94 
Field Experiments on Swedish Turnips. 
ness, it struck me as being well worth a trial, in comparison with 
the experiments on the more expensive coprolite powder. 
As the soil contained only about 1 per cent, of carbonate of 
lime, and as chalk, in many instances, has a good effect upon 
root-crops, and was procurable in the neighbourhood of Woburn 
at a cheap rate, a moderate dressing of chalk was put upon two 
of the quarter-acre plots. In making field-trials exclusively with 
phosphatic fertilisers, it may be maintained with some reason 
that the more or less complete failures with a purely phosphatic 
manure do not necessarily prove its ineflRcacy, for inasmuch as 
such a manure supplies only phosphoric acid and lime, or 
merely two constituents of plant-food, it cannot possibly pro- 
duce a healthy and abundant crop of swedes or other roots if 
the requisite amounts of potash, sulphuric acid, magnesia, and 
other mineral or ash-constituents of roots, and the needful pro- 
portions of organic nitrogenous plant-food for securing a good 
crop, do not occur in the land upon which the experiments are 
made. Thus, for instance, I showed, years ago, by actual field- 
experiments, that whereas superphosphate alone, applied to 
certain light soils, or potash alone, had comparatively little 
effect upon clover, the two united together produced a very 
satisfactory increase. 
As Warren-field possibly might have been deficient in one or 
more of the essential elements of plant-food, it appeared to me 
advisable to manure some of the quarter-acre plots with well- 
rotted dung, a perfect manure, which supplies all the organic 
and mineral constituents which are required for the healthy and 
vigorous growth of any kind of agricultural produce. 
As a heavy dressing of dung per acre is expensive, and even 
the best rotten dung contains but a small proportion of phos- 
phoric acid, it occurred to me to experiment upon the effects of 
a comparatively moderate dressing of rotten dung, supplemented 
by phosphoric fertilisers. Accordingly, quarter-acre plots were 
set aside, upon which half a dressing of dung and ground copro- 
lites were put, and others upon which dissolved coprolites were 
put in addition to the same amount of dung. 
Two of the 24 quarter-acre plots were left unmanured, and 
thus furnished experimental evidence of the root-growing powers 
of the land in 1880, unaided by farmyard-manure or any arti- 
ficial fertiliser. In field-experiments extending over a number 
of years, which I conducted at the Royal Agricultural Col- 
lege, Cirencester, and elsewhere, I generally found a mixture of 
superphosphate and Peruvian guano one of the best artificial 
manures that can be applied to light and loamy soils or mode- 
rately strong land, as a manure for root-crops. Although a 
mixture of superphosphate and Peruvian guano may not appear 
