But although it cannot be stated with finality on what land wheat can be grown, or cannot be grown, at a profit, nevertheless accumulated experience has shown that wheat grows best on the heavier kinds of loam5 soils where the rainfall is between 20 and 30 inches per annum. It grows nearly as well on clay soils and on lighter6 loams7, and with the methods of dry farming followed in the arid8 regions of the Western States and Canada, it will succeed with less than its normal amount of rainfall.
It is now about a hundred years since chemistry was applied9 with any approach to exactitude to questions affecting agriculture; since for instance it was first definitely recognised that plants must 3 obtain from their surroundings the carbon, hydrogen, oxygen, nitrogen, phosphorus, sulphur, potassium, calcium10, and other elements of which their substance is composed. For many years there was naturally much uncertainty11 as to the source from which these several elements were derived12. Experiment soon showed that carbon was undoubtedly13 taken from the air, and that its source was the carbon dioxide poured into the air by fires and by the breathing of animals. It soon became obvious too that plants obtain from the soil water and inorganic14 salts containing phosphorus, sulphur, potassium, calcium, and so on; but for a long time the source of the plants’ supply of nitrogen was not definitely decided15. Four-fifths of the air was known to be nitrogen. The soil was known to contain a small percentage of that element, which however amounts to four or five tons per acre. Which was the source of the plants’ nitrogen could be decided only by careful experiment. As late as 1840 Liebig, perhaps the greatest chemist of his day, wrote a book on the application of chemistry to agriculture. In it he stated that plants could obtain from the air all the nitrogen they required, and that, to produce a full crop, it was only necessary to ensure that the soil should provide a sufficient supply of the mineral elements, as he called them, phosphorus, potassium, calcium, etc. Now of all the elements which the farmer has to buy for 4 application to his land as manure16, nitrogen is the most costly17. At the present time nitrogen in manures costs sevenpence per pound, whilst a pound of phosphorus in manures can be bought for fivepence, and a pound of potassium for twopence. The importance of deciding whether it is necessary to use nitrogen in manures needs no further comment. It was to settle definitely questions like this that John Bennet Lawes began his experiments at his home at Rothamsted, near Harpenden in Hertfordshire, on the manuring of crops. These experiments were started almost simultaneously18 with the publication of Liebig’s book, and many of Lawes’ original plots laid out over 70 years ago are still in existence. The results which he obtained in collaboration19 with his scientific colleague, Joseph Henry Gilbert, soon overthrew20 Liebig’s mineral theory of manuring, and showed that in order to grow full crops of wheat it is above all things necessary to ensure that the soil should be able to supply plenty of nitrogen. Thus it was found that the soil of the Rothamsted Experiment Station was capable of growing wheat continuously year after year. With no manure the average crop was only about 13 bushels per acre. The addition of a complete mineral manure containing phosphorus, calcium, potassium, in fact all the plant wants from the soil except nitrogen, only increased the crop to 15 bushels per acre. Manuring with nitrogen on the other hand increased the crop 5 to 21 bushels per acre. Obviously on the Rothamsted soil wheat has great difficulty in getting all the nitrogen it wants, but is well able to fend21 for itself as regards what Liebig called minerals. This kind of experiment has been repeated on almost every kind of soil in the United Kingdom, and it is found that the inability of wheat to supply itself with nitrogen applies to all soils, except the black soils of the Fens22 which contain about ten times more nitrogen than the ordinary arable23 soils of the country. It is the richness in nitrogen of the virgin24 soils of the Western States and Canada, and of the black soils of Russia, that forms one of the chief factors in their success as wheat-growing lands. It must be added, however, that continuous cropping without manure must in time exhaust the stores of nitrogen in even the richest soil, and when this time comes the farmers in these at present favoured regions will undoubtedly find wheat-growing more costly by whatever sum per acre they may find it necessary to expend25 in nitrogenous manure. The world’s demand for nitrogenous manure is therefore certain to increase. Such considerations as these inspired Sir William Crookes’ Presidential address to the British Association in 1898, in which he foretold26 the probability of a nitrogen famine, and explained how it must lead to a shortage in the world’s wheat supply. The remedy he suggested was the utilization27 of water-power to 6 provide the energy for generating electricity, by means of which the free nitrogen of the air should be brought into combination in such forms that it could be used for manure. It is interesting to note that these suggestions have been put into practice. In Norway, in Germany, and in America waterfalls have been made to drive dynamos, and the electricity thus generated has been used to make two new nitrogenous manures, calcium nitrate and calcium cyanamide, which are now coming on to the market at prices which will compete with sulphate of ammonia from the gas works, nitrate of soda28 from Chili29, Peruvian guano, and the various plant and animal refuse materials which have up to the present supplied the farmer with his nitrogenous manures. This is welcome news to the wheat grower, for the price of manurial nitrogen has steadily30 risen during the last decade.
Before leaving the question of manuring one more point from the Rothamsted experiments must be referred to. It has already been mentioned that when manured with nitrogen alone the Rothamsted soil produced 21 bushels of wheat per acre. When, however, a complete manure containing both nitrogen and minerals was used the crop rose to 35 bushels per acre which is about the average yield per acre of wheat in England. This shows that although the yield of wheat is dependent in the first place on the nitrogen supplied 7 by the soil, it is still far from independent of a proper supply of minerals. A further experiment on this point showed that minerals are not used up by the crop to which they are applied, and that any excess left over remains31 in the soil for next year. This is not the case with nitrogenous manures. Whatever is left over from one crop is washed out of the soil by the winter rains, and lost. Translated into farm practice these results mean that nitrogenous manures should be applied direct to the wheat crop, but that wheat may as a rule be trusted to get all the minerals it wants from the phosphate and potash applied directly to other crops which are specially32 dependent on an abundant supply of these substances.
At Rothamsted, Lawes and Gilbert adopted the practice of growing wheat continuously on the same land year after year in order to find out as quickly as possible the manurial peculiarities33 of the crop. This however is not the general system of the British farmer, but it has been carried out with commercial success by Mr Prout of Sawbridgeworth in Hertfordshire. The Sawbridgeworth farm is heavy land on the London clay. Mr Prout’s system was to cultivate the land by steam power, to manure on the lines suggested by the Rothamsted experiments, and to sell both grain and straw. Wheat was grown continuously year after year until the soil became infested34 with weeds, when 8 some kind of root crop was grown to give an opportunity to clean the land. A root crop is not sown until June so that the land is bare for cleaning all the spring and early summer. Such crops also are grown in rows two feet or more apart, and cultural implements35 can be used between the rows of plants until the latter cover the soil by the end of July or August. After cleaning the land in this way the roots are removed from the land in the winter and used to feed the stock. By this time it is too late to sow wheat, so a barley36 crop is sown the following spring, and with the barley clover is sown. Clover is an exception to the rule that crops must get their nitrogen from the soil.
On the roots of clover, and other plants of the same botanical order, such as lucerne, sainfoin, beans and peas, many small swellings are to be found. These swellings, or nodules as they are usually called, are produced by bacteria which possess the power of abstracting free nitrogen from the air and transforming it into combined nitrogen in such a form that the clover or other host-plant can feed on it. The clover and the bacteria live in Symbiosis37, or in other words in a kind of mutual38 partnership39. The host provides the bacteria with a home and allows them to feed on the sugar and other food substances in its juices, and they in return manufacture nitrogen for the use of the host. 9 When the clover is cut for hay, its roots are left in the soil, and in them is a large store of nitrogen derived from the air. A clover crop thus enriches the soil in nitrogen and is the best of all preparations for wheat-growing. After the clover, wheat was grown again year after year until it once more became necessary to clean the land. This system of wheat-growing was carried on at Sawbridgeworth for many years with commercial success. It never spread through the country because its success depends on the possibility of finding a remunerative40 market for the straw. The bulk of straw is so great compared with its price that it cannot profitably be carried to any considerable distance. The only market for straw in quantity is a large town, and there is no considerable area of land suitable for wheat-growing near a sufficiently41 large town to provide a market for the large output of straw which would result from such a system of farming.
The ordinary practice of the British farmer is to grow his wheat in rotation42 with other crops. Various rotations43 are practised to suit the special circumstances of different districts, one might almost say of special farms. This short account of wheat-growing does not profess44 to give a complete account of even English farming practice. It is only necessary to describe here one rotation in order to give a general idea of the advantages of that form of husbandry. 10 For this purpose it will suffice to describe the Norfolk or four course rotation. This rotation begins with a root crop, usually Swede turnips45, manured with phosphates, and potash too on the lighter lands. This crop, as already described, provides the opportunity of cleaning the land. It produces also a large amount of food for sheep and cattle. Part of the roots are left on the land where they are eaten by sheep during the winter. The roots alone are not suitable for a complete diet. They are supplemented by hay and by some kind of concentrated food rich in nitrogen, usually linseed cake, the residue46 left when the oil is pressed from linseed. Now an animal only retains in its body about one-tenth of the nitrogen of its diet, so that nine-tenths of the nitrogen of the roots, hay and cake consumed by the sheep find their way back to the land. This practice of feeding sheep on the land therefore acts practically as a liberal nitrogenous manuring. The trampling47 of the soil in a wet condition in the winter also packs its particles closely together, and increases its water-holding power, in much the same way as the special cultural methods employed in the arid western States under the name of dry farming. The rest of the roots are carted to the homestead for feeding cattle, usually fattening48 cattle for beef. Again the roots are supplemented by hay, straw, and cake of some kind rich in nitrogen. The straw from former crops is used for litter. Its 11 tubular structure enables it to soak up the excreta of the animals, so that the farmyard manure thus produced retains a large proportion of the nitrogen, and other substances of manurial value, which the animals fail to retain in their bodies. This farmyard manure is kept for future use as will be seen later.
As soon as the sheep have finished eating their share of the turnips they are sold for mutton. It is now too late in the season to sow wheat. The land is ploughed, but the ploughing is only a shallow one, so that the water stored in the deeper layers of the soil which have been solidified49 by the trampling of the sheep may not be disturbed. The surface soil turned up by the plough is pulverised by harrowing until a fine seed-bed is obtained, and barley is sown early in the spring. Clover and grass seeds are sown amongst the barley, so that they may take firm root whilst the barley is growing and ripening50. The barley is harvested in the autumn. The young clover and grasses establish themselves during the autumn and winter, and produce a crop of hay the following summer. This is harvested towards the end of June, and the aftermath forms excellent autumn grazing for the sheep and cattle which are to be fed the next winter.
As soon as harvest is over the farmer hopes for rain to soften51 the old clover land, or olland as it is called in Norfolk, so that he can plough it for wheat 12 sowing. Whilst he is waiting for rain he takes advantage of the solidity of the soil, produced by the trampling of the stock, to cart on to the olland the farmyard manure produced during the cattle feeding of the last winter. As soon as the rain comes this is ploughed in, and the seed-bed for the wheat prepared as quickly as possible. Wheat should be sown as soon as may be after the end of September, so that the young plant may come up and establish itself, while the soil is yet warm from the summer sun, and before the winter frosts set in. The wheat spends the winter in root development, and does not make much show above ground until the spring. It is harvested usually some time in August. The wheat stubble is ploughed in the autumn and again in the spring, and between then and June, when the roots are sown, it undergoes a thorough cleaning.
The complete rotation has now been described. It remains only to point out some of its numerous advantages. In the first place the system described provides excellent conditions for growing both wheat and barley in districts where the rainfall is inclined to be deficient52, say from 20 to 25 inches per annum, as it is in the eastern counties, and on the Yorkshire wolds. Not only is an abundant supply of nitrogen provided for these crops through the medium of the cake purchased for the stock, but the solidification53 of the deeper layers of the soil ensures the retention54 13 of the winter’s rain for the use of the crop during the dry summer. The residue of the phosphates and potash applied to the root crop, and left in the soil when that crop is removed, provides for the mineral requirements of the barley and the wheat. Thus each crop gets a direct application of the kind of manure it most needs. Rotation husbandry also distributes the labour of the farm over the year. After harvest the farmyard manure is carted on to the land. This is followed by wheat sowing. In the winter there is the stock to be fed. The spring brings barley sowing, the early summer the cleaning of the land for the roots. Then follow the hay harvest and the hoeing of the roots, and by this time corn-harvest comes round once again.
It must not be forgotten that each crop the farmer grows is subject to its own pests. On a four course rotation each crop comes on the same field only once in four years. Whilst the field is under roots, barley, and clover, the wheat pests are more or less starved for want of food, and their virulence55 is thereby56 greatly diminished. The catalogue of the advantages of rotation of crops is a long one but one more must be mentioned. The variety of products turned out for sale by the rotation farmer ensures him against the danger which pursues the man who puts all his eggs in one basket. The four course farmer produces not only wheat and barley, but beef 14 and mutton. The fluctuations57 in price of these products tend to compensate58 each other. When corn is cheap, meat may be dear, and vice59 versa. Thus in the years about 1900, when corn was making very low prices, sheep sold well, and the profit on sheep-feeding enabled many four course farmers to weather the bad times.
The system of wheat-growing above described is an intensive one. The cultivation is thorough, the soil is kept in good condition by manuring, or by the use of purchased feeding stuffs, and the cost of production is comparatively high. Such systems of intensive culture prevail in the more densely60 populated countries, but the bulk of the world’s wheat supply is grown in thinly populated countries, where the methods of cultivation are extensive. Wheat is sown year after year on the same land, no manure is used, and tillage is reduced to a minimum. This style of cultivation gradually exhausts the fertility of the richest virgin soil, and its cropping capacity falls off. As soon as the crop falls below a certain level it ceases to be profitable. No doubt the fertility of the exhausted61 soil could be restored by suitable cultivation and manuring, but it is usually the custom to move towards districts which are still unsettled, and to take up more virgin soil. Thus the centre of the area of wheat production in the States has moved nearly 700 miles westward62 in the last 50 years.
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1
adaptable
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| adj.能适应的，适应性强的，可改编的 | |
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temperate
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| adj.温和的，温带的，自我克制的，不过分的 | |
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cultivation
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| n.耕作，培养，栽培（法），养成 | |
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isles
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| 岛( isle的名词复数 ) | |
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loam
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| n.沃土 | |
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lighter
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| n.打火机，点火器；驳船；v.用驳船运送；light的比较级 | |
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loams
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| v.（尤指适合植物生长的）壤土，沃土( loam的第三人称单数 ) | |
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arid
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| adj.干旱的；(土地)贫瘠的 | |
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applied
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| adj.应用的；v.应用，适用 | |
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calcium
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| n.钙(化学符号Ca) | |
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uncertainty
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| n.易变，靠不住，不确知，不确定的事物 | |
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12
derived
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| vi.起源；由来；衍生；导出v.得到( derive的过去式和过去分词 )；（从…中）得到获得；源于；（从…中）提取 | |
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13
undoubtedly
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| adv.确实地，无疑地 | |
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inorganic
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| adj.无生物的；无机的 | |
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decided
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| adj.决定了的，坚决的；明显的，明确的 | |
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16
manure
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| n.粪，肥，肥粒；vt.施肥 | |
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costly
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| adj.昂贵的，价值高的，豪华的 | |
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18
simultaneously
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| adv.同时发生地，同时进行地 | |
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collaboration
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| n.合作，协作；勾结 | |
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20
overthrew
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| overthrow的过去式 | |
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fend
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| v.照料（自己），（自己）谋生，挡开，避开 | |
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fens
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| n.（尤指英格兰东部的）沼泽地带( fen的名词复数 ) | |
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arable
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| adj.可耕的，适合种植的 | |
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virgin
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| n.处女，未婚女子；adj.未经使用的；未经开发的 | |
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expend
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| vt.花费，消费，消耗 | |
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foretold
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| v.预言，预示( foretell的过去式和过去分词 ) | |
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utilization
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| n.利用，效用 | |
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soda
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| n.苏打水；汽水 | |
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chili
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| n.辣椒 | |
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steadily
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| adv.稳定地；不变地；持续地 | |
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remains
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| n.剩余物，残留物；遗体，遗迹 | |
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specially
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| adv.特定地；特殊地；明确地 | |
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peculiarities
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| n. 特质, 特性, 怪癖, 古怪 | |
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infested
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| adj.为患的，大批滋生的（常与with搭配）v.害虫、野兽大批出没于( infest的过去式和过去分词 )；遍布于 | |
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35
implements
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| n.工具( implement的名词复数 )；家具；手段；[法律]履行（契约等）v.实现( implement的第三人称单数 )；执行；贯彻；使生效 | |
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barley
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| n.大麦，大麦粒 | |
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symbiosis
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| n.共生（关系），共栖 | |
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mutual
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| adj.相互的，彼此的；共同的，共有的 | |
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partnership
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| n.合作关系，伙伴关系 | |
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remunerative
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| adj.有报酬的 | |
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sufficiently
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| adv.足够地，充分地 | |
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42
rotation
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| n.旋转；循环，轮流 | |
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rotations
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| 旋转( rotation的名词复数 )； 转动； 轮流； 轮换 | |
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profess
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| v.声称，冒称，以...为业，正式接受入教，表明信仰 | |
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45
turnips
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| 芜青( turnip的名词复数 )； 芜菁块根； 芜菁甘蓝块根； 怀表 | |
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46
residue
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| n.残余，剩余，残渣 | |
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trampling
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| 踩( trample的现在分词 )； 践踏； 无视； 侵犯 | |
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48
fattening
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| adj.（食物）要使人发胖的v.喂肥( fatten的现在分词 )；养肥（牲畜）；使（钱）增多；使（公司）升值 | |
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49
solidified
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| （使）成为固体，（使）变硬，（使）变得坚固( solidify的过去式和过去分词 )； 使团结一致； 充实，巩固； 具体化 | |
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50
ripening
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| v.成熟，使熟( ripen的现在分词 )；熟化；熟成 | |
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51
soften
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| v.(使)变柔软；(使)变柔和 | |
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52
deficient
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| adj.不足的，不充份的，有缺陷的 | |
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53
solidification
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| 凝固 | |
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54
retention
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| n.保留，保持，保持力，记忆力 | |
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55
virulence
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| n.毒力，毒性；病毒性；致病力 | |
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56
thereby
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| adv.因此，从而 | |
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57
fluctuations
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| 波动，涨落，起伏( fluctuation的名词复数 ) | |
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58
compensate
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| vt.补偿，赔偿；酬报 vi.弥补；补偿；抵消 | |
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59
vice
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| n.坏事；恶习；[pl.]台钳，老虎钳；adj.副的 | |
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60
densely
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| ad.密集地；浓厚地 | |
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61
exhausted
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| adj.极其疲惫的，精疲力尽的 | |
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62
westward
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| n.西方，西部；adj.西方的，向西的；adv.向西 | |
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