LOSS OF NITRATES 153 



use of fresh manure. This, they maintained, was due to the pro- 

 duction in the latter of formic, acetic, and butyric acid, indol, skatol, 

 and hydrogen sulphid, which are toxic to the plant. Under some 

 conditions, the large quantities of carbon dioxid liberated from the 

 rapidly decomposing fresh manure may be valuable in rendering the 

 plant-food soluble. Bornemann found that soil constantly supplied 

 with carbon dioxid through a pipe buried in the ground gave an 

 increase in yield of 12.2 per cent, over the crop grown on untreated 

 soil. Wollny has shown that manure greatly increased the carbon- 

 dioxid production in a soil. 



Ammonification and Nitrification. Moll considered that the season 

 of the year, and not the kind of fertilizer used, nor even the weather 

 conditions, is the principal factor in determining the extent of pep- 

 tone decomposition, nitrification, and nitrogen fixation of a soil. 

 According to Wohltmann, Fischer, and Schneider, ammonification, 

 nitrification, and nitrogen fixation were all more or less increased 

 by the application of manure. Heinze found that manure was 

 especially beneficial to the nitrifying organisms. Warington reports 

 that much more nitric nitrogen was found in the soil of plots which 

 had received annually for thirty-eight years a dressing of 14 tons of 

 manure to the acre than in any of the other manured or unmanured 

 plots. Stevens found that nitrification was much more active in 

 manured than in unmanured soil, but Frankfurt and Duschechkin 

 observed an increase in nitrification only on those manured plots on 

 which the yield had increased. Welbel has shown that the chief 

 factors controlling nitrification in fallow soil were the humus and 

 the humus-nitrogen content, the nitrification having increased 

 directly with the humus. He noted, however, a certain amount of 

 denitrification at first, but later in the summer nitrification became 

 more rapid on the manured than on the unmanured soil, the effect 

 of the manure being still perceptible after four years. Some investi- 

 gators have reported a reduction of nitrates, but the quantity of 

 manure applied was excessive, or else of a very coarse nature, or the 

 soil poorly aerated. Barthel found that nitrification did not take 

 place in the presence of soluble organic matter, but he considered 

 it unlikely that sufficient quantities of soluble organic constituents 

 occurred in normal agricultural soils to interfere greatly with nitri- 

 fication. Niklewski maintained that nitrification occurred in solid 

 stable manure when there was not much liquid present. He stated 

 that on the first day some nitrite bacteria were present and at the 

 end of four weeks there were 10,000 in each gram. Associated with 

 these were nitrate bacteria which were identical with those isolated 

 by Winogradsky. Millard, however, was unable to find many nitrify- 

 ing bacteria in manure. 



Loss of Nitrates. Many of the cases in which individuals have 

 reported a disappearance of nitrates in soil are due to synthetic 



