THE CULTIVATION OF FARM CROPS. 



cleaning of the land. It is a plan often resorted to in order to obtain sheep 

 keep, but it should only be practised when the land is clean, and if con- 

 rinued it is apt to render it foul. 



THEORY OF ROTATIONS. 



1. When we compare the composition of some of our ordinary crops with 

 each other, we find that the proportion of ash ingredients and nitrogen 

 differ widely. This is in itself a key to one of the advantages of a rotation. 

 If the same crop be grown year after year upon the same field, the soil is 

 called upon to deliver up certain constituents in large quantities, while- 

 others are allowed to remain untouched. Turnips remove five times, bean< 

 three times, and oats twice as much potash from a soil as wheat. Oats 



lire almost five times as much lime as wheat ; and barley takes twenty- 

 times the amount of silica from the land as an equivalent crop of 

 wheat. Such illustrations might be multiplied, but the above example- 

 sufficiently show that a succession of crops must be a relief to the drain 

 upon certain constituents. 



2. Plants search for their food differently. A plant which feeds in the 

 upper layers of the soil, like peas or barley, is not likely to exhaust land 

 for deeper-rooted crops, such as beans or red clover. The contrast between 

 the root distribution of wheat and barley has been noticed by Mr. Law.-- 



Dr. Gilbert, who grew these two plants in pots. Only one fibre of 

 barley found its way through the bottom of the pot, but " the wheat th: 

 out such a mass of ramifications that the whole surface of the dish in 

 which the pot rested was covered with a thick network of roots, as also 

 the bottom, and to a great extent the sides of the inside of the pot 

 f. Tin- barley roots were congregated near the surfaiv, and were n 

 ML, r ly d-vi-lnj 



in plants or crops aiv .specially fitted to precede others. 1 

 ininous . beans, p''as, and clover are, for example, excellent piveur- 



wh.-at. Tin- reason la thai these plants have a store of nitrogen 

 wheat crup, in the form of roots, and through the fall of 

 leaf during thi-ir irn.wth. A. good OTOp of do V61 in seem 



<od crop of wheat. Turnips and other root crops and potatoes are 

 tin- aft | ._rj-.-iin oropA Henee we shall find in most 



D of rrps is determined by the natun- of the 

 dim: crop. 

 4. Certain Cl DQ to injure the soil for other crop 



iniilar to eaeh ot her do not IUOC 1 \\ell in 



