334 MASS. EXPERIMENT STATKlN BULLETIN 260 



this advantage was greatly minimized. In 1929, however, there was no 

 blast, and differences in earliness of bulb formation were not so impor- 

 tant because quite favorable growing conditions prevailed throughout the 

 season, allowing ample opportunity for the bulbs on both the limed and 

 imlimed plots to mature. While 33 per cent increase in 1929 on the 

 limed plot seemed small in comparison to that of previous years, the actual 

 increase in yield per acre was approximately as large an any yet obtained. 



When it was recognized that considerable lime must be added to acid 

 soils to grow onions satisfactorily, there was some apprehension that 

 severe damage might result through black root-rot injury should the 

 grower wish to plant the ordinary strains of tobacco on his highly limed 

 onion land. The Station therefore undertook some experiments looking 

 toward the successful' growth of onions at a soil reaction sufficiently 

 acid to prevent any serious injury by black root-rot in case tobacco was 

 grown later. Superphosphate has been credited by the Rhode Island Ex- 

 periment Station and others as having an effect on acid soils, similar in 

 some respects to that of lime. Large applications of superphosphate, alone 

 and in combination with small amounts of lime, have been tried for the last 

 two years. There is evidence that 500 to 1000 pounds of agricultural 

 lime per acre in combination with 600 to 1000 pounds of superphosphate 

 in addition to that in the regular fertilizer may be as effective as two tons 

 of agricultural lime; but superphosphate alone, even in large applications, 

 has not given satisfactory results. It has also been learned in this con- 

 nection that onions can be grown satisfactorily at a reaction of pH 6.0. 

 If the lime used in growing the onions has not raised the pH above this 

 point, little injury may be expected from black root-rot should tobacco 

 be grown on the land subsequently, especially if the soil is well drained. 



Fertilizer Ratios for Onions. (J. P. Jones and M. E. Snell). This ex- 

 periment was begun in 1925 with the idea of getting some estimate (1) 

 of the relative amounts of nitrogen, phosphorus, and potash required by 

 onions, (2) of the merits of fractional application of nitrogen, and (3) 

 of the value of organic forms of nitrogen. All fertilizers have been 

 applied at the rate of 2500 poimds jier acre. The results at present show 

 that increasing the phosphorus without at the same time increasing the 

 potash is unproiitable. For instance, the 4-12-4 has given no better results 

 than the 4-8-4, but the 4-12-8 has given an average increase of 18 per 

 cent in yield over the 4-8-4 during the past four years. However, in 1929 

 the 4-12-8 did not give appreciably better results than the 4-8-4 or the 

 4-12-4, the large average increase being due to the large difference ob- 

 tained in the three previous years. 



The data on the amount of nitrogen indicate that a fertilizer carrying 

 4 per cent ammonia, applied at the rate of 2500 pounds per acre, will 

 provide adequately for the first application. If necessary more nitrogen 

 can be added later as a top-dressing, either in the form of fish or of 

 nitrate of soda. Increasing the ammonia from 4 to 6 per cent by top- 

 dressing has improved the yield by about 12 per cent over applying the 

 entire 6 per cent in the first application of fertilizer. It is interesting to 

 note that during the dry season of 1929 top-dressing with fish gave no 

 increase in yield, while top-dressing with nitrate of soda gave a 13 per 

 cent increase. 



