104 Bulletin 174. 



izei's. It is enough for the present to saj that tlie roots which are 

 left in the ground after the crop is harvested are very valuable in 

 improving the soil. This is particularly true if they are tap-roots, 

 — if they run deep into the soil. Clover bores holes into the soil, 

 letting in air, draining it, warming it and bringing up its plant-food. 

 Roberts reports (" Fertility of the Land," p. 345) that a second 

 growth of clover, two years from seeding, gave a yield of air-dried 

 tops of 5,417 lbs. per acre, and of air-dried roots 2,868 lbs. in the 

 first eight inches of soil. Add to this latter tigure the weight of 

 roots below eight inches and the stubble of waste, and it is seen that 

 the amount of herbage left on the clover field is not greatly less than 

 that taken off. In this instance, the roots contained a greater per- 

 centage of nitrogen and phosphoric acid than the tops, and about 

 the same percentage of p(jtash. 



Make an estimate of what proportion of the plant growth you 

 raise is actually taken off the field. Figure up, as accurately as you 

 can, the part left in roots, stubble, leaves, and refuse. Even of 

 maize, you do not reincve all from the field. This calculation will 

 bring up the whole question of the kind of root-system which each 

 sort of plant has. Have you ever made a close examination of 

 the roots of potatoes, maize,, wheat, clover, cabbages, buckwheat, 

 strawberries, Canada thistles, or other crops ? From what part of the 

 soil do these plants secure their nourishment ? What power have 

 they of going deep for water? What proportion of them is root? 

 Because the roots are hidden, we have neglected to examine them. 



10. Tlie soil is j^lant-food j hut this food hecomes tisahle or 

 available slotoly. — Roberts has compiled the analyses of 49 repre- 

 sentative soils, made by American chemists, and the following is 

 the result : " The tables reveal the fact that even the poorer soils 

 have an abundance of plant-food for several crops; while the richer 

 soils in some cases have sufficient for two hundred to three hundred 

 crops of wheat or maize. The average of 34 analyses gives to each 

 acre of land, eight inches deep, 3,217 pounds of nitrogen, 3,936 

 pounds of phosphoric acid, and 17,597 pounds of potash, and this 

 does not include that which is contained in the stones, gravel and 

 sand of the soil which will not pass through meshes of one-fiftieth 

 of an inch, which, by weathering and tillage, slowly give up their 

 valuable constituents." — Roberts, " Fertility of the Land^'' p. 16„ 



