U MASS. EXPERIMENT STATION BULLETIN 297 



The results indicate a fair degree of correlation between the burning quality 

 and grading quality of the tobacco as influenced by cropping system. Manure has 

 given the longest average burn, closely followed by no cover and the several cover 

 crops. Tobacco from the rotations had a definitely short duration of burn. As 

 will be brought out later in the discussion of the effect of cropping systems on 

 soil conditions, nitrates accumulated in the greatest amount where manure was 

 used, and this maj' account in part for the long burn shown by tobacco from this 

 treatment. 



From the standpoint of seasons it is interesting to observe that the longest burn 

 for all treatments was obtained in 1928, a year of heavy rainfall, low yield, and 

 poor grading quality. A possible explanation of this relationship lies in the 

 correlation which Anderson and others (2) have pointed out between wet seasons 

 and the potash content of tobacco leaf on the one hand, and potash and fire-hold- 

 ing capacity on the other. 



6. Effect of the Cropping Systems on Soil Conditions 



In Table 6 is shown the effect of the cropping systems on the reaction of the soil. 

 The reaction was determined on air-dried samples taken at the beginning of the 

 experiment and in 1932. The results are as would be expected from theory. In 

 general, the continued cropping of soil without the addition of lime or organic 

 matter may be expected to make it more acid because basic materials are removed 

 faster than acidic, both by the crop and through leaching. Continuous culture of 

 tobacco without a cover crop caused the reaction to drop (become more acid) 

 0.5 pH unit. With cover crops and manure, probably because of the ash residue 

 of the organic matter, the change was 0.2 to 0.4 of a unit. Likewise, the rotation 

 with corn and timothy lowered the reaction only 0.,3 unit. In the cash-crop rota- 

 tion a total application of 2 tons of limestone off'set a decrease due from cropping, 

 and in addition raised the reaction 0.2 unit. 



Table 6 — Effect of Cropping Systems on Soil Reaction* 



. (Reaction pll) 



Contmuous lobacco: Initial Final 



No cover (check 5.3 4.8 



Manure 5.0 4.7 



Manure and timothy cover 5.3 5.0 



Red top cover 5.2 4.8 



Rye cover 4.9 4.7 



Rotation Tobacco: 



With corn and timothy 5.3 5.0 



With potatoes and onionsj 5.2 5.4 



♦Determined on air-dry soils with potentiometer using qiiinhydronc and saturated calomel half- 

 cell. 1 part of soil mixed with approximately 2 parts water. 



tThis rotation was used 1923-1929; changed to tobacco, corn, and timothy in 1930. 



Since many of the students of the problem of decreasing productivity of certain 

 Connecticut Valley tobacco soils suggested as a remedy practices which would add 

 more organic matter to the soil, it was decided to determine the effect of the differ- 

 ent cropping systems studied on the content of soil organic matter. Organic 

 carbon was determined by a wet-combustion method, and organic matter was 

 calculated. Analysis was made of composite soil samples representing the several 

 treatments drawn at the beginning of the experiment and at the close of the 

 cropping season of 1932. The results are given in Table 7. It will be seen that the 



