CROP INDICATORS. 



257 



and especially during certain years, this may amount to ordinary cropping 

 on one and dry-farming on the other. Kearney and others (1914: 416) have 

 shown that sagebrush (Artemisia tridentata) is an indicator of both dry-farm- 

 ing and irrigation farming in Utah when it makes a good stand and vigorous 

 growth. Communities of Kochia vestita or Atriplex confertifolia generally 

 indicate the necessity of irrigation to rid the soil of the excess of salts. The 

 mixed community of Sarcobatus and Atriplex has essentially the same signifi- 

 cance, though it indicates the desirability of drainage as well. Hilgard (1906: 

 536) regards Sporobolus airoides, Spirostachys, Salicornia, Suaeda, Sarcobatus, 

 Frankenia, Cressa, and Distichlis as indicators of the necessity of underdrainage 

 as a prerequisite to successful irrigation farming. 



CROP INDICATORS. 



Nature and kinds.— While the factor-complex must always be kept in mind 

 in the correlation of indicator communities and crops, water is the paramount 

 factor practically throughout the West, The importance of temperature as 

 a direct factor increases with latitude and especially with altitude, but it is 

 regularly less than that of water. The water relations are primarily a ques- 

 tion of rainfall and evaporation, more or less modified locally by topography 

 and soil. As a consequence, it is desirable to distinguish climatic and edaphic 

 indicators of crops. The former denote the general climatic regions for 

 particular kinds or varieties of crops, the latter the soil or topographic differ- 

 ences which break up the climatic uniformity of a particular region and render 

 other kinds or varieties preferable. Climatic indicators are primarily climax 

 communities of varying rank, while edaphic indicators are mostly serai or 

 developmental communities. Crop indicators may serve to denote (1) the 

 type of crop, as grain or forage; (2) the species in a general sense, as wheat, 

 oats, or rye; (3) the kind, as winter and spring, or hard and soft wheat; and 

 (4) the variety, such as Marquis, Fife, or Preston. They also permit cor- 

 relations with differences in methods of practice, such as dry-farming with and 

 without summer tillage, etc. 



Little use has been made of plant communities as indicators of the type or 

 kind of crop. This has been a natural outcome of the enormous amount of 

 crop experimentation carried on by the Department of Agriculture and the 

 various State experiment stations during the past two decades. Nearly 100 

 stations and substations have been concerned in this work, and it is a logical 

 conclusion that they have made the use of crop indicators unnecessary. It 

 seems, however, that the very extent and thoroughness of the experiments 

 with various crops must increase the accuracy and readiness with which 

 indicators can be used. In spite of the numerous stations, there are many 

 large regions still unrepresented. In addition, the climatic gradations and 

 edaphic variations are so numerous that the native vegetation alone affords an 

 adequate method of taking them all into account. As a consequence, the 

 opportunity for working out a general system of crop indicators seems excep- 

 tionally good. This would be based upon the correlations between native 

 communities found about each station and the types and kinds of crops dem- 

 onstrated to be the most desirable for that region. While such correlations 

 can be obtained from the results of practically all stations, the investigations 

 carried on at those of the Office of Dry-Land Agriculture are of the greatest 



