3178 



SOIL 



SOIL 



arrangement of the particles, and the relation of these 

 to each other and to the organic matter; also the soil 

 atmosphere, the soil moisture, and the physical forces 

 of heat and gravitation. In these there is an intimate 

 relation with physiography or the form and exposure of 

 the surface of the land, as well as to climatology. 



There are, undoubtedly, constant physical changes 

 going on in the soil, as well as chemical changes, which 

 have much to do with the best development of vegeta- 

 tion. The soil-moisture may be looked upon as a 

 nutrient solution, dissolving its material from the 

 difficultly soluble compounds in the soil and from fer- 

 tilizers artificially applied. The amount of substances 

 in solution varies with the moisture content and with 

 the way moisture is supplied to the soil. The dissolved 

 substances, naturally present in the soil or derived from 

 fertilizers, influence the solubility of the soil components, 

 rendering them more or less soluble according to their 

 nature and existing conditions. It is probable that 

 there is a normal weathering of the soil material which 

 produces a certain concentration in the soil solu- 

 tion which will be maintained on the gradual withdrawal 

 of nutrient material by the plant. However, this 

 natural weathering is often not sufficient in amount to 

 produce the yield and quality of crops desired, and 

 this may be increased by methods of cultivation and 

 fertilization so that crops may annually remove larger 

 quantities of nutrient substances without any particu- 

 lar exhaustion to the soil. 



It is certain that these nutrient materials dp not 

 accumulate to any considerable extent in soils in 

 humid countries, as they are liable to be leached away 

 and also to recombine, forming difficultly soluble com- 

 pounds with the material of the soil-grains. A soil is in 

 good heart or good condition when the physical condi- 

 tions, such as the water-supply, soil atmosphere, and 

 temperature relations, are favorable, and when the 

 weathering of the material is sufficient to furnish an 

 abundant and constant nutrient solution in the soil 

 moisture. 



One of the most potent agents in the weathering of 

 soils is the organic material contained. This is unques- 

 tionably due largely to the amount of carbon dioxid 

 formed, which renders many of the nutrient matters 





3625. How the gardener makes his soil, by letting it decay in 

 piles. The larger pile is composed of sods. 



much more soluble. Moreover, the organic matter 

 forms a culture medium for bacteria, ferments, and the 

 various organized and unorganized agents which assist 

 in breaking down the organic material, and facilitate as 

 well the weathering of the other soil components. Soils 

 in general have remarkable power of absorbing on the 

 surface of the soil-grains vast quantities of carbon 

 dioxid, ammonia, and other gases, and of other nutrient 

 materials, which, while soluble and actually dissolved, 

 do not readily diffuse out into the solution between the 

 soil-grains. 



The influence of fertilizers is therefore twofold: the 

 direct addition of plant-food for the immediate use of 

 plants, and the action of the fertilizing components 

 upon the solubility of the otherwise difficultly soluble 

 compounds in the soil. There are other offices which 

 are very strikingly shown in the case of lime. This sub- 

 stance, when in the form of either caustic or slaked 

 lime, corrects the acidity which is very often present 

 in soils. It changes the structure of soils. It renders 

 some of the soil components much more soluble, espe- 

 cially when the lime is in the form of the sulfate or 

 gypsum, and it has undoubtedly a physiological role 

 which enables the plant to assimilate larger quantities 

 of other nutrient matters even in amounts which would 

 be detrimental if the lime-salt were not present in 

 excess. 



The principal objects of the cultivation of the soil are 

 to secure proper aeration, to conserve the moisture sup- 

 ply, and to improve the drainage. The irrigation and 

 artificial drainage of soils are treated elsewhere. 



The physical properties of texture and structure, that 

 is, the size and arrangement of the soil-grains, have a 

 greater practical importance with field crops and the 

 relation of crops to soil under extensive cultivation than 

 upon horticultural crops either in the field or greenhouse, 

 where intensive methods are used. Particularly in the 

 eastern states, where the natural rainfall is relied upon 

 for the water supply, these physical properties have 

 great influence in determining the relation of crops to 

 soils. This is due in large part to the influence of the 

 physical properties upon the water supply, and the 

 commercial values of many soils are dependent largely 

 upon this one condition. This is notably the case with 

 the early truck crops, with corn, wheat, and grass lands, 

 and with special products such as celery, cranberries, 

 and other horticultural crops. With intensive cultiva- 

 tion, however, the flavor, appearance, texture, and 

 general quality of the crop assume greater commercial 

 importance, and even with intensive methods these are 

 largely influenced by the character of the soil. This is 

 shown in a striking manner in the localization of cer- 

 tain interests, even under the most intensive system of 

 agriculture, such as the production of the fine lettuce 

 around Boston, of the carnations, violets, tomatoes, 

 and roses in other districts. With the present specializa- 

 tion in these lines, it is not only necessary that one 

 should have a knowledge of the methods of cultivation, 

 but should have the proper soil conditions as well as 

 suitable climatic conditions; and to such an .extent has 

 this specialization been carried that different varieties 

 of roses, for example, are best grown in different locali- 

 ties where the soils are slightly different. These matters 

 must be realized by the horticulturist in order to attain 

 the highest degree of success in any particular under- 

 taking. MILTON WHITNEY. 



Soils for potting. 



Strictly speaking, there are but two distinct kinds of 

 soils, though there are several modifications or physical 

 differences in both. These are mineral soils and organic 

 soils or peat. Peat is formed in temperate climates by 

 the accumulation of vegetable matter in swamps, or in 

 some parts of the world under peculiar atmospheric 

 conditions (see Peat). Mineral soils, which cover the 

 greater portion of the earth's surface, are formed by the 

 disintegration of rocks and stones through the agency of 

 water, frost, or the atmosphere. Peaty soils are com- 

 posed almost entirely of vegetable matter, with but 

 little mineral matter. Mineral soils are just the reverse. 

 The physical differences in peat are practically reduced 

 to two, viz., the absence or presence of fiber. The 

 physical differences . in mineral soils vary considerably 

 from almost pure clay to almost pure sand ; indeed, the 

 mechanical (or physical) analysis of mineral soils is 

 based largely upon the proportions of day and sand. 



