CULTURAL METHODS L\ ORCHARDS 153 



and in some instances of plant-food materials, and this 

 should be avoided. 



135. Effect of moisture. — Hilgard,^ in discussing the 

 effect of moisture on crop production, says: "Production 

 is almost directly proportional to rainfall during the period 

 of active vegetation." In studying the moisture relation, 

 it is important to consider the type of soil. A clay by its 

 nature holds more moisture than a light soil, so that when 

 a heavy soil contains 12 per cent of moisture, a light one 

 under the same conditions may only have about 7 to 9 per 

 cent, and the consequent effect on the trees would be as det- 

 rimental under the one as under the other condition, be- 

 cause of the factor of availability. It has usually been ob- 

 served that the soil-moisture in an orchard standing in sod 

 is less than when the soil is tilled, but under some condi- 

 tions this has not held true. 



Woodbuiy ^ shows from an orchard experiment that 

 moisture was less under sod culture than under tillage. 

 "During the season of 1913 and 1914 we have a positive 

 indication of the effects of different treatments on soil mois- 

 ture. In both of these seasons, the rain-fall during the ac- 

 tive growing period of the trees (May, June, and July) was 

 considerably below the five-year average for those months. 

 Inasmuch as the cultural practices are conservation meas- 

 ures, preventing the loss of water after it enters the soil, it 

 is largely in such dry periods that the value of certain sys- 

 tems of management in conserving soil moisture are made 

 manifest. 



"In both of these years, during the month of June, the 

 upland plots either where the grass was cut and let lie or 

 piled under the trees, were low in soil moisture. Where an 

 adequate mulch was maintained on the surface of the soil 



1 Soils, p. 193. 



2 Purdue Agr. Exp. Sta. Bull. 205. 1917. 



