30 THE BANANA 



to the mulch) is unable to take any water from a wet brick. 

 A friend wrote a short time ago : "I have been practising 

 the dry earth mulch (see Macdonald's ' Dry Farming '*) 

 for some time in suitable soils, i.e. free sandy loam, and 

 alluvial, which can be ploughed and harrowed at all times 

 except after heavy rains. The principle is sound, and, 

 so far as I can judge, the earth mulch is effectual as far 

 as it can be so. I know others who are trying it with 

 good results." 



Earth Mulch. Surface mulching, which consists in 

 keeping a deep layer of the top soil in a dry, loose, granular 

 state, has two effects. First, by rendering the top layer 

 more porous, or rather by rendering the surface pores 

 larger, it lessens considerably the run-off in the case of 

 heavy showers. Its chief object, however, is to make 

 evaporation difficult by destroying the capillary pores and 

 tubes through which the soil moisture is brought under 

 the active evaporating influences of the atmosphere. 

 44 The height f to which at ordinary temperatures water 

 rises in capillary tubes depends entirely on the diameter 

 of the tube. If the diameter is y^^^y of an inch, water will 

 rise about 100 ft. ; if the diameter is y-^ of an inch, the 

 water will rise 1 in. ; if the diameter is -^ of an inch, the 

 water rises about ^ of an inch. Now in compact soils 

 the pores form the equivalent of continuous tubes which 

 may be within the range of the foregoing figures. The 

 American experts in their soil surveys have determined 

 the number of particles of many loamy soils. In an 

 ordinary loamy soil they find from two to four billion 

 particles per cubic inch. It is easy to compute from this 

 that the size of the particles may be as low as -j^ko ^ an 

 inch, and we may assume consequently that the pores 

 are of the same order of magnitude. The theory of 



* " Dry-Farming in America : being a Report presented to the 

 Transvaal Government." By W. Macdonald. Pretoria, 1909. 



t "Rainfall in Relation to Dry Farming." By Rev. E. Goetz, S.J., 

 Director of the Bulawayo Observatory. Rhodesia Agric. Journ., is. 487 

 (1912). 



