TILLAGE 



235 



The Depth of the Mulch. The deeper the mulch the more 

 effective it is. King has shown very conclusively that evaporation 

 is prevented to a very large extent by deeper mulches. The fol- 

 lowing table gives his results : 



Effectiveness of Soil Mulches of Different Kinds and Depth 



100 Days 



-Water Loxt in 



It will be noted from this table that the four-inch mulch was 

 no more effective than the three-inch. 



Deep mulches are very effective in conserving moisture, but 

 there are serious objections to their use where crops are grow- 

 ing. The objections apply more directly to farming in humid 

 than in semi-arid and arid regions. If in humid areas a mulch 

 three or four inches deep is produced on a sail with an intertilled 

 crop, serious root injury will occur which will materially decrease 

 yields. Deep mulches are practical only on bare soils. The effec- 

 tiveness of a mulch depends upon its looseness and drynoss. A 

 three-inch mulch means the loss of a large amount of water if it 

 is to be effective to its full depth. To maintain a mulch of this 

 depth more frequent cultivation is necessary than for shallow 

 .ones. Every cultivation turns under dry soil and brings moist soil 

 to the surface, resulting in loss of moisture. Shallow mulches are 

 easily maintained with a minimum of cultivation. Tn humid 

 climates, if the crop is free from weeds, there is little necessity for 

 cultivation of sands, sandy loams and silt lo;uns. 



Besides the moisture lost from the mulch the plant food that 



