RESPECTIVE VALUES OF ORGANIC AND INORGANIC MANURES. 223 



and to show how this affects the feeding and consequent growth of 

 the plant. 



The outstanding feature of organics from a chemical point of 

 view is that the food materials they contain are not all present in 

 one form, but exist in a large number of different and complicated 

 chemical compounds ; and it follows that these compounds, being 

 differently constituted, vary greatly in their availability as plant 

 food, and therefore come into use (chiefly by the aid of bacteria, 

 as we shall see later) gradually and continuously. 



On the other hand, the minerals are mostly definite chemical 

 salts of known and comparatively simple composition ; it follows, 

 therefore, that the conditions — of temperature, moisture, &c. — that 

 render one of their food units available for the plant will have the 

 same effect on the rest, so that the whole becomes available for the 

 plant at the same time. This not only means that while this pro- 

 cess is taking place the plant has too much food, but, being unable 

 to take it all, the remainder is washed out of the soil and lost, and 

 is not there when the plant is ready to take in further supplies. This 

 objection, of course, particularly applies to the highly soluble 

 nitrogenous manures, nitrate of soda, and sulphate of ammonia. 



It has been abundantly proved that, for good quality in the 

 product, manures that come steadily into use throughout the season 

 are required, rather than the very active ones that induce a sudden 

 rush of growth. 



Further, the gradual availability of organics builds up a reserve 

 of food materials in the soil, so that eventually the land becomes 

 stored with manurial residues. 



It must be remembered that the soil is more rapidly exhausted 

 of ammonia than of phosphate or potash, so it is particularly necessary 

 that ammonia should be obtained from an organic source. That 

 this fact is realized by horticulturists is proved by the demand for 

 organic ammoniacal manures, the higher price paid for these per 

 unit over the minerals being greater in proportion than that paid 

 for the organic as against the inorganic units of phosphate. 



Hall states in one of his well-known works : " The hop- 

 grower, for instance, won't get the quality he wants by substituting 

 a mixture of super and sulphate for the guanos or organic manures 

 he has been accustomed to use " ; and again : 



It is only a lasting manure which accumulates in the soil to 

 build up ' high condition/ the state of affairs which prevails when 

 reserves of manure in the soil are steadily and continuously passing 

 into the available condition in sufficient amount for the need of the 

 crop, a state of affairs which results in healthy growth of good 

 quality." 



It is evident, therefore, that the slow and gradual solubility and 

 lasting nature of organics is of the utmost importance, and is another 

 reason for their superiority over the minerals, which, as I have shown, 

 do not possess J:hese valuable qualities. 



Q 2 



