520 Miss F. A. Mockeridge. Effects of Auximones on 



bacterised peat in the above Table had practically ceased during the last 

 week, suggested that either the nitrate had accumulated to such an extent 

 that it had become inhibitory to the organisms concerned, or that the whole 

 of the available nitrogen had been nitrified. 



In order to test this, each of the two soils containing bacterised peat was 

 placed on a filter paper in a large Buchner funnel fitted into a vacuum 

 flask. The soils were covered with distilled water, and the flasks exhausted 

 as rapidly as possible by means of a pump. They were then dried down to 

 a suitable moisture content as rapidly as possible at a low temperature by 

 means of a fan, and were re-incubated after samples had been taken for 

 analysis. By this time two days had elapsed since the sampling on the 

 28th day, and during this time the control soils had been incubated as 

 usual. These soils were not re-examined on the 30th day, but in the Table 

 below the figures are given as for the 28th day. The subsequent results 

 obtained were : — 



Table VII. 





Nitrate content (parts per million — mean 

 determinations) . 



of three 



After 30 days. 



35 days. 



42 days. 



49 days. 



1. 





208 



222 



234 



177 



2. 



Soil + bacterised peat . . . 



200 



230 



179 



175 



3. 



204 



230 



298 



337 



4. 



i) >> ji ••■ 



189 



199 



,310 



350 



These results indicated that the addition of bacterised peat to a fertile soil 

 results in a rapid increase in nitrate content up to a maximum, when the 

 concentration of nitrate becomes inhibitory to the growth of the organisms, 

 and nitrification ceases. If this accumulation be partially removed by 

 rapid washing, nitrification again proceeds. 



As in the case of nitrogen fixation, nitrification is essentially an aerobic 

 process, and may have been facilitated by the better aeration of the soil, so a 

 comparison was made of the effect of introducing similar bulky matter in 

 the form of raw peat and stable manure. An examination was also made of 

 the effect of chemically produced soluble humate in the form of peat whi^h 

 had been treated with 2 per cent, of its weight of sodium carbonate. The 

 soil chosen for this experiment was a fertile soil from Chelsea Physic Garden, 

 and the organic manures were added in the proportion of one part in ten by 

 bulk. The soils containing raw peat also received a dressing of 1 per cent, 

 of powdered chalk, in order to counteract as far as possible any inhibitory 



