140 THE GRASSES OP TENNESSEE. 



quantity of nitrogen, amounting to tons, is accumulated in the surface 

 soil, and the better the clover crop the greater is the accumulation of 

 nitrogen. In one of my experiments I tried to determine the amount of 

 nitrogen which is left in the portion of a field where the clover was 

 comparatively poor, and I fonnd that on the brow of the hill in that field, 

 (for it had a considerable declivity), where the clover was weak the 

 amount of nitrogen per acre was 1 ton, 11 cwt., 99 lbs, while at the 

 bottom of the hill where the clover was stronger, there being more soil, 

 it was 2 tons, 2 cwt. and 61 lbs. Observe too, that at the . bottom of 

 the hill the wheat was always better. Now it is in virtue, I believe^ of 

 this nitrogen that the wheat grew so much more luxuriantly. 



Dr. Voelcker, in his very able article, sums up the con- 

 clusions at which he arrived in the following words : 



1. A good crop of clover removes from the soil more potash, phos- 

 phoric acid, lime, and other mineral matters, which enter into the com- 

 position of the ashes of our cultivated crops, than any other crop 

 usually grown in this country. 



2. There is fully three times as much nitrogen in a crop of clover as 

 in the average produce of the grain and straw of wheat per acre. 



3. Notwithstanding the large amount of nitrogenous matter and of 

 ash-constituents of plants in the produce of an acre, clover is an ex- 

 cellent preparatory crop for wheat. 



4. During the growth of clover a large amount of nitrogenous mat- 

 ter accumulates in the soil. 



5. This accumulation, which is greatest in the surface-soil, is due to 

 decaying leaves dropped during the growth of clover, and to an abun- 

 dance of roots, containing when dry from If to 2 per cent, of nitrogen. 



6. The clover roots are stronger and more numerous, and more 

 leaves fall on the ground when clover is grown for seed, than when it 

 is mown for hay ; in consequence more nitrogen is left after clover 

 seed than after hay, which accounts for wheat yielding a better crop 

 after clover seed than after hay. 



7. The development of roots being checked when the produce, in a 

 green condition, is fed off by sheep, in all probability leaves still less 

 nitrogenous matter in the soil than when clover is allowed to get riper 

 and is mown for hay ; thus, no doubt, accounting for the observation 

 made by practical men that, notwithstanding the return of the produce 

 in the sheep excrements, wheat is generally stronger and yields better 

 after clover mown for hay than when the clover is fed off green by 

 sheep. 



8. The nitrogenous matters in the clover-remains on their gradual 

 decay are finally transformed into nitrates, thus affording a continuous 



