Fertilizers and Sfiade-iyrops 191 



primarily for a green-manure, but under eastern condi- 

 tions it cannot occupy the land during the growing season. 

 The trees usually need all of the available moisture during 

 that period, and clean cultivation is practiced to conserve 

 it. As soon as the trees have made their growth for the 

 season, the cover-crop is planted, and its growth uses 

 the surplus moisture, and thus the trees are aided in matur- 

 ing before cold weather comes on. Our conditions are 

 quite different, from the fact that the water is largely 

 under man's control. We think that our conditions 

 demand a cover for the soil far more in the summer than 

 in the winter. And, moreover, nearly as much protection 

 is afforded in the winter if the crop is plowed under late 

 in fall, as if the plants are allowed to stand. We therefore 

 propose the name " shade-crops," for a system which we 

 hope may come into general use in the semiarid region. 



Many orchardists have seen young trees killed by run- 

 ning water close to them during a hot day, the reflection 

 of the sun from the water causing sun-scald. It is thought 

 that reflection from a hot, baked soil may cause similar 

 injuries. 



As has been noted, arid soils are very deficient in de- 

 caying vegetable matter, and this material is very rapidly 

 dissipated when it is supplied. A summer cover will 

 perform one of its most important functions in prevent- 

 ing at least a part of this loss. 



Examine a moderately heavy soil in an orchard where 

 a manurial crop is growing. The surface soil under the 

 plants will be found to be cool, moist, and friable, while 

 adjacent, unprotected land will be found to be hot, dry, 

 and compact. This difference is due not alone to the 



