306 HOAV CROPS FEED. 



that 99 per cent and more of the soil, exclusive of water, 

 does not in the slightest degree contribute directly to the 

 support of the present vegetation of our ordinary field 

 products. 



The hay crop is one that takes up and removes from 

 the soil the largest quantity of mineral matters (ash- 

 ingredients), but even a cutting of 2^ tons of hay car- 

 ries off no more than 400 lbs. per acre. From the 

 data given on page 158, we may assume the weight of 

 the soil upon an acre, taken to the depth of one foot, 

 to be 4,000,000 lbs. The ash-ingredients of a heavy 

 hay crop amount therefore to but one ten-thousandth of 

 the soil, admitting the crop to be fed exclusively by the 

 12 inches next the surface. Accordingly no less than 100 

 full crops of hay would require to be taken off to consume 

 one per cent of the Aveight of the soil to this depth. "We 

 confine our calculation to the ash-ingredients because we 

 have learned that the atmosphere furnishes the main sup- 

 ply of the food from which the combustible part of the 

 crop is organized. Should we spread out over the surface 

 of an acre of rock 4,000,000 lbs. of the purest quartz 

 sand, and sow the usual amount of seed upon it, maintain- 

 ing it in the 2:)roper state of moisture, etc., we could not 

 produce a crop ; we could not even recover the seed. Such 

 a soil would be sterile in the most emphatic sense. But 

 should we incorporate with such a soil a few thousand 

 lbs. of the mineral ingredients of agricultural plants, to- 

 gether with some nitrates in the appropriate combinations 

 and proportions, we should bestow fertility upon it by this 

 addition and be able to realize a crop. Sliould we add to 

 our acre of pure quartz the ashes of a hay crop, 400 lbs., 

 and a j^roper quantity of nitrate of potash, we might also 

 realize a good crop, could we but ensure contact of the 

 roots of the plants with all the added matters. But in 

 this case the soil would he fertile for one crop only, and 

 after the removal of the latter it would be as sterile aa 



