WHEAT-GROWING AND ITS PROBLEMS 293 



of doing this have been known in dry countries from very ancient 

 time and have even in recent years been improved upon only in 

 details. The Syrian peasant, no doubt following the practice of 

 a civilisation long since passed away, adopts essentially the 

 same methods as the modern "dry farmer" in the Western 

 States. It cannot be said, however, that the underlying 

 principles are yet thoroughly elucidated, the distribution and 

 movement of water in the soil especially needing further study. 

 From the economic point of view, however, the details of the 

 methods are so far perfected that rain-water can be kept with 

 comparatively little loss in the surface soil available to the plant, 

 so that wheat is grown successfully in regions of 15 to 20 inches 

 of rainfall or, if recourse be had to frequent fallowing, in regions 

 of 10 to 15 inches only. Small dressings of phosphates are 

 found to be extraordinarily effective in Australia, probabl}^ as 

 Hall has suggested, because they stimulate root production 

 and thus enable the plant roots rapidly to get into the moist 

 subsoil. 



The temperature requirements of wheat, like the water 

 requirements, differ at the various periods of its growth, but 

 they have scarcely been investigated because of the experi- 

 mental difficulties. In its early stages the plant will tolerate 

 temperatures but little above the freezing point and it always 

 survives a cold winter in England ; it does not, however, survive 

 the Western Canadian winter, so that wheat is always sown in 

 the spring in that region, but at the time of ripening warmth is 

 indispensable, and this circumstance, more perhaps than any 

 others, sets a northern limit to the wheat belt of the world. 

 Two methods are being used to extend the present limit. Early- 

 ripening varieties are being produced that will be ready for 

 harvesting before the short northern summer is over ; much 

 success is obtained by their use in Canada. In the north of 

 England small quantities of nitrogenous manures are used in 

 spring to cause early growth — for it is found that in presence of 

 nitrates growth begins at a lower temperature than it otherwise 

 would — and phosphatic manures are applied to hasten ripening. 

 No serious efforts have yet been necessary to extend the 

 southern limit set by high temperatures, but it seems probable 

 that late varieties manured with potassium salts to enable them 

 the better to withstand the adverse conditions could be grown 

 much southward of the present line. 



