104 COCONUT PLANTER'S MANUAL. 



also that there is a continual movement of water, called the transpira- 

 tion current, from the roots to the leaves, where it is lost by evapora- 

 tion, and further that if this transpiration current be not maintained 

 the leaves droou and die, we begin to realise what a tremendous drain on 

 the soil moisture growing crops are and how important it is to supply 

 them with enough moisture. 



This transpiration current has no visihle effect because the water 

 evaporated at the surface of the leaves goes off in the form of invisible 

 vapour, and this accounts for the common failure to recognise that such 

 a current exists. 



The vigour of th\> transpiration current varies with different plants, 

 they do not all transpire the same amount of water, but consideration 

 of a few of the figures arrived at by similar experiments will convince 

 one that in all cases the quantities of water withdrawn from the soil oy 

 this means are enormous. 



For instance, measurements of the water transpired by a sun-flower 

 plant 3J feet high shew that 2 lbs. are transpired in 12 hours. An 

 average crop of cabbages transpires 3 oi 4 tons of water per acre every 

 day. An average wheat crop transpires 750 tons of water per acre 

 during its period of growth, while a single oak tree accounts for over 

 7(10 tons in a year. Of special importance is the figure of 3-J lbs. of 

 water transpired by every square foot of grass land per day. Assuming 

 that the grass were growing all the year round, the amount transpired 

 by aii acre in each year would reach the enormous total of over 

 24,000 tons. 



With these figures before us, the importance of soil moisture and 

 the necessity for husbanding it to the utmost becomes apparent, and 

 every agriculturist should make himself acquainted with the various 

 methods for preventing waste of water from his land. 



How to Prevent Waste of Soil Moisture, 

 Before we can discuss this question we must understand how soils 

 lose water by other means than by the transpiration of living plants just 

 described. For practical purposes we may take it that all the water in 

 a soil is derived from rain which falls on its surface. Part of this rain 

 soaks into the soil and part runs off the surface without penetrating. 

 If the surface is soft nearly all the rain soaks in, but very little pene- 

 trates througn a hard surface. Since the water which runs off the 

 surface is wasted we see already how we can prevent some waste by 

 keeping the suiface of the ground soft 



The rain which soaks into the ground sinks down through the small 

 spaces between the noil particles until it either reaches the underground 



