Vol. XIII. No. 318. 



THE AGRICULTURAL NEWS. 



213 



such as pen manure, combined with the growth of green 

 dressings in the case of arable crops, and the application of 

 mulches and pen manure together with the utilization of 

 grass and weeds by cutlassing in the case of orchard soils. 



SOIL INVESTIGATION, 



BACTERIAL ACTION AND ORGANIC 



MATTER IN SOILS OF THE 



LEEWARD ISLANDS. 



The following is the summary of Mr. H. A. 

 [i'empany's paper on the above subject;, which appears 

 in the recently issued number of the West Indian 

 Bulletin (Vol. XIV, No. 2):— 



To investigate the changes likely to take place in soils 

 Utdei tropical conditions, small plots of land weie subjected 

 to clean weeding for periods varying between twelve and 

 fifteen months at the experiment stations in Antigua, 

 St. Kitts, Montserrat and Dominica. At the outset of the 

 experiment, the soils of the plots were sampled to a depth 

 of 1"2 inches, and on the sample;) were determined the 

 content of organic carbon, nitrogen, and calcium carbonate. 

 At the end of the period the soils were re sampled, and the 

 organic carbon and nitrogen were redetermined. Lots of 

 the original samples were also kept in the laboratory for 

 si.x months under moist conditions, and at the end of that 

 time the organic carbon, nitrogen and nitrate contents were 

 also determined. The soils of the Dominica, St. Kitts and 

 Mont.serrat plots are all light in texture, while that at 

 Skerretts, Antigua, is stiff and heavy. 



At the end of the experiment it was found that both in 

 the field and in the laboratory considerable losses of organic 

 carljon had taken place as the result of bacterial activity, the 

 losses varying between 2-5 per cent, and -50 per cent., in the 

 case of the Antigua, Montserrat and St. Kitts samples: at 

 Dominica, only a small loss is recorded. 



With regard to the nitrogen contents, consideralde 

 decreases are seen in the field in the case of the Antigua, 

 St. Kitts, and ilontserrat samples; in the case of the 

 Lorainica sample, the loss is small. In the laboratory, an 

 appreciable loss of nitrogen occurred in the case of the 

 Antigua soils; in the case of the Montserrat and St. Kitts 

 samples, no loss was observed, while the Dominica sample 

 showed a small loss. All the soils exhibit nitrifying power: 

 this is greatest in the case of the Antigua and Montserrat 

 samples and smallest in the case of that from Dominica. 



The losses of nitrogen which occur in the field is 

 attributed to nitrification and subsequent loss by leaching at 

 St. Kitts and Montserrat, and probably in some measure to 

 denitrification at Antigua. In view of the small content of 

 calcium carbonate, the suggestion has been put forward that 

 ammonia formed in the course of ammonification may serve 

 as a base for the neutralization of a part of the nitric acid 

 formed in nitrification. 



The results emphasize the high degree of bacterial 

 activity existing in tropical soils, and indicate the necessity 

 cf maintaining an adequate supply of organic matter. In 

 this connexion it affords direct evidence of the correctness of 

 the policy followed by the Imperial Department of Agricul- 

 ture in advocating the liberal employment of organic manures 



COMPOSITION OF THE NATURAL 



SOIL SOLUTION. 



At the time of its publication, only brief reference was 

 given in this journal to the results obtained by A. D. Hall, 

 Winifred E Brenchley and Lilian M. Underwood in regard to 

 the soil solution and the mineral constituents of the soil. 

 Wheat and barley, according to the Experiment Station 

 Record (February 1914) were grown in solutions made from 

 .soils on which wheat and barley had been grown for sixty 

 years. The general conclusions arrived at were as follows: 

 'The composition of the soil solution as regards phosphoric 

 acid and potash is not constant but varies significantly with 

 the composition of the soil and its past manurial history. 

 Within wide limits the rate of growth of a plant varies with 

 the concentration of the nutritive solution, irrespective of 

 the total amount of plant food available. AVhen other 

 conditions such as the supply of nitrogen, water and air are 

 equal, the growth of the crop will be determined by the 

 concentration of the soil solution in phosphoric acid and 

 potash, which in its turn is determined by the amount 

 of these substances in the soil, their state of combination, 

 and the fertilizers supplied. On normal cultivated soils, the 

 growth of crops like wheat and barley, even when repeated 

 for sixty years in succession, does not leave behind in the 

 soil specific toxic substances which have an injurious effect 

 upon the growth of the same or other plants in that soil. 

 The net results of these investigations is thought to uphold 

 the theory of the direct nutrition of the plant by fertilizers. 



In connexion with another note in this issue (on page- 

 "J21) dealing with the function of calcium, the observations 

 reported in the Experiine7U Station Record, Vol. XXX, No. 2), 

 as the outcome of H. B. Hutchinson's work on the action of 

 quicklime on the soil, are of interest It was found in these 

 experiments that the addition of small quantities of quick- 

 lime to soils stimulates general bacterial growth, but large 

 quantities cause a depression and a destruction of certain 

 large protozoa, and finally a cessation of all biological 

 processes. When lime is converted into carbonate or com- 

 bines with soil constituents there is a great increase in the 

 number of bacteria and an acceleration of ammonification. 



A note appears in the Experiment Statim Record, 

 (Vol. XXX, No. 6), pointing out some of the important 

 relations of colloidal chemistry to the soil. Most soil gels 

 are considered to be reversible and most soil colloids are 

 considered to lie negatively charged, which is said to 

 explain their power for absorbing the positive bases of basic 

 salts. Heat and dryness are said to coagulate the soil 

 colloids and improve the structure, but too heavy rains form- 

 soils of the reversible gels, and also by washing out the soil 

 salts cause a return of the compact, badly aerated structure. 

 Soil formation by weathering is thought to be based on 

 colloidal chemistry, and the beneficial effect of lime salts on 

 soil structure is attributed to the higher gel-forming power 

 of bases of higher valence. Moreover, the beneficial effect of 

 green manure on soil structure is attributed to the addition 

 of new colloids, which not only form gels, but also dissolve- 

 lime. 



