WHEAT SOILS OF Till': ALl-.X A .\ DK I A DIVISION. 22^ 



Organic Mattek. 



Before proceedinj.;^ to discuss the proportions of mineral 

 plant food in the soil, a word or two may be said regardinjj^ the 

 organic matter and the moisture present. Except in the case of 

 the pronouncedly calcareous samples, the loss on ij^nition was 

 inconsiderable, which means that the soils were ])oor in organic 

 matter generally, and more ])articularly in humus. Such soils 

 are usually deficient in moisture, a defec: which is accentuated 

 when the soil is inclined to be sandy. The addition of an organic 

 fertiliser, sucii as kraal or stable manure, would tiierefore be 

 beneficial, and this, as well as the stubble and waste of former 

 crops that would be ploughed into tiie soil from time to time, 

 would enrich its content of humus, luider the action of the soil 

 bacteria, and would, moreover, increase the water-holding capa- 

 city of the soil, which is now low throughout the area. Naturally, 

 green-manuring would further improve this condition, by tend- 

 ing to enrich the soil wnth humus, not to mention the nitrifica- 

 tion which goes on in the soil during the growth of the catch 

 crop. 



That the conversion of organic substances into humus and 

 plant food is effected by bacteria, there is good reason to believe, 

 but the evidence is not yet regarded on all hands as conclusive.* 

 At the same time, no thread or clue should be left unpursued, and 

 the work that Prof. Bottomley has devoted to this line of research 

 should be followed up wherever possible. There is now an 

 opportunity of doing so, also in the present connection. The 

 rather sandy nature of the Alexandria soils and their lack of 

 humus more than suggest that the requisite soil bacteria that 

 convert cellulose and other organic matter into humus mav also 

 be lacking; if so, inoctilation of the soil b}' the agency of bac- 

 terised peat may undoubtedly produce good results. At the same 

 time, it must be quite clear that even the soil bacteria cannot 

 convert organic matter into humus if there is no organic matter 

 to convert ; hence the addition of stable and green manure may 

 be found of advantage, particularly if the latter be derived from 

 a leguminous catch crop, which is enabled, in the presence of 

 suitable nodule-forming bacteria, to draw sup])lies of nitrogen 

 from the air. 



Plant Food Constituents. 



The nitrogen in these analyses was determined by the 

 Kjeldahl method, as described in my book on 'Flic Soils of Cape 

 Colony, p. 8. The lime, magnesia, potash, and phosphoric oxide 

 were also determined, as there described (pages 13-14), by ex- 

 tracting the soil for five days with cold hydrochloric acid of 

 specific gravity 1.115. Phosphorus pentoxide was determined in 

 addition by oxidising the soil with concentrated sulphuric Jiili^ _^ 

 nitric acids, according to M.-ercker's method.f y^^^^A/ ^ 



* Russell: "Soil conditions and plant growth," 100. ',^ /^O- fi^>^'^ 



tSee the author's book above quoted, p. 14- '^ A -^a^ft-*- >\ ^ i 



'^(Lie'RARY) 3ol 



