ANNUAL REPORT, 1930 239 



after clover. It has now been established that this particular rotation is 

 unsuitable for tobacco, producing symptoms of a malady known as brown 

 root-rot. It remains to determine the underlying causes of the effect, and 

 efforts are now directed particularly to that study. With that in mind the 

 field experiments were redirected in the spring of 1930, the cash-crop ro- 

 tation being replaced by a duplication of the animal husbandry rotation, 

 and the so-called "criss-cross" rotations dropped. 



In an experiment involving different quantities of nitrogen, phosphoric 

 acid and potash remaining constant, 164.5 pounds nitrogen per acre (500 

 pounds ammonia) gave the highest yield, followed in order by 205.6, 123,1. 

 and 61.7 pounds nitrogen. From this and previous years it seems that for 

 Massachusetts conditions 100 to 150 pounds of nitrogen are necessary for 

 maximum yields of tobacco. 



In a further comparison of different carriers of nitrogen, ammonium 

 sulfate produced more tobacco than sodium nitrate, cottonseed meal or 

 the regular mixture containing several forms of nitrogen. Furthermore, 

 and of particular interest in view of results of previous years and other 

 experiments, yields were slightly greater from plots which had one year 

 of timothy preceding tobacco than from the plots which had tobacco the 

 previous year. However, all yields were good. 



The following miscellaneous tests were made on a small scale, too small 

 to give more than indicative results: 



(1) Both Nitrophoska (15-30-15) and regular tobacco fertilizer con- 

 taining considerable cottonseed meal, plus magnesium sulfate, failed to 

 produce normal crops of tobacco without lime, when used on a very acid 

 soil (pH about 4.5). 



(2) With potash omitted from the regular tobacco fertilizer, but sup- 

 plied in ground tobacco stems, a good yield of tobacco was obtained. 



(3) Colloidal phosphate at rates of 1000 and 2000 pounds per acre, in 

 addition to the regular fertilizer mixture, slightly increased yield. 



(4) Milorganite, an organic fertilizer made from processed sewage, 

 proved a good substitute for the more expensive cottonseed meal, produc- 

 ing 1801 pounds per acre. It remains to be seen what the quality of the 

 crop will be. 



(5) Fertilizer applied in the row produced slightly more than an equal 

 amount applied broadcast. One-half the standard ration in the row pro- 

 duced 1663 pounds, which compares with 1859 pounds from a full ration 

 broadcast. This is the first year of this experiment and results are only 

 indicative; but in view of results from a similar experiment with corn, It 

 is worth repeating. 



Magnesium Requirements of Crops. (A. B. Beaumont and M. E. Snell). 

 This investigation was continued in pot and field experiments according to 

 plans made by J. P. Jones. No outstanding symptoms or depression of 

 yields were obtained in either case. It is now suspected that, except in 

 cases of exceptional deficiency in soil magnesium, plants will hardly be 

 affected in dry years or the next year or two following dry years, owing 

 to the supply of native magnesium through the natural weathering pro- 

 cesses. It is planned to continue this investigation. 



