June 15, 1916] 



NATURE 



333 



is called "green manuring," and even to-day is not 

 so fully developed as it ought to be. Instead of 

 ploughing in the crop it may be fed to animals on 

 the ground; there are other methods also, but the 

 object is always the same. 



The cultivator's aim, however, is not to accumulate 

 fertility but to use it. We must therefore turn to the 

 other part of the cycle and see how far the down 

 grade can be controlled. The most obvious method 

 is to try to control the soil organisms. This has 

 proved very difficult, and only the fringe has yet been 

 touched. Soon after bacteriologists had picked out 

 the organisms that cause clover to fix nitrogen they 

 conceived the idea of breeding them in quantity and 

 putting them on to the seed or into the soil, with a 

 view of getting better clover crops, and therefore a 

 greater store of fertility. These hopes were dis- 

 appointed. Inoculation succeeded only in one case; 

 when a new leguminous crop was introduced it some- 

 times proved more economical to add the proper strain 

 of organisms than to wait until the native organisms 

 had had time to adapt themselves. This has happened 

 in Scotland, Canada, and the United States. But 

 usually in this country the proper bacteria appear 

 already to be present, and little is gained by adding 

 to their numbers ; they merely die down to the proper 

 number the soil can carry. If one wishes to increase 

 the number it is necessary to improve the soil condi- 

 tions. Even this does not settle the matter, for, as 

 already shown, the soil population is very mixed, and 

 improvements in soil conditions may benefit the whole 

 crowd, bad and good. Indeed, under specially intense 

 glasshouse conditions the harmful population may 

 prosper so much that the efficiency of the soil becomes 

 lowered and the soil becomes " sick." The remedy is 

 obvious : it consists in improving the soil population, 

 and this is done by taking advantage of the fact that 

 the harmful organisms are more easily killed than the 

 useful ones. Steam is used successfully in glass- 

 houses ; antiseptics would be cheaper, but in spite 

 of considerable search, nothing has yet been found 

 suitable for field work. The problem is still under 

 investigation. 



More success has been attained in the control of soil 

 conditions. Fortunately these are the same for organ- 

 isms as for plants, so that anything benefiting the one 

 helps the other as well. But there is one fundamental 

 law that always holds ; the plant must have all its 

 requirements satisfied or it will fail; for example, no 

 amount of food or water makes up for the lack of 

 temperature^ Anything setting a limit to growth is 

 called a limiting factor. Common limiting factors in 

 the soil are sourness, wetness, dryness, poverty, thin- 

 ness of soil, etc. In soil fertility problems the first 

 step is always to discover the limiting factor, and then 

 to put it out of action. 



One of the commonest defects is sourness or lack 

 of lime. From the dawn of history this has been one 

 of the troubles of the Celtic tribes^ and before History 

 began they had discovered the remedy. Pliny tells 

 us that they drew chalk out of the earth to " nourish " 

 the soil ; to this day the process is still carried out in 

 Hertfordshire much as he describes it. In modern 

 times ground lime is more convenient, and ground 

 limestone sometimes proves even better still. 



Wetness can be remedied only in one way — by 

 drainage. This is an old art that was forgotten for 

 a long time; it is not mentioned in the great English 

 agricultural revival of the sixteenth century. Gervase 

 Markham, for instance, wrote books on every branch 

 of farming — so many, indeed, that his publishers made 

 a contract with him to write no more — but never one 

 on drainage. By the middle of the seventeenth 

 century it was well known, though not much practised ; 

 by the middle of the nineteenth century, however, it 

 NO. 2433, VOL. 97] 



was extensively carried out. Much of it wants re- 

 doing. Pipe drainage is out of the question nowadays 

 on any large area, but a cheap and effective substitute 

 seems to be forthcoming in mole drainage, which con- 

 sists in making tunnels through the soil about 9 to 

 18 in. below the surface with a special form of plough. 



Dryness can either be overcome by adding water, as 

 in the big irrigation schemes, or by taking more care 

 of the natural water supply. Addition of clay or 

 organic matter reduces the loss of water ; so also does 

 the preservation of a fine soil mulch on the surface. 

 Implements have been devised to produce this soil 

 layer. Much can be done also by selecting suitable 

 crops or varieties; special drought-resisting wheats 

 have been bred in Australia, and maize in the western 

 States of America. 



Shallowness of soil is, however, more serious, 

 especially when the thin soil is underlain by gravel or 

 very coarse sand ; indeed, in this case no one has 

 evolved any satisfactory method of treatment. Some- 

 thing may be done if a soft rock lies beneath, and 

 especially if it forms only a thin layer which can be 

 removed. But when all is said and done, there remain 

 great areas of waste land that cannot be dealt with on 

 our present methods. 



Apart from these cases, however, a very considerable 

 degree of control of the soil cycle is possible. The 

 question naturally arises : How far can the process 

 go? Not indefinitely. In any scheme of improvement 

 we are soon brought up against the fundamental law 

 that plants must have all their requirements fulfilled, 

 anything lacking setting a limit to their growth. 

 Agricultural investigators aspire to a good deal in the 

 way of control and improvement, but they admit they 

 cannot overcome the weather. Here, then, is one 

 limiting factor which has wrecked many schemes of 

 soil improvement. 



Another is the soil type. In spite of all efforts a clay 

 remains a clay and a sand remains a sand. A gar- 

 dener on sandy soil may with great pains be able 

 to grow clay-soil plants, but they will never " do " as 

 well as if equal care were bestowed on theoi in their 

 natural habitat. The farmer cannot lavish care on 

 individual plants, but has to deal with masses ; he 

 therefore is less able to overcome the difficulties of 

 soil type. This problem, however, is not insuperable, 

 and attempts are now being made to deal with it. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



Cambridge. — ^The General Board of Studies has pub- 

 lished a report to the Senate on the desirability of 

 instituting degrees, other than the doctorate, to be 

 given for original research; the board is of opinion 

 that the present is a favourable opportunity,- for insti- 

 tuting a more distinctive recognition of research work 

 than is at present available. Two classes of student 

 have to be considered : first, that composed of gradu- 

 ates of the University ; and, secondly, that consisting 

 of graduates of other universities who may, under the 

 present regulations, obtain the Cambridge degree by 

 two years' research work carried out in the Univer- 

 sity. The Board recommends that the degrees of 

 Bachelor of Letters and Bachelor of Science be estab- 

 lished ; that a Bachelor of Arts of the University may, 

 in or after his eleventh term, submit for approval a 

 dissertation upon original research for the degree of 

 Bachelor of Letters or Science ; that a research student 

 who is not a graduate of the University may submit 

 a dissertation upon original research for one or other 

 of the new degrees after six terms' residence. It is, 

 also recommended by the board, although with dis- 

 sentients, that holders of the new degrees may pro- 



