250 SECTIONAL ADDRESSES 
of the ‘ Effect-Factors.’ Notwithstanding these criticisms, Mitscherlich 
had such faith in the usefulness of his method that he has developed 
stations in different parts of Germany for testing soils by his methods. 
The Soil-Testing Society in East Prussia had in 1931 no less than five 
stations and the number of pots in use was 25,000, equivalent to 2,500 
soils tested. The original cost of a test was {5—-£6, but this has been 
very much reduced in later years. This is direct evidence, at any rate, of 
the belief of the practical farmer in the value of the test. It is satisfactory 
to know that an installation of Mitscherlich pots has been set up at the 
Macaulay Institute for Soil Research at Aberdeen, and that in addition a 
large series of field pots have been laid down on different types of soil 
according to the Mitscherlich plan. It will be interesting to see what 
agreement is found between the results of the tests and the results obtained 
by laboratory methods of extraction. 
The Neubauer method, on the other hand, depends on the estimation 
of the nutrient content of the soil by the growth of young seedlings. The 
method depends on the absorption of phosphates and potassium by plants 
in the early stages of their growth. By adopting a standard technique, 
and using rye seedlings as his crop, Neubauer proved that the amount 
absorbed was constant for a given sample of soil. By using a large 
number of seedlings and by diluting the soil with sand, he considered 
that the phosphates and potassium taken up by the seedlings would 
represent the total available supply of nutrients in the soil. This would 
give the nutrient content of the soil without any reference to the manurial 
requirements of a particular crop, the estimation of this being the same 
problem which is met with in all chemical extraction methods of analysis. 
Having determined the root-soluble nutrients in this way, the next 
problem was to calculate from the figures obtained the manurial require- 
ments of the various crops. ‘To do this he makes two main assumptions— 
(1) that under the conditions of the test the seedlings absorb the total 
quantity of available phosphates and potassium, and (2) that crops under 
field conditions can utilise only a certain fraction of the total amounts 
present owing to the different conditions of growth. Making the above 
assumptions and estimating the quantities of phosphates and potassium 
removed by the various crops, he then calculates the ‘ limit values’ for 
the various crops. In order to calculate the amount of fertiliser to be 
applied to soils showing less than the ‘ limit values,’ he again assumes 
that only 60 per cent. of the potash applied and 20 to 33 per cent. of the 
phosphates are availing during the year of application. 
Neubauer’s method has also been subjected to considerable criticism 
on the analytical details, the influence of external factors and the deter- 
mination of the ‘ limit values.’ 
The analytical work concerned requires a high degree of accuracy and 
possibly some of the criticism of the method has been based on results 
obtained without sufficient care having been taken in the analytical work. 
The question of practical interest is how do the results obtained by the 
two methods agree, and which method is the more reliable as to the 
manurial requirements of a particular soil and crop? Neither of these 
questions is easily answered. It may be said at once that there is a wide 
