122 



MASS. EXPERIMENT STATION BULLETIN 229 



cover crop (2) with timothy cover crop and (3) with clover cover crop.5. One- 

 half of the field was inoculated while the duplicate half was not inoculated. 

 All cultivation was in the direction of the cover crop strips, thus avoiding as 

 far as possible carrying the fungus to the uninoculated half. 



The limed plots were treated year by year as follows: 



1921, ground limestone, 4000 lbs. per acre 



1922, precipitated lime (51 per cent CaO), 2000 " 



1923, agricultural lime (60 " " CaO), tOOO 



1924, no lime 

 192.5, no lime 



The fertilizers applied each year just before setting the plants are descrilied 

 in the following table. 



Fertilizers Used — Pounds per Acre 



Material 1921 1922 1923 1924 1925 



Cottonseed Meal 1200 1200 1481 1270 8i:8 



Total rate per acre 2020 2020* 25001 2083J; 1642t 



* Plus a quickly available side dressing at the second hoeing. 

 t Plus 250 lbs. nitrate of soda per acre applied in July. 

 t Equivalent to 3000 lbs. per acre of a 5-4-5 fertilizer. 



Tliat half of the field which was inoculated (see Figure I) was first inocu- 

 lated in 1921 by setting in it diseased plants taken from a badly infested seed 

 bed. In order to secure heavier infection on the inoculated half, a handful 

 of soil from a heavily infested greenhouse bed was placed in the fnrrow 

 where each plant was .set in 1922. The inoculated half of the field was again 

 inoculated just before setting the plants in 1923, when two cartloads of heavily 

 infested soil from a greenhouse bed were scattered broadcast over it and 

 harrowed in. 



Timothy and clover cover crops were sown after harvesting the tobacco in 

 1921, 1922, and 1923. None were sown in 1924. 



Soil samples for pH determination were taken from all plots each year, 

 and the hydrogen ion concentrations which were determined are recorded in 

 Table 1.6 These soil samples were taken before the ground was broken in 



5 Since the clover winter-killed every year, its effect if any must be attributed to 

 the very small growth between sowing and freezing of the soil. 



6 These and subsequent determinations were made by F. W. Morse, Henri D. 

 Haskins, and L. S. Walker, chemists on the staff of the Massachusetts Agricultural 

 Kxperiment Station. The determinations were made on air dried soils by the Clark 

 and Lubs colorimetric method. The water e.xtract was juade by adding 200 cc. of 

 distilled water to 20 grams of air-dry soil in a flask and allowing it to stand about 1 

 hour with frequent shaking. Tlie extract was then filtered by turning the soil mixture 

 on a small filter in a large funnel. The first portions of the filtrate were returned to 

 the soil flask until the extract was running clear By this time, the paper was filled 

 with soil, and the filtration was through soil supported by a small paper. By this 

 means, any absorption by the paper was reduced to its lowest terms. 



