108 EXPERIMENTS UPON ROOT-CROPS 



it induces. If we compare the plots receiving potash, viz., 4, 

 6, and 7, those which are cross-dressed with ammonium-salts 

 are dead ripe and the leaves all yellowing off, when the corre- 

 sponding nitrate of soda plots are still green and growing 

 vigorously. The droughts and heat of the summer and the 

 autumnal fall of temperature all have a greater effect on the 

 more shallow -rooted mangels grown with ammonium -salts, 

 and bring their growth to an earlier conclusion ; the pro- 

 longed growth with the nitrate of soda helps also to explain 

 the greater weight of produce on these plots. If, however, 

 we compare the appearances presented by the mangels grown 

 with nitrate of soda and with ammonium-salts on Plots 5 and 

 8, where the manure contains no potash, the nitrate of soda 

 plants are far healthier and more mature. In this case the 

 nitrate of soda seems to be also able to do some of the work of 

 the potash, both by enabhng the plant with its extended root- 

 range to draw more freely upon reserves of potash in the soil 

 and subsoil, and also by the soda acting itself as a potash 

 substitute, or perhaps more correctly, as a potash economiser. 

 Here, with no potash supplied, the superiority of the plots 

 receiving nitrate of soda over the corresponding plots with 

 ammonium-salts has been a progressive one, increasing from 

 year to year ; while the relative effect of nitrate of soda and 

 ammonium-salts when potash is also supplied in the manure 

 is constant, or only varies with the character of the seasons, 



D. Efect of Nitrogenous and Mineral Manures when used in 

 Conjunction with Dung. It has already been indicated that the 

 crops on plots receiving dung are on the average much better 

 than those grown with artificial manures only. To a large 

 extent this is due to the imjDrovement in the texture and water- 

 retaining capacity of the soil which has been effected by the 

 repeated application of farmyard manure. The seed always 

 germinates better on these jDlots and grows away at an earher 

 date, so that in some years of great heat and drought, like 

 1895 and 1901, a crop is obtained on the dunged plots when 

 the plant fails almost entirely on the plots receiving no organic 



