February, 1930] agricultural experiments 1929 25 



frequent light applications of manure result in its more economical use 

 than infrequent heavy appHcations. 



Nitrate vs. Sulphate in Fertilizing Potatoes 



Two years of results of tests of the relative effectiveness of nitrate and 

 sulphate fertilizers as a source of inorganic nitrogen for potatoes indicate, 

 both from a standpoint of total yield and size of tubers, that sulphate 

 alone is not quite as desirable as nitrate alone and that neither alone is as 

 good as a mixture of the two. The plots treated with the mixture yielded 

 ten bushels more to the acre than the nitrate plots and twelve bushels 

 more than the sulphate plots. 



Very little difference was noted in the yields from plots fertilized with 

 450 pounds of concentrated 16-32-16 fertilizer and plots treated with 1800 

 pounds of the 4-8-4 grade. (Hatch Fund.) 



TEMPERATURE AND THE PRODUCTION OF SEED POTATOES 



A close correlation exists between temperature and the appearance of 

 mosaic symptoms in potato stock, finds 0. Butler. A low mean daily 

 temperature is favorable for mosaic, and a high daily mean temperature is 

 unfavorable. A high mean daily temperature accompanied by tempera- 

 tures above 25 degrees Centigrade causes a masking of mosaic symptoms; 

 and the number of hours the temperature remains above 25 degrees Centi- 

 grade seems to be particulai'ly significant when the mean daily tempera- 

 ture for the growing season is above 17 degrees. 



The experiment is in its sixth year, and in the years that the mean tem- 

 peratures at Colebrook and East Kingston were approximately the same 

 the mosaic readings were nearly alike in the two widely separated plots. 

 Difficulty has been experienced in preventing deterioration of the stock 

 from leaf-roll at East Kingston. On the Irish Cobbler plots this was 

 effectively done by early harvesting. 



In 1928 an experiment was begun to determine the value of early har- 

 vesting in checking leaf-roll with the Green Mountain variety. The 

 stock planted produced plants showing 6.40 per cent mosaic and .56 per 

 cent leaf-roll. Following the first inspection the field was rogued, and, as 

 the season was unusually cool for the locality, the roguing for mosaic was 

 thorough. Potatoes harvested at 81 days after planting showed no 

 mosaic and 6.9 per cent leaf -roll; at 90 days, no mosaic and 3.29 per cent 

 leaf -roll; at 101 days, no mosaic and 2.19 per cent leaf -roll; at 110 days, 

 .24 per cent mosaic and 1.41 per cent leaf-roll; and, finally at 143 days, .21 

 per cent mosaic and 21.27 per cent leaf -roll. 



At North wood stock was grown in 1927 that showed on the average 

 before roguing 2.78 per cent leaf-roll and no mosaic. Seed saved from 

 this stock was greened before planting in 1928, and 39.3 per cent of the 

 tubers were removed on account of leaf-roll, the diagnosis being verified 

 by actually growing the rejected seed. The remaining seed, presumably 

 healthy stock, was planted, and at the time of the first inspection showed 

 1.59 per cent mosaic and 35.63 per cent leaf-roll. The climate at North- 

 wood, in temperature characteristics at least, is very similar to that of 

 East Kingston. 



Small seed produced plants as free from leaf -roll and mosaic as standard 

 size seed. (Purnell Fund.) 



