28 FIELD, FOREST AND FARM 



soil contains humus. Wheat requires nearly eight 

 per cent, oats and rye only two per cent. In poor, 

 sandy soils, to increase the amount of vegetable 

 mold, it is customary to plow certain green crops 

 under, as the farmers express it ; that is, the surface 

 soil is turned over and the growing crop intended 

 for manuring purposes is buried and left to decay 

 in the ground. That is what is done when the plow- 

 man turns under a field of growing grass or a stretch 

 of clover. When it is proposed to improve a piece 

 of land by this process, it is the practice to begin by 

 raising a crop (which will later be turned under) 

 that derives the greater part of its nourishment from 

 the air, since the soil in this instance cannot of itself 

 furnish this nourishment. Among the plants satis- 

 fying these conditions are buckwheat, clover, lupine, 

 beans, vetches, lucerne, and sainfoin. 



' ' Soils rich in humus have for their chief constitu- 

 ent the brown substance that results from the decay- 

 ing of leaves and other vegetable matter. Turf land 

 stands first as rich in humus. Turf is a dark, 

 spongy substance that forms in moist lowlands from 

 the accumulation of vegetable refuse, especially 

 mosses. Turf, or peat, as it is also called, is used 

 for fuel. To turn such a soil to account, it must first 

 be made wholesome by drainage, it must be mellowed 

 by paring and burning and by the addition of sand 

 and marl, and a proportion of lime must be mixed 

 in to hasten the decomposition of all vegetable mat- 

 ter. Turf lands are recognized by their sphagnei, 



