8 MASS. EXPERIMENT STATION BULLETIN 318 



phorus per acre, an amount considered low for best plant growth. Samples drawn 

 in 1932 from plots which had received the 4-12-8 fertilizer showed 176 pounds, 

 and from those which had received the 4-8-4 fertilizer 98 pounds, of available 

 phosphorus 1 . Since a good crop (300 100-lb. bags) of onions removes only about 

 40 pounds of phosphoric acid, the soil in question must have had a very high 

 fixing power. Presumably, after this fixing power becomes satisfied by repeated 

 application of a high-phosphorus fertilizer the proportion of phosphorus in the 

 fertilizer may be reduced. 



Since no advantage was shown by 6 per cent of ammonia over 4 per cent, an 

 experiment was introduced to furnish further information on response of onions 

 to nitrogen. The 4-12-8 was taken as the basis, and with it were compared a 

 2-12-8 and 6-12-8. The results showed no advantage from the extra nitrogen, 

 while the lower amount appeared to be too low. 



Organic versus Inorganic Nitrogen 



A question of considerable economic importance in the selection of a mixed 

 fertilizer is that of the nature of the nitrogen carrier. Organic fertilizer nitrogen 

 usually costs considerably more per unit than does inorganic nitrogen. On this 

 account the trend in recent years has been away from the organic forms toward 

 the inorganic forms. In order to obtain some information on this point a 4-12-8 

 fertilizer composed entirely of inorganic materials was prepared and compared 

 with the standard mixture of 4-12-8 which carried half its nitrogen in organic form. 

 Considerable superiority was shown by the "organic" mixture in the production 

 of seed onions and a slight though probably insignificant advantage with the set 

 onions. This result appears to be closely related to the length of the growing 

 season of the two types of onions. It is to be expected that the seed onions with a 

 longer growing season would benefit more by the more slowly available organic 

 nitrogen than would the set onions. 



Side Dressing with a Nitrogen Fertilizer 



It is a more or less common practice among growers in the Connecticut Valley 

 to side-dress the crop with a nitrogen fertilizer about the first week of July, for 

 seed onions, and the first of June for set onions. Fish meal is commonly used at 

 the rate of 400 to 800 pounds per acre, but other nitrogen fertilizers are also used. 

 An experiment was conducted for the purpose of comparing side-dressing with no 

 side-dressing, and an organic with an inorganic carrier of nitrogen. Fish meal 

 and sodium nitrate were chosen as the materials, and enough of each was added to 

 furnish nitrogen equivalent to 50 pounds of ammonia per acre. The sodium nitrate 

 was added to plots which had previously received an initial treatment of 4-8-4 

 fertilizer, but the fish meal, because it contained a small amount of phosphoric 

 acid, was added to an initial application of 4-7-4. In this way the total nutrients 

 applied in the comparative treatments were equal, and were equivalent to a 

 6-8-4 fertilizer. 



First, it was noted that set onions were not benefited by the extra nitrogen. 

 This result is as might be expected. Set onions ordinarily make their maximum 



linationa made by John N. I 



