The Effect of Climate and Weather on the Soil. 13 
temperature easily obtained in hot regions. Right from the 
outset the dried and sun-baked soils gave the best results, and 
a .photograph of the crops taken at the end of the season is 
shown in Fig. 3. 
These are the same kind of results as we get with partially 
sterilised soils, and it is probable that the same cause is at work 
in both cases. 
However, we do not often get summers like 1911, and crop 
increases of this size must necessarily be exceptional in this 
country, although they could more regularly be obtained in 
hot regions. 
The remarkable fact has recently been brought out that the 
manufacture of nitrates in the soil (which, as we have seen, is 
an indispensable process for the welfare of the crop) takes 
place most rapidly in our climate in late spring or early 
summer. It then slackens down while the plant is growing, 
but it may speed up again in autumn, especially in such an 
autumn as 1913. The amount produced in spring is of the 
most importance, because this is the time of most rapid nitrate 
production. If for any reason only a small quantity is formed 
then the amount tends to remain low throughout the year, 
with consequent loss of fertility. On the other hand, if the 
amount runs up high the plant has plenty of food to draw 
upon, although of course it may still fail if the season is bad. 
Now the quantity of nitrate formed in spring depends partly 
on the weather at the time, as this regulates the activity of the 
organisms, partly on the weather of the preceding winter, and 
also on the wetness of the land. As the soil becomes moist 
the pores fill with water, so that there is less room for air, and 
finally when the soil becomes really wet the air supply in the 
pores is much reduced, and may become too small for active 
nitrate formation. So much for the effect of spring. 
Now for the effect of the summer. In a dry summer the 
nitrate formed is all left in the soil or taken by the crop ; in a 
wet summer some of it leaches out. These results are well 
illustrated by a comparison of the nitrates present on one of 
the Rothamsted plots during the wet summer and autumn of 
1912 with the amounts present in the dry summer of 1913. 
These particular plots are unmanured and have been for long 
past ; both were fallow during the summer. The amount of 
nitrate present in the top eighteen inches of soil was equivalent 
to the following quantities of nitrate of soda, in lb. per acre : — 
Dry summer, 1913 
Wet summer, 1912 
Feb. May Sept. 
126 312 378 
180 138 114 
Difference in favour of dry summer, reckoned 
as nil rate of soda, lb. per acre 
174 264 
93355 
