348 SOIL CONDITIONS AND PLANT GROWTH 



Agric. Sri., 1915, 7, 144-153, and Leather, Trans. Chem. Soc., 1902, 

 8l, 883-886. 



For American methods of sampling see Bot. Gazette^ 1919, Feb., 

 p. 173. C. B. Lipman and D. E. Martin 1 show that no further or 

 unusual precautions need be taken when the sample is required for 

 bacteriological purposes. 



The Analysis. On arrival at the laboratory the soil is spread 

 out to dry, and is then pounded with a wooden pestle and passed 

 through a 3 mm. sieve. The stones that do not pass through, and 

 the fine earth that does, are separately weighed, and the proportion 

 of stones to 100 of fine earth is calculated. Subsequent analytical 

 operations are made on the fine earth. 



Moisture. Four or five grms. of the soil are dried at 100 C. 

 till there is no further change in weight. 



Organic Matter. No accurate method of estimation has yet 

 been devised. It is usual to ignite at low redness the sample dried 

 as above. The loss includes organic matter, water not given off at 

 1 00 C., and carbon dioxide from the carbonates ; allowance may be 

 made for the latter, but not for the combined water. The carbon is 

 sometimes determined either by the ordinary combustion or by some 

 wet combustion method. Methods have also been described for 

 determining " humus," but they have not come into general use. 

 For ordinary purposes it is sufficient to take the loss on ignition as 

 organic matter. 



Total Nitrogen. Kjeldahl's method is almost invariably adopted. 

 About 25 to 30 grms. of soil are ground up finely in an iron mortar ; 

 10 to 15 grms. are heated in a Kjeldahl flask with 20 to 25 c.c. of 

 strong sulphuric acid for three-quarters of an hour; 5 grms. of 

 potassium sulphate are added, and then a crystal of copper sulphate. 

 The heating is continued till all the black colour has gone. Then 

 cool and dilute the mixture, transfer the fluid part to a distillation 

 flask, but leave as much as possible of the sand behind, wash well to 

 remove all the adhering liquid. Add saturated soda solution till the 

 liquid is strongly alkaline, distil, and collect the ammonia in standard 

 acid. 



Nitrates must be determined in a sample taken direct from the 



field and dried without any delay at 55 C. ; 200 to 500 grms. of the 



dried soil are pressed firmly on to a Buchner funnel fitted to a filter 



flask, and distilled water is poured on. The first 300 c.c. of water 



1 Soil Sd., 1918, 6, 131-36. 



