18 CHEMISTRY AND AGR CULTURE. 



Some apparently good soils are yet barren in a high degree. In en- 

 deavouring to improve such soils, practical men have no general rule — 

 they can have none. They vi^ork in the dark — like a man who makes 

 experiments in a laboratory, without a teacher or without a book, till, 

 after many blunders and much expense, he discovers some fact, to him- 

 self new, but to others long known, and forming only one of many ana- 

 logous facts, flowing from a common, and probably well understood, 

 principle. 



" The^pplication of chemical tests to such a soil," says Sir Humphry 

 Davy, " is obvious. It must contain some noxious p'Vinciple, for be de- 

 ficient in some necessary element. — J.] which may be easily discovered 

 and probably easily destroyed. Are any of the salts of iron present, 

 they may be decomposed by lime. Is there an excess of siliceous sand, 

 the system of improvement must depend on the application of clay and 

 calcareous matters. Is there a defect of calcareous matter, the remedy 

 is obvious. Is an excess of vegetable matter indicated, it may be re- 

 moved by liming, paring, and burning. Is there a deficiency of vege- 

 table matter, it is to be supplied by manure." — [Agricultural Chemistry, 

 Lecture 1.] 



What was true in regard to the applications of chemistry in the time 

 of Sir Humphry Davy is more true in a high degree of the chemistry 

 of our time. Not only is the nature of soils better understood, but we 

 know in many cases what a soil must contain before it will produce a 

 given crop. Why do pine forests settle themselves on the naked and 

 apparently barren rocks of Scotland and of Northern Europe, content if 

 their young roots can find but a crevice in the mountain to shelter them 1 

 Why does the beech luxuriate in the alluvial soils of Southern Sweden, 

 of Zealand, and Continental Denmark ? Why does the birch spring 

 up from the ashes of the pine forest — -why the rapid rush of delicate 

 grass from the burned prairies of India and of Northern America ? 

 Whence comes the thick and tender sward of the mountain limestone 

 districts — whence the gigantic wheat stalk of a virgin soil ? Why do 

 the same forest trees propagate themselves for ages on the same spots 

 without impoverishing the soil — why do the natural grasses, the longer 

 they are undisturbed, render he land only the more fertile ? 



These, one would think, aie scarcely cheiirical questions, and yet to 

 all of them, and to a thousand such, chemistry alone can and will give 

 a satisfactory answer. 



The rotation of crops is a practical rule, the benefit of which has 

 been proved by experience ; it becomes a true philosophical principle 

 of action, when we discover the causes from which this benefit springs. 

 Botany has thrown considerable light, and of an interesting and impor- 

 tant kind, upon this practice, but chemistry has fully cleared it up and 

 established the principle. 



Sir Humphry Davy speaks of the use of lime. Can you explain the 

 mysterious, and apparently fickle and diversified, agency of this sub 

 stance in reference to vegetation ? Are the advantages so frequently 

 attendant upon its use to be ascribed to the chemical character of ihe 

 soil to which it is applied, to the kind and quantity of the vegetable 

 matter it contains, or to the geological nature of the rocks on whicn it 

 rests? Are they dependent upon the drainage and exposure of the 



