a sharp spade, with a man's weight upon it, was scarcely enough to make an impression upon the surface. I am certain, therefore, that further experimentation will sustain my contentions.
The abandonment of the first season's work in order to let nature cure the ills of the sod may seem a waste of time. The economy of such a procedure must await confirmation until the outcome of subsequent crops can be observed. The eventual result will contain its own proof. And my guess is that those who know soils best will be the last to doubt the eventual outcome, for the renovating effect of decaying organic matter, which induces granulation of the soil, is well known and accepted. The only new thing about it is the method proposed for securing that effect.
Doubtless, the creation of soil where none now exists, through incorporation into the surface of materials grown upon the particular area, presents many difficulties not touched upon in this chapter. The idea is entirely too new to have been thoroughly investigated in all of its ramifications by a single unsponsored student in a single season of work. It is extremely doubtful, though, that the actual re-creation of soils presents any technical difficulties which cannot be surmounted. The only requirement for the establishment of a new tillage system, apparently, is investigation along one or both of two lines: first, the adaptation of our customary use of existing surface-stirring implements to the job of incorporating liberal quantities of green manure; or, second, the invention of new equipment capable of disposing of all organic matter by surface mixing. No further time should be lost from the accomplishment of one or both of these objectives.
8. King Weather Deposed
ALL practising farmers and students of agriculture are well aware of the controlling influence of weather in the growing of crops. To the city man a sunny day in midsummer may be a thrilling event, because it provides the ideal conditions for picnicking, hiking, and swimming. For thousands of farmers nearby the same day may be an occasion of disaster involving the local food supply, in which the city dweller, as well as the husbandman, has a vital stake. Rains that arrive a day too late to save potatoes, beans, and lettuce affect both producer and consumer, but the producer more seriously.
Weather has always been considered in the category of "acts of God," and so it may very well be. Equally, how. ever, it may be said that "God helps those who help themselves." There is nothing to be achieved here by bringing up once again the famous dispute between the Forest Service and the Weather Bureau as to whether forests actually increase the rainfall. Nor is it to the point, perhaps, to conjecture with the scientists concerning the effect of England's deforestation in past centuries on present-day climate in the British Isles. But it may be useful to point out that man has it in his power to disturb some of the moisture conditions essential to plant growth, and that, by extension, he partly controls some of those conditions.
Man can conserve the moisture laid down by the heavens, or he can waste it. The earth he took over originally was covered everywhere by a water-soaked, sometimes odorous sponge of humus. Nature maintained this water-catching cover through successive plant generations, wherever man did not disturb, and continues to maintain it down to this very hour. By imitating nature, man could have enjoyed such benefits as he has never dared hope for; by disregarding the obvious example she set for him, he has courted disaster.
Irregular moisture has been regarded as the most important weather condition controlling crop growing. With respect to moisture, the absorbent mat we find everywhere in nature serves a purpose which has not been recognized in agricultural literature. For lack of a better term, we may call this its "reservoir" purpose.
Farmers leave their hay stacked in the field exposed to all the rain that falls. They know that none of the rainfall can sink deeper than the upper few inches, because the porous tissues of the hay must first be filled. Since every inch of this top layer of hay will catch and hold nearly an inch of rainfall the underlying hay is protected.
Knowing this, we should understand that if enough organic matter is disced into the soil surface it will constitute to its full capacity a reservoir in which a large proportion of the rainfall will be retained. If enough absorbent material has been provided to hold an inch or two of rainfall, then, when rain is falling, an inch or two of it will be retained in the surface. Naturally, this spongy mass will supply water -- richly endowed with the minerals it takes from the decaying material in which it is held -- to crops which otherwise would suffer seriously in the intervals between rains.
Not having this conception of the service of such a mantle of porous material, scientists have reasoned about water chiefly in terms of capillary movement within the soil. And, strangely enough, some scientists have believed, from results of their tests, that there is little such movement in the upper layers of soil. If anybody doubts that such conclusions have been introduced into serious scientific literature, it may be interesting to relate a brief conversation I had in September, 1937, with a crop specialist I had known for nearly twenty years. It ran about like this: I had suggested doubt as to the propriety of ploughing. He quickly asked, "What's wrong with ploughing?" "Interferes with capillarity," I replied. He had a ready answer: "Tests show that there isn't as much capillary movement in the soil as we used to believe existed -- it's relatively unimportant in many cases." "Well," I replied, "in unploughed land there must be enough upward capillary movement between rains to keep the vegetation alive." Mine was the last word.
He was correct in his statements. Such tests have been made. They were made, like all soil experiments, on ploughed soil. The "reservoir" for water lies several inches deep in the ploughed soil; and, since it literally robs the upper soil layers of their water as well as shutting off upward movement of capillary water rising from deeper in the soil, no other results of such tests could have been expected. If such tests were made in soil where grass is growing, the story would be entirely different.
The very nakedness of ploughed land should of itself indicate a lack of capillary water in the surface. If capillary water were present, seeds would sprout and grow, for seeds are always present. Or had you noticed that the only bare soil in most landscapes is that which has recently been ploughed? I discovered that highly significant fact only a few months ago, though I had seen it daily throughout a lifetime. Since ploughed land is always bare, and since practically all other land, save areas like the Sahara, is covered with greenery of some sort -- which could not exist without a continual supply of water -- it follows, even without tests, that there is no capillary water in the upper layers of freshly ploughed soil.
It may be repeated here that, while God, not man, controls the weather, it is nevertheless given to man to control some of the fruits of weather, and of these perhaps the most important is the natural moisture of the soil surface. The first essential in this respect is to grasp the dissimilarity of water relations in ploughed and unploughed lands. The next is to understand that the weather which kills vegetation on cultivated land may also cause vegetation to thrive, or at least to show no ill effects, on uncultivated land. The final phase is to connect logically the importance of the organic matter profile with both plant growth and the weather conditions under which plants may prosper.
For purposes of this discussion we may assume as normal any soil surface that has been left unploughed, or any ploughed soil that has had time to recover its normal capillary water movement (because of the disappearance by decay of the organic matter ploughed in). All meadow and pasture land on farms, then, as well as the land occupied by the farm fences, may be considered as part of the natural landscape, even though it is also part of the land normally subject to ploughing. It is natural landscape because in its profile there is nothing to prevent water from rising to the surface. Whatever interference may have been introduced in previous times by ploughing has been disposed of by decay.
By and large, the "voltage" of any soil depends upon the accumulations of decayable material available in its surface. By this standard it would be true almost always that wilderness soils, unploughed for many years if ever ploughed at all, would be more productive than similar soil that had been included regularly in rotation cropping. The unploughed soil has the advantage that economical use of all decay products has been the rule for the entire period since its last ploughing. The grassland in rotation, on the other hand, has periodically had a large percentage of its accumulated material removed from the surface, resulting in the wasting of the decay products. This deliberate (though unwitting) periodic waste of soil resources, after being repeated several times, finally results in a low-grade soil where formerly the productivity was high. The final result is erosion. And, when erosion has started, we may be sure there is not much absorbent material left in the surface of the soil. The remaining light-coloured stuff is almost identical with that which the glaciers shunted about in their time.
An experienced farmer allows some of his land to lie in grass for a few years in order that its "voltage" may be stepped up. The longer the area is in sod the more productive it is when it is again put to corn. However, the period in which it accumulates a new supply of organic matter to be wasted again by ploughing is not sufficient to enable it to make the gains that would put it in its natural condition. Indeed, the progress seems always to be slightly on the down side. No trick yet discovered has made it possible to achieve positive gains regularly on land operated in continuous three-or four-year rotation. There are probably a few exceptional cases, but this is the general rule. The wastage caused by ploughing usually more than balances the accumulations made in the interim. In fine, rotation of the type described is not a cure-all for impoverished soil, and, what is more important to the thesis of this chapter, it does not get at the water relations which are ultimately desirable.
It was shown in the last chapter that a farmer may quite abruptly step up the productiveness of his soil by simply short-circuiting the wasteful practice of ploughing. By mixing into the surface the decayable material which the plough would inter, the farmer sets the stage for biologically economical practices hitherto unknown to modern farming. Aside from questions of plant nutrition, there are several ways in which the surface mixing of organic matter brings to focus friendly forces of growth which are unable to operate when land is ploughed.
Every ton of organic matter mixed into the surface of the soil will be able to contain much more absorbed water than it could if buried at plough depth Why? Because, being weighted down by so much less overlying soil, its volume will be greater. And organic matter, it must be remembered, retains water volumetrically, while the minerals of the soil must hold it only upon the outer surfaces of the particles. Water runs into organic fragments, while it squeezes in between particles of sand, silt, and clay. We can rightly expect, then, that any absorbent material we work into the surface of the soil will retain rain water much more effectively than would the same material if ploughed in.
Indeed, if ploughed in, organic matter gets no opportunity to catch and hold rainfall until that water has first forced its way several inches down between the mineral crystals. Under most conditions it is much easier for some of the water to run off the surface than for all of it to force its way down into the soil. This means, then, that when all the organic matter is in the surface of the soil, it is able to take in water from both above and below -- and in greater volume because of the greater volume of the organic matter itself.
Undoubtedly the original black soils our forefathers knew could absorb directly, and as rapidly as it fell, several inches of rainfall in a few hours. It is unlikely that very much water ever leached through the zone of surface organic matter in those highly absorbent soils. The light, fluffy leaf mould, or the springy layer of grass roots, gradually became filled with rain water as it fell. In this connection I like to remember the story told by one of the best-known agronomists in this country. He was inspecting some highly organic soil lying near the top of a mountain slope when a heavy shower developed. The slope was a little less than 45 degrees. Those familiar with geometry will recognize this as rather steep land. This agronomist remained through the storm to observe the course of the water as it fell. He said that, so far as he could determine, none ran off. If any did so, he said, it certainly did not take any soil with it.
Discing heavy green manure crops into the surface of the soil, then, is an excellent way to create, precisely in the surface of the soil, a reserve of water upon which crop roots can draw continuously until it is used up. Such an arrangement is obviously superior to the principle of permitting the water to run down through the soil and hoping it will be brought back by capillarity. Aside from holding a plentiful reserve of water in the root zone, the mass of organic matter receives capillary water continually from below, which replaces, at least in part, the reserve from which plants are drawing. This reserve supply of water serves to tide crops over extended periods of drought which otherwise would damage them seriously. From such a source water can be made available during many more days of the growing season than could possibly be the case when surface conditions are such as to let some of the rainfall run off and be wasted. Here is "conservation of natural resources."
This, however, is only part of the story. The water stored in surface organic matter is constantly being used to assist in the decomposition of the material which holds it. It not only assists in this decay, but it dissolves and in turn holds the products released. Thus, as long as water is retained in the organic tissues, it is constantly being enriched by the cast-off substances of which the organic matter was composed. And all of this enrichment is in addition to the minerals which the capillary water has picked up and dissolved in the soil depths before the water has been absorbed by the organic matter. It can readily be seen that under these conditions many influences are working together effectively which could not do so if the organic matter were located six to eight inches deep, where relatively few plant roots reach.
At this point the reader should recall that, in the ploughed soil, carbon dioxide is released into the upper layer of soil; and that this gas is prevented from becoming carbonic acid because of the necessary dryness of the upper layers. In the newer situation, with all of the organic matter just in the surface, there is provided an abundance of water in the vicinity in which the carbon dioxide can be dissolved. And, since carbonic acid is one of the most efficient of known natural solvents of minerals, its work in the surrounding crystalline rock particles serves to release for plant use quantities of phosphorus, potash, and other needed plant nutrients which would not otherwise be available.
The extent to which this release of minerals from the rock itself can take the place of applications of mineral fertilizers is something I am not prepared to discuss. It is an interesting and a very important question. Every farmer will want to know, and is entitled to know, the answer. If it is possible that the carbonic acid released in the soil will supply enough fresh minerals to supplement adequately the minerals drawn from organic sources, then the purchase of mineral fertilizers would be unnecessary. Only this much can be said safely: If a farmer succeeds in working into his soil enough organic matter to equal the supply held when the land first was opened for cropping, then he might reasonably hope to grow maximum crops without fertilizers. An easy way to test this principle is to leave unfertilized strips in all such fields. When it becomes impossible to find those unfertilized strips at harvest time, because the crop is equally good everywhere, then the necessity for fertilizers has vanished. Within a few years, no doubt, we shall have official information on this point.
And how may we expect the plant itself to react to the optimum conditions described? Just as any other being reacts to a constant supply of food. Plants will establish most of their millions of roots in the organic fragments. There is not the slightest chance here for plant food to be lost. The instant it is released, the water that contains it is moved into a plant root and sent upward into the plant. The matter of deep rooting of plants, which has been widely discussed in past years, becomes a dead issue. There ceases to be any need for roots to penetrate soil depths. Their food supply is in the surface. The water in this organic matter is busily engaged in wrecking the dead tissues in order to provide materials to be built into the new growth. Bacteria, too, are involved, and without them this process could not occur. The point is that "all things work together for good"' in this instance; so close knit is the process that no opportunity is left anywhere for the loss of nutrient materials. Plant roots that go deep, other than for anchorage, in such a situation are working to the disadvantage of the plant they represent.
It will now be apparent that man can control to a very considerable extent the rainfall with which his land is endowed from season to season. The reasons sustaining this conclusion may be summarized as follows:
Under proper management, the soil may be caused to hold natural precipitation at just the level where plant roots normally seek the essential nutrients. The presence of an organic mass in the surface so enriches the water by solution that, volume for volume, the water thus treated will produce more plant growth than water held in the minerals alone. Water thus held in the organic mass becomes available to plants without the opportunity for essential plant nutrients to be wasted in any way.
Considering these important factors, it is not too much to suppose that ten inches of rainfall might accomplish as much as is ordinarily expected of twenty. Again, with ample rainfall, it may easily be possible to produce several times the average production figure for the country as a whole.
The truth about the weather is that man can indeed make the best of it -- if he will.
Next: 9. Tile Treachery
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