288 Mineral Nutrition of Plants 



changing from lime-sulfur to elemental sulfur fungicidal spray pro- 

 grams to find that it was desirable to reduce the rate of nitrogen ferti- 

 lization. Recently, an experiment reported by Dr. D. H. Palmiter has 

 indicated that elemental sulfur sprays may also reduce vegetation and 

 that nitrogen fertilization may offset these effects. He found that over 

 a six-year period apple trees sprayed with Fermate (ferric dimethyl 

 dithiocarbamate) and given no nitrogen fertilizer yielded as much as 

 trees sprayed with elemental sulfur and given 5 pounds of urea annu- 

 ally. Both of these treatments resulted in an increase in yield of 38 per 

 cent or more over the yield of trees unfertilized and sprayed with sulfur. 

 While there was some nitrogen in the Fermate spray, analysis of leaves 

 indicated that the increase in yield could not be attributed to that; 

 rather, it seems to be due to absence of spray injury. 



OTHER CONDITIONS AFFECTING NITROGEN RESPONSES 



There are, of course, a large number of conditions that may limit 

 nitrogen responses besides the ones that have been discussed. In New 

 York Mcintosh orchards, excess or deficiency of soil moisture and 

 serious injuries to the leaf surface from insects, disease, or spray ma- 

 terials are not uncommon limiting conditions; occasionally potassium 

 and magnesium deficiencies may be significant factors. Their effects 

 on nitrogen responses are of several sorts. Excess moisture in heavy soils 

 results in poor soil aeration which may both reduce the absorbing sur- 

 face of the root system and the ability of the absorbing surface that is 

 there to function efficiently. This will ultimately lead to the death of 

 the tree. Most commonly, the periods of poor aeration occur in the 

 spring and are short enough to permit survival of mature trees in 

 marginal locations; the effect is one of general devitalization and 

 failure to respond to good management in growth and productivity. 

 Soil moisture deficiency, occurring usually in midsummer or later, may 

 have no influence on growth or set of fruit, and may actually result in 

 increased bloom the following spring. However, the size of the fruit 

 in the year of drought is decreased in proportion to the duration of the 

 period of moisture unavailability in the soil. Fruit color may be some- 

 what improved as a result of some moisture deficiency but, if the 

 deficiency period is prolonged and continues until harvest, the quality 



