On Agricultural Chemistry. 



259 



of potash or soda, though the course he would probably adopt 

 would indh'ectly increase the available sources of those sub- 

 stances. 



The quantity of alkalies taken up from the soil by a crop of tur- 

 nips is very great, and yet the artificial manures most commonly 

 applied to grow these turnips contain but little and often no alkalies 

 whatever. As long as bone-dust, superphosphate of lime, or guano, 

 will produce a good crop of turnips, the farmer need be under no 

 apprehension of his soil being destitute of alkalies. The only 

 mineral which, under a proper system of agriculture, it is neces- 

 sary to restore directly to the soil, is phosphate of lime. Where 

 large breeding flocks are kept, the phosphate of lime exported in 

 the bone of the animal is very great, and many soils are incapable 

 of yielding this in sufficient quantity. Previously to the intro- 

 duction of guano into this country, large quantities of nitrate of 

 potass and soda were employed as manures. Their value was, 

 by many persons, attributed to the alkalies they contained ; but 

 the almost universal substitution of guano shows very clearly that 

 the potash and soda were not the constituents to which their 

 effects were due. At one time I thought it probable that the 

 silicates of potash or soda might prove of some service to grain 

 plants, but repeated experiments with these substances have 

 caused me to alter my opinion. 



The strength of the straw in grain crops seems to depend upon 

 a healthy condition of the plant, arising from a properly balanced 

 supply of mineral and organic constituents, as well as upon the 

 influence of certain physical conditions of soil, especially during 

 the early stages of growth. Thick sowing, a cold wet summer, 

 and excess of ammonia, are all injurious to the strength of 

 straw. 



Unless straw is sold, there is a constant accumulation of silicate 

 of potash upon farms, arising from the annual decomposition of the 

 soil ; and upon some farms the production of straw increases to an 

 injurious extent. It is a common opinion, that artificial manures 

 act as stimulants, and that the continual employment of them 

 tends to exhaust the soil. This idea is to a certain extent correct ; 

 and where they are used injudiciously (as, for instance, when a 

 mineral manure is employed upon corn crops) it would lead to 

 such a result. But if they are employed to increase those crops 

 which are consumed upon the farm, such as turnips and clover, 

 they then become valuable aids to the natural resources of the 

 farmer. 



To obtain agricultural crops of clover, tares, and turnips, 

 purely artificial conditions of growth, quite at variance with the 

 natural tendency of the plant, are induced : and it is w^ell known 

 that the crop of clover which will yield the most hay is by no 



