12 MASS. EXPERIMENT STATION BULLETIN 297 



Towards the end of the growing season, there is usually more or less recovery 

 from these conditions. The final results of the malady are reflected in the low 

 yields and poor quality of the crop. In these experiments brown root-rot has 

 been slightly more severe following clover than following timothy in rotation. 



4. The Effect of Tobacco and Other Crops on Each Other 



The effect of certain other crops on the yield and quality of tobacco when grown 

 in rotation with it has been discussed. Any rotation suitable for tobacco should 

 give at least fair returns of the other crops. In Table 20 are given the yields of 

 all the crops grown in the cash-crop rotations. The yield of potatoes was rather 

 variable from year to year. This can be explained partly by seasonal variations 

 and partly by the fact that there were only duplicate plots of each treatment, 

 which was too few to take care of differences in soil. Nevertheless, with an 

 average yield of 268 bushels of marketable potatoes, the evidence is strongly in 

 favor of the conclusion that potatoes may be expected to do well in rotation with 

 tobacco in the Connecticut Valley. For both crops the reaction of the soil should 

 not be above pH 5.5, because above that point potatoes may become infected 

 with common scab (Actinomyces scabies Thax.), and tobacco with black root-rot 

 {Thielavia basicola (B. & Br.) Zopf.). 



Additional evidence bearing on the question of the effect of potatoes and 

 tobacco on each other when grown in the same rotation was obtained from a 

 supplementary field experiment in which tobacco was grown alternately with other 

 crops. For checks, each of the crops was grown continuously on an adjacent plot. 

 In one series of plots, tobacco, onions, and potatoes were thus grown; and in the 

 other, tobacco, corn, and hay were grown. This experiment differed from the 

 rotations previously described in that the crops were grown either continuously 

 or in alternating pairs. There was no rotation of the three crops. The experi- 

 ment ran six years, but the first year's results are not taken into account because 

 one year was needed to establish the desired conditions. Since there was only a 

 single plot for each treatment, except for tobacco which was duplicated, the results 

 may be considered mainly as showing trends. (See Table 23.) 



Here again, the results indicate that potatoesand tobaccodoabout as wellasany 

 of the combinations studied. Continuous tobacco appears to have a slight ad- 

 vantage over the tobacco-potato combination, but potatoes did slightly better 

 following tobacco than in continuous culture. 



Onions did poorly in rotation with potatoes and tobacco, probably because of 

 the strong acidity of the soil in this rotation. Infestations of thrips and the pres- 

 ence of "blight" in some years reduced the yields to a low point. The yield of 

 onions was better under continuous and alternate cropping systems than in the 

 3-year rotation as shown by figures in Tables 20 - 23. This was probably due to 

 the fact that more lime was applied under the former system than in the latter. 

 It will be seen, also, that continuous culture of onions was better than alternate 

 cropping, which may be attributed to the use of more lime. Other experiments 

 conducted at this experiment station showed that onions have a high lime require- 

 ment. For best results, onion soil should have a pH value of 6.0 - 6.5. 



In the so-callevl animal-husbandry rotation manure was applied to the tobacco 

 in such amount as would theoretically be produced from crops grown in the other 

 two years had they been fed to livestock, and this in addition to a normal appli- 

 cation of fertilizer. .As shown by Table 2 this method caused the total amount 

 of applied nutrients to be rather high. In addition a timothy or clover sod was 

 plowed under. Nevertheless, as has been shown, the tobacco was low in yield and 



