importance. It is well known that certain organisms living free in the 

 soil and quite distinct • from those associated with the nodules on 

 clover roots^ have the power of assimilating gaseous nitrogen from the 

 atmosphere, but as this process requires considerable energy it is 

 essential to provide the organism with easily oxidisable material. 

 Straw contains certain substances and on decomposition yields others 

 which are eminently suitable for this purpose. It is possible to start 

 with straw, soil, chalk and the proper organisms, and with these raw 

 materials alone to secure both the decomposition of cellulose and the 

 fixation of nitrogen, so that a manure is finally obtained which 

 contains considerably more nitrogen than the original components, 

 the excess being derived from the atmosphere. So far this has 

 been done only as a laboratory experiment on the small scale. Before 

 we can say whether the process be feasible on the large scale, it is 

 necessary clearly to define the conditions. 



The problem is also being attacked in another way. Mr. Richards 

 has shown that horse faeces contain something suitable for the 

 process of nitrogen fixation. Moreover he has obtained from the 

 faeces an organism which works in conjunction with the nitrogen fixers ; 

 hence, like Dr. Hutchinson, he can start with straw and the appropriate 

 organisms, and by a process which is simple in principle obtain a 

 considerable enrichment of the manure in nitrogen. 



The two investigations are now converging and both are being 

 tested on the semi-practical scale. It is too soon to express any 

 opinion as to their practicabiHty on a large scale, but if the ploughing 

 up of grass land continues the country will be faced with a large 

 production of straw for which an outlet must be found ; considerable 

 quantities of bulky organic manure will also be required. If the 

 nitrogen fixation plan prove feasible in practice it will afford a con- 

 venient solution of both problems. 



Besides making the most economical use of farmyard manure, it is 

 equally necessary to use the artificials and other fertiHsers to the best 

 advantage. A considerable amount of information on this subject has 

 been obtained at various times both at Rothamsted and elsewhere ; 

 this has been collected and issued in a form convenient for farmers 

 in a book written by the Director entitled " Manuring for Higher Crop 

 Production." 



Work on the effect of liming, to which reference has been made in 

 the previous Report, has been continued. 



II. THE BREAKING UP OF GRASSLAND. 



The second group of problems under investigation arises out of 

 the breaking up of grassland. When, in 1915, it became evident that 

 this policy must ultimately be adopted, a grass field was broken up and 

 sown with various experimental erops. These suffered considerably 

 from the depredations of birds, so that the experiment lost much of its 

 quantitative value ; the hedges and trees, which had given a charm to 

 the landscape and afforded shelter to the beasts while the land was used 

 for grazing, became a pestilential harbour for sparrows and wood 

 pigeons as soon as it was used for arable purposes ; in addition the 

 hedgerow weeds supported a population of injurious insects. Con- 

 siderable clearance had to be effected. 



A second difficulty threatened to be much more serious. Wireworms 

 began to appear and to attack the crops. Provision was therefore at 



