In deze terugkerende rubriek geef ik een uittreksel van een boek welke een bijdrage heeft geleverd aan mijn kijk op Natuurlijk Tuinieren.
Deze keer betreft het An Agricultural Testament van Sir Albert Howard. Het volledige boek kan kan hier worden gelezen.
Leeswijzer. Per hoofdstuk heb ik de, naar mijn idee, belangrijkste stukken weergegeven. Wanneer ik naar aanleiding van het geschrevene een opmerking maak laat ik dit voorafgegaan door [Opmerking] om zo het onderscheid weer te geven tussen het boek en mijn persoonlijke mening.
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The main characteristic of Nature’s farming can therefore be summed up in a few words. Mother earth never attempts to farm without live stock; she always raises mixed crops; great pains are taken to preserve the soil and to prevent erosion; the mixed vegetable and animal wastes are converted into humus; there is no waste; the processes of growth and the processes of decay balance one another; ample provision is made to maintain large reserves of fertility; the greatest care is taken to store the rainfall; both plants and animals are left to protect themselves against disease.
Mixed cropping is perhaps most universal when the cereal crop is the main constituent. Crops like millets, wheat, barley, and maize are mixed with an appropriate subsidiary pulse, sometimes a species that ripens much later than the cereal. The pigeon pea (Cajanus indicus Spreng.), perhaps the most important leguminous crop of the Gangetic alluvium, is grown either with millets or with maize. The mixing of cereals and pulses appears to help both crops. When the two grow together the character of the growth improves.
Whatever may be the reason why crops thrive best when associated in suitable combinations, the fact remains that mixtures generally give better results than monoculture.
Cultivation is generally superficial and is carried out by wooden ploughs furnished with an iron point. Soil-inverting ploughs, as used in the West for the destruction of weeds, have never been designed by Eastern peoples. The reasons for this appear to be two: (1) soil inversion for the destruction of weeds is not necessary in a hot climate where the same work is done by the sun for nothing; (2) the preservation of the level of the fields is essential for surface drainage, for preventing local waterlogging, and for irrigation. Another reason for this surface cultivation has recently been pointed out. The store of nitrogen in the soil in the form of organic matter has to be carefully conserved: it is part of the cultivator’s working capital. Too much cultivation and deep ploughing would oxidize this reserve and the balance of soil fertility would soon be destroyed.
The manuring of the rice seedling illustrates a very general principle in agriculture, namely, the importance of starting a crop in a really fertile soil and so arranging matters that the plant can absorb a great deal of what it needs as early as possible in its development.
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If the soil is deficient in humus, the volume of the pore space is reduced; the aeration of the soil is impeded; there is insufficient organic matter for the soil population; the machinery of the soil runs down; the supply of oxygen, water, and dissolved salts needed by the root hairs is reduced; the synthesis of carbohydrates and proteins in the green leaf proceeds at a lower tempo; growth is affected. Humus is therefore an essential material for the soil if the first phase of the life cycle (growth) is to function.
It follows therefore that the correct relation between the processes of growth and the processes of decay is the first principle of successful farming. Agriculture must always be balanced. If we speed up growth we must accelerate decay.
The influence of humus on the plant is not confined to the outward appearance of the various organs. The quality of the produce is also affected. Seeds are better developed, and so yield better crops and also provide live stock with a satisfaction not conferred by the produce of worn-out land. The animals need less food if it comes from fertile soil. Vegetables and fruit grown on land rich in humus are always superior in quality, taste, and keeping power to those raised by other means.
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A good example of such a system of farming without manure is to be found in the alluvial soils of the United Provinces in India where the field records of ten centuries prove that the land produces small crops year after year without any falling off in fertility. A perfect balance has been reached between the manurial requirements of the crops harvested and the natural processes which recuperate fertility. The greatest care, however, is taken not to over-cultivate, not to cultivate at the wrong time, or to stimulate the soil processes by chemical manures.
The streams and rivers which carry off the surplus rainfall also contain appreciable quantities of combined nitrogen and minerals in solution. Much of this could be intercepted by the cultivation of suitable plants on the borders of these streams which would furnish large quantities of easily decomposable material for humus manufacture.
The principle followed, based on the Liebig tradition, is that any deficiencies in the soil solution can be made up by the addition of suitable chemicals. This is based on a complete misconception of plant nutrition. It is superficial and fundamentally unsound. It takes no account of the life of the soil, including the mycorrhizal association — the living fungous bridge which connects soil and sap. Artificial manures lead inevitably to artificial nutrition, artificial food, artificial animals, and finally to artificial men and women.
The ease with which crops can be grown with chemicals has made the correct utilization of wastes much more difficult. If a cheap substitute for humus exists why not use it? The answer is twofold. In the first place, chemicals can never be a substitute for humus because Nature has ordained that the soil must live and the mycorrhizal association must be an essential link in plant nutrition. In the second place, the use of such a substitute cannot be cheap because soil fertility — one of the most important assets of any country — is lost; because artificial plants, artificial animals, and artificial men are unhealthy and can only be protected from the parasites, whose duty it is to remove them, by means of poison sprays, vaccines and serums and an expensive system of patent medicines, panel doctors, hospitals, and so forth. When the finance of crop production is considered together with that of the various social services which are needed to repair the consequences of an unsound agriculture, and when it is borne in mind that our greatest possession is a healthy, virile population, the cheapness of artificial manures disappears altogether. In the years to come chemical manures will be considered as one of the greatest follies of the industrial epoch.
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It was observed in the course of these studies that the maintenance of soil fertility is the real basis of health and of resistance to disease. The various parasites were found to be only secondary matters: their activities resulted from the breakdown of a complex biological system — the soil in its relation to the plant and to the animal — due to improper methods of agriculture, an impoverished soil, or to a combination of both.
…it was gradually realized that the full possibilities of the improvement of the variety can only be achieved when the soil in which the new types are grown is provided with an adequate supply of humus.
Improved varieties by themselves could be relied upon to give an increased yield in the neighbourhood of 10 per cent.: improved varieties plus better soil conditions were found to produce an increment up to 100 per cent. or even more. As an addition of even 10 percent to the yield would ultimately impose a severe strain on the frail fertility reserves of the soils of India and would gradually lead to their impoverishment, plant-breeding to achieve any permanent success would have to include a continuous addition to the humus content of the small fields of the Indian cultivators. The real problem was not the improvement of the variety but how simultaneously to make the variety and the soil more efficient.
No permanent or effective system of agriculture has ever been devised without the animal. Many attempts have been made, but sooner or later they break down.
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The chief factors in green-manuring are: (1) knowledge of the nitrogen cycle in relation to the local agriculture; (2) the conditions necessary for rapid growth and also for the formation of abundant nodules on the roots of the leguminous crop used for green-manuring; (3) the chemical composition of the green crop at the moment it is ploughed in; (4) the soil conditions during the period when decay takes place. These four factors must be studied before the possibilities of green-manuring can be explored.
(1) The importance of the nitrogen cycle in relation to the local agriculture is a factor in green-manuring to which far too little attention has been paid. As will be shown more fully in Chapter 14, the full possibilities of green-manuring can only be utilized when we know at what periods of the year nitrate accumulations take place, how these accumulations fit in with the local agricultural practice, and when nitrates are liable to be lost by leaching and other means. If the crop does not make the fullest use of nitrate, this precious substance must be immobilized by means of green-manure or by means of weeds and algae. It must not be left to take care of itself. It must either be taken up by the crop or banked by some other plant.
(4) As growth proceeds the chemistry of a green crop alters very considerably: the material in a young or in a mature crop, when presented to the micro-organisms of the soil, leads to very different results. Waksman and Tenney have set out the results of the decomposition of a typical green-manure plant (rye) harvested at different periods of growth. When the plants are young they decompose rapidly: a large part of the nitrogen is released as ammonia and becomes available. When the plants are mature they decompose much more slowly: there is insufficient nitrogen for decay, so the micro-organisms utilize some of the soil nitrates to make up the deficiency. Instead of enriching the soil in available nitrogen the decay of the crop leads to temporary impoverishment.
The amount of humus which results from the decay of a green crop also depends on the age of the plants. Young plants, which are low in lignin and in cellulose, leave a very small residue of humus. Mature plants, on the other hand, are high in cellulose and lignin and yield a large amount of humus.
It follows from these results that if we wish to employ green-manuring to increase the soil nutrients quickly, we must always plough in the green crop in the young stage; if our aim is to increase the humus content of the soil we must wait till the green-manure crop has reached its maximum growth.
The soil conditions after the green crop is ploughed in are no less important than the chemical composition of the crop. The micro-organisms which decay the green-manure require four things: (1) sufficient combined nitrogen and minerals; (2) moisture; (3) air; (4) a suitable temperature. These must all be provided together.
The factor which so often leads to trouble is the poverty of the soil — insufficient combined nitrogen and minerals. It follows, therefore, that when a mature crop is ploughed in the effect of its decay on the next crop will always depend on the fertility of the soil. If the soil is in a poor condition most of the combined nitrogen available will be immobilized for the decay of the green-manure; the next crop will suffer from starvation; green-manuring will then be a temporary failure. If, however, the soil is fertile or if we plough in freshly prepared humus with the green crop, the extra combined nitrogen needed for decay will then be present; the next crop will not suffer. Soil fertility in this, as in so many other matters, gives the farmer considerable latitude. All sorts of things can be done with perfect safety with a soil in good heart which are out of the question when the soil is infertile. A good reserve of fertility, therefore, will always be an important factor in green-manuring.
Finally, the temperature factor is important in countries like Great Britain which have a winter. Here green-manure crops must often be turned in during the autumn before the soil gets too cold, so that the early stages of decay can be completed before winter comes.
The uses of green-manuring in agriculture can now be considered. Generally speaking they fall into three classes: (1) the safeguarding of nitrate accumulations; (2) the production of humus, and (3) a combination of both.
The uncertainties of humus manufacture in the soil can be overcome by growing the green crop to provide material for composting.
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The consequences of the improvement of grassland in a country like Great Britain can now be summarized. The land will carry more live stock. The surplus summer grass can be dried for winter feeding. The stored fertility in the pastures can be cashed in at any time in the form of wheat or other cereals. A valuable food reserve in time of war will always be available. As Mr. Hosier has shown, there will be no damage from wireworms when such fertile pastures are broken up and sown with wheat.
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In temperate regions the chief factor which cuts off the sub-soil from the atmosphere is shortage of humus aggravated by impermeable pans (produced by the plough and by the soil particles themselves) or a permanent grass carpet accompanied by the constant treading of animals. The result in all cases is the same — the supply of air to the sub-soil is reduced.
The conventional method of dealing with arable pans in this country is by means of some sub-soiling implement which breaks them up and restores aeration. This should be accompanied whenever possible by heavy dressings of farm-yard manure, so that the tilth can be improved and the earthworm population restored. Some deep-rooted crop like lucerne, or even a temporary fey, should be called in to complete the cure. Sub-soiling heavy land under grass is proving even more advantageous than on arable areas. This leads, as we have seen, to humus formation under the turf and to an increase in the stock-carrying capacity of the land.
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The root of this soil erosion trouble in the United States is misuse of the land. The causes of this misuse include lack of individual knowledge of soil fertility on the part of the pioneers and their descendants; the traditional attitude which regarded the land as a source of profit; defects in farming systems, in tenancy, and finance — most mortgages contain no provisions for the maintenance of fertility; instability of agricultural production (as carried out by millions of individuals), prices and income in contrast to industrial production carried on by a few large corporations. The need for maintaining a correct relation between industrial and agricultural production so that both can develop in full swing on the basis of abundance has only recently been understood. The country was so vast, its agricultural resources were so immense, that the profit seekers could operate undisturbed until soil fertility — the country’s capital — began to vanish at an alarming rate.
Why is the forest such an effective agent in the prevention of soil erosion and in feeding the springs and rivers? The forest does two things: (1) the trees and undergrowth break up the rainfall into fine spray and the litter on the ground protects the soil from erosion; (2) the residues of the trees and animal life met with in all woodlands are converted into humus, which is then absorbed by the soil underneath, increasing its porosity and water-holding power. The soil cover and the soil humus together prevent erosion and at the same time store large volumes of water. These factors — soil protection, soil porosity, and water retention — conferred by the living forest cover, provide the key to the solution of the soil erosion problem.
Grass is a valuable factor in the correct design and construction of surface drains. Whenever possible these should be wide, very shallow, and completely grassed over. The run-off then drains away as a thin sheet of clear water, leaving all the soil particles behind. The grass is thereby automatically manured and yields abundant fodder.
If we regard erosion as the natural consequence of improper methods of agriculture, and the catchment area of the river as the natural unit for the application of soil conservation methods, the various remedies available fall into their proper place. The upper reaches of each river system must be afforested; cover crops including grass and leys must be used to protect the arable surface whenever possible; the humus content of the soil must be increased and the crumb structure restored so that each field can drink in its own rainfall; over-stocking and over-grazing must be prevented.
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A similar rule applies to crops: the diseased crop is quietly but effectively labelled prior to removal for the manufacture of humus, so that the next generation of plants may benefit.
Mother earth has provided a vast organization for indicating the inefficient crop. Where the soil is infertile, where an unsuitable variety is being grown, or where some mistake has been made in management, Nature at once registers her disapproval through her Censors’ Department. One or more of the groups of parasitic insects and fungi — the organisms which thrive on unhealthy living matter — are told off to point out that farming has failed.
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In other words, one of the chief causes of disease on the farm is bad soil management.
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…that a watery extract of humus gave little or no residue on evaporation.
…the humus theory… According to this theory the plant fed on humus. Liebig believed he had shown that this view was untenable; humus was insoluble in water and therefore could not influence the soil solution.
With the introduction of artificials there has been a continuous increase in disease, both in crops and in live stock.
[Opmerking] Er moet een juiste correlatie zijn tussen de grond en de verbouwde gewassen.
Hand-made trenches always give better yields than those made by mechanical means — an interesting result, which has often been obtained elsewhere, but which has never been adequately explained. It may be that speed in cultivation is an adverse factor in the production of tilth.
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The slow poisoning of the life of the soil by artificial manures is one of the greatest calamities which has befallen agriculture and mankind.