L 



TUK TKXTrRE OF THE SOIL 41 



choinical ftM'tilizors aro both {nnciHliiionts and 

 (liivi't fortilizors, siiico tlioy nuxlily the f>tnic'ture 

 of the soil as well as add ])hiiit-fo()d to it. 



')9. Tho oxtranoous or suppkMiientaiy iiia- 

 t«'rials {7)A) which diivctly inodil'y tlio stiuctiirt* 

 of soils aro thoso that make humus (.'i.'!), 

 as i^ft'cn-iuaiiurcs, faiMii-iiiaiiurfs, and tlif lik'-. 

 Stahlt'-nianuro is usually more inii>()rtant in im- 

 proving^ soil structure than in directly sui>i>lyiii«i: 

 plant- food. 



4. StrKctKrc and Mn)/i(rcs 



tlO. \Vc have now sfcn that the farmer 

 shotiM irive attention to the structure of his soil 

 before ho worries about its ri(diness. The con- 

 ditions must first be made fit or comfortable 

 tor tin' i^rowin.LC of i>lants: then the stimulus 

 of s{»eei;d or iiii^h feedini^ may lie aj»plied. 

 But maniM'es and fertilizers nniy aid in secui- 

 in.ii^ this t?ood sti'uctme at tlu» same time that 

 they add ]»laiit-food. Vet fertilize)-, how.ver 

 rieh, may be applied to .soils wholly without 

 avail; and the best j'esults from condensetl 

 or chemical fertilizers are usually secured on 

 > >ils that are in the best tilth. That is, it is 

 almost useless to ap|»ly commercial fertilizers 

 to lands that are not in proper physical coii- 

 dition for tlie best prrowth of crops. 



