An Encyclopedia of the History of Technology part 80 ppt

PART FIVE: TECHNOLOGY AND SOCIETY 772 pattern that was created, known as ridge and furrow, is generally associated with mediaeval practice, but in fact the method was employed well into the nineteenth century, by which time other means of drainage were becoming available. Soil drainage Originally designed to turn the soil before seed bed preparation, the plough has several other forms. Improvements in drainage can be achieved with a conventional plough (see above), but also by creating a ditch with a plough which has two mirror-image mouldboards attached side by side. In the early nineteenth century a highly specialized plough was developed specifically for draining clay soil. Clay, being plastic, can be moulded, and if a solid cylinder is passed through it, a hollow tube will be formed which will retain its shape for a considerable period, acting as a drain for excess soil water. The mole plough, as it was christened, gained particular significance because John Fowler, an engineer from Leeds in Yorkshire, began to experiment with steam traction engines and winches to provide the power for this work. By the 1850s he had developed a two-engine system which was to provide a comparatively cheap and fast method of drainage, with the result that hundreds of acres of cold wet land in Britain and elsewhere were brought into productive use. Extending the idea further, he devised a system whereby the mole would drag behind it a string of clay pipes, thus creating an instant and durable drainage system. Although the materials may have changed, plastic tubes replacing clay pipes, much of modern drainage is achieved in the same way. Fowler took the process a stage further by creating a conventional reversible plough with six furrows a side, which could then be pulled backwards and forwards across the field, turning the soil at each pass. Although these machines never ploughed huge acreages, part of the significance of Fowler’s achievement was that his were the first successful attempts to apply mechanical power to field operations. SOWING To maximize the yields from a given area of land, it is necessary to sow the seeds as evenly as possible, so that each developing plant will have its own source of nutrient without competition from its neighbours. It is also necessary that the seeds are placed at a particular depth, so that the young seedlings can establish themselves before emerging from the soil, but not so deep that the nutrient reserves in the seed are used up before the new leaves are able to start photosynthesizing. An even depth of seed will ensure an AGRICULTURE 773 even growth throughout the crop, and this in turn will result in the crops reaching maturity simultaneously. Any variation from these optimum spacings will result in a fall in yield. The easiest way to spread seed on to a prepared area of land is to broadcast it. This method involves taking handfuls of seed and hurling them out in an attempt to cover a given area as evenly as possible. After broadcasting the land will be harrowed so as to cover the seed, and therefore make it less available to birds and other pests. A major disadvantage of broadcasting is that it leaves seeds randomly distributed, and it is therefore impossible to weed between the plants. Whatever the skill of the broadcaster, the sowing will only be an attempt at the optimum and will never achieve it, and almost since seeds have been sown, methods have been sought for a mechanical means to regulate depth and spacing. The earliest known information concerning the design of a seed drill is to be found in the pictorial representations carved on Sumerian seals dating to the third millennium BC. These implements resembled the ard used in the area, except that attached to the handle was a funnel and tube passing down behind those parts which moved the soil. The seed was dropped into the funnel, and was then deposited at an even depth and in as straight a line as the ploughman was able to achieve. A similar device still exists in India, and indeed it was noticed and commented upon by European travellers as early as the eighteenth century. Despite various attempts to design a machine in Europe, it was not until the late nineteenth century that the drill became a standard part of farm equipment. This does not mean that the drilling of seed in rows was not practised, but rather that it was achieved by other means. One method was to broadcast seed immediately after ploughing, and then to cultivate the ground. In this way the seed tended to roll down the steep sides of the furrow slice and thus formed a row along the furrow bottom. This method may have created straight rows, and may even have placed the seed at an even depth, but it was still an expensive practice as far as the seed itself was concerned. An alternative method was to use a stick to make holes at a set spacing and at a set depth, and then to drop seeds into them by hand. Again this would have produced the desired result, but this time the cost was in terms of labour. By the third century BC the concept of sowing crops in rows was already well established in China. This was accomplished either by sprinkling seed along a ridge, or else the seeds could be individually planted by hand. The latter was used in dry land corn farming and also for wet land rice production. A further refinement to individual planting is that of transplanting, which although generally associated with rice can also be applied to other crops. The earliest references to this occur in literature dating to the second century AD. The process is not only extremely efficient in terms of land productivity, but also increases the yield from individual plants. It is utilized in highly intensive enterprises such as market gardening and horticulture. PART FIVE: TECHNOLOGY AND SOCIETY 774 FERTILIZERS Since animal and plant exploitation have always been closely linked, it is reasonable to suppose that the earliest agriculturalists noticed, if they did not understand, the boost to plant growth that could be derived from animal manure. Similarly the early farmers who were dependent on seasonal river flooding to provide soil moisture, would also have been aware of the fertilizing properties of the silt contained in that water. Human manure was also known for its fertilizing properties, and while its use tends to be associated with Far Eastern farming, its value was well recognized in Europe, and it continued to be used as a fertilizer well into the twentieth century, passing under the title of ‘night soil’. Another practice with a long ancestry and wide distribution is that of green manuring, whereby growing plants are ploughed back into the soil, and then allowed to decompose. The plants ploughed in may be the weeds established after harvest, or they may have been specifically sown for the purpose. The Romans and Greeks favoured the use of legumes, recognizing their high nitrogen content centuries before its existence was established, or the reasons for its presence in these plants was understood. Most of what society has viewed as waste has found its way on to the land at one time or another. Animal and human manure have been joined by blood, bone, rags and sundry other materials which were thought to be of benefit to the soil. There was certainly an amount of artificially manufactured material that joined this, though the references to it are limited. In a curious premonition of future developments, the German chemist J.R.Glauber suggested in 1648 that the methods used to produce the chemicals necessary for the manufacture of gunpowder during the Thirty Years War should be put to use for the benefit of agriculture. For the most part the benefit of a particular material has been observed and acted on, but scientific experiment was not part of the process, though the use of trial plots was mentioned in Blith’s The English Improver, published in 1652. Just how little the processes involved in plant nutrition were understood is well illustrated in Jethro Tull’s The New Horse-Hoeing Husbandry, first published in 1731, which advocated frequent hoeing between the crop plants in the mistaken belief that it would release nutrients from the soil. It was for this reason that he advocated drill husbandry, rather than the reason for which it was subsequently adopted, which was as a method of weed control. By 1807 the chemist who had been appointed by the Bath and West Society was offering soil analysis to farmers, utilizing a system devised by Humphry Davy. In 1835 the first imports of guano arrived in Britain, and at about the same time the first imports of nitrate of soda arrived from Chile. In the early years of the nineteenth century coprolites found in Suffolk were being used in the manufacture of superphosphates. The German chemist Justus von Liebig, AGRICULTURE 775 published his discovery of a method for producing an artificial phosphate manure in 1840. John Bennet Lawes is said to have discovered the same method in 1839, but did not patent it until 1842. However with the profits derived from this process he bought land and a house at Rothamsted in Hertfordshire, where he was joined in 1843 by Joseph Gilbert. Together they set up field experiments and laboratories and produced a standard of experimentation which established Rothamsted as one of the major research institutes engaged in soil research, a reputation it still holds today. Sulphate and nitrate salts of ammonia were generated as by-products of the manufacture of coal gas, and these were utilized as a rich source of nitrogen fertilizer. However as early as 1898 the British Association was warning that mass starvation would be caused by a lack of nitrogen fertilizers brought about by the depletion of natural nitrate resources. At about the same time it was discovered that atmospheric nitrogen and hydrogen could be made to react to form ammonia, and in 1913 the chemical idea conceived by Fritz Haber was being used, in the industrial process devised by Carl Bosch, to produce the gas in quantity (see p. 223–4). The ammonia was used both for the manufacture of explosives and also for fertilizer, thus finally realizing the suggestion made by Glauber three centuries before. Liquid fertilizers, in the form of town sewage or farmyard effluent, have long been used and recognized as a source of fertilizer, and less obvious by- products of manufacturing industry have been used on the land, such as the ammonia solutions derived from gasworks. However the impurities contained in such by-products, and the general bulk and difficulty in handling, precluded the extensive use of liquid fertilizer until the 1950s. The production of highly concentrated liquids such as urea and ammonium nitrate, and a better understanding of the effects of application rates, have now made it an efficient method in which to make the chemicals available to the crop plant. The growing understanding of the plant nutrition cycle that was occurring in the mid-nineteenth century was matched by a similar increase in the study and understanding of the chemical and physical properties of the soil itself. Some of the earliest work took place in the United States, as a result of which the first soil map was produced in 1860, based on a survey of Maryland. The careful study of soil and the matching of chemical application to the requirements revealed by this study, is now an essential part of the process of maximizing production from the land. PEST CONTROL It would have been obvious to both the early farmers and the contemporary gatherers of wild plants, that if something ate or damaged the plants which they themselves valued, then the returns they could expect from their labours PART FIVE: TECHNOLOGY AND SOCIETY 776 would be reduced, whether the unwelcome intruder had been an elephant or an aphid. The larger pests could partly be controlled by fencing, and evidence for this appears quite early in the archaeological record. Insect damage, and that caused by fungal parasites, is less easy to control, but would have been no less apparent. In the natural world there is a wide diversity of plants and animals living in a state of approximate stability one with the other. This diversity is achieved by the often very limited environment that any one species will tolerate, and this will apply whether the relationship of species is of mutual benefit, of rivalry or is parasitic. Agriculture reduces this diversity, and therefore reduces the land’s ability to withstand environmental changes without significant effect on the human economy. A plant species normally found scattered over a wide area is more difficult to harvest than one which is cultivated in a defined location. Unfortunately, it is also much easier for other species whose existence is detrimental to that crop, to spread within it when it is sown to the farmer’s best advantage. There are a number of ways in which plant pests can be eliminated, or at least their damage limited. Chemical control is the most commonly used in western agriculture, and although there is evidence even in classical times for its use, its true significance is very recent. The first method of control used by the early farmer was the attempt to limit the availability of the crop to its pests, whilst trying to maximize it to their own use. This could be achieved by practising a swidden, or slash and burn, regime, so that a given area of land would be exploited on a monocultural basis for only a short period and was then left to revert to its natural state. In this way the crop pests were not given long enough to build up their population to an extent that was potentially dangerous to the farmer. However, where the human population was too large to allow this continual movement from one piece of virgin land to the next, a different approach was necessary. Chemical control of pests was initially limited to substances that could be derived from natural sources, such as plants themselves. Certainly used in classical times, it was not until the mid-eighteenth century that experimentation led to an understanding of the principles involved. Early workers in France, recognizing that the tobacco plant was toxic to aphids, initially used the ground-up plant as an insecticide. Later it was recognized that the chemical nicotine contained in the plant was the responsible agent, and this knowledge led to the identification of a number of other useful plant derivatives which could be used in the same way. Of the chemicals used for insect control one of the most significant was dichlorodiphenyltrichloroethane, isolated in 1939 by the German chemist Paul Müller. Though DDT has now passed out of use because of its more recently discovered and damaging effects within the food chain, its use in the control of insects which act as carriers of disease in domestic and agricultural animals, AGRICULTURE 777 but more particularly in the control of the carriers of human diseases such as malaria, had a profound effect in many regions of the world. This has not only been to improve the health of those populations living in affected areas, but has also allowed the settlement and exploitation of land previously unusable because of the insect pests within it. One of the earliest documented successes against fungal attack also occurred in France, when in the 1840s a mixture of sulphur and lime was found to be an effective agent against a powdery mildew which attacked grape vines. Thirty years later lime was to appear with copper sulphate in a mixture which effectively controlled the fungus which caused potato blight. This particular combination, known as Bordeaux mixture, had originally been used to spray on plants at the edge of vineyards in the hope that the violent colour would put off prospective pilferers. Its fungicidal properties were recognized when it was noticed that the crops at the edge were healthier than those deeper into the vineyard which had been affected by downy mildew. Although chemical pesticides are economically the most important, biological control can sometimes be more effective. In 1762, Indian mynah birds were introduced into Mauritius in a successful attempt to control the red locust, the first of many examples in which a pest in one country has been controlled by the introduction of a potential predator from another. One of the major successes of this method was the introduction of a South American caterpillar into Australia to control the prickly pear cactus. It has been claimed that up to 25 million acres of previously unusable land was reclaimed in this way. While there are great advantages in this method the dangers of a poorly researched project are all too apparent, and it is inevitable that there have also been disasters. Another type of biological manipulation that has been used in recent years has been the introduction of sexually sterile insects into an insect population in order to reduce, if not completely check, its breeding. There is a political advantage to be gained from the application of pest control schemes which have the appearance of being natural, but in fact any attempt to eradicate a particular plant or animal species will alter the ecological balance and therefore carries with it the dangers of unexpected and often spectacular side effects. WEED CONTROL One of the essential differences between an agricultural economy and one based on the collection of wild plants is that the former is dependent on the successful harvest of a very limited number of plant species. Any unwanted plants that grow within the crop are a threat to the nutrient supply of that crop, and by the nature of things weeds were often more suited to the newly prepared ground than were the crops themselves. The practice of fallowing, PART FIVE: TECHNOLOGY AND SOCIETY 778 that is, leaving land free from crop exploitation every alternate or third year, was partly because of the need to re-establish fertility after a crop, but it was also used to attack any build-up of weeds. Fallowing did not mean that land was left unattended, but was in fact a period when the land was continuously ploughed and cultivated so as to create an ideal environment for the weeds to germinate and develop slightly, before being destroyed by the next cultivation. In this way the number of weed seeds remaining in the ground when the crop was sown would be much reduced. Fallowing will serve to limit the build-up of a weed population, but it will also limit the time in which a piece of land is in productive use. An alternative would be to choose a crop which will smother the seedling weeds, while also being of value to the farmer, and alternating this crop with those which were necessary for survival, but which created conditions suitable for the establishment of weed populations. For example the thick, spreading top of turnip will cover anything which germinates at the same time, and if the crop is then fed to livestock by fencing them on to a small area each day, the tight pressure of hooves will further clean the land. By introducing the turnip into a rotation, a check on weed plant intruders can also be controlled mechanically, by weeding, and this very labour-intensive method was all that was available to most farmers in the past, and is still utilized within many present economies. Chemicals will also kill plants, but to be of any use to the farmer they must kill only those plants which are unwanted. Early experiments on weed control made use of the fact that the major crop plants were grass derivatives, and therefore had long narrow leaves, while the major weeds were broad-leaved. If a chemical mixed in water is poured on to the former it tends to run straight off, but on the latter it will form into droplets on the hollows and angles of the leaf, and therefore remain in contact long enough to do damage. Experimental work in France at the end of the nineteenth century identified iron and copper sulphates and nitrates as suitable chemicals for use with cereals. Since the end of the Second World War the research and application of herbicides has relied less on mechanical selectivity and more on the differences in chemical and particularly hormonal activities which occur in different plants at different stages of their development. The earlier complicated chemicals, which have become known by their abbreviations such as 2,4-D or 2,4,5-T, have now given way to a whole cocktail of chemicals which are available to farmers. These chemicals have become vital to the achievement of high yields from continuously cropped land, and with a reliance on single species enterprises. A new move in chemical control is to utilize natural amino acids found in plants to exaggerate processes that take place naturally. By the careful selection of the correct amino acid for a specific weed, it is hoped that a new generation of herbicide will be developed which will be environmentally safer than those in present use. AGRICULTURE 779 CROP ROTATION A single crop grown repeatedly on the same area of land allows the expensive back-up facilities of capital and machinery to be spread over a number of years, but does raise problems of loss of fertility or build-up of pests. This singleminded approach can be tempered by the use of a sequence of enterprises which are mutually beneficial. A rotation is devised to suit a particular set of circumstances and requirements. At its simplest it is to be seen in the slash and burn technique. As simple, but more productive, is the system known as alternate husbandry, in which an area of land is used for a short time for arable production, and then sown to grass and grazed for a number of years, the animal manure making a significant contribution to the fertility of the land. There is increasing evidence for the practice of crop rotations even in the very earliest settlement areas, but the first references to alternate husbandry appear in the agricultural writings of Columella in the first century AD. It was later practised by the Cistercians in France, where as early as 1400 they were advocating five years of grass, followed by two years of corn and then reseeding with grass. More complicated rotations were created to resolve more difficult problems and in Europe all the traditional constituents of rotations were known and being used at least as early as the Roman period. Legumes, turnips and corn were all documented if not widely grown. In mediaeval East Anglia extremely complicated rotations of fourteen-year duration have been recorded. It therefore seems likely that formal rotations were in use over a much wider area, and at a much earlier period than the seventeenth-century English writers would suggest. By 1880 leguminous crops were an established part of the farming regime throughout Europe, and they represented a significant proportion of the total arable acreage. This situation is significantly different from that of a hundred years earlier and is an indication of the recognition of the nitrogen fixing properties of this crop. Over the same period the reduction in the acreage left fallow is significant and highlights the benefits derived from the change of rotation made possible by the additional use of legumes, not only in terms of increased yield per acre, but also in terms of the increase in the numbers of productive acres. HARVESTING Reaping and binding By the careful preparation of the land, and the attention paid to the plant from germination to maturity, the farmer will come to harvest, which is perhaps the most critical stage of all. One of the most common finds in an archaeological PART FIVE: TECHNOLOGY AND SOCIETY 780 context is that of microlithic flint blades which are thought to have been used in the construction of sickles. These thin, sharp pieces of flint were mounted into a handle and fixed with pitch or similar material. They occur with early Ubaid pottery at Eridu, in Iraq, and have been dated to the sixth millennium BC. In these cases the handle and blade holder is made of clay, the blades being made up from a series of small flakes of carefully prepared flint. The presence of these flints, or the complete sickles themselves, is frequently cited as one of the vital pieces of evidence for the transition from the hunter gatherer economy to an agricultural one, together with pottery and grinding stones forming the traditional agricultural package, but in fact each could also have been of value to the gatherer. Under the microscope these flint blades frequently show a particular gloss which is certainly of plant origin, but may as easily have been caused by the cutting of grass or reeds for roofing materials as by the cutting of corn stems, and therefore their presence on a prehistoric site should not be seen as automatic proof of a sedentary farming existence. The wild cereal species are very brittle just below the ear, and recent experiments have shown that it might be easier to pick this corn by hand, rather than cutting it with the primitive sickle; ethnographic evidence suggests that in light sandy soil it may have been harvested merely by uprooting. Less fragile strains were to be developed as domestication and selection occurred, and a cutting blade became more necessary for the harvest. The flint sickle gave way to one made of bronze, and then of iron. Examples of this implement in use can be seen in the Egyptian wall paintings, and later still in Roman mosaics. Innumerable examples have also been discovered in archaeological sites. Mosaics and actual examples also provide evidence for the existence of the scythe by at least the Roman period, but there is no indication that it was used on corn. The scythe consists of a blade of about a metre (3ft) in length, attached to a long handle which allows for its use in a more upright posture than is possible with the sickle. It is potentially a more effective tool for harvesting corn than the sickle but, in Europe at least, their widespread use seems to have been restricted to the cutting of grass until the nineteenth century. However in China by the Han period, between 200 BC and AD 220, an implement was in use which should perhaps be called a scythe, although its form differed considerably from the European equivalent. Resembling an upturned walking stick, it has remained an essential harvest tool to the present day. The earliest application of the scythe to corn in Europe is of unclear date. To gain the full advantage from the long blade it is necessary to attach a basket or cradle to the handle. This cradle will collect all the corn cut in one sweep, and allow it to be deposited out of the way of the next sweep, and conveniently placed for the workers following, whose job it was to bind the corn into convenient sheaves. The earliest representation of a scythe and cradle is in a AGRICULTURE 781 thirteenth-century illustration, and it is also to be seen in Brueghel’s Spring, dated to 1565. The sickle was slower to use than the scythe, but it was much cheaper and could be afforded by the harvest labourer. The more expensive scythe was generally purchased by the farmer, and it has been suggested that this situation changed the status of the harvester from one in which he was essentially a contractor, to one in which he became purely a hireling, and that this produced a resistance to its introduction in certain parts of Britain. Even today, in those parts of the world where the corn is cut by hand tool rather than by machine, there is great variety in the distribution of the two types of implement. Speed is a necessity of the harvest more than any other aspect of the farming year. A mechanical means to bring in the corn has therefore been a matter of interest for centuries. The earliest references to a successful device can be found in the first century AD writings of Pliny, and also those of Palladius about three centuries later. Both authors referred to a harvester which was supposed to have been used in northern France at the time in which they were both writing. The machine consisted of a two-wheeled barrow, along the front edge of which was a metal comb. When it was pushed into the standing corn, the stalks passed between the teeth, and the ears of corn were plucked off and fell back into the container. Until quite recently this description was thought to have been fanciful, or at least describing an oddity without very much practical use. However in recent years four stone relief carvings have been found or identified which carry a clear representation of the device that the writers had been describing. No further evidence for this machine or any developments from it exists. However, centuries later on the other side of the world something based on a similar line was to appear. Whether John Wrathall Bull read the classics or had a knowledge of the Roman texts is unclear, but in 1843 he submitted a model of a harvesting machine to the Adelaide Corn Exchange Committee in the hope of winning a prize being offered for a harvester suited to Australian needs. Sad to relate, neither Bull nor any of the other competitors won the prize, but a miller and farmer by the name of John Ridley saw the model and built himself a fullscale example based on the same principles. Having proved to himself that the idea worked, he took out patents and began production. This basic design was continuously improved, and in 1885 the stripper- harvester was produced (see Figure 16.1). This machine was capable of harvesting, threshing and winnowing the corn in one operation. It has been suggested that this Australian invention had such an effect on binder sales in the Australian, Argentine and American markets that the two major manufacturers, International Harvester and Massey Harris, were forced into combine harvester production. By 1909 the first self-propelled example had been built, using an internal combustion engine, though it was not to become a production reality until twenty years later. . variety in the distribution of the two types of implement. Speed is a necessity of the harvest more than any other aspect of the farming year. A mechanical means to bring in the corn has therefore. grass and grazed for a number of years, the animal manure making a significant contribution to the fertility of the land. There is increasing evidence for the practice of crop rotations even in the. and the contemporary gatherers of wild plants, that if something ate or damaged the plants which they themselves valued, then the returns they could expect from their labours PART FIVE: TECHNOLOGY