412 PROCEEDINGS OF THE CHEMICAL DEPARTMENT. 



pears, however, that it may sometimes be desirable to carry it 

 out, at least on light soils. 



Taking the whole of the experimental results together, they 

 appear to bear out the opinion that there is no difference in the 

 effects of soluble phosphates derived from the three different 

 sources employed. There is a slight advantage in favour of 

 bone-ash, which may be attributed to the quantity of insoluble 

 phosphates contained in the manure used, although it is too small 

 to be of any importance. The individual experiments, however, 

 are not so conclusive in this respect, for in some instances the 

 dissolved guano has produced a somewhat larger crop than the 

 others, and there are cases in which the dissolved coprolites 

 .have the advantage. At first sight it appeared possible that 

 this might depend on the nature of the soil, but a more minute 

 examination showed that this explanation would not hold good, 

 for in scarcely any case Mas it found that all the plots contain- 

 ing, for example, coprolites (whether alone or mixed) had the 

 advantage, but that in general the superiority was brought out 

 by that of one which, for some reason not easily traceable, 

 exceeded the others. As very trifling circumstances may affect 

 the results derived from a single plot, no stress can be laid on 

 this. 



One of the most remarkable features of the experiments is 

 the entirely negative effect of nitrogenous manures v/hen ap- 

 plied alone — the plots Nos. 10 and 11, which were dressed 

 with these manures, giving no more than the nothing plots, and 

 in some instances even less. Even when mixed with phosphates 

 their effect in some cases is insignificant, but most generally the 

 two together produce a better effect than either alone, and some- 

 times the difference in this respect is very striking. In those 

 in which the previous treatment of the soil had been liberal the 

 effect of nitrogen is least marked, no doubt because a supply 

 had accumulated in it sufficient for the requirements of the 

 crop ; while in the poorer soils, and in those of a sandy char- 

 acter, on which these manures are more rapidly exhausted, their 

 effect is very manifest. 



The general result as regards the comparison between ready 

 formed and what has been sometimes called potential ammonia, 

 tends to show that there is no marked difference between them, 

 the glue having on the whole produced as favourable an effect 

 as the sulphate of ammonia. It would be wrong, however, to 

 conclude that this result will always be obtained, because the 

 season was peculiarly favourable to the decomposition of the 

 glue ; and it is quite conceivable that there may be times when 

 a marked difference might occur. 



The great variety in the produce of the nothing plots is also 

 especially worthy of notice, and shows how important it is that 



