SOILS FERTILIZERS, 17 



cubic meters per hectare (32,174.2 cu. yds. per acre). This is a slij^litly larger 

 apiilication tlian tliat lixecl l)y law but it was readily absorln'd aud produced 

 no iujurious effects. The extension of the irrigated area and tlie installation 

 of planls for l)acterial purification are recommended. 



Sewage disposal at Birmingham and Salisbury, England, J. D. Watson 

 and W. J. ]•:. r.iNXiE (Ah.s. in Engiii. lire, Gl (liUO), No. IG. pit. 526-528).— A 

 system combining lime precipitation, biological purification, and land irrigation 

 emi)l<tyt'd at Birmingham is described. 



SOILS— FERTILIZERS. 



Soil fertility and permanent agriculture, ('. G. Hopkins (Boston, New York, 

 Chicago, London, JOIO, })[>. XXIII+G53, [jls. 9, figs. 5). — In this book, which is 

 the fourth in the Country Life Education Series, edited by Charles William 

 Burkett, and which is dedicated to the Association of American Agricultural 

 Colleges and Experiment Stations, the chief purpose is, as stated by the author, 

 '• to bring together in convenient form the world's most essential facts gathered 

 from the field aud laboratory, and to develop from them some foundation prin- 

 ciples of permanent agriculture," in other words, "to teach the science of soil 

 fertility aud permanent agriculture." 



The book is based to a large extent upon the fundamental thesis, developed 

 mainly l)y the investigations of the Illinois Experiment Station, that " phos- 

 phorus and decaying organic matter are the two substances which constitute 

 the key to profitable systems of permaneiit agriculture on most of the normal 

 soils of America : although, when soils become sour, or acid, ground natural 

 limestone should also be regularly applied." The supply of nitrogen for ordi- 

 nary systems of grain cropping can be maintained by the use of farm manure 

 and the growing and plowing under of leguminous green manures, although 

 conunercial nitrogen can usually be profitably used in market gardening and 

 other more intensive systems of farming. Potash salts are needed only on the 

 comparatively limited class of soils which are positively deficient in potash, as 

 for example, certain i)eaty swamp lands. 



The author emphasizes the importance of soil surveys, but aLso points out 

 the need of more detailed study than is given in ordiuary surveys to local soil 

 variations and conditions. 



While recognizing that the natural adaptation of soil and crop is an impor- 

 tant factor in many cases, the author is of the opinion that this is a matter 

 which has been given undue consideration in comparison with other factors of 

 plant production. 



"Even in the common ]iractice of agriculture, soils at first well adapted lo 

 the growing of a certain crop do not remain so adapted. The fact is too well 

 known to need illustration that specific crops are often grown with success for 

 years finally to fail and be abandoned for some other successful crops, which 

 in turn finally give way to others. Thus good wheat land finally becomes poor 

 wheat land, but .still remains good for timothy bay, which in turn gives way 

 to redtop, and this may be followed by iiartial abandonment of the land for 

 crop production. 



"At any stage in this process of soil deidedon the land may be ri'stored to 

 its original jiower to produce wheat by adopting the proper systems of soil 

 enrichment. . . . 



"The most connnon staiile crops can be grown on almost any soil if it is well 

 drained, well watered, .-iiid siilliiiciil ly rich. Of coin-se, the matter of crop 

 adaptation nnist not be ignored, but if we would grow either plants or animals, 

 we must not neglect tlie food supply." 



