^431, 432, 433, 434] guanos — superphosphate op lime. 227 



will be still greater than in the first case. If lime, magnesia, etc., were also 

 wanting, the etfects of the guano will be still more perceptible. 



43 1. When is Mtnure Most Profitable ? — As a matter of course, the application 

 of any kind of manure to land pays best, when all the ingredients contained in 

 the latter are immediately required by the soil. We do not want to expend 

 m >ney and labor in introducing into the soil, substances which, though useful 

 in the end, will remain inert for years to come ; tor so long as this is the case, 

 we lose the interest on the capital which they represent. If our soil requires 

 stimulation merely, i. e., the rendering available of nutriment it contains, while 

 it is not deficient in any particular ingredient, then guano is too expensive to be 

 used for the purpose ; for we utilize only the ammonia it contains, while we pay 

 for phosphoric acid, lime, magnesia, etc., besides. 



It is obvious, therefore, that in the case of two adjoining fields, originally 

 possessing the same soil, the application of guano may be profitable in one, 

 while almost ineffectual in the other — according to the culture each one has 

 received, and the length of time it may have been in cultivation. And what is 

 true of guano, is equally so with reference to all other partial manures — i. e., 

 such as do not contain in the proper quantities all the ingredients required by 

 plants, but only one or a few of these. Hence the great practical importance of 

 the analysis of soils, as well as of the manures intended to improve them. 



432. Columbian Ouano. — There is at present imported from South America, 

 under the appellation of "Columbian Guano," a substance very different from 

 the Peruvian article ; which consists chiefly of phosphate and carbonate of lime, 

 but contains no ammonia or only traces of it. It may be used in the same cases 

 as ground bones, or superphosphate of lime; it is not, however, as energetic in 

 its action as the latter, being much less soluble. It has been attempted, and 

 apparently with considerable success, to remedy this slowness of action by inter- 

 mixture of the finely ground mineral with stimulants, such as Peruvian Ouano 

 or ammoniacal salts. — Of the effects of a similar mixture (sold in commerce, 

 at present, under the title of " Kettlewells Manipulated Guano " there have been 

 very favorable reports. 



433. Superphosphate of Lime. — Of late years, the substance now generally 

 known as Superphosphate of Lime has attracted the constantly increasing atten- 

 tion of agriculturists. The material sold by this title is, essentially, a mixture 

 in various proportions, of gypsum or sulphate of lime with the true phosphate ; 

 which is usually obtained by the action of sulphuric acid or oil of vitriol, on 

 bones, or, latterly, on the article just described under the appellation of Colum- 

 bian Guano. 



The important part which phosphoric acid plays in the vegetable economy, 

 has already been dwelt upon (TT365); it cannot, therefore, be surprising that its 

 addition to the soil should in most cases prove highly beneficial. The energetic 

 action of the commercial article just referred to is not, however, attributable 

 alone of the few nutritive ingredients which it furnishes directly ; this circum- 

 stance alone could not render it so generally beneficial. It is, over and beyond 

 this, a powerful stimulant. A discussion of the mode of action of gypsum as 

 such, will be found below (H436, ff".); that of the superphosphate of lime is 

 quite analogous, for not only does it greedily absorb, and fix in the soil, the 

 ammonia of the air, but its powerful acid (phosphoric) undoubtedly exercises 

 an energetic action on the undecomposed portions of the soil, the nutritive 

 ingredients of which it liberates and renders available to vegetation. 



434 Its exclusive use 's, therefore, necessarily exhaustive, in the end, of those 

 ingredients which it does not furnish, and among these especially of potash, 

 which must, therefore, in time be supplied to the soil from other sources, e. g. t 

 from ashes, greensand, etc. A mixture of the commercial superphosphate of 

 lime, with natural greensand. and ammoniacal salts obtained from gas-works, is 

 probably the nearest approach to a universal fertilizer, of any artificial com- 

 pound brought into commerce, and might in most cases successfully replace 



