16 MASS. EXPERIMENT STATION BULLETIN 297 



due to the presence of corn in the rotation. How can the difference in the effects 

 of red top and timothy be explained? The answer possibly lies either in the rate 

 of decomposition or the nature of the decomposition products of the two grasses. 

 The data obtained indicate but do not prove that red top decomposes more 

 rapidly than does timothy. Possibly certain toxic products result from timothy 

 which do not arise from red top, or they exist longer in the soil. Or considered 

 from the positive side, certain beneficial products may be produced from red top 

 which do not come from timothy, or they may be produced in greater quantity, 

 or persist for a longer time. A similar line of reasoning may be applied to a 

 comparison between some of the other cropping systems and the use of manure. 

 It has been shown by earlier investigations at this experiment station reported 

 elsewhere (4) that the nitrate form of nitrogen was the most easily assimilated 

 of a number studied. Studies of the formation of nitrates in the field soils of this 

 experiment have shown some degree of correlation between the rate of accumula- 

 tion of soil nitrates and the yield and quality of tobacco. This relationship has 

 been particularly marked in the case of the quality of tobacco grown continuously 

 with a manure supplement. Under this treatment the accumulation of soil ni- 

 trates has been highest, especially near the end of the growing season, and the 

 tobacco has been of outstandingly superior quality as shown by both grade index 

 and burn test. In addition to the possible agronomic benefits from cover crops 

 there are some unmeasured and unmeasurable benefits not hitherto mentioned. 

 At certain times of the year, particularly within the winter and spring, strong winds 

 sweep down and across the Valley, sometimes for days at a time. Considerable 

 soil is removed (3) from bare fields and is transported in dense clouds (see Figure 

 3). This is not only an economic loss to tobacco growers but constitutes a public 

 nuisance for the farmers and villagers of the Valley. In addition to allaying this 

 wind erosion of soils, cover crops in tobacco fields are also used by some farmers 

 for temporary fall pasture, and this may be an important advantage. 



Massachusetts Compared with Other States 



Since comparisons are frequently drawn between practices in growing tobacco 

 in the Connecticut Valley and elsewhere, a discussion of results obtained here in 

 comparison with those reported from other experiment stations will be worth 

 while. In such a discussion it should be recognized that differences in climate, 

 soil types and conditions, types of tobacco grown, fertilizer and cultural practices 

 and other indefinable factors limit the value of strict comparisons. 



In the early years of the industry in the Connecticut Valley rotation of tobacco 

 with other crops was the rule; but in recent years, for reasons which have been 

 stated, tobacco has been grown mainly in continuous culture on the land best a- 

 dapted to it, and an intensive culture involving large amounts of commercial 

 fertilizer has developed. Until the past decade this system has enabled the Con- 

 necticut Valley to lead all other sections of the United States in the yield per acre, 

 but recently yields have not been maintained, and Pennsylvania has taken the 

 lead. 



Until rather recently it was common practice in the shade-tobacco district ol 

 Florida (19) to follow a system of continuous culture. 'I'his was largely a matter 

 of economy. Recently, due to the increase of certain soil-harbored diseases, to- 

 bacco growers in that section have been forced to rotate crops or let the land re- 

 main idle for a period. In all other sections of the South tobacco has from the 

 beginning of the industry been grown on "new" or recently cleared land, or in 

 some sort of a rotation, or the land has been "rested" or allowed to remain idle. 



