IRRIGATION. PLANTING. COST. 95 



317. The amendments suited to light, dry, siliceous 

 lands, are clay, as already suggested, to give them cohe 

 sion, and argillaceous marls, whenever they are to be had. 

 Irrigation not only gives moisture to a dry soil, but 

 always brings useful additions in the substances which 

 have been dissolved in the water and are deposited when 

 the water is at rest. 



318. Planting with trees, especially planting dry, barren 

 hills with forest trees, permanently increases the moisture, 

 not only of the surface covered by the trees, but of the 

 neighborhood, and thus improves the climate. Draining 

 is a valuable amendment. 



319. In reference to a proposed amendment, the ex 

 pense must be calculated, and the question must be 

 settled whether the increased produce will pay for the 

 outlay. 



When the materials are near at hand and it will cost 

 little to get them and transport them, the question is 

 easily settled. 



320. The character of the amendment must also be 

 considered. A sandy soil amended by the addition of 

 clay becomes permanently better. The clay can never 

 be exhausted, and will always give to the soil the power 

 of absorbing and retaining the elements of the food of 

 plants. 



An amendment produced by the introduction of humus 

 or any form of carbonaceous matter will give value to 

 the land, as long as it continues to be well cultivated and 

 manured, but, like manure, the added matter is liable to 

 be exhausted. 



The quantity to be used will vary with the depth of 

 ploughing. 



9* 



