444 SECTIONAL TRANSACTIONS.— M. 



Dr. R. K. Schofield. — The behaviour of soil moisture in the field 

 — The soil as a water reservoir (11.20). 



A true picture of the soil as a water reservoir can only be obtained by 

 determining the pore-space and its variation with depth, and finding under 

 known conditions what percentage of the pore-space is filled with water. 

 Where the soil is variable the determination of pore-space, sample by sample, 

 though it adds considerably to the labour, is an important safeguard against 

 the drawing of unwarranted conclusions, and may enable useful deductions 

 to be drawn where moisture percentages alone can give nothing of value. 



Not all the pore-space is capable of storing water for the use of plants. 

 Some is of so fine a texture that, even at the highest suction that plant roots 

 can exert (10 to 20 atmospheres or pF 4 • o to 4 • 3 on the author's logarithmic 

 scale), its water is not released. Another portion is coarse enough to lose 

 its water by drainage (pF 1 to 3, according to circumstances). There is 

 rarely as much as 3 inches of available water stored in a foot depth of well- 

 drained soil. Losses by surface evaporation must also be considered in 

 estimating the storage capacity, particularly during long periods of fallow. 



Dr. A. B. Stewart .■ — Soil research and the fanner's problems of 

 liming and manuring (11 .40). 



The numerous methods which have been devised for the estimation of 

 the plant food content of the soil may be grouped under (a) Field Experi- 

 ments ; (b) Pot Experiments ; and (c) Laboratory Examination. An outline 

 of these methods and of their relative advantages and disadvantages is given, 

 and the present position in regard to the advising of farmers on the liming 

 and manuring of their soils is discussed in the light of data which have been 

 accumulated at the Macaulay Institute. 



Field experiments have been laid down on different types of soil, and 

 samples of soil taken from the experimental areas for pot and laboratory 

 examination. The field and pot trials have been conducted on the lines 

 followed by Mitscherlich in Germany, and the results used to check those of 

 various laboratory methods. The volume weight of the soil is taken into 

 account, and the laboratory tests, which are found to give the best correla- 

 tion with field and pot results on a particular soil type, are then used in 

 advisory work on similar soils. 



The results of field and pot experiments generally show good agreement 

 for the potash content of the soil. For phosphates agreement is not so 

 good, and comparison indicates that the subsoil content may be a factor of 

 considerable importance. In advisory work it is considered necessary to 

 examine samples of subsoil as well as of surface soil. 



No single laboratory extraction method affects the soil in the same way 

 as does the growing plant, but it is found that, if the results of a laboratory 

 examination of the soil are interpreted in the light of field data, past treat- 

 ment, cropping rotation, etc., information can be obtained which is of 

 definite value to the farmer. Such information can help him to avoid the 

 wasteful application of unnecessary fertiliser ingredients, which a safe 

 dressing of a complete manure may entail. 



Afternoon. 



Joint Discussion with Section D (Zoology) (q.v.) on Scientific problems 

 of the poultry industry (Section D room). 



