724 



Journal of the Department op Agriculture. 



Tins pliosplioric oxide, amounting' to one-third of the total in 

 sample 1977 and one-quarter in sample 2039, cannot be in any way 

 available to plants (2). 



Mechanical Composition. — The predominant mechanical fractions 

 in soils of this type are the clay, the sand, and the fine sand, the silt 

 fractious being subordinate, as is illustrated by the following 

 mechanical analysis : — 



No. 1977. 



No. 20H4. 



No. 2089. 



Moisture 

 Loss on ignition 

 Fine gravel ... 

 Sand ... 

 Fine sand 



Silt 



Fine silt 

 Clay ... 



per cent. 



3-40 



9-43 



8-80 

 l.-)-82 

 12-92 



6-80 



9-29 

 33-20 



per cent. 



2 - 25 

 12-12 



3-37 

 18 -.50 

 11-8(1 



4-73 



9 • 50 

 36-00 



per cent. 



4-01 



9-33 

 10-80 

 13-97 

 15-89 



6-19 



8-60 

 30-96 



The clay is usually in a liighly flocculated condition, owing to 

 which fact a good tilth can be obtained after a short period of cultiva- 

 tion. The flocculating- agent is finely divided ferric oxide, which is 

 found in considerable amount in the clay fraction: — 



Apart from its flocculating action on tJie clay, this fine ferric 

 oxide is the cause of the colour of these soils, the browner varieties 

 being also partly coloured by organic matter. 



Under continued irrigation the Koedoespoort loam is apt to 

 puddle after a time and to form hard crust on the surface. These 

 conditions can easily be avoided by good cultivation and reasonable 

 care. The soil is easier to handle than one would expect from tlie 

 clay content, and would be called a stiff loam by the farmer rather 

 than a clay. The sub-soil is generally rather heavier than the surface 

 soil. The depth is variable, from 2 feet to well over 4 feet is usual. 

 The drainage is fairly good considering- the amount of clay. On no 

 account should the sub-soil be brought to the surface by trenching 

 or otherwise. For some reason, at present uncertain, the sub-soil is 

 unfertile, and if brought to the surface will cause trouble which 

 can only be rectified at great expense. If it is considered necessary 

 to trench, the method known as " false trenching" must be adopted. 



The occurrence of brak (alkali) in the Koedoespoort loam has 

 not been observed or reported. 



* The figures for both total ferric oxide and ferric oxide in the clay refer only to such 

 as is soluble in boiling concentrated hydrochloric acid. 



