bacterial activity. We have thus been able to render intelligible a 

 number of obscure and paradoxical effects that have hitherto caused 

 considerable perplexity. It has already been observed by practical 

 men in various countries that certain soil conditions harmful to the 

 growth of organisms were ultimately beneficial to productiveness : 

 such are long continued and severe frost, long drought (especially if 

 associated with hot weather), sufficient heat, treatment with appro- 

 priate dressings of lime, gas lime, carbon disulphide, etc. Further, it 

 has been observed that conditions which are undoubtedly favourable 

 to life, such as the combination of warmth, moisture and organic 

 manures found in glass houses, lead to reduced productiveness after 

 a time. We are investigating a number of such problems from this 

 new point of view. 



The survey of the soil fauna is in the hands of Mr. Goodey,.who 

 has already picked out and identified a number of the ciliates 

 commonly present, and is now turning his attention to the more 

 difficult problems presented by the amoebae and flagellates. 



The decomposition processes in the soil lead to a reduction of 

 the stock of the soil nitrogen. Part of the ammonia and nitrates 

 is taken up by the plant : this represents a profitable use. Part, 

 however, is lost, and for some long time past investigations have 

 been in hand to measure and, if possible, reduce these losses. 

 Drain gauge or lysimeter experiments, continued over a period of 25 

 years by Dr. iVIiller and still going on, have shown that about 50 lb. 

 per acre of nitrogen compounds, chiefiy nitrates, were washed out 

 each year in the drainage water during the earlier part of the period, 

 and about 35 lb. later on. The lysimeters are kept without crop or 

 manure; they are uncultivated except in so far as is necessary to 

 remove weeds. When last the percentage of nitrogen in the soil 

 was determined, the loss of nitrogen was found to be equal, within 

 the error of experiment, to the amount of nitrogen recovered in the 

 drainage water. Under these conditions, therefore, the essential 

 change in nitrogen compounds is confined to ammonia production 

 and nitrification. But on the cropped plots where large quantities 

 of manure are added other losses appear to go on, which are now 

 under investigation. 



Fortunately there are gains from natural sources. Analyses 

 made on a systematic plan by Dr. Miller have shown the low 

 amount of nitrogen compounds in rain collected at out-lying light- 

 houses, and the uniform and somewhat higher amount contained in 

 rain collected in country districts. In the rain of towns a still larger 

 quantity is present. About 4 lb. of nitrogen per acre is thus brought 

 down each year to the soil. The chief gain, however, appears to be 

 brought about by bacteria. When land at Rothamsted is left in 

 grass or allowed to cover itself with wild vegetation, its percentage 

 of nitrogen rapidly increases. How much is due to symbiotic 

 fixation in the nodules of leguminous plants and how much to the 

 free living Azotobacter is not easy to decide; but Dr. Hutchinson has 

 shown that Azotobacter can fix considerable quantities of nitrogen 

 under the conditions actually obtaining. The percentage of nitrogen 

 present in a mixture of sand and crop residues increased when 

 cultures of Azotobacter and cellulose-decomposing organisms were 

 added, but not otherwise. Growing plants were able to utilise the 

 nitrogen thus fixed. Again, when sugar was added to some of the 



