Nature of the Mangel Plant. 29 other crop indeed yielding so large a weight of dry matter per acre. The mangel possesses a greater development of leaf in proportion to the root than does the swede, though it falls below the common white turnip in this respect. It also roots more deeply and throws off fewer roots near the surface, so that it searches the subsoil very thoroughly for food and water. The mangel has been derived by cultivation and selection from the wild beet (Beta maritima), a typical seaside and saltloving plant, and it still shows its ancestry in its dependence upon large supplies of saline constituents in manure, and in its toleration of soils containing amounts of alkaline salts which would injure ordinary vegetation. Considered from the standpoint of its after use as a food for stock, the mangel contains a rather higher proportion of dry matter than either swedes or turnips, and this dry matter consists mainly of sugar; in fact the mangel must be regarded as essentially a sugar crop. As a rule there will be in the twelve to fourteen per cent. of dry matter in the mangel root, sugar accounting for eight to ten per cent.; in swedes the proportion of sugar is only four to seven per cent., but in the sugar beet proper it rises to sixteen or eighteen or even twenty per cent. At Rothamsted it was found impossible to continue the growth of swedes upon the same land year after year with any success. In Sir Henry Gilbert's words this was "mainly due to the incidental circumstance that in growing the same description of crop, with the same comparatively limited and superficial root-range, for so many years in succession, the surface soil became less easily worked, and the tilth, so important for turnips, was frequently unsatisfactory; whilst for want of variety and depth of root-range of the crop, a somewhat impervious pan was formed below."1 At the outset of the trials with mangels it was thought not unlikely that a similar difficulty would be experienced, and that after a time the soil would be rendered unsuitable for the further growth of the crop. This has, however, not proved to be the case; the crop, except on the continuously unmanured plots, has shown no tendency to deterioration when the later periods are compared with the earlier; indeed, the twentyfifth crop, that of 1900, was the best of the whole series, and the last crop in 1902 has also been exceedingly good. Doubtless the deep rooting habit of the mangel, and the fact that its roots are not specially confined to any particular layer of soil, helps to render this continuous growth possible. Something also must be attributed to the freedom of the mangel from insect or fungoid attacks. Agricultural Students' Gazette, New Series, Vol. III., Part V., 1887. All the experiments at Rothamsted, where crops have been grown continuously, go to show that, with the one great exception of the leguminous crops, it is only secondary causes, such as the difficulty of keeping the land clean or in proper tilth, the prevalence of pests and diseases peculiar to the crop, &c., which render a rotation of crop necessary. The following account of the results which have been obtained during the continuous growth of mangels on the Barn Field deals with a period of twenty-seven years, beginning in 1876 and including the crop which has just been harvested. From the averages two years have been excluded, 1885 and 1901, years in which so poor a plant was secured on the plots receiving no organic manure that it was not thought desirable to apply the usual cross-dressings of ammonium salts and nitrate of soda. The crop returns only will be dealt with in this paper, leaving the very important question of the effect of the various manures upon the character and composition of the plant for a future occasion. For the details of the crop obtained year by year the "Memoranda of the . . . Field and other Experiments at Rothamsted," for 1901, should be consulted. SCHEME OF THE EXPERIMENTS. The Barn Field has an area of about eight acres, the land under experiment being about 340 yards long and 90 yards across. The upper end is pretty level, then the field slopes down to a hollow and rises again somewhat to the path by which it is generally approached. That portion of the field which lies immediately in the hollow is cut out of the experimental area, because of the drainage towards this point; in very heavy rains there is even a certain amount of washing across the plots at this point, so that soil and manure are carried over the boundaries of the plots. The soil is a stiffish clay loam, very flinty, there being a greater proportion of stones in this than in any other of the Rothamsted soils; the subsoil is a strong clay, stiffer in some parts of the field than in others. The land is naturally drained by the chalk which underlies the subsoil at a variable depth of 8 to 20 feet. The chemical composition of the soil need not be considered in detail here; it will suffice to say that it contains a fair proportion of carbonate of lime, and possesses very considerable reserves of potash, amounting to two per cent. or so of the whole soil, though only a portion of this is in such a state as to be soluble, even in strong hydrochloric acid. The land is divided longitudinally into eight strips running the whole length of the field; each of these strips receives one particular manure, called the "Standard Manure," which Scheme of the Experiments. 31 consists in two cases of farmyard manure, in the others of various combinations of the mineral manures, except the two strips, which receive no standard manure at all. The field is further divided into plots by cross-dressings of the various nitrogenous manures which run across all the strips, thus giving plots dressed with every combination of the standard manures and the nitrogenous cross-dressings. The standard manures are: 1. Farmyard manure only. 2. Farmyard manure, plus superphosphate, and, for the last eight years, sulphate of potash. 3. No manure. 4. A complete mineral manure-superphosphate, sulphate of potash and magnesia, and common salt, but no nitrogen. 5. Superphosphate only. 6. Superphosphate and sulphate of potash, but no sulphate of magnesia nor salt. 7. The same mineral manure as 6, but in addition a small quantity of nitrogen. 8. No manure. The cross-dressings form a series of five, and are :— 0. No manure. N. Nitrate of soda. A. Ammonia salts containing nitrogen equal in amount to that of Series N. Thus the plots show successively each of the standard manures 1 to 8, in combination with each of the cross-dressings, making forty plots in all. Of these, however, the plots in strip 3 will be dismissed from further consideration; the strip is narrow, and has evidently derived nutriment from the adjacent dunged plot ; strip 8 also forms a much larger but similarly unmanured strip. The remaining thirty-five plots give therefore-unmanured plots,-plots receiving mineral or nitrogenous manures only— plots showing no potash, potash alone, or potash, magnesia and soda, in conjunction with superphosphate and various sources of nitrogen--and lastly plots receiving dung alone, and in combination with various nitrogenous and mineral manures. The quantities of manure applied are very large-on many of the plots far beyond the usual dressings in practice; but no injurious effects upon the state of the soil are apparent, except that in some dry seasons it is difficult to secure a plant on the plots where no organic manure has been applied for so long a period. The seed was dibbled in the earlier years of the experiment; it is now drilled, twenty-six inches between the rows, and the plants are singled out to ten inches apart, gaps being repaired when possible by transplanting. The plots are each about one-seventh acre in area, except in strip 4, where they are about one-fifth acre. The whole produce from each plot is weighed; the roots only are carted away; the leaves, after weighing, are spread and ploughed in. PREVIOUS HISTORY OF THE EXPERIMENTAL Field. The experiments on the continuous growing of root crops were begun on the Barn Field, Rothamsted, in 1843; for the first six seasons, 1843-48, Norfolk White turnips were grown, followed by swedes for four seasons, 1849-52. Barley was afterwards grown for three seasons to remove the residues of the previous manures and equalise the soil conditions again. The plots were then re-arranged on substantially the plan they occupy to-day, and swede turnips were grown for fifteen seasons, 1856-70. The swedes were followed by sugar beet for five seasons, the manuring being continued on the same lines, except that in the last two years of the sugar beet, 1874-5, all nitrogenous manures were omitted, though the mineral manures were applied as before. In 1876 the growth of mangel wurzel began, and has been continued without interruption ever since, so that the present year, 1902, is the twenty-seventh season of the growth of mangels on the same land with the same scheme of manuring. The seed has always been Yellow Globe. During a period of forty-seven years the character of the manuring of the plots has suffered little change, so that although the mangels have only been growing for twentyseven years, the character of the plots had already been well established by twenty years previous manuring on the same lines. RESULTS OF THE EXPERIMENTAL PLOTS. The following Tables give (I.) the average weight of roots grown on each plot during the 27 years, 1876-1902; (II.) the weight of roots and leaf grown in the best season, 1900. The Tables also set out in detail the nature and quantities of the manures applied each year. A first inspection of the results shows the enormous value of farmyard manure in growing mangels, especially when they are grown continuously on the same land, as in these experiments. In good seasons it is possible to grow large crops by the aid of manures containing no organic matter, but the soil becomes so depleted of its reserves of humus that it dries out readily near the surface and in many seasons the seed fails to germinate satisfactorily. The texture of the soil is also affected by the absence of organic matter; if the conditions are unfavourable the land cakes at the surface on the plots which do Plot Results of the Experimental Plots. TABLE I.-BARN FIELD MANGEL Wurzel. 33 Average Produce of Roots per Acre, over 27 years,1 1876 to 1902. Tons! 17.44 24.74 Tons 21.73 Tons Tons 24.05 23.96 1 Omitting 1885 and 1901, when owing to drought, &c., the cross-dressings of nitrate of soda and ammonium salts were not applied. 2 Plot 7 also received each year, as a standard manure, 36 lb. ammonium salts= 7-8 lb. nitrogen per acre. In 1896 and subsequent years basic slag replaced the superphosphate. 4 In 1895 and since, only. 5 Ammonium salts consist of equal parts sulphate and muriate ammonia of commerce. not receive either dung or rape cake, again injuriously affecting the germination of the seed. Of course the long continued application of rape cake on the plots of Series AC and C has also stored the soil with organic matter, so that on these plots the germination and early growth is as satisfactory as on the dunged plots. The other fact immediately apparent is that though farmyard manure alone grows a very fair crop, a considerable increase may be obtained by the addition of quickly-acting nitrogenous manures. It will perhaps be most convenient to review the results given by each class of manure separately, taking first the effect of the varying amounts and compounds of nitrogen, then the effects of the mineral manures, and considering the dunged plots last, as receiving the most complex treatment. VOL. 63. 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