Archaean rocks. Pedogenetic considerations, therefore, indicate a lower fertility 

 level for the north- west soils and this has been confirmed by practical observation 

 of herbage responses following rains and the stock fattening capacity of the two 

 districts. 



As part of the present study, the productivities of a range of semi- arid and arid 

 soils were compared in a series of pot culture tests with that of a moderately fertile 

 red-brown earth soil from the Waite institute and representative of the better agricul- 

 tural areas of the State. (Table 5- Fig. .7) 



The results indicate the low fertility of the arid soils and particularly of those 

 from the North- west District. Marked responses were obtained to soluble nitrogen 

 on all the arid soils although there was little response to phosphorus ; even with the 

 heavy application of nitrogen and phosphorus, however, the productivities of these 

 soils were considerably below that of the red -brown earth, indicating the possibility 

 of a further limiting factor or factors in the former soils. 



One indication of the limitation of productivity imposed by deficient nutrient 

 supply is given by the wide differences in the transpiration ratio for Atriplex vesi- 

 caria in pot culture tests (series A) conducted on the respective soils: on red - brown 

 earth soil a transpiration ratio of 370 indicated a production of 5.4 cwt. dry forage per 



Figure 7. 

 Growth of barley without fertilizer on various soils (left to right). Red- brown earth, U'aite 

 Institute; solonized brown soil, Pallamana; arid red earth, N.E. District; arid red earth, N.U'. 



District. 



141 



