334 Journal of Agriculture, Victoria. [lo June. 191. 



consequently, they cannot hold moisture interstitially, as a sponge. 

 Moisture is held by the soil in the form of films surrounding the 

 soil particles. The water holding capacity of a soil is dependent 

 on its physical constitution, i.e., the amount of organic matter, clay, 

 sand, &c., present, and also on the minuteness of subdivision of the 

 soil particles, i.e., the tilth of the soil. A soil in a good state of 

 tilth is not only capable of conserving a maximum of moisture, but it is 

 also in the best possible capillary condition, i.e., the moisture from the 

 subsoil is able to move up more freely than in a similar soil with a poor 

 tilth, composed of large cloddy particles. Consolidation of the soil is 

 an important factor, because the presence of large air spaces in the soil 

 promotes evaporation and interferes with the movements of capillary water. 

 The method of achieving this will be referred to later. A finely divided 

 and firmly consolidated stratum of soil resting on the welbmoistened sub- 

 soil is in the very best condition not only for the storage of moisture, but 

 for the movement of that moisture upward by capillary action. 



{c) The moisture must be prevented from evaporating at the 

 surface. A shower of rain readily causes the surface to run together 

 and set. The hard surface then enables unbroken capillary connexion 

 between the moisture-laden subsoil below and the dry crust at 

 the top. By breaking the continuity of these capillary tubes by means 

 of a cultivator the soil is effectively mulched, and evaporation is reduced 

 to a minimum. In this connexion it may be mentioned that it is not neces- 

 sary, from the point of view of moisture conservation, to have the surface 

 of the soil finely pulverized. We often observe farmers harrowing away at 

 the surface of the soil until the tilth is like an onion bed. The important 

 po:nt is to have the finely divided and firmly consolidated soil below ; and 

 it is not of great moment if the surface be rather rough and cloddy, 

 provided only that it is loose. 



2. Bare Fallowing Increases the Supply of Available Plant l-'ood. — 

 One indirect result of the moisture cnn.served by the process (jf bare 

 fallowing is that during the suimiier months many chemical and biological 

 changes take place within the body of the soil, and result in the liberation 

 of plant food. 



Just exactly what these changes are has not been completely demon- 

 strated. There is no doubt, however, that the process of nitrification goes 

 on rapidly in well-tilled bare fallows under Victorian conditions. By this 

 process, nitrogenous organic matter is slowly converted by three stages 

 into nitrates, and the action is brought about bv specific bacteria. It has 

 been estimated that at Rothamsted 80 lbs. of nitrogen as nitric acid 

 are formed in i acre of land during a year of bare fallow. Further, 

 losses through drainage over a period of thirteen years v/as 37 lbs. per 

 acre. The rate of nitrification under Victorian conditions has not yet been 

 completely worked out, but, owing to the high-soil temperature during 

 summer, it is fairly rapid in our well-tilled bare fallows. For example, in 

 the fallowed land at Longerenong, on 7th December, 191 1, there were 

 57.75 lbs. per acre of nitrogen present as nitrate in the first 5 feet. On 

 ist April, 191 2, this amount had increased to 105 lbs. in the same volume 

 of soil. 



In addition to the increase in nitrates, there can be little doubt that 

 other important plant foods, particularly potash and phosphoric acid, are 

 converted from unavailable to available forms. 



3. Bare Fallowing Distributes the Farm ^york evenly through the Year. 

 -One of the great advantages of bare fallowing is in the fact that it 

 enables the wheat-grower to have ready in autumn large areas in the best 



