[f401, 402 X , 402 S ] LIGHT AND HEAVY SOILS. 219 



or "open" to admit the air freely, in order that the carbonic acid, ammonia and 

 moisture which it contains, should have access to the roots of the plant ; yet 

 again not so freely as to allow the frequent and rapid changes of moisture, 

 temperature, etc., to afft-ct the roots of pi mts. All these changes are so tempered 

 by a soil of th" proper physical constitution, that only a long continuance of the 

 same condition of the atmosphere will sensibly affect vegetation. 



401. Light or Study Soils — The clnypy portion of soils is highly attractive and 

 tenaciously retentive of moisture, [rivaling in this respect some of our m >st 

 powetlul chemical agents (^378)1, and of the nutritive ingredients of plants, 

 wlien in a soluble condition. Vegetable matter, such as is usually present in 

 soils, possesses similar properties; while sand is but very slightly endowed with 

 this quality, even when very fine. This peculiarity is well pronounced in the 

 determinations of the absorbent power of soils, which will be found accompa- 

 nying the analyses. Compare, in this respect, the amount of moisture absorbed 

 by the sandy soil of the Ch'ckasaw Flatwoods (No. 165, ^572), and that of 

 the Pinj Hills soil (No 206)* (both soils almost destitute of vegetable matter 

 also), with the heavy clay soil of the Pontotoc Flatwoods (No. 230, y 5^1) op the 

 one hand, and wih the sandy Marsh soil from Pascagoula (No. 215)f on the 

 other. The last named soil is a very sindy one, but it contains nearly 20 per 

 cent, of vegetable matter ; the former (No 230) is almost void both of sand and 

 ve^utable matter. Both the latter possess a strong attraction for moisture, 

 as shown by the respec ive percentages of hygroscopic m >isture (9^ and \h% 

 per ce n t ) ; while both the f'ortnsr will readily surrender to a dry atmosphere all 

 the moisture they may contain (2 and 2j/X per cent.), beyond a mere pittance, 

 inadequate to the support of vegetable life. 



402 1 Heavy Clay Soils — Such is the main disadvantage of soils of excessive 

 lightness. When, on the other hand, there is a great excess of clay in the soil, 

 disadvantages not less serious will arise. In the case of drouth, such a soil 

 will shrink and crack open, thus not only exposing parts of the roots of plants 

 to the dry atmosphere, but even mechanically injuring them. 



But perhaps the greatest evil to which such soils are liable in this case, is the 

 circumstance of their sutatance becoming so dense, that no access of air to the 

 roots can take place, thus excluding from them both the ammonia and the car- 

 bonic acid of the air, so necessary to the nourishment of all plants ; while at 

 the same time, the stony hardness which the material sometimes acquires, 

 forbids the further development and expansion of the delicate rootlets which 

 the plant sends forth in all dinctions, in search of nourishment. Thus, of 

 course, the whole organism is paralyzed in its action, languishes and finally dies. — 

 And all these phenomena will take p. ace equally, whether the soils be in them- 

 selves fertile or not ; save that a strong, healthy plant, grown in a productive 

 soil, will naturally resist longer than another, grown in a medium or poor soil. 



Thus, for instance, the phvsical constitution of some of the Monroe prairie 

 soils is scarcely less objectionable than that of the heavy soil of the Flatwoods ; 

 yet the respective average crops are much oftener made in the rich prairie soil 

 than in the second rate (so far as its chemical constitution is concerned) soil of 

 the Flatwoods, because the vitality and capacity of resistance of plants grown 

 in the prairie region is much greater than in the other case. 



402 2 In case of excessive tvet. such soils are no less troublesome. The greafc 

 difficulty encountered in tilling them during seasons of either wet or drouth, is 

 too well understood to require discussion ; yet it is precisely in such soils that 

 tillage would be most necessary in such seasons. For if, as has been observed 

 above, excessive dryness of the soil closes it ellectually against the access of air 

 (except in the cracks, where there is too much of it), such is no less the case 

 wht-n^ver they are saturated with water. Light and " warm" soils, even when 



*Sje " Long-leaf Pine Region.' 

 -{•See " Sea Coast Counties." 



