Acidification of the Soil in Northeastern Apple Orchards

DURING the past 15 years sulfur fungicides have come to be far more significant in causing acidification of the soil in northeastern orchards than they used to be. There are two reasons for this. First, the variety McIntosh, which is very susceptible to apple scab, has become the most important apple of -the area, replacing Baldwin which is less susceptible. Second, elemental sulfur sprays and dusts which have value only as protectants against scab have largely taken the place of lime-sulfur sprays which have powerful eradicative action and hence were not applied so often. The common use of acid-forming nitrogenous fertilizers has also caused appreciable decrease in soil pH. Besides acidification by these two practices and that resulting from normal leaching of the soil, there may be an average decrease in pH under fruit trees due to the presence of roots in rather great concentration. The maximum possible effects of spray and fertilizer practices may be estimated with reasonable accuracy. For instance, Table i shows the pounds of sulfur uncompensated for by calcium that were applied per tree for the last 5 years in a block of 35year-old McIntosh apple tree,s in the Cornell University orchard. The past 3 years have been difficult scab years. The average annual uncompensated sulfur applied in this orchard would probably bein the order of 10 to 12 pounds per tree (270 to 324 pounds per acre) rather than the 12 to 16 pounds per tree (324 to 432 pounds per acre) that the table indicates. Ammonium sulfate is the most acidifying nitrogenous fertilizer commonly used, and no more than 8 pounds would be applied annually to the ground under such trees. The sulfur contribution of such a dose is 1.9 pounds per tree or 51 pounds per acre, about onesixth of the uncompensated sulfur applied in the 1943