163 



" If wo tiiko iiji now tlio oxtviift nf the soil we find that the addition of linio 

 or of nitr;itt' of soda will have the same effect in increasinji the transpiration 

 and the growth of plants in tliis extract as they did wlien ajiplied to the soil 

 itself. \Vc have oitvionsly. therefore, transferred the cause of the infertility 

 of the soil from the soil itself to the extract. We find that by tn'atinjr this 

 extract with carbon i)lack the transi)iration and the yield of jjreen matter are 

 increast>d almost, hnt not (inite. as nnich as from the use of lime or nitrate of 

 soda, hnt here ajjain, althonjih we know that i-arhon black has a remarkable 

 power of clarifyinj; solutions and r»>movin>; certain orjianic impurities, it does 

 not a<-t on all kinds of orj^anic suiistances. and, whatev»'r effect it may have 

 had upon this soil extract, it does not sensiltly diminish its acidity. IMants 

 j,'rown. therefor*', in this carbon-treated extract, showinj; a satisfactory increase 

 in transpiration and in yield, are ^rowinji in as acid a solution as in the 

 untreated soil or soil extract. It is fair to supi)ose. therefore, that in the case 

 of the wheat plant the infertility of the soil is not directly due to the acid 

 substance, but to some accompanyin;; or^iinic i)r(iduct which is chanj^ed or 

 destroyed by lime, nitrate of soda, or l)y carbon black. 



" In our exi)erience here at Washinjrton we lind on charring a soil, or on 

 treating: it with i>yro«allol or with maiuu'e. that if exanuned innnediately after 

 the treatment the solution may still show the same acid pro]>erties. accompanied 

 nevertheless by increased fertility, or these acid properties may even increase 

 by these treatments to a marked extent even to the present detriment of the 

 soil, as in the cas»> (tf the charred soil which may become caustic and corrosive, 

 but on allowing: the soil so treated to weather for some time the acid properties 

 finally disappear. It may be that in a sinnlar way the soil treated with the 

 nitrate of soda, in which some toxic sul)stance has evidently been changed 

 or removed, will upon standing, and particularly with leaching, lose its acid 

 properties because of the destruction or removal of the agents which produced it, 

 or of the substances from which it was formed." 



It will be observed that Doctor Whitney and Doctor ^'oelckel• agree ill ascrib- 

 ing tlie acidity of these soils to smne other acid tlian sulphuric or hydrochloric 

 acids, and this assumption is supi>orted by the fact that Ohio soils, which have 

 received neither of these acids in fertilizers, show a similar reaction to the 

 litmus test. With respect to Doctor Whitney's assumption that the fact that 

 this acidity disappears after heating the soil to redness is proof that it was due 

 to organic acids. Doctor Hopkins, of the Illinois station, calls attention to the 

 fact that the ash of organic matter is almost invariably alkaline, and holds that 

 '• it is altogetlier probable that this alkaline ash resulting from the organic 

 matter of the soil w(mld be sutHcient to more than neutralize any inorganic- 

 acidity which might exist in the soil." 



Do("tor Whitney discusses this (juestion in the light of experiments on wheat, 

 hut both Doctor Voelcker's test and our own show that wheat is relatively 

 insensible to acidity of soil. In the Ohio experiments wheat is producing a 

 fair and increasing yield on the plats which have received the largest additions 

 of acidulated fertilizers, and on which clover has almost totally refused to 

 grow, the average annual yield of wheat for the last seven years being 18.1 

 bushels per acre on plat 2. V.):2 bushels on plat 8, and 22.S bushels on plat 24, 

 against an average unfertilized yield of S.2 bushels. This means that the 

 addition of phosphorous and lime on plat 2. and these, with potassium on 

 plat 8. have enabled the wheat to secure sutticient nitrogen for the production 

 of a yield more than double that given on the unfertilized land. It is ]iossible, 

 and I think (luite pro1)able. that the time is not far off when the soil sup- 

 ply of nitrogen will Ijeconie exhausted, and the addition of mineral fertilizers 

 alone will be insutticient, except where clover has been brought back to its 

 normal functions by the use of lime, but this is for the future. 



This far. therefore, progress toward the solution of the soil-acidity puzzle has 

 been a matter of exclusion and we find ourselves still asking the questions with 

 which we started out. 



XITRIFICATIOX AND SOIL ACIDITY. 



The work of the nitrifying bacteria of the soil and the oxidation of organic 

 matter is attended with the production of nitric acid, and of perhaps larger 

 quantities of organic acids. This work is going on at the time when the 

 higher plants are in full growth, and their roots, permeating the soil, are in 

 jtosition to absorlt at once the nitric acid thus formed. Tender natural con- 

 ditions the nitrogen supply, aside from the small quantity which may be 

 brought down to the soil by rain, is limited by the action of these organ- 



