342 



Bulletin S2 



of the summer, and by December, 1916, virtually no Johnson grass 

 was noticed in the held except that which had grown from seed brought 

 in with the irrigation water used during July and August. At the 

 time of the germination of these plants the cotton was too large to 

 permit of further cultivation, which would easily have destroyed the 

 seedlings. In January and February, 1917, this land was plowed pre- 

 paratory to a green manuring crop to be turned under before planting 

 to corn. Accordingly the field was irrigated and late in March tepary 

 beans were drilled in very thickly. These beans came up readily and at 



Fig. 3.— Field E, August, 1915. 



first made satisfactory progress, but due to the lack of nitrogen fixing 

 bacteria in the soil their growth during May was slow. At the same 

 time Johnson grass plants, which had come tip from rootstocks devel- 

 oped on the seedlings introduced by the irrigating water of the previous 

 July and August, appeared in such great numbers that the beans were 

 plowed under very early in June. Johnson grass again came u]:» and 

 made necessary the use of a weeder in late June. In the middle of July 

 the land was planted to corn and aside from the necessity for consider- 

 able cultivation and hoeing during the first three or four weeks, the 

 weed was very easily kept under control for the remainder of the sum- 

 mer. Since it was possible to cultivate the corn until quite late in the 

 summer, most of the seedling plants that were brought in with the 



