MANURING AND FERTILIZING 31 



a shallow- rooted root crop. The facts that the potato 

 is a starch-producing crop, and that its period of 

 growth is through the summer and extending well into 

 autumn must be remembered. In these features it is 

 similar to corn, but distinctly different from the cereals 

 which ripen in the summer, as it is assumed that it is 

 able to utilize the nitrates and other plant-food liber- 

 ated during the summer and fall. E. Hecke' states 

 that the demand for nitrogen is especially strong dur- 

 ing the first half of the vegetative period, while the 

 demand for potash is greatest during the second half 

 of the growing period, and that potash aids in the for- 

 mation of starch, and especially in the development of 

 tubers and roots, although the effects were observed in 

 all parts of the plant. 



The Influence of Nitrogen. Wilfarth' showed 

 that when the supply of nitrogen is insufficient the 

 leaves tend to turn yellow, and that if the available 

 supply of potash is deficient heavy applications of nitro- 

 gen tend to reduce the percentage of tubers and starch. 

 L,awes and Gilbert 3 show that nitrogen stimulates the 

 production of starch, provided the mineral constituents 

 are not deficient; but in large quantities nitrogenous 

 fertilizers stimulated luxuriant growth, delayed matur- 

 ation, and produced potatoes richer in nitrogen and 

 much more liable to disease. At the Rhode Island 

 Experiment Station 4 dried blood ranked first of the 

 nitrogenous fertilizers applied, followed by nitrate of 

 soda and sulphate of ammonia; but on soils said to be 

 extremely acid, dried blood was only about half as 



J E. S. R., VII., p. 667. E. vS. R. XIV., p. 561. 



3 Rothamsted Memoirs, Vol. VI. * R. I. Bui. 65, pp. 133, 134. 



