428 EXPERIMENT STATION EECOED. 



acid, and 4.S lbs of nitrogen. Of course there are wide variations in amount and 

 composition of tlie sediments at different times. 



A study of mine tailings which find their way into the Upper (iila River 

 shows that they differ hut little from the natural sediments as regards potash 

 and phosphoric acid, hut that they are lacking in nitrogen and organic matter, 

 the constituents most needed in the desert soils. 



The most pronounced effect of the free use of irrigation water containing 

 large amounts of sediment is the formation of a silt blanket which interferes 

 with the penetration of irrigation waters and in other ways impairs the phys- 

 ical condition of the soil. Experiments on the effects of these silt deposits on 

 the growth of alfalfa during the summer of 1005 on 3 fields situated respectively 

 under the Colorado Kiver near Yuma, under the Salt River near Phoenix, and 

 under the Gila River near Solomonville. are reported. In case of the field on 

 the Gila River the irrigation water used contained a large amount of tailings 

 from the concentration of copper ores. Observations were also made on a num- 

 ber of alfalfa fields along the Upper Gila River. 



The results show in general a marked injurious effect from the accumulation 

 of sediments in alfalfa fields, but like results from the use of water rich in sedi- 

 ments were not in general observed in the case of corn, barley, and wheat. In the 

 case of such crops the ground is cultivated in a manner impossible with alfalfa, 

 and the sediment blanket is broken up, turned under, and incorporated with the 

 soil. In this way the blanketing effect is lessened or entirely done away with 

 and the sediments are left free to exert such fertilizing influence as they may 

 possess. It is therefore concluded that " in all cases cultivation, as deep, thor- 

 ough, and frequent as practicable, is the prime means both of utilizing bene- 

 ficial sediments and of mitigating the effects of harmful ones." 



As compared with the natural sediments the mine tailings were of little or 

 no fertilizing value and, were fully as injurious from the standpoint of the phys- 

 ical properties of the soil. Certain injurious effects which have been popularly 

 ascribed to mine tailings are shown to be due to other causes, such as plant 

 diseases of various kinds, which have no relation to the water sediments. It is 

 believed, however, that sunburning of crops, which is common throughout the 

 Southwest, is due largely to the use of turbid irrigating waters. 



Methods of lessening sediments in irrigating waters, especially the use of set- 

 tling basins, are briefly discussed, and it is stated that " it is proliable that, to 

 an increasing extent, settling basins will be found a necessary adjunct to irri- 

 gating systems in the Southwest." In this connection mention is made of set- 

 tling basins at present in use along the Colorado and Gila Rivers, and a brief 

 account is given of the remains of prehistoric settling basins along the Salt 

 River. 



Assimilation of nitrogen by leguminous plants {Kature [LoimIoii], 7 J/ 

 (IDOG), No. 19.i3, p. JT.T). — A brief reference is uiven to experiments at Midland 

 Agricultural and Dairy College of England with lliltner's pure cultures on 

 tares, peas, alsike clover, alfalfa, and crimson clover grown in pots of boiled, 

 sterilized quartz sand. 



Inoculation proved lieneflcial in all cases. A method of inoculation which 

 consists in mixing dried sterilized soil with crushed healthy nodules from the 

 roots of plants of the same kind as those which it is desired to inoculate is 

 described. 



On the infl.uence of bacteria on the metamorphosis of nitric acid in the soil, 

 J. Stoklasa. .1. .Iki.inkk, and A. Ernest (Ztsclif. LainJir. VcrnncJisir. Osterr., 

 (1906), ;Vo. N. /*//. S'i'/-s:,l : (il)st. ill (Item. Zf(/.. :W (1!)0(!). Ao. !>0. Rcpert. No. J/S, 

 p. 386). — This is an account of a ctmtinnation of previous studies (E. S. R., 18, 

 p. 215) and deals with the evolution of carbon dioxid and free nitrogen in Giltay 



