144 MASS. EXPERIMENT STATION BULLETIN 237 



The reaction of the onion soil on the Hubbard farm at Sunderland 

 was n.ed.un. ac:d, pH-5.5. A good crop of onions was secured. Hydrated 

 hme had been applied in the spring. There was apparently response to 

 ts.se although not nearly as much as when it was applied to more acid 

 soils. Similarly the experiment on the Ryan farm. North Hadley, indicat- 

 ed undoubted response to the use of lime, although a small quantity was 

 apparently as effective as a large quantity in bringing about the desired 

 inxprovement. 



Yellow Tips May Indicate Acidity. 



The best and most reliable guide to the degree of soil acidity is the 

 soil test but the plant growth on that soil is the most dependable criter- 

 ion of the action of any particular degree of acidity. Set onions on verv 

 acid soil often s,tart oif well in the spring. Very shortly golden yellow 

 ips appear-m some fields earlier than others. As the season progresses 

 tbe yellow tip,s extend back on the leaves, witl. varying degrees of rapid- 

 ity. In extreme cases older leaves soon become abnost entirely yellow 

 Jose their turgidity, and gradually curl downward and die; while the 

 newer leaves, already yellow at the tips, gradually follow. In such ^ 

 >case very little growth is secured beyond that accounted for by the origin ■ 

 aLset. There are found variations from this extreme to cases where onlv 

 a few leaves are completely lost, to instances of slight yellowing of the 

 tips, and to fields wbere none of this discoloration appears. With such 

 variations, there are usually corresponding differences in vield The yel- 

 low tips are always suggestive of an acid soil and the soil test usually 

 confirms it. 



In seed onions the symptoms are not exactly the same. In the early 

 part of the season it is the stunting of growth, the absence of a bushv 

 and thrifty appearance, the presence of slight yellowing of the tips that 

 indicate a lime deficiency. Later in the season there is more yellowing 

 and dying back of the tips and also a sluggishness in the formation of 

 bottoms. These symptoms vary according to the degree and activity of 

 the acidity. 



When To Lime 



Undoubtedly the best time to apply lime is in the autumn after the 

 onions are harvested. It may be applied in the spring or even as a top- 

 dressmg after the onions are eight to twelve inches tall. Response to 

 spring applications of lime is recorded above, but no data have been taken 

 on the effectiveness of lime applied after the onions have begun to grow 

 All that can be said at this time is that a ton of limestone can be applied 

 wben the onions are eight to twelve inches high without injury. 



Despite the fact that favorable results m^ay be obtained from applica- 

 tions at other seasons, there are two chief reasons why lime should be 

 applied in the autumn;— (1) there is a longer time for the lime to get 

 thoroughly mixed with the soil, and the chances of altering the acidity 

 before it injures another crop are much greater; and (2) it is usually 

 more convenient to .apply lime in the autumn and thus avoid the risk of 

 not having time to do it in the spring. From both the soil fertility and 

 farm management standpoints, therefore, it is good practice to apply lime 

 in the autumin. 



