3905 



FORESTRY AND IRRIGATION 



67 



feet 7.4 per cent. Comparing the 

 evaporation from the two adjacent 

 areas where, as stated, the evaporo- 

 rometers were similarly and simulta- 

 neously exposed, it is seen that the air 

 coming across the long stretch of 

 naked ground and then passing 

 through the hedgerow, caused meas- 

 urably more evaporation than did the 

 current which had traversed the field 

 of clover ; and these results appear to 

 be in complete accord with the obser- 

 vations cited regarding the stands of 

 grain and clover to the leeward of 

 woods, hedgerows, grass fields and 

 shelters of other kinds. 



JM'i.TENCE Of WOODS AND GRASS 



rlKUJS UPON THE HUMIDITY OI< 



THE AIR TO THE LEEWARD 



OF THEM. 



At the same time that the several 

 sets of observations were taken and 

 at the same places, others were also 

 made with wet and dry bulb thermom- 

 eters of the Henry J. Green make, 

 reading to tenth of a degree C. The 

 remits obtained are given in the fol- 

 lowing table, each value being a mean 

 of 10 readings, which were made in 

 regular rotation, passing from station 

 to station of each series during the in- 

 tervals of exposure of the evaporome- 

 ters. 



RELATIVE HUMIDITY OF AIR THREE FEET ABOVE 



THE SURFACE AT DIFFERENT DISTANCES TO THE 



LEEWARD OF WOODS, HEDGEROWS, CLOVER 



FIELD AND NAKED SOIL. 



Distance Mean Mean Mean 



to the Dry Bulb Wet Bulb Relative 



Leeward. Readings. Readings. Humidity. 



Feet. Degree F. Degree F. Percent. 

 Grove No. i. 



30 65.32 49.46 27.0 



300 63.80 47.35 2 4-o 



Grove No. 2. 



20 75-04 58.35 34-6 



ioo 73.13 56.39 33-o 



'200 72.03 55.83 34-2 



300 7i.47 55-'3 32-8 



400 73.63 55-63 2 9-6 



500 73.31 55-94 30.8 



On Leeward Margin of Clover Field. 



o 52.48 43-97 48.0 



On Lei-ward Margin of Naked Field, 



o 53-24 43-57 44-o 



These four series of observations, 

 although too limited to serve as the 

 basis of general conclusions, are, in a 



general way. quite in accord with the 

 records of evaporation which have 

 been cited, and also in harmony with 

 the very pronounced observed protec- 

 tion afforded to oats and clover to the 

 leeward of the various shelter condi- 

 tions which have been cited. To my 

 own mind, however, the surprise lies in 

 finding such profound differences in 

 crop conditions associated with the ob- 

 served differences in meteorological 

 and surface conditions. It should be 

 borne in mind, however, in considering 

 these relations, that the meteorological 

 observations were not made at the time 

 the destructive work was going on ; 

 hence what differences then existed are 

 not known. The relations which have 

 !;een observed and pointed out are 

 clearly vital to the reclamation prob- 

 lems of the arid and semi-arid West, 

 and merit full investigation, especially 

 from the standpoint of field conditions. 

 The very marked influence which 

 has been observed upon the stand of 

 both oats and clover under the condi- 

 tions cited is undoubtedly, in large 

 measure, due to the character of the 

 soil and to the stage of growth of the 

 crops, the wind coming at a time when 

 the root system of the plants was yet 

 scantily developed and very close to 

 the surface ; but the measurable differ- 

 ences in the stand of clover, at such 

 long distances from the conditions 

 which have evidently produced them, 

 leaves little reason to doubt that crops 

 are sensitive to such differences of 

 temperature, humidity, and velocity of 

 the air near the surface as must result 

 from the conditions whose types have 

 been here considered. There can be 

 no doubt that rows of trees along ca- 

 nals and about reservoirs must very 

 materially reduce the loss of water 

 tli rough evaporation from their sur- 

 faces, and such observations as have 

 been cited make it hopeful that their 

 influence upon the loss of moisture 

 from adjacent fields and their effects 

 upon crops themselves may be of much 

 greater importance, especially in plains 

 regions ; but only fuller investigations 

 can make certain the true relations. 



