Field Truck Crops 245 



both by the character of the soil and of the manures and 

 fertilizers applied. The soils best adapted are dry, sandy 

 loams, and the most useful fertilizers are those which 

 contain an abundance of minerals phosphoric acid 

 and potash and not too large supplies of quickly avail- 

 able nitrogen. It is also true that the yields of sweet po- 

 tatoes of this character are not as large as those that may 

 be obtained when quality is not a prime consideration, and 

 which are grown for the general market. 



Fertilizer constituents contained in an average crop. 



This crop is very similar to the white potato in regard 

 to food required. Two hundred bushels of sweet pota- 

 toes, not including vines, contain, on the average, 30 

 pounds of nitrogen, 10 of phosphoric acid and 45 of potash ; 

 and since the yield of the general crop is larger on the aver- 

 age than one of white potatoes, a liberal supply of the 

 minerals must in all cases be provided. The studies made 

 of this crop have not yet established the best proportions 

 of the constituents in fertilizers, though such experiments 

 as have been conducted show that those that contain a 

 very considerable excess of potash over the other elements 

 are preferable. While nitrogen is needed, too much, 

 particularly in soluble forms, seems to encourage too large 

 a growth of vine, which contributes to yield, but at the 

 expense of quality, which is a very important considera- 

 tion. The best growers use fertilizers containing a small 

 percentage of nitrogen and a high percentage of phosphoric 

 acid and potash. Applications that furnish 20 pounds of 

 nitrogen, 50 of phosphoric acid and 80 of potash to the 

 acre have given excellent results in regions in New Jersey 

 in which market quality up to a certain point is quite as 

 important as increase in yield, though, of course, yield 



