I76 JOURNAL. OF THE ROYAL HORTICULTURAL SOCIETY. 
in other countries green manures are widely used, notably in many 
tropical countries where animal manure is scarce or unobtainable. 
The literature of green manuring is extensive, and it is not 
proposed to review it in detail here. The benefits to the soil of 
burying a green crop are well known ; not only is a wealth of humus- 
forming material added to the soil, with the consequent beneficial 
effect on the texture of the soil and on its water-retaining and 
drought-resisting qualities, but also much of the nitrogen which 
would otherwise have been leached out of the soil and lost is stored 
up in the green crop, to be restored to the soil when the crop is 
buried ; if the green crop is a leguminous one a considerable further 
addition is made to the nitrogen of the soil by the activities of the 
nodule-bacteria which " fix " atmospheric nitrogen and pass it on to 
the green crop. Although, in a general sense, these facts are well 
known, much work is needed to determine the best practical methods 
of green manuring in this country. These methods will necessarily 
vary widely according to a variety of factors, such as the type of 
soil, the climate, the time of the year, and so on. 
The results reported in this paper were obtained in the first year 
of an investigation which was started by the author at Wisley in 
1 91 9, with the double object of demonstrating the value of green 
manuring on a light soil, and of ascertaining the most suitable crops 
and the best methods of applying them on such a soil, in horticultural 
practice. This investigation at Wisley is intended to go on for a 
number of years. 
In those tropical countries where green manuring is widely prac- 
tised, leguminous crops are almost exclusively used ; such crops 
would certainly be expected to have a decided advantage over non- 
leguminous ones by virtue of the extra nitrogen added to the soil 
by equal amounts of organic matter, provided that the soil conditions 
are constant. That the soil type is a factor of importance in this 
connexion is demonstrated by the results of the experiments carried 
out in this country at Rothamsted by Hall,* and at Woburn by 
Voelcker.f On the heavy Rothamsted soil a leguminous crop, 
vetches, gave better results than a non-leguminous crop, mustard. 
At Woburn, on a light sand, the opposite was found. The main 
object of the original scheme of experiments at Wisley was to test 
this point, but circumstances suggested the division of the experi- 
ment into two parts, in which the green crops were buried in early 
winter and in spring respectively ; so that it was also possible to 
compare the relative values of these two times of application. 
Outline of Experiment. 
The soil of the experimental plot was light sand (Bagshot sand) . It 
contained less than o*i per cent, of calcium carbonate, and about 
* Journ. Bd. Agr., 17, p. 969 (191 1). 
f See e.g. Journ. R. Agr. Soc. Eng., 73, p. 304 (1912). 
