38 FUNDAMENTALS OF FRUIT PRODUCTION 



return the extra labor cost; however, when results are equal, costs should 

 be considered. 



Practicability of the Sod-mulch System Influenced by Depth of Rooting. — 

 Mention of depth of rooting, a subject considered in more detail later, 

 is pertinent to this discussion. A tree with a root system penetrating 

 the soil to a depth of 8 or 10 feet can draw upon the moisture supply of a 

 large volume of soil. Such a tree is in a much better position to with- 

 stand temporary surface drying such as may be produced by evaporation 

 from the surface or from weeds and grass, than a tree whose roots are 

 limited to the upper foot or eighteen inches of soil. Consequently 

 it will thrive under the sod-mulch method of culture when a shallow- 

 rooted tree would suffer serious injury. To keep an orchard in sod under 

 conditions such that deep rooting is not possible and where there is not 

 an abundant summer rainfall or plenty of irrigation water, is to invite 

 trouble. However, there are successful orchards in sod where the 

 summers are long and dry and irrigation is not known. The explanation 

 lies in the deep root system of the trees that makes them independent, 

 to a great degree, of surface soil conditions. 



In passing it should be mentioned that the grass, both cut and uncut, 

 of the sod systems of management affords some protection against surface 

 evaporation, the exact degree depending on the thickness of the protective 

 layer. As this layer is frequently rather thin, its importance in checking 

 evaporation is often exaggerated, for the stubble of the cut grass continues 

 to evaporate moisture into the air, even after it has turned brown and has 

 died down to the ground. In some cases this water-dissipating action 

 of the stubble during the summer months may even equal the protective 

 action of the mulch against evaporation. 



Influence of Depth and Frequency of Cultivation Upon Soil Moisture. 

 Since cultivation is in general a means of conserving soil moisture, 

 the presumption is that the deeper the cultivation, within reasonable 

 limits, the more effective it will be. Table 21 affords a fairly accurate 

 idea of how depth of soil mulch influences the loss of water by evaporation. 

 It is worthy of note that with a soil mulch 6 inches deep the water lost 

 by evaporation is less than a quarter of that lost through a 1-inch mulch. 

 Regardless of the texture of the soil, cultivation is equally effective as a 

 protection against water loss : this protective influence is felt to a depth 

 of 6 feet. 



Table 21 is interesting also because it shows the combined effects of 

 depth and frequency of cultivation. It is evident that increasing the 

 frequency of the cultivations, at least up to a certain point, increased the 

 effectiveness of the soil mulch under the conditions of the experiment. 

 Probably under arid or semiarid conditions with few or no summer rains 

 and less weed growth the more intensive tillage would not give materially 

 increased protection against evaporation. 



