286 



IT. 



^ 



Of the different Grasses^ imd other Plants^ adapted for the Alternate 



Musbandry. 



e 



e 



The grasses, and other plants, best fitted for alternation, as green crops with grain are 

 such as arrive at perfection in the shortest space of time, or within the compass of two years • 

 such as have their leaves broad and succulent, and that do not quickly run to seed. Plants of 

 this description are supposed to produce the greatest weight of herbage at the least expence to 

 the soil. 



It is a curious and well-known fact, that any species of plant that has continued till its natu-. 

 ral decay on a particular soil, cannot be again immediately reared with equal success on th 

 same spot, till some other crop intervene ; but that a different species of vegetable will ther 

 succeed better, for its peculiar period of life, than it would on a soil naturally better adapted to 

 its growth, where it had just attained to perfect maturity. This holds good with respect to 

 annual plants as well as to those that continue to live many years. But it is better seen in th 

 former, as their habits and duration in the soil are oftener and more directly within the reach of 

 common observation. 



On this antipathy of plants seems to depend the theory of alternate cropping Avith green 

 crops and grain, varying in some measure according to the circumstances of soil and climate; 

 but the principle appears to remain the same. 



On analyzing a soil immediately before and after producing an impoverishing crop, the re- 

 suits of such analysis do not point out any diminution in the weight or proportions of its consti- 

 tuents, sufficient to account for the weight of vegetable matter produced. The decomposing 

 animal and vegetable matters of the soil^, are the only constituents wherein a sensible loss is per- 



ceived. , 



M. Braconnot grew plants in substances free from any kind of soil, as in flowers of sulphur, 



, w 



r ■ 



and in metal. He supplied the plants with distilled water only. They arrived, by these means, 

 to a perfect state of maturity. The produce was submitted to careful analysis; and the results 

 shewed that the different vegetables so produced, contained all the constituents of the different 

 species, precisely the same as when the plants were cultivated on their natural soils ^. 



Some have supposed that the antipathy of plants arises from the roots depositing a noxious 



4 



matter in the soil. And according to the experiments of M. Burgmanns, Oats are thus killed by 

 the Field Saw-wort; Wheat by the Blue Erigeron; Flax by the Corn Scabious, and the Purple 

 Spurge; and Buck- wheat by the Corn Spurry. 



The analysis of a plant, therefore, and of the soil which produced it, appear insufficient to 

 account for the true cause of the impoverishing principle of vegetables to the soil, and why one 

 species should exhaust it more than another. 



Some useful information, however, on this very interesting point, may probably be drawn 

 from facts obtained by daily practice and observation in the warden and the farm. 



* Annales de Chimie, Fcv. ct Mars, 1808. 



