t 



irrigation is to be preferred to canal-irrigation. Again, generally 

 speaking, rain-water has been found to do more good to crops 

 than either canal or well-water, specially at the beginning of 

 rainy season. If well-water or canal-water, or tank-water under 

 certain circumstances, has the property of doing harm to 

 crops, and if rain-water is more generally beneficial, then 

 we must be cautious before venturing on any scheme of 

 irrigation, lest it should afterwards prove to be a thoughtless 

 scheme. A further complication arises from the different 

 effects of irrigation on different crops. At Sibpur Farm, 

 we have observed that the use of the canal water benefits 

 potatoes and cabbages, while it hurts country peas and beans, 

 when owing to late sowing the latter crops had to be irrigated 

 in December and January. Irrigation with this canal water 

 benefits all kinds of crops in May and June, while at the driest 

 season from December to April, this canal water hurts le- 

 guminous crops and seedlings of all kinds. What is the 

 explanation of this all ? It is only if we understand the 

 theories underlying the question of water adapted for irriga- 

 tion, that we can avoid mistakes in the use of irrigation water, 

 both as regards quantity and quality. 



203. Rain-water. At the beginning of the rainy season 

 rain-water contains in solution and suspension a large amount 

 of foreign substances which are all more or less helpful 

 to agriculture. As the rainy season advances, the water is 

 freer and freer from nitrates, ammonia, organic dust &c. Hence 

 the greater invigorating effect on plant of the early showers 

 of rain. Even in the latter part of the rainy season, 100 

 cubic inches of rain would contain 2 or 3 cubic inches of>; atmos- 

 pheric gases. Every 100 volumes of water are capable of 

 holding in solution under normal conditions of temperature 

 and pressure about \\ volumes of N ; about 3 volumes of O ; 

 about 100 volumes of CO 2 and about 7,800, volumes of 

 ammonia. The capacity of rain-water for holding large quantities 

 of CO, and amtnonia in solution is of special importance for 



