SOIL CONDITIONS AND PLANT GROWTH 



Over large areas of the world the rainfall is insufficient, 

 and recourse is had to irrigation. In endeavouring to ascer- 

 tain the best way of irrigating crops two considerations have 

 to be kept in view: (i) excessive watering has secondary 

 injurious effects on the soil, such as the deterioration of the 

 physical condition, the accumulation of alkali salts, or the 

 formation of toxic reduction products ; (2) the requirements 

 of the plant are not always the same, more water being needed 

 during the period of active growth than during germination 

 or ripening. 



Some of the results obtained in Utah are set out in 

 Table XII. and in Fig. 8 : 



TABLE XII. AVERAGE YIELD OF DRY MATTER AND NITROGEN FROM THE 

 EXPERIMENTAL PLOTS ON GREENVILLE FARM, UTAH. GREAVES, STEWART, 

 AND HIRST (1136). 



(Expressed as Ibs. per Acre.) 



Field experiments like those conducted by the Punjab 

 Irrigation Department l have shown that the cultivator every- 



1 These and similar experiments are discussed by A. and G. L. C. Howard 

 in Wheat in India: Its Production, Varieties, and Improvement (Imperial Depart- 

 ment of Agriculture, India, 1909). German experience is recorded in Erfahrung 

 bei der Ackerbewasserung (Jahrb. Deutsch. Landw. Gesell., 1913, 28, 76). 



