154 MASS. EXPERIMENT STATION BULLETIN 162. 



No effort was made to equalize the lime supply on the different plots, 

 •although the fact that the entire field was limed twice at the rate of a ton 

 to the acre as already described ^ reduces the probability that the excess of 

 lime in the slag exercised an important influence. The possibility, how- 

 ever, that the occasional superiority of the slag and bone meals may have 

 been due to the factors referred to should not be overlooked. 



3. It should be noted that the more soluble phosphates, while not in- 

 creasing the stover of the corn crop so largely as the slag and bone meals, 

 exercise a more favorable influence upon the production of grain. 



4. This is doubtless, at least in part, due to the fact that the more 

 soluble phosphates promote more rapid early growth and earlier maturity 

 than do those less soluble. 



(a) More Rapid Early Growth. — The marked effect of an application 

 of soluble or quickly available phosphates upon the early growth of the 

 corn crop has been many times observed. ^ We have made measurements 

 only once in this series of experiments, viz., in 1914. These measurements 

 were made on July 10, and indicate the extreme height from the ground 

 to the highest leaf-tip. The figures are the averages of 40 plants in each 

 plot, — equichstant individuals each in the fourth and seventh rows. 



Height on July 10. 



The great superiority of the soluble phosphates and the bone meals is 

 clearly brought out by this table, while the average measurement in- 

 dicates the slag meal to be materially superior to the natural phosphates 

 in its effect upon the early growth. 



(6) In favorable years varieties of corn suited to the locality attain 

 maturity on all plots; but in years with summer temperatures much 

 below the average, or those with early autumn frosts, a part of the crop 

 fails to ripen completely. This was notably the case in 1913, in which 

 year the thermometer fell to 31° at 6 a.m. on September 15. The per- 

 centages of soft corn were lowest on the slag meal and dissolved bone, — 



1 See p. 149. 



- On our north corn acre acid phosphate has been used during the past twenty-five years at 

 widely varying rates on different plots; in round numbers 1,100 pounds per acre on two plots, and 

 200 pounds per acre on two. During the first few weeks the growth on the plots receiving the 

 larger application of acid phosphate is always far more rapid than on the other plots. 



