46 



SCIENCE. 



[N. S. Vol. VII. No. 159. 



organisms be present. (Bulletin Minn. 

 Agr. Exp. Sta. No. 41.) 



The remarkable property of vegetable 

 soils, consisting largely of humus, in in- 

 creasing the nitrogen of a cereal crop, has 

 been noticed in the experiments of the 

 Chemical Division of the Department of 

 Agriculture at Washington. In three suc- 

 cessive years roots growing in a vegetable 

 soil from Florida ha.ve shown an increased 

 percentage of nitrogen as compared with 

 roots grown in the same conditions in typ- 

 ical arable soils. The increase in nitrogen 

 content has, in some instances, been as high 

 as 30 per cent, in a whole crop. 



An examination of the character of the 

 nitrogen-content of the soil shows that this 

 increase is largely in the form of amid ni- 

 trogen. 



I have frequently noticed in Florida the 

 mechanical absorption of humus by a plant 

 in the case of sugar cane grown upon the 

 peaty soils. The juices of these canes often 

 have a distinct brown color which is char- 

 acteristic of water which has passed 

 through a soil of this nature. The sugar 

 which is made from these canes does not 

 have the bright ci'ystalline appearance of * 

 ordinary sugars made from cane, but has a 

 brownish tint difficult to remove even when 

 the sugars are of a high degree of purity. 



There is no doubt whatever of the fact 

 that the liquid absorbed by the plant root- 

 lets carries mechanically in solution parti- 

 cles of humus to all parts of the plant. 



It thus appears that humus has a more 

 direct use as a plant food than has been 

 supposed by those who adopted in toto the 

 mineral theory of Liebig, and this is shown 

 by its nitrogen content, as studied by Hil- 

 gard ; by the action of humates in support- 

 ing plant life, as investigated by Snyder, 

 and by the actual increase in the content of 

 nitrogen in plants, grown upon peaty soils, 

 noticed in our own experiments. 



It has been generally supposed by agri- 



cultural investigators that the acidity of a 

 soil injurious to crops is found only in peaty 

 or marshy soils. This idea has been found 

 to be incorrect by the investigations of 

 Wheeler, which have shown that many of 

 the soils of Ehode Island, not subjected to 

 overflow nor in any sense marshy or peaty, 

 are so acid as to prevent the proper growth 

 of crops. These soils are not particularly 

 deficient in plant food, but ordinary crops 

 fail to flourish when planted therein. The 

 simple application of lime, in sufficient 

 quantities to correct the acidity of the soil, 

 is enough to convert those almost barren 

 fields into highly productive areas. 



The difficulty of estimating properly the 

 acidity of the soil has been the chief ob- 

 stacle in the way of a more thorough inves- 

 tigation of this subject. The acid reaction 

 of peaty soils, as well as all others, is due, 

 as a rule, to the presence of free humic 

 acid or of acid humates. The exhaustion 

 of the soil in any way for the determination 

 of the moisture in the filtrate obtained 

 gives imperfect and unsatisfactory results. 

 In the titration of the extracts obtained 

 the processes which are used in the satura- 

 tion may act upon the humus bodies, decom- 

 posing them and producing fresh portions 

 of humic acid and thus increasing the ap- 

 parent acidity. This goes on with especial 

 vigor in the presence of free oxygen. 



To avoid this difficulty, Tacke has de- 

 vised a method of determining the acidity 

 in an environment free of oxygen. The 

 essential principle of the apparatus is in 

 having a flask, from which the air can 

 be removed by any convenient method, 

 preferably by a stream of hydrogen, so ar- 

 ranged that when the oxygen is entirely 

 eliminated precipitated carbonate of lime, 

 suspended in water free of oxygen, can be 

 introduced and brought in contact with the 

 finely divided peat or soil. In this way 

 the decomposition of the finely divided cal- 

 cium carbonate can only be effected by the 



