Darwin - Introduction - Howard


From an edition published by Faber and Faber, London, 1945

by Sir Albert Howard

WHEN I first learned from the publishers of their intention to reprint Charles Darwin's The Formation of Vegetable Mould as one of their contributions to the discussion of the principles underlying farming and gardening, the timeliness of this step needed no argument. At a period when present-day agricultural and horticultural teaching and research are being critically examined with a view to their speedy reform, only good could result from the re-publication of the results of some forty years' observation, experiment, and thought devoted by our greatest naturalist to the part played by earthworms in the history of the world and, in particular, to the manner in which they prepare the ground for the growth of plants and of seedlings of all kinds. When this intimation was followed by a request to write an introduction which would link up Darwin's work with the recent results on the earthworm and with the present controversy about artificially stimulated crops, I at once agreed.

For some time I had been seeking for the most effective and convincing foundation on which the reformed agriculture of the West could be based and which would, at the same time, direct future agricultural research into biological channels. Here lay ready to hand an ideal starting point and, moreover, one which would compel attention to the role of the unseen labour force of the soil and to factors which the advocates of chemical farming could not lightly dismiss. No more effective basis for the organic farming and gardening of to-morrow could be found than the long and painstaking investigations described in this volume. It would help to accomplish for the temperate regions what King's Farmers of Forty Centuries has already done for the tropics and subtropics.

If this book, which deals with the formation of vegetable mould through the action of earthworms, is the real foundation for the study of the principles underlying farming and gardening, why should the renewed study of such a well-known work be necessary to-day? Why did the book fail to influence agricultural teaching and research when it first appeared in 1881? The answer to these questions will be found in the manner in which investigations on farming have developed since 1840, when Liebig's Chemistry in its Applications to Agriculture and Physiology was published. This essay, coupled with the results of the well-known wheat experiments on the Broadbalk field at Rothamsted, exercised a profound influence on the minds of investigators and farmers alike. Till about the end of the nineteenth century agricultural science was still a branch of chemistry. The Formation of Vegetable Mould through the Action of Worms, therefore, appeared when the ideas founded on the Liebig and Rothamsted traditions were at their zenith. It occurred to no one that the manner in which earthworms (1) periodically expose the surface soil to the air, (2) sift it so that no stones larger than the particles they can swallow are left in it, and (3) at the same time mingle the mould intimately together like a gardener who prepares fine soil for his choicest plants -- were all matters of the most profound significance in crop production. The attention of all concerned was directed solely to the chemistry of the soil water, i.e. to a single factor only of a vast biological complex.

That Darwin's work was without influence on agricultural education in the 'nineties I know from personal experience, for it was during the academic year of 1896-7 that I attended the various courses of lectures necessary to obtain the University Diploma of Agriculture at Cambridge. No references to earthworms and their work in preparing the food materials needed by crops were made in the lectures on agricultural chemistry offered to me: I never even heard Darwin's name mentioned in connection with the maintenance of soil fertility, but I was told much of the virtues of artificial manures for increasing crops and of the efficacy of poison sprays for controlling plant diseases. It was not till the next two academic years, 1897-9, when studying for Parts I and II of the Natural Sciences Tripos that I first came into intimate contact with Darwin's books, including the one dealing with his studies of the earthworm. Later, during my Indian service (1905-31) when I became deeply interested in the preparation of humus on a large scale, the place of the earthworm and of the termite in converting crude vegetable matter into food materials for the crop appeared more and more important as the years passed.

But it was after my retirement from service in India in 1931, when steps were taken to bring the large-scale preparation of humus to the notice of the farming community, that I began to realize the urgent necessity of preserving the earthworms in the farms and gardens of Great Britain from destruction. Case after case came under my observation where the continued application of artificial manures and the use of poison sprays like lime sulphur and tar oils for keeping the pests of fruit trees in check led to the destruction of earthworms on a colossal scale.

Eventually during the years 1935-8 I was able to pay the closest attention to the way artificial manures either reduce or eliminate altogether the earthworm population. On some 3,000 acres of land near Spalding in south Lincolnshire, the property of the late Mr. George Caudwell, I spent many weeks in working out an improved method of green-manuring for the potato crop and was given every possible facility and help by my host in getting to the bottom of potato growing on the alluvial soils of Holbeach Marsh. On Mr. Caudwell's farms about 1,500 acres of potatoes were raised every year on artificials only, and for a time exceptionally heavy crops had been obtained. But by 1935 the soil was showing distinct signs of wearing out and steps had to be taken to increase the content of organic matter. My opinion was asked as to the best method of doing this. I recommended a return to mixed farming which should include laying down a few hundred acres every year to temporary leys and the return to the old East Anglian custom of mucking the second clover crop before ploughing under in the late summer. This, however, would have involved a considerable reduction in the area under potatoes, to allow for the maintenance of cattle and pigs and the production of large quantities of farmyard manure. Unfortunately both the beef and the pig trade at that time were under a cloud and Mr. Caudwell considered my proposals would not pay at the prices of meat then ruling.

He pressed me to suggest some alternative for increasing the organic content of his land, making the best use of about 1,000 tons of farmyard manure produced by his team of some hundred horses. This manure was therefore used to activate a green-manure crop of beans raised on the land under peas, which were always grown between two potato crops. The peas were cut in early July, carried to the shelling machines, the pulpy residues being returned immediately to the surface of the same land which, in the brief interval, had been ploughed and sown with beans. On this layer of pea haulm pulp a moderate dressing of farmyard manure (about five tons to the acre) was immediately spread, so that the newly sown bean land was covered with a double layer of organic matter -- pea haulm pulp below and farmyard manure above: the raw materials needed to manufacture a thin coating of humus on the surface of the soil under the growing beans were thus provided. The beans soon grew through this fermenting layer, which the young foliage kept moist. By October the beans were in flower and from three to four feet high. They were lightly turned under, together with the layer of humus which had, in the meantime, formed on the surface. The green crop was in this way provided with a very efficient activator as well as ample oxygen for conversion into humus. Nitrification took place before the next crop of potatoes was planted the following year. This method of green-manuring worked well and the tilth markedly improved. But besides this dressing of organic matter Mr. Caudwell insisted on applying about 15 cwt. to the acre of a complete artificial manure containing a large quantity of sulphate of ammonia. To keep blight at bay the potatoes were frequently dusted with copper salts.

The effect of all this was a heavy crop of potatoes, but the exceedingly sparse earthworm population did not increase as it might have done had no chemicals been used. Here was an excellent opportunity of observing the effect of humus supplemented by artificials on the earthworm population. These animals found such soil conditions unsuitable and no obvious increase in their numbers occurred.

This agreed with another observation of some interest, which was frequently repeated. In following the ploughs in the autumn and spring in the Spalding area, I always found that where heavy dressings of artificials were used every year, with or without organic matter, earthworms were rare. I sometimes walked half a mile after the ploughs and cultivators without seeing one. Further, on this artificially manured land the dense flocks of seabirds which so often follow the plough were seldom to be seen. These birds had evidently learnt from experience that certain areas of Holbeach Marsh were not worth while as feeding grounds.

In the course of these green-manure experiments in Lincolnshire I spent some time in studying the earthworms on land similar to Mr. Caudwell's farms but which were regularly dressed with farmyard manure. Here earthworms were abundant and in some of the old tunnels I frequently observed the reaction of the roots of the potato (King Edward) to fresh worm casts. The fine roots often followed these tunnels downwards, but whenever they passed the earthworm casts a fine network of roots was given off laterally which penetrated the casts in all directions. Obviously the potato was making full use of these accumulations.

Why do the roots of the potato always invade earthworm casts? The answer is to be found in the work of a number of investigators. In 1890 Wollny began a study of the place of earthworms in agriculture (Forschungen auf der Gebiet der Agrikultur-Physik, 13, 1890, s. 381). He found, as a result of five years' work with cereals and legumes, that the mere addition of earthworms to soil led to a marked increase of grain (35 to 50 per cent) and of straw (40 per cent) above that of similar cultures without earthworms. Equally favourable results were obtained with flax, potatoes, and beetroots. In not a single instance did his cultures suffer any damage from earthworms. No support was, therefore, obtained for the common assertion that earthworms pull up young plants and carry them into the mouths of their burrows. Having seen for himself that soil containing earthworms was considerably more fertile than a soil free from these animals, Wollny set to work to ascertain the cause. He found that earthworms markedly improved the permeability of soils and led to better aeration. As regards the chemical composition of the soil inhabited by earthworms, he observed a considerable increase in the soluble nitrogen and in the available minerals as compared with similar worm-free soil. How far these results were due to the worm casts or to the dead earthworms was, however, not determined.

Wollny's work was afterwards confirmed by a number of investigators. In 1910 Russell (Journal of Agricultural Science, 3, 1910, p. 246) showed that earthworms contain 1.5 to 2 per cent of nitrogen and decompose rapidly and completely, thus furnishing plant food to the soil in which they die. In 1942 H. J. M. Jacobson of the Connecticut Experiment Station compared the composition of the earthworm casts and uncontaminated soil from the farm of Christopher M. Gallup at North Stonington and obtained the following results:

Lb. per Million of Soil Castings
Casts Soil 0-6 in. over soil
Nitrate nitrogen




Available phosphate




Replaceable potassium








Curtis has summed up these interesting results in a press note issued by the Connecticut Station, which was reproduced in the Gardeners' Chronicle of 17th July 1943. These analytical results amplify and re-state in terms of chemistry Darwin's conclusion that 'worms prepare the ground in an excellent manner for the growth of fibrous-rooted plants and for seedlings of all kinds'. They also direct attention to a sadly neglected branch of the chemistry of the soil -- the part played by the waste products of the soil population in plant nutrition. A detailed account of these Connecticut investigations has just been published in Soil Science (58, 1944, pp. 367-75).

How does a dressing of a complete artificial manure affect the rest of the soil's animal population? It is a matter of common knowledge that chemical manures influence the number of animals like moles and toads. Both these prey on earthworms. That moles do not work in land which has been treated with chemicals is well known. An interesting confirmation of this fact was recorded in an account of some experiments on grassland in Scotland early this century. Between plots manured with farmyard manure strips were treated with a complete artificial. It was observed that the moles, which were abundant in the two dunged plots, always moved from one of these plots to the other in a straight line across the artificially manured plot between and never threw up any molehills on this land. They seemed to know by instinct that such areas were useless as feeding grounds. From such a simple experiment as this much could be learned. The deleterious effect of artificials on the earthworm population could easily be demonstrated by a set of counts. The reaction of moles to artificials would be obvious from the absence of molehills. If the behaviour of the grazing animal is watched, it will be found that the two dunged plots will be grazed to the ground, while the artificially manured plots are only lightly picked over. When, therefore, in the cycle -- humus-filled soil, the grass carpet, and the animal -- a substitute for humus is introduced in the shape of chemicals, the earthworms first abandon such soil, the moles follow suit, while the grazing animal records an adverse verdict on the quality of the forage.

These results have been confirmed in the United States where sulphate of ammonia is sometimes used to destroy the earthworms on golf putting greens and tennis lawns because the castings interfere with these games by clinging to the ball. In Farmers' Bulletin 1569 of the United States Department of Agriculture published in 1935 it is stated: 'The results of three years' application of ammonium sulphate to sod on the experimental farm of the Department of Agriculture at Arlington, Pa., for fertilizing purposes have shown incidentally that earthworms were eliminated from the plots where this chemical was used. When applied to soils which are naturally neutral or slightly acid in character, this fertilizer creates a strongly acid condition that is distasteful to the worms and they disappear.'

The use of artificial manures is not the only modern practice which destroys the earthworm. Hardly less injurious are the poison sprays such as Bordeaux mixture and other powders containing copper salts, tar oils, and the lime sulphur washes used for the control of insect pests. Perhaps the most complete account of such results is that given by Dreidax in the Archiv für Pflanzenbau, 7, 1921, and in Rationelle Landwirtschaft, Wilhelm Andermann, Berlin, 1927. The first of these papers concludes with a long list of references dealing among other matters with investigations on the earthworm since The Formation of Vegetable Mould was published in 1881. In the latter work Dreidax sums up his observations on the deleterious effects of poison sprays on the earthworm population of vineyards in Germany.

While examining a vineyard situated in the Markgraf near Auggen in South Baden, in which poison sprays were constantly used, he found a surprising fall from the abundant earthworm population of meadows and orchards under grass adjoining the vineyard to that of the vineyard itself. The growth of the vines always corresponded closely with the number of earthworms: the rows next the grass border were well developed: the vines in the centre of the vineyard, where there were no earthworms, did badly. In this investigation the earthworm population under the grass border invariably stopped dead wherever poison sprays reached the turf.

A visit to almost any orchard in Kent during the spring immediately after the trees are sprayed with tar oils or lime sulphur will be sufficient to prove how harmful this spraying is to the earthworm population. The ground soon afterwards is covered with a carpet of dead worms.

It is in the United States of America that Darwin's studies of the earthworm have of recent years attracted most attention and have also been carried further in a number of useful directions. The reader interested in these developments should begin with the work of Dr. Oliver who, in 1937, published Our Friend the Earthworm, which contains a detailed account of his studies. Starting life as a doctor, quite by chance he read Darwin's account of the work of the earthworm and at once began to investigate the relation of these animals to crop production. Soon he obtained evidence which fully confirmed Darwin's findings. Thus was started a series of experiments on the culture of earthworms, on the production of new types by hybridization, and the distribution of egg capsules for the purpose of re-stocking and improving derelict land almost devoid of these creatures. His success was immediate and in two years he sold his medical practice and set up as a landscape engineer, his main work being to improve private estates and public parks. By 1920 he had become independent and was able to move to Los Angeles, where he pursued his investigations on a ten-acre experimental farm. In 1937 he published his results in the above-mentioned work of three volumes, which has helped hundreds of farmers all over the United States to restore fertility to barren land in which the earthworm population had been destroyed by artificial manures and poison sprays.

One factor in Oliver's career must be emphasized. His mind was prepared for the message contained in The Formation of Vegetable Mould by his early connection with farming, a detailed account of which will be found in the issue of Organic Gardening (The Rodale Press, Emmaus, Pa., U.S.A.) of June 1943. As a small boy, he went to live with his grandfather in Huron County, Ohio, on a 160-acre family holding which had been farmed continuously for sixty years on organic lines. This farm was divided into four blocks of 40 acres, one of which was taken up by the homestead, garden, orchard, and park, the other three blocks being used for mixed farming. In the centre of the whole 160 acres was the farmyard of 2 acres, which communicated directly with each of the four 40-acre blocks by large, swinging gates. In the centre of the farmyard, in which the livestock were kept during the winter, was the compost pit, 50 feet wide and 100 feet long, which had been excavated to a depth of 2 feet. Down the middle line of this compost pit about 20 feet from each end were two heavy posts about 12 feet high, each connected with the barn by a cable furnished with large travelling baskets, by which the manure from the great barn was transported each morning to the compost pit, where it was evenly spread. When necessary the contents of the compost pit could be flooded by gravity flow from a neighbouring stream, which also supplied the drinking troughs of the livestock. The heart of this farm, on which crop failures were unknown, was the compost pit and its vast earthworm population of several millions.

An essential item of the daily work of the farm was the care of this compost pit. Every morning the barn was cleared of the droppings of the livestock, which were evenly spread, together with all the available soiled litter, on the compost heap. When about a foot deep, several tons of red clay from the floor of a pond were distributed all over the compost pit. In this way the vast earthworm population was supplied with organic and mineral food. After the spring thaw, the upper layer of the compost pit was removed and the rich dark crumbling layer of sweet-smelling worm casts was removed by shovels into wagons and spread on the fields just in front of the ploughs. In this way an effective addition to the food materials needed by the new crop, as well as a copious supply of earthworms and egg capsules, was given to the land. Care was always taken to leave behind in the compost pit an adequate supply of earthworm castings, which acted 'as a 'mother substance' for the composting of the surplus top material when that was returned to the pit and composting was re-started.

This early experience naturally influenced Oliver in his later work. He had observed in his boyhood that earthworms will thrive and that a concentration of many thousands to the cubic yard is possible, provided a suitable environment, sufficient moisture, and above all ample food are supplied.

Another feature of this Ohio farm was the regular rotation practised -- two straw crops (wheat and maize) -- followed by a temporary ley of mixed timothy and clover. Every year some forty acres of this ley were turned under. These areas always contained an unbelievable earthworm population.

A further detail must be mentioned. Four acres were in orchard, while other fruit trees were planted in the hedgerows. Oliver's grandfather never allowed these trees to be cultivated. His motto was: 'Never disturb the soil under a tree. The earthworms are the best people for taking care of a tree and I don't want them disturbed.'

Oliver concludes the autobiographical fragment, from which the above account of his grandfather's farm is taken, with the following words:

'In this example of my grandfather's earthworm farm, we have the technique of utilizing the earthworm in general farming operations either on a large or on a small scale. From my experience as a small boy growing up on this farm with much friendly and loving instruction from my grandfather on the subject of earthworms, and in my own work covering a period of more than forty years, I am fully convinced that the eventual salvation of the soil of our country will include the harnessing of the earthworm as one of the major measures. And from my experience I know that the soil can be made to produce several times as much food as the present average through the proper harnessing and utilization of the earthworm under control.'

The preceding paragraph will help to explain the origin of the present-day interest in the place of the earthworm in farming, which is rapidly growing in the United States of America and which is now linked up with the campaign against artificial manures and poison sprays.

There is a growing volume of evidence from all over the world that agriculture took the wrong road when artificial manures were introduced to stimulate crop production and when poison sprays became common to check insect and fungous pests. Both these agencies destroy the earthworm and thus deprive the farmer of an important member of his unpaid labour force. There is also a strong case for believing that one of the roots of present-day disease in crops, livestock, and mankind can be traced to an impoverished soil and that these troubles are aggravated by the use of chemical manures.

The publication of the evidence which indicates that all is not well in our farming and gardening has very naturally disturbed the advocates of chemical farming. What has been described as the war in the soil has broken out and is now in full swing. The most effective way for all concerned of conducting this contest will be to pose to Mother Earth herself the question: What is your decision in this battle between organic and inorganic manuring? When this decision has been duly given, it will have to be interpreted. Live stock can be relied upon to say that the grain, fodder and forage raised with humus is far superior to that obtained with the help of chemicals. The earthworms will unhesitatingly plump for organic manuring. We can read their message by a simple count and by observing their general condition and activities.

There is no better soil analyst than the lowly earthworm. Our most experienced gardeners invariably judge the condition of their plots by the earthworm content. If in the autumn cultivation one large well-fed active lob-worm is turned up with each spadeful of soil, they consider that their land is in excellent condition for the next year's crop. If, on the other hand, earthworms are few in number, pale in colour, and rolled up in a ball, they consider that a good dressing of organic manure is needed (King, F. C., Gardening with Compost, Faber and Faber, 1944, pp. 70-76). All this agrees with the way the tribesmen in the Sahara judge the fertility of the soils of the oases by the number of the earthworm casts. These, as we have seen, constitute the perfect food for plants. Obviously we should do all in our power to increase this supply by providing the earthworms with the food and with the working conditions they need.

In directing attention to one of Nature's chief agents for restoring and maintaining the fertility of our soils, the publication of this new edition of Darwin's book will do much to establish the truth that Nature is the supreme farmer and gardener, and that the study of her ways will provide us with the one thing we need -- sound and reliable direction.

-- Albert Howard, 14 Liskeard Gardens, Blackheath, S.E.3. 4th January 1945.


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