II 



Captain Guinness and Mr. Richards have designed a machine by means 

 of which a reduction in cost will be effected, though whether to a 

 sufficient extent is not yet clear. 



A further set of problems arises out of the weed flora. Although 

 the field chosen for the ploughing up experiment had been down to 

 grass for ten years there was a considerable development of arable 

 weeds as soon as it was ploughed. This result had l^een anticipated, 

 and before the land was broken up samples of earth were taken inch by 

 inch in succession down to twelve inches at various points in the field. 

 These were transferred at once to sterilised pans and kept moist in the 

 glasshouse, careful watch being kept by Dr. Brenchley to see what 

 would happen. A number of arable weeds came up from every sample, 

 especially Polygonum aviculare and A triplex patula. Now the conditions 

 of the experiment were such that these young plants could only have 

 arisen from seeds that had lain buried in the soil, dormant so long 

 as the land was in grass, but springing into activity as soon as tillage 

 conditions were restored. The test was repeated in similar manner on 

 other grass fields of known age and history. SjiI from grass fields 30 

 years old afforded a copious flora of arablj weeds, especially at the 

 depth of six to twelve inches ; that from fields 60 years old gave 

 fewer arable weeds, and trom fields 200 years old none at all. These 

 observations prove beyond doubt that ihc sojds of certain arable 

 weeds can survive in the soil over a considcra!)le period when deeply 

 buried by the plough. 



Another series of problems relates to the utilisation of the stored up 

 fertility of grassland. During the years wheii it w.is down in grass, 

 the soil gained fertility through the various p.gencics i.lready studied in 

 these laboratories. Now that it is ploughed up the fertility is being 

 liberated. Unfortunately the process is very vigorous, the decomposi- 

 tion of the organic matter proceeding so rapidly that rhe crop cannot 

 utilise the whole of the nitrogen oompjunds ; ilerj is, therefore, a good 

 •deal of waste. In virgin countries ihe wa;tage of the original soil 

 fertility often amounts to 50 or 60 per coii;,; iii this country a higher 

 level of production is attained a id therefore a greater degree of 

 utilisation may be expected ; but there is still likely to be loss. 



This problem is not a new one ; it has been under investigation here 

 by Mr. Appleyard and Mr. Horton from the soil side, whilst Mr. Richards 

 took up the parallel case of the manure heap. Unfortunately the 

 soil investigation was not able to keep pace with the manure heap work, 

 and so the problem has become urgent before we have found the 

 Solution. Sufficient has emerged, however, from Mr. Appleyard's and 

 Mr. Richards' work to reveal the main factors in the problem. 



So long as the land lies in grass the conditions are not specially 

 favourable to aerobic organisms. The soil atmosphere contains in 

 both samples about one per cent, of carbon dioxide calculated on the 

 entire volume, and locally a good deal more ; there is also a reduced 

 percentage of oxygen. Directly the grassland is ploughed up the 

 conditions become more favourable. 



The nitrogen compounds are broken down in the fi-rst instance to 

 ammonia. This action has been attributed in the past to bacteria, but 

 we have obtained evidence that the process is more than a simple 

 bacteriolysis. The amount of ammonia produced does not show the 

 direct and immediate relationship with the number of bacteria that 

 one would expect. An increase in bacterial numbers is not at once 



