n8 TILLAGE— MOVEMENTS OF SOIL WATER [chap. 



It is thus seen that in both cases the dunged soil, 

 rich in humus, had retained more of the comparatively 

 recent rainfall near the surface, so that the top soil was 

 moister while the subsoil was drier. The difference 

 in favour of the surface soil was about 3-5 per cent, which 

 on that soil would amount to about 30 tons per acre, 

 or approximately 0-3 inch of rain. It is thus seen 

 that the surface soil of the dunged plot had retained 

 practically the whole of the preceding rainfall ; and 

 the greater dryness of the subsoil was due to the way the 

 soil had kept back the small rainfalls, which have 

 been evaporated instead of passed on to the subsoil 

 as they were on the unmanured plots. The same fact 

 is illustrated by the behaviour of the drains which run 

 below the centre of each of the wheat plots at a depth 

 of 30 inches ; below the dunged plot the drain very 

 rarely runs, only after an exceptionally heavy and 

 long - continued fall, whereas the drain below the 

 unmanured plot runs two or three times every winter. 

 Putting aside the greater drying effect of the much 

 larger crop on the dunged plot, the difference is mainly 

 due to the way the surface soil rich in humus first 

 of all absorbs more of the water, and then lets the 

 excess percolate so much more slowly that the descend- 

 ing layer of over-saturation, which causes the drain to 

 run, rarely or never forms. 



The water-retaining power of the dung may also 

 be seen in the superior yield of the dunged plots 

 in markedly dry seasons. The following table shows a 

 comparison of the yield on plot 2, receiving 14 tons 

 of dung, and plot 7, receiving a complete artificial 

 manure, for the years 1879, which was exceptionally 

 wet and cold, and 1893, which was hot and dry 

 throughout the growing period of the plant The 

 rainfall for this period, /.&, for the four months March 



