474 



The Supplement to the Tropical Agriculturist 



slaked witli water is not only highly caustic 

 in its action, but, compared with chalk, being 

 readily soluble in water, exerts a strong 

 caustic or burning action upon tho humus or 

 vegetable matter that may exist in the soil, 

 so that it not only neutralises any acidity 

 existing in the soil, but it positively burns 

 up and converts the valuable hygroscopic 

 vegetable matter into carbonic acid, which 

 subsequently unites with the lime, forming 

 carbonate of lime. Quicklime, therefore, may 

 be used with advantage on soils that contain 

 an excessive amount of vegetable matter, be- 

 cause such matter in its acid state as it exists 

 in damp moorland pastures, is really injurious 

 "to healthy vegetation, and the formation of 

 nitrates ; but on many soils such as granite, 

 "gravel, and sandy soils, the application of 

 the highly caustic quicklime is calculated to 

 do more harm than good, because these 

 soils, though deficient in lime, are usually 

 also deficient in vegetable matter. Bayldon 

 in his book on the valuation of rents and 

 tillages states that on no point in agri- 

 culture does more vague uncertainty pre- 

 vail than on the use of lime. No infer- 

 ence has been drawn either from practice 

 or science to guide the farmer with cer- 

 tainty in applying lime to the land ; in 

 fact, it is applied often by the caprice or indivi- 

 dual judgment of the farmer without any certain 

 knowledge of the result that will be produced. 

 On light soils of all kinds, he states, the bene- 

 fit of lime is very doubtful. The above repre- 

 sents the opinion of an experienced valuer in 

 186-4. At the present time there is a strong 

 opinion gaining ground among practical men 

 that the use of lime in moderate quantity is 

 necessary to counteract the injurious effect pro- 

 duced by the continued application of acid 

 manures on soils naturally deficient in lime, for 

 acid manures certainly tend to remove the avail- 

 able lime as proved by the Woburn experiments. 

 Indeed the great success of the application of 

 phosphates in an alkaline form such a basic slag 

 and the more recently introduced basic super- 

 phosphate has afforded a practical illustration of 

 the great benefit which has resulted from the 

 use of the above manures on certain kinds of soil; 

 the question to be decided is the particular form 

 in which lime can be mo?t efficiently employed. 

 In considering the relative suitability of a ferti- 

 liser it is usual to assume that the availability 

 is dependent upon the solubility in water and 

 in weak solutions of a vegetable acid like 

 citric acid. 



Relative Solubility in Water. 

 Caustic lime is more soluble in cold than in 

 boiling water, while chalk is only very slightly 

 soluble in cold distilled water. According to 

 to my experiments the actual figures are as 

 follows : — 



1 part caustic lime dissolves in 833 parts of 

 water. 



1 part chalk dissolves in 22,22-2 parts of water. 



It will be seen how very much more soluble 

 caustic lime is compared with carbonate of 

 lime in the form of chalk. But the ordinary 

 soil water contains vegetable acids such as 

 carbonic, ulmic, and humic acids, which 

 exert a powerful solvent action on the 



various soil ingredients that constitute the 

 natural food which the roots of plants aidod 

 by the acid nap contained therein absorb from 

 the soil by osmotic action. Consequently it is 

 not the solvent action of pure cold distilled 

 water that should bo considered, but rather the 

 action of soil water impregnated with vegetable 

 matter. It is therefore very natural that some 

 vegetable acid solution should be selected as a 

 standard solution. In Germany, Professor 

 Wagner has suggested a 2 per cent, solution of 

 citric acid as a standard solvent for estimating 

 the probable availability of phosphate of lime in 

 basic slag. In this country Dr Bernard Dyer 

 has suggested a weaker solution of only 1 per 

 cent citric acid, while I in 1901 suggested a still 

 weaker solution, namely, 10 per cent, solution, 

 consisting of 1 part citric acid dissolved in 1,000 

 parts of cold water, which represents an acidity 

 absolutely less than that possessed by the sap 

 of any farm crops, so that any lime, phospho- 

 ric acid, or potash dissolved by such a solution 

 may fairly be regarded as existing in a form 

 available for plant food. When caustic lime 

 and chaltf finely ground are exhausted with this 

 solution the following results were obtained : — 



Relative solubititii in. 10 citric acid solution 

 1 part caustic lime dissolves in 809 parts solution. 

 1 part chalk dissolves in 984 parts solution. 



As 1 part of carbonate of lime in the form of 

 chalk consists of 56 lime and 44 carbonic acid, 

 it follows that 56 lime existing in the 1 part of 

 chalk is dissolved by the above 984 parts of 

 water, which is equivalent to 1 part of lime 

 in the form of chalk being dissolved by 

 1,758 parts of this 10 solution of citric 

 acid. From these figures it appears that in 

 pure cold water caustic lime is about 27 times 

 more soluble than chalk, but that in the weak 

 10 citric acid solution lime as caustic lime is 

 only about twice as soluble as lime in the form 

 of chalk. Consequently if chalk be reduced 

 by grinding to the same state of fineness 

 as caustic lime it will be sufficient if one 

 ton of such ground chalk be applied per acre 

 instead of 10 cwt. of ground lime. In addition 

 to the convenience of the application of chalk 

 instead of the irritating caustic lime there is 

 the less cost to be considered. 



Rough chalk can in many districts be ob- 

 tained at 3s to 4s a ton rail as against lime 

 at 12s to 15s per ton. Further, the mild 

 chalk while supplying the lime necessary for 

 bacterial action in the soil does not burn up 

 and consume the vegetable matter which is 

 so valuable as a plant food and also for the 

 retention of moisture. Indeed, the agricul- 

 tural utility of chalk on all light soils has 

 hitherto been sadly neglected, and the heavy 

 dressings sometimes applied were very costly 

 and quite unnecessary. Chalk should be dried 

 and ground into a fine powder, then applied 

 on the surface, followed by a light harrowing 

 in order to effect the necessary mixing with 

 the soil, so that it may be rendered soluble 

 by the soil water, and the sap acidity of the 

 rootlets of the subsequent crop. 



The red soils of Herefordshire and Worces- 

 tershire furnish good illustrations of the kind 

 of land that would be improved by dressings 

 of finely ground chalk. But all light land such 



