57 



gave a lather higher yield with the first crop of barley than the 

 equivalent of nitrate of soda; slate-bed sludge came a long way 

 behind, but still gave an increase of 22% over the unmanured pots. 

 With the second crop of mustard, activated sludge sho\\ed a con- 

 siderable residual value, while the slate-bed sludge was exhausted. 

 Acti\ated sludge is a fertiliser of great promise, but certain diffi- 

 culties in drying ii must be overcome before its value can be fully 

 realised. 



XLIX, H. B. Hltchinsox and K. H. Richards. " The 



Utilisation of Straw and the Production of Arti- 

 ficial Farmyard Manure/' Journal of the 

 Ministry of Agriculture, 1921. 



i'he large increase in arable area brought about by the war at 

 one time seemetl likely to result in a glut of straw which could not 

 be profitably utilised in agriculture or industry. Experiments have 

 been going on at Rothamsted for some time with the view to 

 making a nitrogenous and humus-forming manure from straw by 

 bacterial decomposition alone. The nitrogen compounds in straw 

 are inert and play little part in the rotting action of the manure 

 heap. A considerable proportion of the carbohydrate material, 

 however, is easily decomposed. This available starch and pentosan 

 may be used to fix atmospheric nitrogen, and under 

 ideal conditions the amount .so gained may double the 

 original nitrogen content of the straw. The cellulose and 

 ligno-cellulose are not decomposed, so that the straw retains its 

 tubular character and in no way resembles w'ell rotted manure, even 

 after prolonged storage. Pot-culture experiments and field trials 

 showed that straw treated in this way possessed little fertilising 

 value. In most cases the depressing action of raw straw on a crop 

 sown at the time of application was merely reduced or eliminated, 

 while under the best conditions the increase of crop over the un- 

 manured soil was very small. 



The conditions necessary to secure thorough rotting of straw 

 were then investigated. The more important w^ere found to be : — 



1. — Air supply. Typical rotting occurs only under aerobic con- 

 ditions. If air is excluded the straw remains unchanged for six 

 months at least. 



2. — Supply of soluble nitrogen compounds in suitable concen- 

 tration. The concentration of even the weakest undiluted urine is 

 above the maximum limit for decomposition. No rotting occurs 

 until the concentration of ammonium carbonate has been sufficiently 

 reduced by volatilisation. 



3. — Temperature. The most rapid changes occur at about 

 35« C. 



If soluble nitrogen compounds are supplied at the rate 

 of 0.72 parts nitrogen per 100 parts of dry straw, all 

 the added nitrogen is converted from a soluble to an in- 

 soluble organic form. Rotting will proceed until about 50 per cent, 

 of the dry matter has been lost. Little or no loss of nitrogen 

 occurs, so that the final product contains about 2.0 per cent, calcu- 

 lated on the dry matter. If soluble nitrogen compounds are added 

 in excess of the limit, loss takes place until the concentration is re- 

 duced to the necessary extent when the action proceeds normally. 



