DRY-LAND GRAINS IN THE GREAT BASIN. 21 



plants must obtain tlieir water supi)ly from the surface soil the im- 

 portance of conserving that water during the fallow season is obvious 

 and the value of cultivation, as illustrated by the data given above, 

 is strikingly noticeable. 



It is often stated that it is impossible to cultivate fallow soil too 

 much. This is not always true, especially on heavy clay soil. If such 

 a soil is harrowed until the surface is a very fine dust, it crusts very 

 readily after a rain, and packs extremely hard. It is well to keep the 

 surface soil loose antl light, but the maintenance of a "dust mulch," 

 strictly speaking, is not desirable. (See PI. I, fig. 2, and PL II, fig. 1.) 

 On light, sandy soils the danger of excessive cultivation, however, 

 is not so important. 



WEED ERADICATION. 



The operations necessary to prevent the growth of weeds on fallow 

 soil are closely related to those employed to conserve soil moisture. 

 A cultivation that will destroy weeds will also break up a soil crust, 

 and cultivation made to pulverize the surface soil will frequently 

 destroy large numbers of small weeds. Ordinarity, if the amount of 

 tillage necessary to maintain a good soil mulch is carried on, the 

 weeds will be destroyed incidentally. There are cases, however, w^hen 

 cultivation is necessary entirely on account of weeds. In such cases 

 the all-important requisite is to do the work at the proper time. If 

 the soil is carefully watched it will be noticed that at times during the 

 summer the ground is literally covered with weeds, so small as to 

 escape casual observation. If the land is treated to a light harrowing 

 at exactl,y the time when these weeds are beginning to appear in great 

 numbers, highly satisfactory results may be obtained. This has been 

 repeatedly demonstrated at the substation. A very few days' delay, 

 however, will make it necessary to use a disk harrow. This operation 

 costs more than a light harrowing and is less desirable because it 

 exposes more moist soil to the drying effects of sun and wind. The 

 more shallow the fallow cultivation is, so long as it keeps dow^n the 

 weeds, the better. 



Where an unusual number of weeds are present on fallow soil, as is 

 sometimes the case when the land has been plowed in the fall and 

 where it is impossible to cultivate at the critical time, the method of 

 plowing in early June, as practiced by the Grace Brothers, is highly 

 satisfactory. When this method is followed the land is left until 

 practically all the weeds likely to grow are up. The plowing is then 

 done, as shallow as possible, to avoid exposing unnecessarily the moist 

 soil near the surface, and the plows arc followed immediatel}' by the 

 spike-tooth harrow. The harrowing reestal)li.shes the desired soil 

 mulch and exposes the roots of the weeds to the destructive action 

 of the sun and wind. 



[Cir. 01] 



