September 22, 192 1] 



NATURE 



119 



ever, it may prove possible to keep this special 

 manuring- within bounds. 



(3) In the case of the clover crop the farmyard 

 manure or the straw in the litter may have a 

 special effect on the organisms living in the root, 

 causing them to increase the amount of nitrogen 

 fixation and thus give larger clover crops and 

 further enrich the soil in nitrogenous organic 

 matter. 



Work on these problems is progressing; the 

 scientific investigator has, of course, to find out 

 exactly what is happening before he can show the 

 practical man how to exercise control. 



But in the meantime it is necessary for us to 

 be practical and to do something, and the most 

 obvious line of action is to increase the amount 

 of farmyard manure or similar substances on the 

 farm. \Ve can proceed in two ways; first, wast- 

 age can be cut down. We estimate that the 

 farmers of the United Kingdom make about forty 

 million tons of farmyard manure a year, and 

 waste about ten million tons. We have shown 

 that the best results are obtained when manure 

 is made under cover and the amount of litter 

 properly adjusted to the amount of nitrogen in the 

 animal excretions. Correct adjustment is a 

 counsel of perfection, but a great improvement is 

 possible over the present haphazard methods. In 

 practice nitrogen is always lost through exposure 

 to weather, greatly to the detriment of the 

 manure. The provision of some shelter for the 

 heap is not difficult, and, as Prof. Berry has 

 shown at Glasgow, it is distinctly advantageous. 



Another method is to increase greatly the 

 amount of farmyard manure or similar sub- 

 stances produced on the farm. This could be 

 done by running on more animals. The number 

 of livestock per acre could be much increased by 

 the general adoption of the methods of some of 

 the Scottish and Danish farmers, who keep their 

 animals largely on the produce of their arable 

 land. The problem is closely bound up with 

 financial considerations, but the experiments of 

 Mr. J. C. Brown at the Harper Adams Agricul- 

 tural College show that more profit is obtainable 

 from the soiling system than from the older 

 methods of the south. 



At Rothamsted we are examining possible sub- 

 stitutes for farmyard manure, green manuring, 

 and the activated sludge method of producing 

 manure from sewage, both of which seem quite 

 promising. We tried using straw as manure, but 

 without success ; so soon, however, as the straw* 

 was rotted, much more promising results were 

 obtained. The conditions for the proper rotting 

 of straw, investigated at Rothamsted by Dr. H. B. 

 Hutchinson and Mr. E. H. Richards, were found 

 to be proper air and moisture supply, suitable tem- 

 perature, freedom from acidity, and the proper 

 proportion of soluble nitrogen compounds. .\I1 

 these conditions are easily obtainable on the farm, 

 and it is now possible to make an artificial farm- 

 yard manure from straw without the intervention 

 of animals. So far the results seem quite satis- 



NO. 2708. VOL. 108I 



factory. Arrangements are being made for 

 demonstrations on an extensive scale during the 

 present season. 



All these problems I have been discussing repre- 

 sent work of interest to the present generation of 

 farmers ; but the scientific investigator cannot be 

 restricted to problems of present-day interest. 

 Some of the best work of to-day may never reach 

 the farmer in our time, and, indeed, unless it is 

 developed, it will never reach the farm at all. We 

 now know that the farmyard manure and the green 

 manure put into the soil are not really agents of 

 fertility, but only raw materials out of which fer- 

 tility is manufactured. The work is done by 

 myriads of living creatures in the soil, which are 

 too small to be seen by the naked eye, and only 

 incompletely revealed even by powerful micro- 

 scopes. Some of them are useful to the farmer 

 and some not, many of them taking their toll of 

 the valuable plant food in the soil. Their activity 

 fluctuates daily, almost hourly, and their numbers 

 are counted and their work is watched in our 

 laboratories. Much of their activity is helpful to 

 the farmer ; it makes nitrates, indispensable for 

 the growth of plants. Much of their time, how- 

 ever, is spent in undoing the good work they have 

 done, and results in the destruction of a large pro- 

 portion of the nitrates made. We are studying 

 this population, and with fuller knowledge we 

 hope to control it and make it serve the 

 farmer just as horses, sheep, and cattle do; but 

 we are a long way from that yet. 



Finally an attack is being made on a much 

 more difficult problem. The growth of a crop is 

 like the movement of a motor-car ; it cannot go on 

 without a continuous supply of energy. In the 

 case of the car the energy comes from the petrol ; 

 in the case of the growing crop it comes from 

 sunlight. The plant as we grow it, however, is 

 not a very efficient transformer ; a crop of wheat 

 utilises only about half of i per cent, of the energv 

 that reaches it. During the last eighty years the 

 growth of crops has been improved, thus increas- 

 ing their efficiency as utilisers of energy ; but we 

 are still a very long way from the 30 per cent. 

 eflSciency which the motor engineer has attained. 

 Better developments of our present methods will 

 no doubt carry us further than we have yet gone, 

 but some wholly fresh ideas are necessary before 

 we can hope to bridge the enormous gap that now 

 exists between the actual and what is theoretically 

 possible. There seem to be at least six ways in 

 which we might improve crop production : — 



(i) We can hope for further improvements bv 

 the use of new varieties capable of making better 

 growth than those ordinarily cultivated. Plant 

 breeders all over the world are attacking this 

 problem with much success, and many of the 

 new sorts show considerable promise. 



{2) Much can be done by control of plant dis- 

 eases. Unfortunately we have no means of know- 

 ing how much is lost each year by pests or 

 disease, but it is undoubtedlv considerable. 

 Laboratories for studying plant pathologv have 



