96 Influence of Plant Residne.s on Xifroyen Fixation 



of such material in any quantity are inadvisable unless the constituents 

 likely to give rise to adverse changes can be previously eliminated. This 

 possibility forms the subject of a separate inquiry which is proceeding 

 at the present time. 



It is apparent that the question possesses something more than 

 purely academic interest, especially in its relation to the present day 

 tendency towards a decreased production of manure and an increased 

 output of straw and similar materials. It is also linked up more or less 

 directly with a number of minor issues such as the utilisation of green 

 manures, the preparation of compost, and of leaf and turf mould. At 

 the same time it is unfortunately a field in which little more than 

 sporadic investigation has yet been attempted, and where consequently 

 practice not infrequently follows a purely arbitrary course. 



Experimental. 



A. Field Experiment.i on Nitrogeri Fixation. 



In order to ascertain the extent to which nitrogen fixation j^rocesses 

 come into operation in the field, the halves of two of the Hoos Field 

 plots which had been under continuous barley experiments since 1852, 

 were used for this work. Of these two plots, one (6. 1.) had not received 

 any manurial dressing since the above year, while the other (4. 0.) had 

 received annuallv a complete mineral manure without nitrogen. The 

 experiment was continued from 1906 to 191], an application of one ton 

 of sugar per acre being given each year with the exception of 1907, when 

 potato starch was applied at the same rate. The immediate effect of the 

 application of sugar in 1906 was a practical extinction of the barley crop, 

 but owing to the proximity of the sugar application to the sowing of the 

 crop it was thought that this effect might have been due to the primary 

 decomposition products of the carbohydrate. During the next three 

 vears, therefore, a longer interval was allowed to elapse between the 

 time of treatment and the introduction of the crop, but although the 

 injurious effect was not so marked it was nevertheless evident in all 

 the cases where the sugar was applied in spring. Examinations of the 

 soil showed that the treatment had resulted in a very great increase 

 of bacteria, and it was presumed, for the time being, that these were 

 acting prejudicially on the crop either by the decomposition of the 

 soil nitrates with the liberation of free nitrogen, or by the assimilation 

 and retention of available nitrogen compounds. 



