MANURING IN THEORY AND PRACTICE. 



259 



here the quantity of nitrate in the soil amounted to 

 52-2 lbs. of nitrogen per acre, exceeding in richness 

 every other enumerated plot. 



From some analyses of a rich kitchen- garden soil, 

 which had grown Clover experimentally for twenty- 

 nine years in succession, it was found that the lii-st 

 nine inches of soil contained nearly four times as 

 much nitrogen as average arable soil, and nearly five 

 times as much as some exhausted Clover-land soil. 



The facts indicated by these results are of great 

 practical importance. Soil contains nitrogenous 

 matters which nitrify with different degrees of 

 facility. The bulk of the organic nitrogen of a soil 

 is only capable of very slow oxidation, but a certain 

 proportion is very readily converted into nitric acid. 

 In thoroughly exhausted land the easily nitrifiable 

 matter has to a large extent disappeared, but in soil 

 in a good state of fertility it is being continually 

 renewed by fresh crop residues. This readily nitri- 

 fiable matter constitutes a chief part of the floating- 

 capital of the soil, on which its immediate produc- 

 tiveness depends. The larger quantity of more inert 

 plant-food forms the sunk capital, which only very 

 slowly becomes available. 



The nitrates in a moist soil, rich in organic matter, 

 are found rapidly to disappear at a summer tempera- 

 tirre if only a very small and limited amount of air 

 is present. The same result will occur in ordinary 

 arable land if the soil be completely saturated with 

 water, and all oxygen thus excluded. 



This destruction of nitrates is attended with the 

 production of ammonia and of nitrogen gas. 



Only quite recently it has been shown that the 

 change in question is brought about by the Bacteria 

 of the soil ; so that this, as weU as so many of the 

 other transformations within the soil previously 

 refen^ed to, is a result of life. The information thus 

 brought to light supplies a good reason why atten- 

 tion should be paid to drainage in the case of all 

 soils liable to become saturated with stagnant water. 



ACTION OF MANURES. 



By the word manure we imply all those substances 

 which, by elaboration within thB soil, are sufficient 

 to supply the nutritive juices to vegetation, whether 

 the plants are grown in the open field, the garden, 

 or the green-house. It, therefore, includes a great 

 variety of materials, which may be arranged under 

 two separate heads : first, organic— t^dut is, derived 

 from, organised bodies, and once forming part of 

 their structure or their secretions ; and, secondly, 

 inorganic — that is, having an earthy origin, and not, 

 properly speaking, traceable to organic sources. 



Organic manures are those which are capable of 

 yielding to the plant, by decomposition or otherwise, 

 carbon, hydrogen, oxygen, and nitrogen — consti- 



tuents which uncultivated plants derive originally 

 from the atmosphere and rain. 



Inorganic manures are those substances which 

 supply the mineral ingTcdients, of which the struc- 

 ture of plants is found to consist. 



Many of the substances employed as manure con- 

 tain both organic and inorganic constituents. The 

 greater jDortion of soils, too, consist of minerals in a 

 greater or less degree of decomposition, combined 

 with a small amount of organic matter. 



It has been already observed that the atmosphere 

 may be considered as the natural source of organic, 

 and the soil that of the inorganic, supply of plant- 

 food. As, however, it is the object of the horticul- 

 turist to increase the produce of the soil beyond its 

 natural yield, he adopts various methods for accom- 

 Ijlishing that end. In the first place, a proper 

 mechanical texture in soils is necessary to fertility ; 

 for on the fii-mness or looseness of a soil depends 

 not only its suitableness for the growth of difterent 

 crops, but likewise the rapidity of action. 



The produce of the soil may also be increased by 

 means of manures — that is to say, by supplying 

 those ingredients which the soil, the atmosphere, and 

 the rain combined are incapable of yielding in suffi- 

 cient quantity for the nom-ishment and %-igorous 

 growth of those plants placed in the soil by the 

 gardener. 



Every soil is capable of yielding a certain amount 

 of vegetable produce under the influence of climate, 

 without the assistance of an artificial supply of 

 plant-food ; this may be called its natural fertility, 

 and whether high or low in degree, is, comparatively 

 speaking, a permanent quality. The proportion 

 will vary each year according to the amount -ef 

 rain, the temperature of the season, and the descrip- 

 tion of the growing plant. It is known, however, 

 that although the climate of any place may vary one 

 year as compared with another, it nevertheless main- 

 tains a certain average which has an important bear- 

 ing upon the actual productiveness of the soil in a 

 particular locality ; and this, to a very gi'cat extent, 

 must control both the cropping and the manuring 

 of the soils of that district. 



If abundant and nourishing food be given to an 

 animal, it becomes vigorous and fat ; on a scanty and 

 poor diet, it continues thin and weakly. It is pre- 

 cisely the same with plants. If they find in tlie 

 soil all those substances which they require to build 

 up their fabric, in sufficient quantity and in suitable 

 form, they will grow more vigorously, and put forth 

 more shoots, leaves, flowers, and fruits than when 

 they meet with those substances, or even only one of 

 them, in insufficient amount. 



Thus, if an ordinarj- soil be supplied with a 

 manure containing a very small quantity of one 



