COMPARISON OF MANURES. 209 



This function of the humus of the soil can also come into 

 use, with respect to the plant food added in manures. To me, 

 one of the most interesting properties of soil is that remarkable 

 power it has of absorbing certain valuable plant nutrients, holding 

 them in a difficultly soluble condition near the surface, so that, how- 

 ever much rain may leach through the ground, they will be only 

 very slowly carried down deeper, or washed out altogether. Thus 

 the soil behaves with phosphoric acid, with potash, and with the 

 ammonia that is so valuable for its nitrogen. For these three sub- 

 stances an}'^ arable soil that is not too sandy is a most trustworthy 

 savings-bank. Therefore, although we should make much account 

 in buying a fertilizer of the proportion of soluble phosphoric acid, 

 or potash, or nitrogen compounds in it, yet, in all probability, to 

 sa}' the least, our crops take up but a little of these nutrients be- 

 fore they are changed by this fixing power of the soil into a diffi- 

 cultl3' soluble condition. 



Why, then, it will naturall}^ be asked, should we pay ten cents a 

 pound or more for soluble phosphoric acid when we can get good 

 insoluble acid for six cents or less, if what we put on the soil as 

 soluble so soon becomes insoluble? For this reason, parth', that 

 the even distribution of the food through the soil is a matter of 

 much importance. Any one can easil}' understand that if a bottle 

 of the much-advertised, and I suppose very useful tonic, Hors- 

 ford's acid phosphate, were poured over half a bushel of soil, and 

 washed in with a slight drenching of water, phosphoric acid would 

 be far more thoroughly mixed with that soil than, by au}^ reason- 

 able amount of stirring such as one could afford to give to a 

 cultivated field, he could distribute two ounces of dry superphos- 

 phate through the same quantity- of soil. So, when 400 pounds of 

 superphosphate are applied to an acre of soil, in spite of the best 

 of the usual cultivation that could be given to that soil the fertil- 

 izer would remain in little scattered particles here and there ; but 

 let the rain take it into solution for a short time, and distribute it 

 over the surfaces of many hundred thousand particles of soil, so 

 that the feeding rootlets find it wherever they go, and how much 

 wider and more even the mixing of the fertilizer with the soil 

 will be ; and yet, so quickly does the soil seize hold of this trav- 

 eling plant food, and insolubilize it, if I may borrow a very con- 

 venient French word with a very plain meaning, that it cannot 

 stray far oflT. 



Practically, then, every crop has to procure all its phosphoric 



