Chemical Analysis of Soils. 845 



problem in this countiy is that of tlie supply of phosphates to the soil. 

 Of the South African soils, the analyses of which have been recorded, 

 some 90 per cent, are deficient in this essential constituent. JN^ot only 

 is the deficiency indicated in t!ie analyses but it is well known that 

 markedly increased yields aie almost invariably o))taiued when phos- 

 phatic manures are used. When the g-reat deficiency in phosphoric 

 oxide in the soils is coupled, as it is in vSouth Africa, with a system 

 of farming in which large quantities of grain and forage crops con- 

 taining relatively enormous quantities of phosphoric oxide are sold oi¥ 

 the farms it is obvious tJiat the supply of phosi)hates is of prime 

 importance. In one year's maize crop alone phosphoric oxide equiva- 

 lent to about 35,000 tons of 16 per cent, superphosphate is removed 

 from the soils of the Union. The greater part of this is not returned 

 to the soil from which it was drawn. 



(;') Nitrogen. — The nitrogen in tJie soil occurs chiefly in the 

 organic matter, but before it can be utilized by plants it must be 

 converted by micro-organisms into other forms, chiefly nitrates, 

 which can be assimilated. Most soils deficient in organic matter and 

 nitrogen are also deficient in nitrates. The amount of nitrogen which 

 must be present in the soil in order to render tlie application of 

 nitrogenous manures unnecessary is for South Africa rather lower than 

 is supposed to be necessary in Europe. The problem of the supply of 

 nitrogen in the soil is not one which should worry the farmer. In a 

 good S3'stem of farming no nitrogenous manures need be bought since 

 the supply in the soil can always be maintained by green manuring. 



(k) " Avnil(il)lc " /^otaslt and PhospJioric O.ride. — These repre- 

 sent the quantities ot these constituents which are supposed to be 

 immediately available lo, or assimilable by, plants. While the 

 " total " potash and phosphoric oxide may be said to represent the 

 reserve stocks present in the soil the "available" potash and phos- 

 phoric oxide represent what is at the immediate disposal of the plant 

 and serve as an indication of the necessity or olherwise for the supply 

 of these constituents in the manure. 



Partial Analysis. 



2. The partial analysis to determine uianurial needs consists of 

 the determination of lime, magnesia, nitrogen, available potash, and 

 available phosphoric oxide. This partial analysis does not gi^^e much 

 information as regards soil classification or on the ultimate potentiali- 

 ties of the soil. It merely serves to indicate the lines which, manurial 

 treatment should take. 



The following is a statement of the i-esults obtained by a jiartial 

 analysis of a sample of soil : — 



Per cent. 



Lime 3.66 



Magnesia ... ... ... .. ... 0.45 



Xitrogen 0.092 



" Available" i)otash 0.0145 



" .\vailable " phosphoric oxide 0.0060 



It should be noted that the information furnished by such a 

 partial analysis is much less complete than that furnished by a com- 

 plete analysis, and tliat on lliis account the interpretation is 



