12 



Campbell's 1902 Soil (.'ultukk Manual. 



not be better illustrated than by the movement of the oil up the lamp wick. 

 No matter how deep the bowl of the lamp is if the wick reaches the bot- 

 tom the blaze continues to burn, not only until the oil is all taken from the 

 lamp but until the wick has become quite dry. The same rule or fact ap- 

 plies to the growing plant. So long as there is plenty of moisture below it 

 will move up through the soil to the plant, keeping it in a perfectly healthy 

 condition until the moisture is not only exhausted for several feet down, 

 but the soil near the plant has become apparently quite dry. Then the 

 plant begins to fade and wither. 



Study well, by close observation, this question of percolation or get- 

 ting water into the soil below. It is interesting and of great value. 



The deeper you can store the moisture the greater are your chances 

 of securing a large crop. 



A piece of ground that is moist for two or three feet down will take in 

 the water of a heavy rain much quicker than ground that is dry. Here 

 again is illustrated what moisture will do for us when we understand her 

 ways and will try to help ourselves. 



EVAPORATION. 



A thorough understanding of the principles and processes of evapor- 

 ation is another thing of great importance to the farmer who lives in the 

 semi-arid belt. In fact there is nothing more serious for the farmer than 

 the loss of rain water by vapor, the direct result of the sun's heat and the 

 hot winds. The remark is common in the semi-arid belt that we do not 

 have rain enough, or if we had a little more rain it would be the greatest 

 country on earth, or that all we lack is more rain. To all this we take 

 exceptions. It is true that if we could always have just rain enough, at 

 just the proper time, to enable us to grow mammoth crops without any 

 special effort on our part, it would be very nice; but this is not true in any 

 part of the country. In the more humid sections of the country crops not 

 only suffer at times from extreme drouth, but it is not uncommon that fine 

 crops are lost by too much rain after all the processes of growling and har- 

 vesting have been successfully carried out. 



The real difficulty in the semi-arid belt is not a lack of rainfall, but 

 the loss of too much by evaporation, and this can be largely controlled by 

 proper cultivation, at least sufficiently to secure a good growth of crops 

 every year. It has been demonstrated b}' careful laboratory and field work 

 by Profs. King, Whitney, Hillgard, and others, that 7 inches of rainfall is 

 ample to grow a good crop of any kind, providing the water is all utilized 



