316 



EXPERIMENTS OX TUENIPS. 



Notwithstanding the much larger quantity of tricalcic phos- 

 phate applied as ground mineral, the dissolved phosphates 

 produced on the average about 8 per cent, more turnips in 1882.. 

 and 3 per cent, more in 1883 ; and it makes little difference 

 whether the plots receiving artificials alone are considered or the 

 dunged plots included in the average. If plot 9 in 1882, 

 previously mentioned, were excluded from the comparison, the 

 average superiority of superphosphate in that season would be 

 increased to about 10 per cent. 



It has been mentioned that in 1883 the ground mineral was 

 comparatively dearer than the superphosphate. The small 

 additional quantity of tricalcic phosphate that might have been 

 added to the ground mineral plots would probably have gone 

 far to increase the average yield from them by 17 cwt., and so 

 make them equal to the superphosphate plots. In any case, much 

 dependence cannot be placed in a difference of 3 per cent, in 

 field trials ; and ground mineral may be said to have had 

 ultimately as good an effect as an equal money value of super- 

 phosphate on the experimental ground of 1883. A long grow- 

 ing season and a large crop seem to favour the ground mineral 

 phosphate, as in that case advantage is taken of the large amount 

 of phosphates that can be supplied in that form. On this class of 

 soil, however, under circumstances the most favourable for ground 

 mineral, an equal money value of superphosphate has so far 

 produced at least as heavy a crop, and unless it can be shown 

 that future crops are better on the ground mineral plots there 

 seems no reason to desert the dissolved in favour of the ground 

 phosphates. It may also be adduced in favour of superphos- 

 phate that in loth seasons the plants on the plots receiving the 

 manure grew more rapidly at first, and were decidedly larger 

 when singled than on the ground mineral plots, and had they 

 been attacked by fly would probably have struggled more 

 successfully against it. 



Four plots — Nos, 7, 8, 21, and 22 — were added to the experi- 

 ment to decide whether a mixture of soluble and insoluble 

 phosphates was better than either alone. 



