232 



On Superj)hos2)hate of Lime. 



If superphosphate of lime be properly made, the farmer receives 

 from the dealer a soluble compound of phosphoric acid and lime, 

 which by the influence of moisture will be distributed through 

 the soil, and, meeting with bases capable of combining with it, be 

 reconverted into a compound insoluble indeed in water, but of 

 easy solubility in nature's solvent, water impregnated with car- 

 bonic acid. I have already said that the production of the 

 precipitated phosphate is one thing — its distribution is another : 

 the latter is fully as important as the former. Those who use 

 superphosphate of lime must therefore take care that nothing that 

 they mix with in the act of applying the manure to the soil shall 

 have the effect of destroying its solubility before it has a chance of 

 becoming properly distributed. 



The usual mode of applying this manure is to drill it with some 

 dry substance under the seed — burnt earth, cinders, coal or wood 

 ashes, charcoal, &c., are the substances employed for this pur- 

 pose. To burnt earth there would appear to be no objection, 

 provided that it does not contain too much carbonate of lime. 

 Coal or wood ashes appear to me undesirable for the purpose 

 on account of the alkaline carbonates which they contain, espe- 

 cially the wood-ashes. By neutralizing the phosphoric acid of 

 the bi-phosphate, they reduce by one half at least the power of 

 distribution upon which we have ventured to lay much stress : 

 the nature of this action has been before explained in speaking 

 of the addition of kelp. To charcoal, as a substance with which 

 to drill superphosphate of lime, these arguments do not apply, 

 and its use appears quite free from objection. 



The question of the best method of applying manures is one 

 which involves theoretical and practical considerations of the 

 greatest moment. In the old or broadcast system of manuring 

 it is evident that the ivhole soil, to a given depth, was made to par- 

 ticipate in the benefits of the application, and the whole soil 

 therefore was in the position of what TuU called a pasture" or 

 feeding ground for plants. The natural tendency of the roots of 

 plants is undoubtedly to spread themselves and to run out in every 

 direction in search of food. 



The practice of drilling manures in close proximity to the seed 

 is founded upon the supposition that, by supplying the plants 

 with lood immediately within reach, you thereby diminish the 

 amount of energy which they are otherwise called upon to expend 

 in seeking for it, and enable them in a given time to obtain the 

 means of building up a greater amount of vegetable structure. 

 But the acceptation of this theory involves two assumptions — the 

 first, that plants with a supply of food within their reach do really 

 content themselves with that supply and cease to throw out their 

 roots to a greater distance ; the second, that the manures are such 



