664 



Journal of Agricultural Research 



Vol. XX, No. 8 



2,000 



«3>,000 



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v: 6,000 



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6,000 



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/£?000 





Tt/R>/V/R\S. 



—aorsf beans. 

 RorAy oes. 



■CORN. 

 UNCROPPED. 



X 



.* * 8 



11 



S I 



EFFECT OF TYPE AND NUMBER OF PLANTS 



A large portion of Yolo silty clay loam soil was sifted into a group of 

 eight containers. Each container was of the same size as those previously 



used, 30 inches wide, 

 60 inches long, 18 

 inches deep, and held 

 approximately 1 ,800 

 pounds of soil. 



One container was 

 planted to Golden 

 Ball turnips, one to 

 horse beans, one to 

 Early Golden Bantam 



Fig. 1. — Decrease of water-soluble nutrients from the growth of various J 



crops, as shown by increases in specific resistance. Crops were COrn, One to Burbank 

 planted May 13, and soil was sampled on dates given. n+atri A +h 



to barley, the latter having, respectively, 24, 50, and 72 plants each. 

 In addition, one container was left uncropped as a control. 



Water extractions were made at intervals of one to two weeks through- 

 out the major portion of the growing season. This period extended from 

 the middle of May to the end of September. All the crops except the 

 corn matured normally. The cool nights of the San Francisco Bay 

 region prevent corn planted in the spring from maturing till late in the 

 fall. The results with this crop, however, were of such a nature that 

 observations thereon became unnecessary after the maturation of the 

 other crops and were accordingly discontinued at that time. 



The extractions were made in the proportion of 1 part of soil to 2 parts 

 of water. The mixture was triturated in a mortar for three minutes and 

 then filtered upon a 

 medium grade of semi- 

 quantitative paper in 

 an ordinary funnel. 

 The first portions were 

 poured back until 

 reasonably clear fil- 

 trates were obtained. 

 The conductivity of 3 8 « 2 S ;; $ « f; 8 <o 



this solution was then I I I ^ S § ^ ^ *i i I § 



determined by the Fig. 2.— Decrease of water-soluble nutrients from varying numbers of 

 Wheatstone b r i d PJ e barley plants, as shown by increase in specific resistance. Crops were 

 , . 1 - 1 planted May 13, and soil was sampled on dates given. 



and is expressed m the 



graphs as ohms of specific resistance. An increase of resistance, therefore, 

 represents a lowering of the concentration of electrolytes present. Work 

 performed in this laboratory on similar solutions has shown that this 

 method gives results which are comparable to those obtained by accurate 



4000 



3,000 



4000 



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BARLEY Z9-RLRNTS. . 



- • — BARL EY 60 PLATA/ TS. \ 



BARLEY 72 PLAN TS. 



—UNCROPPED. 



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