30 MASS. EXPERIMENT STATION BULLETIN 318 



same grade but containing inorganic nitrogen only. Only a slight advantage, if 

 any, appeared in this respect with onions grown from sets. These results seem to 

 be closely related to the length of the growing season of the two types of onions. 



4. Deferring application of one-third of the nitrogen until the tops were about 

 three-fourths developed gave erratic, but on the whole beneficial results with seed 

 onions. Set onions were not benefited. Rainfall and temperature during the 

 growing season, as well as the length of the growing season, appear to have been 

 important factors in this experiment. 



5. A double-strength mixture (8-16-8) proved as satisfactory as the standard 

 single strength 4-8-4. Ordinarily high-analysis mixtures are more economical 

 than low- or medium-analysis mixtures. 



6. Muriate of potash proved fully as satisfactory as the sulfate, as a carrier 

 of potash for onions, so far as yield is concerned. The muriate is usually cheaper 

 than the sulfate per unit of potash. 



In experiments with cover crops, it was found that certain grass and clover 

 crops could be grown by seeding them in onions about the last week of July, but 

 no particular benefit was derived from them. Difficulties were encountered in 

 curing the onions with the cover crops present. For the purpose of checking 

 losses of plant food, reducing water and wind erosion (dust storms), and increasing 

 organic matter in the soil, cover crops in onions may have their place. Against 

 slight possible advantages, however, must be weighed the cost of seed and extra 

 labor in curing. It is believed that cover crops may be more successful with set 

 than with seed onions because of the early maturity and removal of the set onions 

 from the field. 



In experiments in spacing and rate of seeding, onions were seeded at the rates 

 of 3.5, 4.5, and 6.85 pounds per acre, with rows 13, 15, and 18 inches apart. The 

 heavier rates of seeding gave larger yields, but a higher percentage of small 

 bulbs. The greater distances between the rows slightly increased the percentage 

 of large bulbs, but the total area was not used so advantageously with the 15- 

 and 18-inch distances as with the 13-inch distance. The rather common practice 

 of 4 to 5 pounds of seed per acre with rows 13 inches apart appears to be satis- 

 factory, if not the best, for the Connecticut Valley. 



Experiments in the effect of the size of the set on yield and quality of the crop 

 gave the following results: 



1 . Onion sets below % inch in diameter developed a very small percentage 

 of seed stalks. Sets larger than % inch developed such a high percentage of seed 

 stalks that the resulting crop was of poor quality. 



2. Removing the seed heads by breaking them off as they appeared did not 

 significantly affect the number of seed stalks or divided bulbs, but did increase 

 the weight of bulbs and the total yield. The practice of removing seed heads is 

 recommended when large sets are planted. 



3. Greater yields were obtained from large sets (% to 1 inch) than from 

 smaller sizes, but on account of the high percentage of onions with seed stalks and 

 divided bulbs, the quality of the crop was much poorer. Even though a greater 

 yield may be obtained, and in a shorter time, from large sets, a greater net income 



