112 EXPERIMENTS UPON ROOT-CROPS 



been applied continuously for a long time, the application of 

 potash will still result in an increase of crop. The appearance 

 of the crop is even more indicative of the value of the potash 

 dressing ; where it has been applied the crop is altogether 

 healthier and rijjer, especially where the excessive dressings of 

 nitrogen have been used. 



E. Proportion of Root to Leaf. At the time the crop is 

 lifted the leaves are weighed, then they are spread upon the 

 land to be ploughed in again. 



The amount of leaf grown is almost wholly dependent upon 

 the supply of nitrogen, and variations in the mineral manures 

 have but little effect. When the growth is normal, the weight 

 of leaf is about 20 per cent, of that of the root, and the more 

 the alkaline salts, potash, soda, and magnesia, are added in the 

 manure, the more thorough is the maturation of the crop and 

 the lower does the proportion of leaf become. The highest 

 proportion of leaf to root is shown on those plots which receive 

 .a comparative over-supply of nitrogen, but no alkaline salts, 

 potash, soda, or magnesia, to restore the balance of the 

 constituents of the manure. 



In good seasons when the crop of roots is large, the amount 

 of leaf shows little corresponding increase, hardly more than 

 would be accounted for by the comparative absence of blanks 

 <ind missed plant which characterises a good season. 



It is evident that when once the plant has developed a 

 .sufficiency of leaf, the difference between a good and a bad 

 season depends upon the rapidity with which the leaves can do 

 their work of carbon assimilation from the atmosphere, for all 

 the products of that action are at once passed on to the root 

 ^nd stored there, in the case of the mangel chiefly in the form 

 of sugar. A good season with a heavy yield of roots does not 

 involve any greater luxuriance of leaf than usual, just as, in a 

 similar manner, plots which grow a small crop of roots because 

 of the absence of alkaline salts may yet possess a normal 

 •development of leaf 



F. Proportion of the Nitrogen recovered in Crop to that 



