Phospliatic Manures for Root-Crops. 
41 
If we suppose the turnips to have been grown with 3 cwts. of 
superphosphate, containing 20 per cent, of soluble and an inappre- 
ciable amount of available insoluble phosphate, the manure will 
supplv 31 lbs. of phosphoric acid, and the remaining 9 lbs. must 
be derived from the soil. Yet although the larger amount of 
phosphoric acid contained in a crop of turnips accounts to some 
extent for this crop being more benefited bv phosphatic manures 
than wheat, I believe the principal cause of the more energetic 
and striking effect which such manures produce on root-crops 
than on cereals, more especially wheat, will be found in the 
different mode in which green and white crops take up food from 
the soil, and the different duration of their period of growth. 
The roots of wheat, as is well known, penetrate the soil to a 
much greater depth than the more delicate feeding-fibres of the 
roots of a turnip. Wheat, remaining on the ground two to three 
months longer than turnips, can avail itself for a longer period 
of the resources of the soil ; therefore in most cases the phos- 
phoric acid disseminated through the soil is amply sufficient to 
meet the requirements of the wheat-crop; whilst turnips, de- 
pending on a thinner depth of soil during their shorter period 
of growth, cannot assimilate sufficient phosphoric acid to come to 
perfection. This is, I believe, the main reason why the direct 
supply of readily-available phosphates is so beneficial to root- 
crops and not to wheat. 
This view of the matter, if I am not mistaken, gains strength 
by the fact that barley, a crop which in many parts of England 
is often sown late in the season, and generally later than any 
other v.hite crop, is much more improved by superphosphate 
of lime than oats or wheat. On late sown barley this fertilizer 
has a strikingly beneficial effect. When the land has not been 
well done before, or is naturally poor, and the barley backward, 
a top-dressing of 3 cwts. of superphosphate will be found most 
useful. In that case a still better manure will be a mixture of 
superphosphate and guano in equal proportion, applied at the 
rate of 3 to 4 cwts. as a top-dressing. A crop of barley does 
not contain more phosphoric acid than a wheat-crop, and yet I 
have repeatedly noticed the effects produced on it by the applica- 
tion to the preceding crop of 3 to 4 cwts. of superphosphate made 
entirely from mineral phosphates, and containing no ammonia 
whatever. Although the superphosphate was applied to the 
preceding root-crop, and no other manure with it, and the 
turnips were carried off the land, it nevertheless produced on the 
succeeding barley an effect as plainly visible as is the case when 
barley is top-dressed with nitrate of soda or sulphate of ammonia. 
Ammoniacal manures or nitrate of soda, 1 may state in 
passing, have never given a satisfactory economical result in my 
