TRANSACTIONS OF SUB-SECTION K. 713 
or beans once in each four years. Taking the plot which receives no 
nitrogen, but only phosphoric acid and potash, we obtain the following 
figures :— 
Nitrogen in Soil Average Production | Average 
——_ | || Removal 
1867, 1909, viper eae Wheat, seuad, | Barley, | Clover, || fs Bib 
lbs. lbs. per annum | bushels | ewts. bushels | cwts, | per annum 
- = | 
| 
3,240 3,522 +67 | 35°2 297 k 29 | 467 | 46°3 
Had the roots, straw, and clover hay been converted into manure and 
returned to the land, as would be the case in ordinary farming, there is little 
doubt but that the production would be raised to the usual English level of 
32 bushels of wheat, 34 bushels of barley, 12-13 tons of roots per acre. 
8. The Functions, Availability, and Conservalion of Soil Moisture in 
Crop Production. By Professor F. H. Kina. 
The author pointed out the great importance of soil moisture as a factor 
in crop production, not only in dry countries but in moist ones as well; 
indeed, it is doubtful if there are any agricultural soils to be found any- 
where where deficiency of available moisture is not, in most seasons, a 
marked limiting factor of yield. Water is not only an important plant 
food, but is also the medium in which all other plant food derived from 
the soil is elaborated and carried to the plant tissues. To produce a ton 
of dry matter in the crop from 250 to 600 tons of water are withdrawn from 
the soil by transpiration and by evaporation from soil. It is not possible 
to separate these two factors, but in the author’s view the plant takes not 
less than from 200 to 400 tons. To produce twelve bushels of wheat and 
twenty bushels of barley per acre there must be lost from the soil not less 
than 3°6 and 4°3 inches of water respectively, and there must be left in 
the soil at harvest enough water for growth not to have been stopped. 
Only a portion of the water in the soil is available for the crop; the 
rest is held as a film to the soil particles and cannot get into the plant 
roots. The amount of this unavailing water depends on the size and 
arrangements of the soil particles and on the quantity of colloidal matter 
present. Thus a soil may be physiologically dry and yet contain more 
moisture than another soil which is actually supplying water to plants. 
Further, on one soil (e.g., a coarse sand) 03 inch of rain would double 
the water content of the surface foot and place it in a good growing con- 
dition, while on another soil (e.g., a clay) the same rainfall would be 
largely retained near the surface, above the roots, and be quickly lost by 
evaporation. On the sandy soil also the rain would have dissolved any 
soluble salts accumulated near the surface and have carried them down 
about the surfaces of the active root hairs so that the crop would have been 
fertilised as well as watered ; on the clay soil the water might even have the 
effect of strengthening the upward capillary rise from below, leaving the 
deeper soil both drier and less richly charged with soluble plant food than 
before. When the natural particles are caused to agglomerate by tillage, 
the amount of available water increases; suitable soil texture is therefore 
a very important consideration in dry farming. 
Another important matter is the depth of the soil. Where the textural 
conditions of the subsoil are uncongenial and a large root surface is forced 
to be developed in a small volume of soil, the demands of the plant for 
