24 UNIV. OF N. H. AGR. EXPERIMENT STATION [Bulletin 250 



Fertilizing Potatoes in Rotation 



Variations iu the nitrogen content of the fertilizers produced smaller 

 fluctuations in yield of potatoes than variations in phosphorus and potash, 

 in an experiment embracing 60 twentieth-acre plots testing potatoes, 

 oats, and clover and timothy three-year rotation at the Jackson Farm near 

 Colebrook. Potatoes on this farm seem to be quite sensitive to phos- 

 phorus; those plots which had received 1 ton of 5-0-7 grade fertilizer 

 yielding 72 bushels less than the checks while those receiving 1 ton of a 

 5-16-7 grade showed a gain of 61 bushels an acre (the check plots had re- 

 ceived one ton of 5-8-7 fertilizer). 



Still, while the soil does not seem to have sufficient potash, an additional 

 amount over the standard 7 per cent application did not increase the 

 yield to a significant extent. 



The yields of oats were very variable, indicating that cultivation of the 

 land during the wet 1928 season affected the crop. 



Both 2 and 4 tons of limestone gave significant increases on the mixed 

 clover and timothy hay in this rotation. There were no other variations 

 in treatments on the 1929 hay crop. {Purnell Fund.) 



Potatoes Need Potash 



When potatoes are grown on old, neglected lands 10 per cent of potash in 

 the fertilizer is none too much, finds F. W. Taylor. In previous years, 

 when fertilizer tests were conducted on lands in good state of fertility, 3 

 to 6 per cent of potash seemed ample. 



Data on yields were obtained from plots treated with fertilizers varying 

 in potash content from zero to 10 per cent, while the amounts of nitrogen 

 and phosphoric acid remained constant. The land was a sandy loam sod 

 and had not been plowed, manured, or fertilized for twenty years. Certi- 

 fied Green Mountain seed from New Brunswick was used. 



The average yields per acre for each treatment over a seven-year period 

 are: for the check, 168.7 bushels; 4-8-0 fertihzer, 224.3 bushels; 4-8-3 

 fertilizer, 248.5 bushels; 4-8-6 fertilizer, 262.9 bushels; and for the 4-8-10 

 fertilizer, 266.5 bushels. Fertilizer was applied at the rate of 1,500 pounds 

 to the acre in each case. 



Method of Applying Fertilizer to Potatoes 



For the third consecutive year placing the fertilizer widely in the row 

 with the seed at planting time has given better results than placing above, 

 below, or at the side of the seed. Fifteen hundred pounds of 4-8-4 fer- 

 tilizer were used, and the seed pieces were set one foot apart in rows three 

 feet apart. The average yield for the three years, when fertilizer was 

 placed with the seed, is 265.1 bushels to the acre. Placing below the seed 

 gave the second highest yield — -255.6 bushels — at side of seed third, and 

 above the seed the poorest yield. 



Manure Proves Worth in Potatoes 



That manure at the rate of 12 tons to the acre is worth $3.75 a ton, is 

 indicated by a three-year average of the increased yield multiplied by the 

 current price of potatoes. In 1929 an application of 12 tons of manure 

 increased the yield 75.6 bushels over no manure, and 24 tons increased it 

 107 bushels. These findings are in accord with the general theory that 



