154 



DRY-FARMING 



In 1868, Nessler found that during six weeks of an 

 ordinary German summer a stirred soil lost 510 

 grams of water i^er square foot, while the adjoining 

 compacted soil lost 1680 grams, — a saving due to 

 cultivation of nearly 60 per cent. Wagner, testing 



Fi(j. 35. Tillage forms a loose dry mulch on the land surface, which 

 prevents evaporation. 



the correctness of Xessler's work, found, in 1874, 

 that cultivation reduced the evaporation a little more 

 than 60 per cent; Johnson, in 1878, confirmed the 

 truth of the principle on American soils, and hevi 

 Stockbridge, working about the same time, also on 

 American soils, found that cultivation diminished 

 evaporation on a clay soil about 23 per cent, on a 

 sandy loam 55 j^er cent, and on a heavy loam nearly 

 13 per cent. All the early work done on this subject 

 was done under humid conditions, and it is onh' in 



