VALUE OF I'OI'ASIl I II 



half of the diagram ivfrrs to {\w second [x'riod, ls<i;, 1 <)():.'. 

 when potash was being used on Plot '2. 



The dotted cohimns in the diagram rei)reHent tlie crops on 

 Plots 1, where no mineral manm-es are used witli the (hing ; the 

 cross hatched columns represent Plots 2, to wliicli in the first 

 period superphosphate was added ; the black columns the 

 same Plots 2 in the second period, wdien potash was also being 

 employed. Each of the pairs of columns represents a dilfcrent 

 nitrogenous cross-dressing. 



From the left-hand half it is evident that superpliosphate 

 when used with dung has produced no effect upon the crop 

 during the nineteen years of the first period. With no other 

 nitrogenous manures, or when nitrate of soda is used as a 

 cross-dressing, there is a small increase from the use of super- 

 phosphate, but it seems to cause even a faUing-off wlien added 

 to ammonium-salts or rape cake and dung. 



Turning now to the effect of sulphate of potash when added 

 to dung, as represented by the right-hand diagram in Fig. IG, 

 we find that the potash produces a very marked effect. During 

 this last period the crops on Plots 2, receiving potasli and 

 phosphates, have been much superior to those on IMots 1, 

 receiving dung alone ; although in the earlier period, when 

 phosphates but no potash were used on 2, the two series of 

 plots were practically equal. The increase caused by potasli is 

 naturally most seen in Series O, A, C, and AC ; in Scries N, 

 which is cross-dressed with nitrate of soda, nuich less benefit 

 is seen for the addition of potash. 



Considering the large amount of potash contained in <hmg, 

 and the enormous residue which must have accumuhited by 

 the yearly application of 14 tons per acre for the last forty-seven 

 years, the result is very striking, as showing the dependence of 

 the mangel crop on an abundant supply of potash. The a|t|)Ii<a- 

 tion of farmyard manure is generally considered to supply 

 sufficient potash to remove the need for any further spccitic 

 manuring with potash salts even to so potash-loving a crop as 

 mangels, but these experiments show that even when (hmg has 



