124 Deco)upo>^itlon of C;)anaml(h and Dlcyanodiamule 



affected even by the highest amount employed, viz. 1-5 grams per 15 

 kilos soil. The toxic effect was less marked in a loam than in a mixture 

 of sand and loam. Only a small proportion of the dicyanodiamide 

 nitrogen was utilised in the plant and the heavier dressings caused only 

 a '"useless storing up" of proteins in the leaves and stems to which 

 the injury to the plants was attributed. 



J. A. Voelcker(24) found that dicyanodiamide at rates from -23 to 

 •09 cwt. per acre had an increasing depressing effect on mustard grown 

 in pots. Dicyanodiamide injured mustard much more than barley and 

 barley more so than wheat ; the effect of dicyanodiamide was more or 

 less similar whether applied at sowing or as a top dressing. 



The Production of Nitrate from Cyanamide and 

 Dicyanodiamide. 



For the nitrification tests the same soil was employed as in the pot 

 experiments. The bulk was first thoroughly mixed together and the 

 moisture content raised, if necessary, to the optimum level for nitrifica- 

 tion, viz. about 15 per cent. The soil was next passed through a 3 mm. 

 sieve, weighed out into lots of 800 grams and directly transferred 

 to wide-mouthed bottles of 40 ozs. capacity. The bottles were then 

 divided into sets of four, and while one set was kept as controls without 

 nitrogen, the others received equal amounts of nitrogen in the various 

 forms to be tested. After applying the nitrogen to the soil the bottles 

 were plugged with sterile cotton wool and afterwards kept in a dark 

 cellar at the ordinary laboratory temperature. At the beginning a 

 determination of the nitrates in the untreated soil was made, and at 

 each of the periods in question the nitrates were determined in one 

 bottle from each set. 



Where necessary, soils were taken also from the same bottles for 

 the determination of ammonia and bacterial counts. 



The Determination of Nitrates in the Soil. 



In the first series of nitrification tests the nitrates were determined 

 by the reduction method (25). The soil was extracted in the usual way 

 with distilled water and the solution concentrated by boiling to a small 

 volume with a trace of added magnesia. The nitrates were reduced in 

 the concentrated soil solution by the zinc-copper couple and the 

 ammonia afterwards determined in the usual way. Soil treated with 

 dicyanodiamide was found to give by this method at the end of the 

 different periods a practically constant slight excess of ammonia over 



