260 HARMFUL AGENTS IN SOILS AFFECTING FERTILITY 







FIG. 165. A soil infested with cabbage yellows. A strain of cabbage has been developed 

 to resist this disease. Two rows to left are non-resistant cabbage. (Wisconsin Station.) 





FlG. !(?. 



Unproductive spot on a low field due to high water-table. Variation in sub- 

 soil the cause of the difference in water-table. 



