322 



THE AGRICULTURAL NEWS. 



OCTOBKR 12, 1912. 



limitation to soil analysis is that these factors, obviously, 

 eannot be determined in the laboratory. Even when 

 they are known to the analyst and he is able to 

 correlate them with the re^iults of his investigation of 

 the soil itself, they are quite insufi&cient to determine 

 the fertility of any given area. They must be supple- 

 mented by the local knowledge, experience and judg- 

 ment of one, suoh as a planter or investigator, who 

 may be said to be agriculturally familiar with that area. 



The difficulty does not end here, for the analyst 

 up to the present is not able to give any complete 

 information as to the availability of the food bodies in 

 the soil: this may contain nitrogen, phosphates and 

 potash in amounts that are far greater than 

 those required by plants, but one or more of these 

 bodies may be unavailable, or locked up as regards 

 immediate needs, to such an extent that the soil is 

 actually less fertile than one containing them in much 

 smaller amounts but presenting them in forms that 

 are easily taken up by plants. This is the reason why 

 a soil showing lack of fertility will often readily respond 

 to small dressings of certain manures. Such a soil is 

 amenable to treatment other than manuring: it requires 

 that the plant food in it shall be made to become 

 available at a greater rate, and good cultivation, drain- 

 ing and liming are partial means to this end. 



In this consideration regarding availability of 

 plant food in the soil, it must not be forgotten that 

 methods have been devised with the object of ascer- 

 taining roughly the amount of certain soil constituents 

 ready for direct use by the plant: an example is 

 the determination of the proportion of the phosphates 

 soluble in weak citric acid. This is useful for obtain- 

 ing broad indications of what is wanted in certain 

 directions as regards manuring, as well as for compar- 

 ing soils of the same kind. The serious limitation of 

 such methods is that they do not include a ready means 

 of finding the availability of the chief forms in which 

 nitrogen — the most important of plant food elements — 

 usually exists in soils. 



More directly useful results are afforded by the 

 second kind of analysis of soils, under discussion, which 

 is the physical or mechanical analysis. In most cases 

 this gives a means of estimating approximately such 

 matters as the power of the soil to retain water, the 

 ease with which water drains away from it, and its 

 ability to withstand drought; it may even supply indi- 

 cations as to the best methods of cultivation of the 

 soil. Conditions in the tropics nevertheless render the 



humus conteat of the soil of such paramount importance 

 regarding its permeability, water capacity and drain3ge 

 that this factor has to be considered very seriously 

 when interpretation is being given to the results of 

 physical analysis. If this is remembered, these may 

 be used in a most valuable way by the planter and 

 other agriculturists. 



A further complication of the matter is that the 

 results 'jf analyses of the chemical and physical condi- 

 tions of the soil do not enable much to be inferred con- 

 cerning its biological condition. These pages have 

 been often employed recently to explain and emphasize 

 the importance of the modern conception of the work 

 of bacteria in the soil. It is here that the physical 

 analysis again shows its usefulness, provided that its 

 results are interpi-eted in the light of knowledge 

 mainly concerning the water and lime content of the soil, 

 and regarding its aeration. To make the matter plain, 

 it is only necessary to contrast the nitrification and 

 maintained fertility in an open soil, with an efficient 

 water-supply, with the loss of nitrogen and non- 

 productiveness in a waterlogged clay soil. 



It can be concluded from these matters that, while 

 their proper employment may be most useful, chemical 

 and physical analyses of the soil — especially the former 

 kind of investigation — are rarely capable by themselves 

 of providing direct conclusions regarding fertility in 

 a particular area. Their main use, in a broad way, 

 is for supplying material in such work as a soil 

 survey, by which the soils of a country may be usefully 

 classified so that general predictions as to the manurial 

 requirements of these may be made. They can never 

 replace the simple field experiment as a means of 

 ascertaining the suitability of a given area of soil for 

 raising any crop that it is intended to cultivate on 

 that area. 



The Purification of Camphor.— With reference 

 to the information concerning camphor given on page .302 of 

 the last number but one of the Agricultural Sfeivs, the 

 following note on its purification, by R. D. Anstead, in the 

 Planters' Chronicle for August 3, 1912, is of interest. 



'The impure camphor should be mixed with about its 

 own bulk of lime, which acts as a drying agent, or powdered 

 charcoal, and spread out in a thick layer on a copper plate 

 and covered with a gla.ss bell jar supported at a little height 

 above it. Heat should then be gently applied to the plate. 

 The camphor in the mixture will then evaporate, or sublime 

 leaving the impurities behind and the vapour will condense 

 on the cool sides of the bell-jar in a pure powder-like form 

 known as "flowers". When the process is complete and no 

 more camphor sublimes off, the bell-jar is removed and the 

 pure camphor collected from it.' 



