THE ANALYSIS OF VIRGIN SOILS. 347 



a valuable indication as to the one of these that will first be 

 required to be added when production slackens. 



What are "' Adequate " Percentages of Potash, Lime, Phos- 

 phoric Acid and Nitrogen?- -It is evident that a very critical 

 discussion of cultural experience can alone answer this ques- 

 tion ; and at first sight such experience often appears very con- 

 tradictory when compared with the results of analysis. 



One of the chief causes of such apparent discrepancies is readily in- 

 telligible when we consider the differences in root-development of the 

 same plant in different soils. In "light " or sandy lands the roots may 

 penetrate to several times the depth attained by them in heavy clay 

 soils. Having thus within their reach a soil-mass several times larger, 

 and aerated to a much greater depth, it is but reasonable to expect that 

 in deep, sandy lands plants would do equally well with correspondingly 

 smaller percentages of plant-food than would suffice in clay soils, in 

 which the root-range is very much more restricted. The well-known 

 fact that the production of heavy clay lands may be increased by their 

 intermixture with mere sand, adding nothing to their store of plant- 

 food, emphasizes this expectation and elevates it into a maxim. On 

 this ground alone, therefore, it is evident that the mere consideration 

 of plant-food percentages found, can be a true measure of productive- 

 ness only in the case of virgin soils with high percentages. 



Soil Dilution Experiments. The extent to which dilution 

 with mere " lightening " materials can be carried without im- 

 pairing production, can of course be determined for concrete 

 cases only; but the following experiment made at the Cali- 

 fornia Station is a case in point : 



One kilogram of the heavy but highly productive black clay 

 soil of the experimental grounds of the University of Cali- 

 fornia was used in each of five experimental cultures, each 

 made in duplicate, in cylindrical vessels of zinc-covered (" gal- 

 vanized") sheet iron, all proportioned alike in height and 

 diameter, but containing respectively one, two, four, five and 

 six volumes of total soil. In the smallest was placed one kilo- 

 gram of the undiluted, original soil, in the others successively 

 the same amount of the soil thoroughly mixed with one, three, 

 four, and five volumes of a dune sand fully extracted with 

 chlorhydric acid, and washed with distilled water. The water- 



