8 MASS. EXPERIMENT STATION BULLETIN 333 



DISCUSSION OF TABLES 



Some individuality was shown by the plots without nitrogen. Plot 6 was 

 strikingly superior to Plots 7 and 9 in 1924 with both grasses and clovers. 

 This superiority was shown by the west half of the plot, while the east half 

 was practically like the same areas on the other plots. Plot 6 had been heavily 

 limed in 1923 to overcome the ill effect of continuous use of sulfate of am- 

 monia. The crop of 1924 was its first without nitrogen, and residual nitrogen 

 appeared to be the cause of its superiority over the plots which had been con- 

 tinuously without nitrogen fertilizers in previous years. Plot 6 was again 

 superior in 1926, when its crop of Japanese millet was larger than the crops of 

 the other two added together and its soybean crop was slightly superior to 

 the other two. The sweet-corn crops of 1925 and 1927 were inferior to the 

 like crops on Plots 7 and 9. 



After 1927, the crops on legume and nonlegume subplots were reasonably 

 comparable for the three plots, no one of which was continuously in the lead. 

 Residual effects of the former nitrogen applications on Plot 6 appeared to be 

 completely eliminated. The summary of seven harvests, 1928 to 1935 inclu- 

 sive, follows: 



The effect of a crop on its succeeding crop is of interest as shown by the 

 yields in these tables. In 1925 sweet corn following clover was much superior 

 to the like crop following the grasses; but in 1927 the sweet corn was larger 

 following Japanese millet than following soybeans. Although soybeans were 

 themselves able to use the nitrogen supplied by microorganisms, their stubble 

 and roots were of little benefit to succeeding crops. 



The two successive crops of clovers and grasses in 1928 and 1929 were a 

 paradox. The first-year crops included many weeds; and perhaps for this 

 reason, the grass subplots on all plots bore larger yields than the clover sub- 

 plots. The second-year crops, which were practically free from weeds, were 

 much larger on all clover subplots. The Japanese millet which followed the 

 clovers and grasses in 1930 was so much affected by the weather that yields 

 varied under like conditions. 



In 1931, in the absence of nitrogen fertilizers, oats and peas excelled oats 

 alone; but in 1935 applications of nitrogen caused oats to be superior to oats 

 and peas. On plots without nitrogen, oats were a second time inferior to oats 

 and peas. 



In 1932 Hungarian millet with applied nitrogen exceeded soybeans in yield, 

 but without nitrogen the soybeans took the lead. In 1934, Hungarian millet 

 followed plowed-under crops of alfalfa and barley with and without residual 

 nitrogen. With residual nitrogen the crops were virtually equal; without, the 

 crop on alfalfa subplots was slightly superior. 



In this investigation clover was the only legume to have a striking effect on 

 the following crop. The presence and absence of nitrogen have not caused 

 any appreciable variation in the percentages of nitrogen in the crops when 

 the grand averages of the series of crops are compared. 



