C. CllOWTllER AND A. G. RUSTON 217 



Thus at the end of 48 hours the ammonia output on Plot 2 was 

 64 per cent, more than on Plot 12, whilst by the end of the third day 

 (72 hours) the superiority had been reduced to 17 per cent., and after 

 103 hours the two plots showed practically equal recoids. Had we 

 been able to establish conditions such as prevail on the plots, where 

 the ammonia is largely removed as it is produced, the superiority 

 shown by Plot 2 in the earlier stages would doubtless have been main- 

 tained throughout. It will be noted further that whereas the maximum 

 output in the case of the soil from Plot 2 was practically reached in 

 48 hours, more than twice this period was required in the case of Plot 12. 



Generally speaking, the ammonia-production was decidedly more 

 active on the dunged plots (Plots 2-6) than on the ''artificials" plots 

 (Plots 7-12). This is exemplified by the following data obtained by 

 incubating 5-gram portions of the different soils with 100 c.c. of 1-5 

 per cent, peptone solution. 



MiUigrams of Ammonia produced during 



The superiority of the dunged plot (Plot 2) throughout the first 

 half of the incubation period is seen to be very marked, whilst Plot 7 

 (complete artificials including nitrate of soda) shows to advantage in 

 the earUer stages in comparison with Plot 8 (complete artificials, in- 

 cluding sulphate of ammonia). This latter dift'erence was reproduced 

 also in the comparison of the other nitrate plots (9, 11) with the corre- 

 sponding ammonia plots (10, 12). The poverty in respect of calcium 

 carbonate of the soil throughout the plots is doubtless largely responsible 

 for this relatively unfavourable biological condition of the ammonia plots. 



Summary. 



The experiments reviewed in the preceding pages have been carried 

 out on a light loam soil very poor in lime, in a district of medium rain- 

 fall (20-2.5 inches). 



The chief conclusions drawn from the results are as follows: 

 1. Although the heaviest crops have been obtained with an annual 

 application of dmig, they are little heavier, and more costly to obtain, 

 than the crops obtained with a biennial apphcatiou of dung, especially 



15—2 



