328 QUANTITY OF SALINE MANURES USEFUL TO THE SOIL. 



in moist weather — and generally wherever wood ashes are found useful 

 to vegetation. 



Many experiments have shown that both of these substances may be 

 employed in the field with advantage to the growing crop — but further 

 trials are necessary to show how far the practical farmer may safely use 

 then! with the hope of profit. In gardening, they greatly hasten the 

 growth and increase the produce of the strawberry,* and in garden cul- 

 ture, generally, where the cost of the manure employed is of less con- 

 sequence, more extended trials would, no doubt, lead to useful results. 



The quantity of these substances which ought to be applied to our 

 fields, in order to produce the beneficial effect which theory and practice 

 both lead us to expect, will depend much upon the natureof the soil in 

 each locaHty and on the kind of manuring to which it has previously 

 been subjected. By referring to our previous calculations (page 222,) 

 it will be seen that upwards of 800 lbs. of these carbonatesf would 

 be necessary to replace all that is extracted from the soil by the entire 

 crops during a four years' rotation. But in good husbandry every thing 

 is returned to the soil in the form of manure which is not actually 

 sent to market aud sold for money. That is — the grain only of the corn 

 crops, the dairy produce, and the live stock, are carried off the land.J 

 Less than 40 lbs. per acre of the mixed carbonates would replace all thai 

 is contained in the grain, and if we suppose as much to be present in the 

 other produce sold, we have 80 lbs. for the quantity necessary to be re- 

 stored to the land by the good husbandman every four years, in order to 

 keep his farm permanently in the same condition. There are, however, 

 in most soils, certain natural sources of supply (pp. 207, 208) by which 

 new portions of these alkahes are continually conveyed to them. Hence 

 it is seldom necessary to add to the land as much of these substances as 

 we carry off'; and therefore from 40 to 60 lbs. per acre, of either of 

 them, may be considered as about the largest quantity which, in a well- 

 managed farm, need be added in order to give a fair trial to their agri- 

 cultural value. Half acwt. of tl e potash will cost less than 15s., and 

 of the soda less than 6s., or of a m xture, in equal quantities, less than 

 21s. at their present prices. 



Theory of the action of potash and soda. 



But upon what theoretical grounds is the beneficial action of potash 

 and soda upon vegetation explained? This question, to which I have 

 already more than once drawn your attention (pp. 83 and 187), it will 

 be proper here briefly to consider. 



a. The first and most obvious purpose, served by the presence of these 

 alkalies in the soil, is that of yielding readily to the growing plant such 

 a full supply of each as may be essential to its healthy growth. If the 

 roots can collect them from the soil slowly only, and with difficulty, the 

 growth of the plant will necessarily be retarded ; while in situations 



' Mr Fleming, of Barochan, has informed me that he found this to be the case with the 

 common potash ; and Mr. Campbell, of Islay, with the common soda of the shops. They 

 should be applied early in the spring, and in the state of a very weak solution. Wocd- 

 ashes would probably produce a similar eflfect, 



1 390 lbs. of dry pearl ash and 440 lbs. of crystallized carbonate of soda. 



X In bad husbandry much more is carried off the land by the waste of liquid and other 

 manure.—See the succeeding chapter, " On aninud manures.'' 



