18 MASS. EXPERIMENT STATION BULLETIN 297 



applied. The marked increase in the organic matter content reported by the 

 Connecticut workers suggests that decomposition was not very rapid in the soil or 

 else there was an appreciable inert residue. Finally, soil differences may account 

 for some of the discrepancies in results between the two stations. 



There is a measure of agreement between the manure experiments of the two 

 stations with respect to the prevalence of black root-rot. In the Connecticut 

 experiment the soil became heavily infested with black root-rot, and the severity 

 of the infestation was considered a strong factor in the decline of yield and quality. 

 In the Massachusetts experiments the manured plots developed slightly more root- 

 rot than did the check plots, but considerably more than those with timothy and 

 red top covers. The average percentage of infected roots for the period 1926-1932 

 was: Manure, 19.3; no cover (check), 15.0; timothy cover, 7.0; red top, 5.0. 



The experimental evidence from other sections of the United States regarding 

 the effects of rotation, cover crops, and manure on tobacco is briefly summarized 

 as follows: In the southern tobacco sections crop rotations give good results. 

 With the exception of the intensive shade-tobacco district of Florida, there is no 

 experimental evidence that continuous culture might not give better results. Un- 

 der the conditions and practices which generally prevail in the South — soils com- 

 paratively low in nitrogen, little fertilizer used and a long growing season — it is 

 likely that the rotation system is the best available. Cover crops have produced 

 variable effects, some having been beneficial and some injurious. In the northern 

 tobacco sections, likewise, effects of cover crops have been variable but on the whole 

 beneficial. Rotations have also produced variable effects. The highest tobacco 

 yields of the United States now are obtained in Pennsylvania, a section in which 

 rotation is the common practice, but here also there is no evidence that the 

 rotation is superior to continuous culture.^ From Wisconsin, however, there is 

 evidence that rotations containing sod-forming crops are injurious to tobacco, 

 but not so injurious as in Massachusetts (Whately experiments) where more 

 fertilizer was used. In both Pennsylvania and Wisconsin as well as in the south- 

 ern sections some manure resulting from dairy farming is used for tobacco, and 

 apparently with benefit. In the Connecticut experiments manure reduced both 

 yield and quality, but here much larger quantities were used than in other sections 

 and this in addition to a heavy application of commercial fertilizer. 



Suminary and Conclusions 



Several cropping systems for tobacco either used or suggested for the Connecti- 

 cut Valley were compared. Results for eight years, 1924-1931, are reported in 

 the preceding pages. Data for the year 1932 are presented in Table 19 of the 

 appendix. Tobacco was grown in continuous culture without a cover crop, with 

 timothy, rye, and red top as cover crops, in two types of rotation, and with manure. 

 In supplementary experiments timothy, corn, potatoes, and onions were grown in 

 alternate years in comparison with tobacco grown continuously. The results and 

 conclusions are summarized as follows: 



1. Cover crops as a group gave tobacco of both better cjuality and higher yield 

 than did no cover. However, there was a difference in the effects of the cover crops 

 used, and only in the case of red top was the advantage of sufficient magnitude to 

 convince one that it was due to the treatment instead of to chance. 



2. Besides the agronomic advantages of certain cover crops for tobacco, there 



'Dr. P. J. Anderson, in a private communication, states that continuous culture of tobacco is not 

 practiced in Pennsylvania because in Lancaster County the soil reaction is so high that black root-rot 

 becomes serious after about the second year, and it is necessary to grow otiier crops. 



