ORCHARD SOIL MANAGEMENT METHODS 37 



June and July, brought up the averages in both soils to well above the 

 danger point for plant growth and the cultivated soil averaged only 2 to 

 5 per cent, more moisture during those months. 



In General. — That the sod-mulch, or any other sod method of manage- 

 ment, makes something of a draft upon the water supply of the soil, as 

 compared with a tillage method of management, cannot be denied, though 

 this draft is often less than is supposed. It would be a very good sod- 

 mulch indeed that, would produce 1 dry-weight ton of mulching material 

 per acre. More frequently the amount does not exceed half that figure. 

 One-half ton of dry mulching material would require from 31,250 to 

 62,500 gallons of water, assuming from 250 to 500 parts of water for each 

 part of drj-- matter. This would be the equivalent of 13^ to 2}^ acre-inches 

 of rainfall or irrigation. Furthermore, most of this water is used by the 

 grass during the months of April, May and June, when the soil is most 

 likely to be well supplied with moisture and best able to part with it. If 

 the growing season of the grass is followed by moderate or heavy summer 

 rains or irrigation the requirements of the trees will be well taken care of 

 in this respect. On the other hand, if there should follow a period of 

 drought, it is easy to understand why trees under sod treatment would 

 suffer. An important factor, then, in determining the practicability of the 

 sod-mulch method of management is the likelihood or certainty of summer 

 precipitation, or, what amounts to the same thing, available irrigation 

 supply during the summer months. In sections such as the Willamette 

 valley of Oregon where winter and spring rains are abundant but the 

 summer is dry, the sod-mulch method of management cannot be employed 

 safely without irrigation. In such regions it is wise to use every means 

 of conserving the natural water supply. On the other hand, there are 

 many sections and many locations where summer rains can be counted 

 on to supply the requirements of the trees during their growing season 

 year after year; in other cases an orchard may be so located in a valley 

 floor or a piece of bench land that it is sub-irrigated by means of seepage 

 water. Under these conditions the sod-mulch method of management is 

 entirely practicable, though it should be stated that such orchards may 

 need somewhat different treatment, so far as nutrition is concerned, than 

 orchards in cultivation. A study of the records of the United States 

 Weather Bureau showing monthly precipitation over a series of years 

 will give important data as to the relative desirability or practicability 

 of these several methods of soil management for any particular region 

 or district. 



Sometimes the choice of methods is influenced by considerations 

 of the cost of the systems. Hedrick^"* reports that the operations 

 involved in the sod-mulch and tillage systems cost per acre respectively: 

 for the Auchter orchard 80 cents and $7.39, for the Hitchings orchard 

 72 cents and $16.28. In many cases the tillage method will more than 



