THE SOUTHERN PLANTER. 



685 



VIII. Cohesiveness of the soil. — A soil 

 is said to be heavy or light, not as it weighs 

 more or less, but as it is easy or difficult 

 to woik. The state of dryness has great 

 influence on this quality. Sand, lime and 

 humus have very little cohesion when dry, 

 but considerable when wet. Soils in which 

 they predominate are usually easy to work. 

 But clay has entirely different characters, 

 and upon them almost exclusively depends 

 the tenacity of a soil. Dry clay, when 

 powdered, has hardly more consistence 

 than sand, but when thoroughly moistened 

 its particles adhere together to a soft and 

 plastic, but tenacious mass; and in drying 



ducting power. The black soils never become 

 so warm as the two just mentioned, demonstra- 

 ting that color does not influence the absorption 

 of heat so much as other qualities. After the 

 black soils, the others came in the following 

 order; Garden soil, yellow sandy clay, pipe 

 clay, lime soils having crystaline grains, and 

 lastly a pulverulent chalk soil. 



To show what different degrees of warmth 

 soils may acquire under the same circumstances, 

 the following maximum temperatures may be 

 adduced. At noon of a July day. when the tem- 

 perature of the air was 90°, a thermometer 

 placed at a depth of little more than one inch. 



gave these results : 



In quartz sand, - . - - 126° 



la crystaline lime soil, - . - 115° 



In garden soil. - - - 114° 



In yellow sandy clay, - * - - 100° 



In pipe clay, - - - 94° 



In chalk soil, - . , - - 87° 



Here we observe a difference of nearly 40° in 

 the temperature of the coarse quart? and the 

 chalk soil. The experimenters do not mention 

 the influence of water in affecting these results — 

 they do not state the degree of dryness of these 

 soils. It will be seen, however, that the warni- 

 est soils are those that retain least water, and 

 doubtless something of the slowness with which 

 the fine soils increase in warmth is connected 

 with the fact that they retain much water, which 

 in evaporating appropriates and renders latent a 

 large quantity of heat. 



Malaguti and Durocher also studied the effect 

 of a sod on the temperature of the soil. They 

 observed that it hindered the warming of the 

 soil, and indeed to about the same extent as a 

 layer of earth of three inches depth. Thus a 

 thermometer four inches deep in green sward, 

 acquires the same temperature as one seven 

 inches deep in the same soil not grassed. 



It is to be remembered that the soils that warm 

 most quickly, also cool correspondingly fast, and 

 thus are subjected to the most extensive and 

 rapid changes of temperature. The green sward 

 which warms slowly, retains its warmth most 

 tenaciously, and the sands that become hottest 

 at noon-day, are coldest at midnight. 



away, at a certain point, it becomes very 

 hard, and requires a good deal of force to 

 penetrate it. In this condition it offers 

 great resistance to the instruments used 

 in tillage, and when thrown up by the 

 plough, it forms lumps which require re- 

 peated harrowings to break them down. — 

 Since the cohesiveness of the soil depends 

 so greatly upon the quantify of water con- 

 tained in it, it follows that thorough drain- 

 ing, combined with deep tillage, whereby 

 sooner or later the stiffest clays become 

 readily permeable to water, must have the 

 best effects in making such soils easy to 

 work. 



The English practice of burning clays 

 speedily accomplishes the same purpose. 

 When clay is burned and then crushed, the 

 particles no longer adhere tenaciously to- 

 gether on moistening, and the mass does 

 not acquire again the unctuous • plasticity 

 peculiar to unburned clay. 



Mixing sand with clay, or incorporating 

 vegetable matter with it, serves to sepa- 

 rate the particles from each other, and 

 thus remedies too great cohesiveness. 



When water freezes, its volume increas- 

 es, as is well known. The alternate free- 

 zing: and thawing of the water which im- 

 pregnates the soil during the colder part 

 of the year plays thus an important part 

 in overcoming its cohesion. The effect is 

 mostly apparent in the spring, immediate- 

 ly after " the frost leaves the ground," 

 but is usually not durable, the soil recov- 

 ering its former consistence by the opera- 

 tions of tillage. Fall-ploughing of stiff 

 soils has been recommended, in order to 

 expose them to the disintegrating effects 

 of frost. 



IX. Absolute weight of soils. — Accord- 

 ing to Johnston, a cubic foot of dry sili- 

 cious or calcareous sand weighs about 



110 lbs. 



Half sand and half clay, . 96 " 

 Common arable land, - 80 to 90 " 

 Heavy clay, . . . 75 " 



Garden mould, rich in vegetable 



matter, .... 70 " 

 Peat soil, . . . 30 to 50 " 



This concludes our study of the physical 

 characters of the soil, as the}^ affect its 

 fertility. It is seen that our knowledge is 

 very incomplete, and the whole subject is 

 in the highest degree worthy of an extend- 

 ed investigation. Such a research is an 



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