18 BULLETIN 1410, U. S. DEPARTMENT OF AGRICULTURE 



of the land following fertilizer treatment. On the other hand, 

 this soil was much improved for tobacco by the liberal application 

 of fertilizer, so that no sharp line of distinction can be drawn 

 between failure due to brown root rot and that due to lack of 

 fertility. 



Liming the soil in combination with the fertilizer treatment appar- 

 ently increased the injury, but the application of sulphuric acid had 

 little effect. Formalin sterilization of the soil resulted in the pro- 

 duction of roots free from disease. In this case the beneficial action 

 was probably due largely to the formalin rather than to the effects 

 of desiccation or aeration, as might be the case in the laboratory 

 experiments where the soil was spread out to dry after treatment. 



In 1920, fertilizer plat experiments were placed on the farm of 

 W. A. Havilancl, at East Windsor Hill, Conn. The nature of the 

 trouble on this land was not definitely known, except that it was 

 regarded as " tobacco sick." Various combinations of fertilizers 

 were applied, and varieties differing in resistance to black root rot 

 were grown. Nitrogen was found to be the controlling fertilizer 

 element, and smaller increases were obtained with phosphorus and 

 potassium. Thielavia root rot was so abundant, however, that any 

 results bearing on brown root rot were obscured. It is interesting 

 to note, however, that lime again retarded growth and maturity on 

 these plats. 



In 1921, preliminary arrangements were made to conduct rotation 

 experiments on the farm of Helen Crafts at Whately, Mass., on a 

 soil which was affected with typical brown root rot. Land was also 

 selected for a similar set of plats at the tobacco substation of the 

 Connecticut Agricultural Experiment Station at Windsor. The lat- 

 ter land was not affected with brown root rot, but the expectations 

 were that it would develop during the course of the experiments. 

 The experiments on these soils were started in 1922 and continued 

 through 1923 and 1924, forming the basis of the present report. 



PLAN OF THE EXPERIMENTAL PLATS 



The experiments were planned primarily to determine the in- 

 fluence of rotating crops, both susceptible and immune to brown 

 root rot, with tobacco. Other plats were added, however, to deter- 

 mine the influence of fallowing, liming, and heavy fertilizer appli- 

 cation. 



Included in each experiment were 22 twentieth-acre plats. Corn, 

 onions, and timothy were selected to represent crops not attacked 

 by brown root rot, and tobacco, tomatoes, potatoes, beans, and clover 

 represented crops more or less definitely affected. The selection was 

 to some extent influenced by the agricultural crops commonly grown 

 in the community. In the original plan these crops were to be 

 grown on their respective plats two years, followed by tobacco on 

 all plats the third year. In 1923 it was decided, however, to divide 

 the Whately plats into halves and to plant one of each to tobacco, 

 in order to determine the influence of one season of the respective 

 crops on the growth of tobacco. In 1924 all plats were planted to 

 tobacco, so that the effect of two years' growth of the various crops 

 was obtained, as well as the residual effect of one year's cropping 

 in comparison with tobacco in continuous culture. 



