20 The Effect of Climate and Weather on the Soil. 
Given a sufficiently long spell of favourable weather at 
a convenient time a good man would soon improve matters 
considerably, but this is largely a matter of chance, and we 
want to have some means of soil treatment that will be 
helpful without having to depend on anything so tickle. 
Unfortunately only few experiments have been made in this 
direction, although it is a highly promising field that would 
well repay investigation. 
One very hopeful method is by a development of catch 
cropping or green manuring. While the land lies bare in 
a hot dry summer or a cold dry winter it is gaining benefits, 
but when it lies bare in a wet season it is losing. The results 
given in the preceding pages show that land may easily lose 
as much nitrogen as is contained in 300 lb. of nitrate of soda, 
or a 30 bushel wheat crop, while it lies bare between harvest 
and seed time. By putting a catch . crop in directly the 
harvest is over the main portion of this is saved ; the catch 
crop can be ploughed in and it then returns the whole of the 
nitrogen to the soil. This ought invariably to be done after 
a dry summer unless there is some very good reason to the 
contrary. 
During the very dry summer of 1913, some of the Rotham- 
sted land perforce lay fallow because the mangolds failed, and, 
later on, the swedes put in to take their place did. the same. 
But a great accumulation of nitrate took place, and in Septem- 
ber the amount present was equivalent to 600 lb. nitrate of 
soda per acre on one plot, and 420 lb. on another. This stock 
was obviously too valuable to risk, and in anticipation of 
the need for saving it mustard had been sown on such of the 
land as was available ; the vigorous growth as soon as the rain 
came was visible proof of the presence of abundant plant food. 
The mustard took up the nitrate and held it safe for the 
following spring. 
There is a further advantage of green manuring. So far as 
our present incomplete knowledge goes, the ploughed in green 
crop does very much towards maintaining the texture of the 
soil during a bad season and improving it afterwards. 
Thus green manuring has a steadying effect on the fluctua- 
tions of soil productiveness produced by bad seasons. This is 
well illustrated by a comparison of the wheat crop taken after 
clover (supplemented by artificial fertilisers) on the Agdell 
Field at Rothamsted, with that on the Broadbalk Field where 
no green crop is ever ploughed in but where a liberal dressing 
of artificials is given. On an average the Agdell plot gives 
a yield of 34f bushels against 29 on Broadbalk, and it is a 
much steadier crop. It has only twice fallen below 25 bushels, 
once in 1867 and again in that notorious year of disaster, 1879, 
