"n 



are being- inveslij^ated in the Soil Phvsics Department under Mr. 

 K. A. Keen. 



The factors are very complex, and closely inter-related : under 

 field conditions alteration in any one almost always produces varia- 

 tion in most of the others. 



Soil cultivation was developed into an art when animals were 

 the motive power on the farm. The chang^e to mechanical power 

 is a fundamental one, and it is by no means certain that the imple- 

 nients designed for horse traction will prove most suitable for 

 mechanical traction. The study of the methods and eflects on the 

 soil of tractor cultivation has already begun at Rothamsted. The 

 various factors contributing to the resistance offered by the soil to 

 the ploug-h are being analyzed in order to disentangle those due to 

 soil conditions and those inherent in the design of the plough. 



For purposes of this work it is necessary to obtain field data 

 on soil cultivation, and on the moisture and temperature relations 

 in the soil, from a diversity of soil types and under varying climatic 

 conditions. The co-operation of various educational institutions 

 situated in the country has been invited for the collection of the 

 required information, and arrangements have been made for 

 teachers to visit Rothamsted in order that they may become 

 familiar with the methods of observation. 



Over much of England loss of water by evaporation 

 from the soil represents a serious source of loss to farmers. 

 Investigations on thi^ subject have been made and are now 

 being extended to different soil types and varying manurial treat- 

 ment. The percentage of clay in the soil has a preponderating 

 influence on the rate of evaporation, while the manurial treatment 

 is responsible for minor differences in the rate. 



Other studies deal with the surface effects associated with 

 clay particles, the method used being the absorption of certain 

 dyes from their solutions ; the effect of the clay fraction on various 

 physical properties of soils ; and the behaviour of the soil colloids 

 when in contact with different liquids. It has also been shown 

 that the experimental results obtained in America on the depression 

 of the freezing point of soil solution measured in situ, are capable 

 of quantitative investigation ; a definite relation holds over a wide 

 range of moisture content between the " free " and " unfree " 

 water. 



These results, together with earlier work in the laboratory, 

 have formed the basis of a general review of the relations existing 

 between the soil and its water content, which was published in 

 1920, and they were incorporated, together with other material, 

 in a series of lectures on wSoil Physics delivered in the University 

 of London, and now being expanded into a Monograph (p. 59). 



A detailed examination of the meteorological data collected at 

 Rothamsted and their effect on the temperature of the soil has been 

 published (p. 47). Material is at present being collected for a 

 discussion of percolation and evaporation under field conditions 

 and their relation to meteorological influences. 



The investigation of soil acidity by physico-chemical methods 

 which was started by Mr. E. A. Fisher (see p. 48) is being con- 

 tinued by Mr. E. M. Crowther. A hydrogen electrode and potenti- 



