262 AGRICULTURAL INDICATORS. 



sandy soil, lack of humus, and the maze of steep hills with intervening wet and 

 dry valleys constitute a complex of factors marked by distinctive indicators 

 and demanding a specialized type of agriculture (Cowan, 1916:5). Such a 

 region not only requires different methods and crops from those of the general 

 climatie area, but the varying areas of wet valleys, dry valleys, and hillsides 

 demand corresponding differences in treatment. 



Indicators of native or ruderal forage crops.— The detailed study of sec- 

 ondary seres in fallow fields and similar disturbed areas has revealed a num- 

 ber of species of native herbs and weeds which give more or less promise as 

 forage crops. During the three years of drought from 1916 to 1918, particular 

 attention has been directed to those which made a vigorous growth or a good 

 stand in fields in which forage crops were a failure, or in areas adjacent to such 

 crops. A considerable number of weeds of much promise has been observed 

 over an extensive region, and in addition a number of native species have 

 been suggested as of possible forage value by their behavior during drought. 

 By far the most valuable are Melilotus alba, Helianthus annuus, and Salsola 

 kali. The former is rapidly taking its place as a forage crop in some regions 

 and there seems little doubt that it will ultimately be grown as a dry crop 

 over a wide area. Helianthus annuus has but recently been tested under field 

 conditions (Arnett, 1917), but the results agree with the evidence in nature 

 to the effect that it is of much value in dry regions, and especially during 

 drought years. Salsola has been grown scarcely at all as a crop, but it has 

 been cut as a weed crop and utilized as hay of a fair quality at least. While 

 its tonnage is less than that of sunflower, it will often grow luxuriantly in 

 places where the latter will not. This is true also of Helianthus petiolaris, 

 which may be regarded as a dwarf native form of the common sunflower. 

 The other coarse weeds whose behavior indicates that they will be found to 

 have some forage value are Chenopodium album, Amarantus retroflexus, A. 

 hybridus, Erigeron canadensis, Iva xanthifolia, I. axillaris, and Brassica nigra. 

 The native species of weedy habit and of such vigorous growth as to suggest 

 the probability of forage value are Amarantus palmeri, A. powellii, A. torreyi, 

 A. wrightii, A. fimbriatus, Acnida tamariscina, Psoralea lanceolata, Franseria 

 tenuifolia, F. discolor, Atriplex rosea, A. expansa, Corispermum hyssopifolium, 

 and Cycloloma plahjphyllum. The last four are adapted to saline soils, and 

 the last two to sandhill areas as well (plate 63). 



AGRICULTURAL PRACTICE AND CLIMATIC CYCLES. 



Cycles of production. — The close dependence of annual crops upon seasonal 

 and annual rainfall makes it clear that they will reflect the various climatic 

 cycles in some degree. The correlation is less exact than with the natural 

 perennial crops of grasses, shrubs, and trees, owing to the effect of cultural 

 methods and the choice as to times of planting. It is also more or less ob- 

 scured by rotation and by changes of variety and method such as are con- 

 stantly taking place in ordinary practice. Moreover, it may be completely 

 destroyed for a particular year by hot winds of a few days' duration if they 

 occur at a critical period, such as that of the tasseling of corn. In addition, 

 the correlation of cycles, rainfall, and crop production is most in evidence in a 

 region such as the prairies and plains, where the rainfall is moderate, ranging 



