ORCHARD SOIL MANAGEMENT METHODS 



45 



Table 



-Effect of Various Cover Crops on Soil Moisture During the 

 Spring of 1901 « 



Kind of crop 



Percentage of soil moisture 



Apr. 19 Apr. 27 May 20 June 3 



Winter-killed crops: 



Oats 



Millet 



Cane 



Average 



Winter-surviving crops: 

 Rve 



28.7 

 26.0 

 24.0 



26.2 



22. G 



20.2 

 21.8 

 22.1 



21.4 



17.4 



20.5 

 21.9 

 21.7 



21.4 



12.2 



20.1 

 20.7 

 20.7 



20.5 



11 2 



abundant and cheap irrigation water, but in 



those seasons with a light late spring and ^7 



summer rainfall it could easily occasion 26 



much more financial loss than would be is 



compensated by the advantages accruing ^4 



from the use of the cover crops. A certain ?3 



quantity of organic material produced in ?2 



the autumn is just as valuable for soil '21 



improvement purposes as an equal amount eo 



grown in the spring. c 19 



Wind Velocity and Evaporation : Wind- ^ 18 



breaks. — Attention has been called to the ^^ n 



almost continual evaporation of water from 16 



the soil. In regions of low precipitation 15 



this amounts to a much larger percentage i4 



of the total supply than in regions of fre- i3 



quent and abundant rains. Assuming 12 



uniform soil management methods, evap- >i 



oration may be expected to rise with an 'O 

 increase in wind velocity and to vary 

 with temperature of the soil water, with 

 temperature of the air close to the evapo- 

 rating surface, with vapor pressure in. the 



those sections 



April 



June 



May 



1901 



Fig. 2. — Percentages of soil 



moisture in plots of winter-killed 



and winter-surviving cover crops, 



spring of 1901. The dots show the 



. . dates of making the moisture de- 



air near the water and with atmospheric terminations and the exact percent- 

 humidity. The Onlv one of these factors ages of moisture found. The curved 

 ill" 1 ,. 1 "'^^^ indicate the probable fluctua- 

 at present under the control of the grower tions in moisture between these 



to any considerable extent is wind velocity, ^^t^^- (^-^'«'' Emerso7i.''^) 

 Consequently it is discussed at this time. In one series of determinations 

 when the relative humidity was 50 per cent, and the air temperature 84°F. 

 evaporation was found to be 2.2 times as rapid with a wind velocity of 5 



