155 



chloric or nitric, ina.v not serve a l)etter purpose than a supposed natural sol- 

 vent. Indeed, taking; into consideration our present knowledge of the process 

 of nitrification in the soil, we are justified in cla.ssiiif; nitric acid as one of the 

 natural solvents. The writer gives the preference to nitric acid, not from 

 theori'tical considerations, hut hecause it dissolves less iron from the soil than 

 either hytlrochloric, oxali<-, or citric acids. In the lahoratory of the Kentucky 

 station N ."> nitric acid has 1k>(>ii adopted as the solvent for measuring the avail- 

 ahility of phosphorous and |)otassiuni compounds in soils. The digestiontj are 

 made at room temperature for live hours, with occasional shaking, using tho 

 calculated weight of air-dry soil ecpiivalent to 220 grams moisture-free and 

 2,2(Mt cuhic centimeters of solvent an<l taking for the potassium and phosphorous 

 detenninations, usually, ali(iuots (Mpiivalent to (50 and 100 grams of moisture- 

 free soil, respectively. If a nitrogcMi determination he made and also a diges- 

 tion in IICl 1.115 si)ecitic gravity, and determin.itions of potassium and phos- 

 jthorus in that solution, a very satisfactory statement is i)ossihIe of the amounts 

 of the iuunediatel.v .ivailahie and reserve plant food present. After several 

 yeai-s" use we think the metiiod gives results that are in reasonahle agreement 

 with conclusions from held exi>erlence. The following is presented as an illus- 

 tration of the itractical application of comparative soil analysis. 



A field of ahout 15 acres of apparently good l)luegrass soil in Clark County, 

 Ky., was plowed from clover in the spring of 1S04 and planted in tohacco. On 

 a rectangidar area of ahout 4 acres in one corner of this field the clover had 

 Itecn jihuost a total failure. The tohacco hegan to grow well, hut after two or 

 three weeks the tohacco on this same area stoi)i»ed growing, and at cutting time 

 ver.v few of the plants were worth s.-iving, wliereas on ad.jacent jtarts of the 

 Held — indeed, on nearly all the rest of it — there was an excellent crop. The 

 longest houndary line between the good and had tohacco was straight and well 

 defined, i-unning at right angles to the rows, and as the tohacco had been set b.v 

 machine, working continuously, the i)ossibillt.v of differences in time of plant- 

 ing, kind of plants, or manner of setting was here eliminated. Neither was 

 there any ap])reciahle diff\>rence in the ai)pearance of the soil on opposite sides. 

 The writer collected for comparison two sets of average samples, each contain- 

 ing ten cores by the sam])ling tube, taken in iiarallel lines about 20 feet apai't 

 on each side of the apparent line of divisi«Mi lietween the good and bad tobacco. 

 A set of sam])les was taken also from a bluegrass pasture on another part of 

 the same farm, which had not been in cultivation for a great many years. 

 These samples were given a ver.v thorough analysis, including determination of 

 acidity, nitrites, 'nitrates, and humus. Onl.v the most important determinations 

 are here given. 



Analyses, calculated on the moisture-free samples, parts in 1.000,000. 



The low solubility of the potassium compounds in the soil where the crop 

 failed points to the cause of the failure, and warns the farmer against planting 

 tobacco again on any part of this field unless artificial fertilizers be used to 

 supply the want. The same cause is suggested for the failure of the clover. 

 The relatively large proportion of nitrogen in the form of nitrates and nitrites 

 in the l)ad part of the tobacco field shows that this part was equivalent to a 

 fallow, the tobacco not having made growth enough to consume the nitrates. 

 The effect of this was very apparent on the wheat and bluegrass sown after th^ 

 tobacco, much the best growth being on the part where the tobacco had failed. 

 If these analyses had been made before the tobacco was planted instead of after- 

 wards, it is probable the crop on 4 acres of this field would have been saved by 

 the use of ten or twelve dollars' worth of potash salts. 



