162 IRRIGATION PRACTICE 



a larger proportion of the whole plant when the soil is 

 kept somewhat dry throughout the growing season. The 

 roots seem to go in search of water and food, when little 

 is at hand, thus increasing the root-development. It does 

 not follow that the actual weight of roots produced in 

 dry soil is much larger than when produced in wet soil. 

 The experiments conducted on the subject indicate 

 that the total weight is somewhat larger in dry than in 

 wet soil; but, the differences are not great and do not 

 approximate the differences in the proportions of roots 

 in. the whole plant. 



Gain has conducted a number of especially valuable 

 experiments on this subject and has come to the conclus- 

 ion that, whenever little water is added, the main or 

 primary roots are large and well developed, while the side 

 or secondary roots are small and poorly developed. If 

 much water is used, the main roots are smaller and the 

 side roots become relatively larger. That is, with little 

 water a much larger volume of soil is reached by the root- 

 system than when much water is used. 



The lesson to the irrigation farmer is clear. A plant 

 with a small root-system, poorly developed, cannot make 

 as good use of the water added to the soil, or of the food 

 in the soil, as can a vigorous plant. It is important, 

 therefore, that as early as possible the root-system be 

 made large and well developed. When this has been 

 accomplished, water may be added in considerable quan- 

 tities without the fear that plant roots are unable to make 

 proper use of it. As intimated above, to develop a large 

 root-system it is necessary to keep the soil only mode- 

 rately wet in early spring. In districts where the winter 

 precipitation is fairly large, deep irrigated soils are fairly 

 well stored with moisture in the spring, at the time of 



