12 FUNDAMENTALS OF FRUIT PRODUCTION 



rule, cool weather crops have a lower water requirement in a cool than 

 in a warm climate, the reverse being true of warm weather crops. In 

 the latter instance, however, the difference is less pronounced, due to 

 the effect of increase in temperature upon transpiration in general. 



As will be shown later, however, plants are able to adapt themselves 

 in certain ways to dry conditions, the result being a lowering of what 

 otherwise would be a very high transpiration rate. Only limited data 

 are available as to how these tendencies balance each other and as to 

 what is the final resultant. Leather^^ has found that at Pusa, India, 

 the water requirements of wheat, barley, oats and peas are nearly twice 

 those of maize, though this ratio does not hold in most sections (see 

 Table 6) . Apparently this high water requirement of these cool season 

 crops is associated with their maturing during the dry season, while 

 in India maize matures during the more humid season of the monsoon. 

 The greater water requirement of plants cropped by means of pasturing 

 as compared with that of plants which are allowed to continue their 

 growth uncropped,^^'' may be taken as an indication that new growth 

 has a higher water requirement than older growth. It would seem that 

 the water requirements of different plants vary mainly because of differ- 

 ences in the economy of their nutrition and })ecause of different physio- 

 logical and structural modifications affecting their rate of transpiration. 



Some Applications to Practice. — The influence of both the chemical 

 and the physical conditions of the soil upon the water requirement 

 of the plant is of practical importance to the grower, the influence of 

 soil productivity being particularly significant. Few realize that, when 

 the soil provides conditions for tree growth that are optimum from the 

 standpoint of nutrient supply, actually less water is required for a given 

 yield than when the plant is handicapped because of the lack of some 

 nutrient as well. This difference in water requirement is not one of 

 academic interest only; it is large enough frequently to account for crop 

 failure or crop success under conditions of limited water supply. 



A quotation from King^^ jg to the point: "In the long series of studies made 

 by the writer on the amounts of water required for a pound of dry matter, it was 

 found true, almost without exception, that strong vigorous growth and high 

 yields of dry matter are always associated with a small transpiration of water 

 when measured by the dry matter produced." 



Even more significant is the statement of Leather,*'' who made a careful 

 study of this question in the dry climate of Pusa, India: "The effect of a suitable 

 manure in aiding the plant to economize water is the most important factor 

 which has yet been noticed in relation to transpiration." 



It would probably be a mistake to advise watering or irrigating trees 

 by fertilizing them, because the advice would be taken too literally. 

 Nevertheless, the reduction of the water requirement of the plant by 

 maintaining the soil in a condition as near as possible to the optimum 



