ARTIFICIAL MANURES AND HORTICULTURAL PRACTICE. 55 



salts of potash, soda and magnesia, to just over 3§ tons, that is 

 to a little more than by the superphosphate alone, showing that 

 up to this amount of produce the character of the soil exhaustion 

 was much more that of available phosphoric acid than of potash. 

 The beneficial effects of mineral manures, and especially of phos- 

 phates, are usually observed with ripened as well as with succu- 

 lent crops that are spring sown in the garden, and which have, 

 with a short period of growth, comparatively superficial rooting, 

 and which rely, therefore, much on the stores of plant-food in 

 the surface soil. 



It is remarkable that there is much less increase of potato 

 tubers by nitrogenous manures alone than by mineral manures 

 alone. 



Thus by ammonium salts alone there is an average produce 

 of only 6 cwts. more than without manure ; and with nitrate 

 of soda alone there is an average increase of about double this 

 amount, namely 12 j cwts. per acre. The better result by nitrate 

 of soda than by ammonium salts is doubtless due to the nitro- 

 genous supply being more immediately available and more 

 rapidly distributed within the soil, and so inducing a more 

 extended development of feeding-roots. The next plot with the 

 mixed mineral manure and ammonium salts together shows that 

 there was an average of 134J cwts. per acre, a gain of 94| cwts. 

 over the plot without manure ; and with the mineral manure 

 and the same amount of nitrogen as nitrate of soda, an average 

 of 133 cwts. of tubers per acre was produced, that is nearly twice 

 as much as with the mineral manure alone, and about times 

 more than with the nitrogenous manure alone. Finally, the 

 bottom line gives the results obtained by farmyard manure, 

 which, besides supplying to the soil an abundance of mineral 

 matters, and a large amount of organic substance rich in carbon, 

 yielding about 200 lbs. of nitrogen, yet gave considerably less 

 produce of potatos than an artificial mixture of mineral manure 

 and ammonium salts or nitrate of soda, supplying only 86 lbs. 

 of nitrogen per acre per annum. 



The fact is, that it is only the comparatively small proportion 

 of the nitrogen in farmyard or stable manure which is due to the 

 liquid dejections of the animals, that is in a readily and rapidly 

 available condition ; whilst that due to more or less digested 

 matter passing in the faeces is more slowly available, and that 



