292 ADUK3;o.\ ov soils to the plough. 



Soils also adhere to the ploug'i in different degrees, and, therefore, pre- 

 sent a more or less [)o%verfLil obstruction to its passage. All soils present 

 a greater resistance when wet than when dry, and all considerably more 

 to a wooden than to an iron plough. A. sandy soil when wet offers a re- 

 sistance to the passage of agricultural implements, ecpial to about 4 lbs. 

 to the square foot of the surface which passes through it — a fertile vege- 

 table soil or rich garden mould about 6 lbs., and a clay from 8 to 25 lbs. 

 to the square foot. These differences will naturally form no inconsider- 

 able items in the calculations of the intelligent farmer when he estimates 

 the cost of working, and the consequent rent he can afford to pay for this 

 or that soil, otherwise equal in value. 



II. RELATIONS OF SOILS TO WATER. 



1°. Power of imbibing moisture from the air. — When a portion of soil 

 is dried carefully over boiling water, or in an oven, and is then spread 

 out upon a sheet of paper in the open air, it will gradually drink in watery 

 vapour from the atmosphere, and will thus increase in weight. In hot 

 climates and in dry seasons this property is of great importance, restoring 

 as it does, to the thirsty soil, and bringing within the reach of plants, a 

 portion of the moisture which during the day they had so copiously ex- 

 haled. 



Different soils possess this property in unequal degrees. During a 

 night of 12 hours, and when the air is moist, according to Schiibler, 1000 

 lbs. of a perfectly dry 



Clay Loam ... 25 lbs. 

 Pure Agricultural Clay 27 



Quartz Sand will gain lbs. 

 Calcareous Sand. . 2 

 Loamy Soil . . 21 

 and peaty soils, or such as are rich in vegetable matter, a still larger 

 quantity. 



Sir Humphry Davy found this property to be possessed in the highest 

 degree by the most fertile soils. Thus, when made perfectly dry, 1000 

 lbs. of a 



Very fertile Soil from East Lothian gained in an hour 18 lbs. 



Very fertile Soil from Somersetshire 16 



Soil worth 45s. per acre from Mersea, in Essex . . 13 

 Sandy Soil worth 28s., from Essex ...... 11 



Coarse Sand worth only 15s 8 



Soil of Bagshot Heath . 3* 



Fertile soils, therefore, possess this property in a very considerable de- 

 gree, and, though we cannot, by determining this property alone, infer 

 with safety what the fertility of a soil is likely to prove — since peaty 

 soils and very strong clays are still more absorbent of moisture, and 

 since this property is only remotely connected with the special chemical 

 constitution of a soil — yet among arable, sandy, and loamy lands, it cer- 

 tainly does, as Sir Humphry Davy mkes, afford one means of judging 

 of their relative agricultural capabilities. 



2°. Power of containing or holding water. — If water be poured drop 

 by drop upon a piece of chalk or of pipe-clay, it will sink in and disap- 

 pear, but if the dropping be continued, the pores of the earth will by de- 



• Sir H. Davy's Works, vol. vii., p. 326. 



