SECTIONAL TRANSACTIONS.— M. 4I5 



making it unsuitable for many agricultural crops. This change is of great im- 

 portance in irrigation areas, and it is an important factor in the evil efEects of over- 

 watering. 



Mr. C. G. T. MoRisoN.— <So»?e Factors controlling Soil Fertility. 



Variations in soil composition — the soil as a succession of changing horizons — 

 change in horizon character with season — the content in exchangeable bases, and in 

 degree of saturation of definite horizons varies through the year. The effect of loss 

 of water upon the H ion content of soil suspensions, and upon the exchangeable base 

 content of the soil. Possible effect of de-hydration upon soil fertility. 



Physical Factors and their Control. (Dr. B. A. Keen, Dr. W. G Ogg and 

 Prof. N. M. Comber.) 



The soil moisture is undoubtedly the most important physical factor in plant 

 growth. Measures of control seek as far as possible to maintain it at its optimum 

 value, which lies between the deleterious extremes of excess (waterlogging) and 

 deficiency (drought). 



Methods of soil treatment to encourage rapid drainage of excess water are quite 

 well understood, but there is still very considerable divergence of opinion as to how 

 far it is possible by appropriate methods of cultivation to conserve soil moisture in 

 regions of deficient rainfaU. It is frequently stated that the preservation of a mulch 

 of dried soil is an effective means of conserving from evaporation the water in the soil 

 below the mulch. On the other hand, extensive work on the influence of moisture 

 on crop production in the Great Plains area of America has led to the conclusion that 

 the loss from a mulched surface is practically the same as from an unmulched one ; 

 the effect of cultivation is to prevent weed growth and hence transpiration losses, and 

 the mulch is, in fact, only incidental. The theory on which the supposed action of a 

 mulch is based likens the soil to a mass of fine capillary tubes up which water can 

 ascend from the free water table to the surface. The mulch is supposed to break these 

 channels, and thus to prevent water in liquid form from rising higher than the bottom 

 of the mulch. Work at Rothamsted and elsewhere has shown this idea to be incorrect 

 and has also demonstrated that the distance to which water can ascend above the free- 

 water table is much less than that predicted by the laws of capillary rise. 



Wednesday, July 24. 



Joint Discussion with Section F [q.v.) on The Problemof stabilising Agri- 

 cultural Prices, with special reference to Control Boards, Equalisation 

 Funds and other methods of Price Regulation. 



Thursday, July 25. 



Discussion on South African Wools and Wool Growing : 



(a) Dr. S. G. Barker. — The Scientific Measurement of the Attributes of 

 the Wool Fibre and their Importance as a Link betiveen Producer and 

 Manufacturer, ivifh particular reference to South African Wools. 



The measurement of fibre characteristics is dependent largely on the proper design 

 of physical instruments for carrying out the work. The relationship of wool quality 

 to spinning power can only be defined when these characteristics are being properly 

 analysed. Apparatus is described for the determination of cross-sectional area, 

 crimp, fibre length, rate of growth, &c. The relationship between these attributes and 

 actual manufacturing conditions is discussed, and the relative importance and develop- 

 ment of these in South African wools is described. Mathematical relationship between 

 crimp and fibre thickness, as well as the development of international standard 

 jnethods of wool examination, is investigated. 



