MANURES, THEIR KINDS AND USES. 23 



Rich alluvial soils with decaying vegetable matter con- 

 tain ten times as much, and fertilized field soils still 

 more. Ammonia is only found in the surface soil, and 

 generally at a depth of six feet there is no trace of it. 



Sir J. B. Lawes found that in one year the drain water 

 took nitrogen from a field bare of vegetation at the 

 rate of forty pounds per acre; from a field of wheat, 

 which after the harvest contained no weeds, twenty-five 

 pounds, and from a field upon which grass seed had been 

 sown with the wheat, and continued to grow on the stub- 

 ble field, only five pounds. 



POUNDS OF NITROGEN WASHED AWAY PER ACRE. 



From soil without vegetation 40 pounds. 



From soil with wheat, 15 pounds retained by crop. .. 25 " 

 From soil and grasses, 15 pounds retained by wheat. 



25 pounds retained by grasses 5 



He found that the drain water was much richer in am- 

 monia than the rain water which fell upon the field. * He 

 also found another fact of importance to our subject of 

 green-manuring, that the drain water carried away more 

 ammonia in the fall than in any other part of the year. 

 It is therefore exactly at this season that the soil of the 

 truck-farmer should be covered by a dense growth of 

 vines. It has been shown that even a perfectly inert 

 body, like a board, lying upon the surface will improve 

 the fertility of the soil, by preventing evaporation. 



Now the mulch of pea vines acts like the covering of 

 snow. It shades the soil from the rays of the sun, by 

 which the volatile elements of fertility are exhausted with 

 the vaporized water; it keeps the soil moist, mellow, and 

 of even temperature; and as a secondary matter prevents 

 the growth of troublesome weeds. The friable, unbaked 

 condition of the surface, as has been before stated, is an 

 element of fertility, by facilitating the absorption of fer- 

 tilizing gases from the atmosphere. Under this dense 

 covering, so retentive of moisture, the carbonic acid dis- 

 integrates particles of the soil and prepares it for plant 



