RESULTS OF MEASUREMENTS. 



33 



II. SOIL MOISTURE SAPPING. 



It is very commonly stated that the damage done by windbreaks 

 is due to the "sapping" of the soil by the roots of the trees, which 

 are said to take not only large quantities of the moisture needed by 

 crops, but also the soil fertility. The matter of soil fertility is con- 

 sidered separately in this bulletin. That the importance of sapping 

 is usually overestimated was very apparent in the season of 1908, 

 when moisture was abundant even in the root zones of windbreaks, 



O .2 



D/S7XA/CE f#OM 



/ 2 



EXPRESSED W TERMS 



FAST, 



DIAGRAM 14. Effects of shading and sapping on the growth of field crops. Relative importance of 

 two factors on north and east sides. 



when the effects of shading were perfectly clear. The effects 

 of these two factors are easily confused and difficult to separate. 



EXTENT OP SAPPING. 



No attempt has been made to determine what quantity of soil 

 moisture is taken by trees in a windbreak, since it may bo supposed 

 that in exceedingly dry years this may be sufficient to practically 

 prohibit the growth of field crops in the zone permeated by the well- 

 established roots of the trees. Such being the case, it is of greatest 

 92290-jBull, SS-H - 3 



