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.) 



Fig. 166. — Unproductive spot, on a low field due to high water-table, 

 soil the cause of the difference in water-table. 



Variation in sub- 



