THE FARMER'S MAGAZINE, 



207 



TOP-DRESSING FOR PASTURES. 



Top-dressing of land means the laying on the surface 

 of the ground of such substances as are known to in- 

 crease the quantity of the vegetable produce from the 

 soil. It may be very reasonably supposed that this 

 mode of using fertilizing substances would precede the 

 application of them under the soil, or mixed with it, as 

 the effect of substances accidentally dropped on the 

 ground would first attract observation, and would sug- 

 gest the use of the acting materials in that way, and 

 also the modes that were subsequently adopted. The 

 very oldest writers on agriculture do not mention ma- 

 nures at all ; and, although their successors notice the 

 substances as being an essential part of cultivation, we 

 are left in utter ignorance of what way the dung was 

 applied to the land. 



Since the date of the earliest records of modern agri- 

 culture, the mode of using manure by spreading it on 

 the surface of the ground has always held a very promi- 

 nent place ; and even at the present day it forms the 

 manner of using fertilizing substances that is impera- 

 tively directed by the nature of the substances, that are 

 used, and not far from being sanctioned as the most bene- 

 ficial modeby the results of practice and the investigations of 

 science. Observation, both intuitive and practical, has 

 ever acknowledged that all fertilizing substances which 

 are reduced in particle and minute in coherence, arc 

 most economically used by being spread over the sur- 

 face of the ground, as the distance between the elements 

 is more reduced, and affords more opportunities for 

 combinations and reciprocal affinities. 



The materials that are more gross in nature and 

 larger iu bu]k, require to be reduced by preparation, 

 and mixed in opposite qualities, in order to attain a 

 state of minute adherence. Experience has ever re- 

 corded the fact that the effect of substances used as ma- 

 nures, on the surface of the ground, is in a direct ratio 

 with the minute or aggregated form in which they 

 exist, and that they are efficacious or fail in effect ac- 

 cording as they are reduced in particles or concreted 

 into masses. All chemical combination is the result of 

 electric attraction ; and bodies unite according to the 

 distances at which the power is exerted. It is a general 

 law that the efficacy is in the inverse ratio of the affinity 

 of aggregation ; for this latter power holds together the 

 homogeneous particles, and prevents their separating, 

 and joining the parts of another body ; and the greater 

 the power is, the less efficacious must be the affinity of 

 composition. Bodies combine from being in opposite 

 electrical states ; and decomposition, consequently, pro- 

 ceeds from the same electrical condition. This action 

 cannot take place unless the substances be mixed in the 

 most intimate manner ; and it happens only between the 

 ultimate particles of bodies, and at insensible distances. 

 If the attraction of cohesion only happens, in which the 

 bodies retain the qualities they possessed before they were 

 joined, and can be separated by mechanical force, there 

 will be wanting the combination that results from the 

 uniting of the different substances, whether simple or 

 compound, and incapable of being reduced mecha- 

 nically, and of which the properties are often different 

 from, and Fometimes opposite to, its former consti- 

 tuents. This affinity of composition is one chief agent 

 in the operations of Nature and of Art ; and the ease 

 and rapidity with which bodies are decomposed or enter 

 into new combinations, are directly as the quantity of 

 the surface which thej present, or inversely as their 



masses. The efficacy of composition is inversely as the 

 attraction of adhesion. The absolute force remains the 

 same, but increases on account of the diminution of the 

 opposing attraction. Electric attraction is the principle 

 in action ; and chemical affinity is the power by wliich 

 bodies unite — the one being, in this sense, a measure of 

 the other. All chemical forces are subordinate to the 

 causes of life, and to heat and electricity, and to me- 

 chanical friction and motion. The latter power is able 

 to change their direction, increase or diminish their 

 tendency, and also completely to stop and reverse their 

 action. Causes must exist to produce chemical affinity, 

 or the cycle of life would stand still ; and, from our 

 ignorance of these causes and of the application, it is 

 probable that in many cases their action is arrested and 

 stopped, often rendered useless and not produced at all, 

 or, at best, but accidentally. Bodies that have little or 

 no affinity, and do not enter into combination, are made 

 to do so by the addition of one or more substances ; 

 and this principle shows the necessity of applying a 

 number of substances at one time, and of bringing them 

 into contact with each other in a state of very minute 

 adherence.' Many kinds of chemical action are effected 

 by heat, electricity, and other agencies, over which any 

 control is impossible, and which do not take place from 

 mere comminution and mixture ; yet by that process a 

 ready accession of means will be offered of producing 

 combinations which, in another state of existence of the 

 substances, would not have happened. Science shows 

 that quantity is in many cases necessary to produce any 

 combination whatever ; for an increase of quantity is 

 known to be equivalent to a superior affinity : and, 

 though no rule has yet been obtained in respect of the 

 quantities to be used in each particular case, yet the 

 strongest presumption may be drawn in favour of the 

 above conclusion being generally applicable. 



The maxims of chemistry that have now been quoted 

 are quite decisive in showing that all bodies from whose 

 union and combination the benefits of new formations 

 are expected, must be brought into contact in a state of 

 comminution, and must be very intimately mixed, in order 

 that the distance may be insensible between the mole- 

 cules of the different bodies which produce the reciprocal 

 action. Though one general principle produces the 

 operation, it is very much influenced by various causes, 

 as by the quantity of the bodies or substances, and by 

 temperature in a great degree, by electricity, and by 

 mechanical pressure, by unsoluhiiity, and by other 

 causes arising from peculiar circumstances. One body 

 at least must be in a state produced by solution or by 

 fusion. Water or some liquid is necessary to produce a 

 heterogeneous affinity, and the union results from the re- 

 ciproc il action of the molecules of the two bodies on 

 each other. Different effects are accordingly produced 

 on different objects in different situations, and the quan- 

 tity and degree of the exertion of the power depend on 

 various and changing circumstances ; for bodies in a chang- 

 ing state, also change capacity. A knowledge of the 

 phenomena of nature, shown in the order and mutual 

 dependence of combinations, would enable us to make 

 them subservient to the improvement of the arts, and 

 direct them to the useful purposes of life. It may be 

 very fairly questioned if agriculture has yet derived the 

 full benefits of comminuition and a mixing of the soil 

 with the substances that are used as fertilizers. Ex- 

 perience has ever shown that the superior effect of sub- 



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