222 EFFECT OF A FOUR-YEARS' COURSE. 



BAKLBY. WHEAT. 



Turnip . . Red Rye , . Total. 



Roots. Grain. Straw. Clover. Grass. Grain. Straw. 



Potash 145-5 5-6 4-5 45-0 28-5 3-3 0-6 233-0 



Soda 64-3 5-8 1-1 12-0 90 35 09 96-6 



Lime 45-8 2-1 12-9 63-0 16-5 1-5 7-2 149-0 



Magnesia. . . . 15-5 3-6 1-8 7-5 2-0 1-5 1-0 32-9 



Alumina .... 2-2 0-5 3-4 0-3 0-8 0-4 2-7 10-3 



Silica 23-6 23-6 90-0 8-0 62-0 6-0 860 299-2 



Sulphuric Acid . 490 1-2 2-8 10-0 8*0 0-8 1-0 72-8 



Phosphoric do. . 22-4 4-3 3-7 15-0 0-6 0-6 5-0 51-5 



Chlorine .... 14-5 0-4 1-5 8-0 0-1 0-2 0-9 25 6 



970-9* 

 On comparing the numbers in the last column — containing the total 

 quantity of matter abstracted — with those contained in the three years' 

 rotation (p. 221), we see how very much larger an addition must be 

 made to the land every fourth year, if we are to restore to it any thing 

 like an equivalent for the inorganic matter carried off'. 



It will be especially observed that the quantity of potash, and of soda, 

 and indeed of nearly every ingredient except the. silica, carried off in 

 this course of cropping, is much greater, even in proportion to the time 

 it occupies, than in the three-year shift — and that nine-tenths of the pot- 

 ash and soda withdrawn from the soil are contained in the green crops. 



To place the relative effect of the green and corn crops upon the soil 

 in a clearer light, I shall exhibit the several quantities of common and 

 artificial salts and manures which it would be necessary to add to each 

 acre at the beginning of this rotation, in order to supply the various inor- 

 ganic substances about to be taken from the land in the next four years' 

 cropping. These quantities are as follow, in pounds : — 



For the . For the 



Total. Green Crops. Com Crops. 



Dry Pearl-ash ..... 325 316 9 



Crystallized Carbonate of Sodaf 333 290 43 



Common Salt 43 38 5 



Gypsum — 30 — 



Quick-Hme 150 100 7 



Epsom Salts 200 150 ' 50 



Alum 83 27 56 



Bone-dust 210 150 60 



"With the exception of the silica, the substances above-named, in the 

 quantities given, will replace all the inorganic matters contained in the 

 whole crop reared, the turnip tops alone not included. A single glance 

 at the second and third columns shows how much greater a proportion 

 of all these substances is necessary to return what the green crops have 

 taken from the land. 



That the fertility of the soil depends in some considerable degree on 



* This is exclusive of the turnip tops, which I have omitted, from not knowing what pro- 

 portion their weight in the green state generally bears to that of the roots. 



t Or for every 100 lbs. of the common carbonate of soda may be substituted 40 lbs. of 

 common salt or 60 lbs. jI dry nitrate of soda. 



