Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
Balancing yield and quality is necessary in processing vegetables. Light skin color in eastern US grown pickling cucumbers is a quality issue for processors and inconsistent length:diameter (L:D) ratio leading to excess length is also a concern.
Fertility programs were evaluated for their effect on yield and quality factors in field studies in 2011 and 2012 at the University of Delaware research center near Georgetown. Two pickle cultivars, ‘Vlaspik’ and ‘Expedition’ were tested in all trials. Nitrogen rate treatments were 80, 120, 160, and 200 lbs/A applied as a split application with 40 lbs/A applied at planting and the remaining 18 days later using urea ammonium nitrate (UAN) solution or ammonium sulfate (AS) dry fertilizer.
In other trials, varied sources for sulfur and magnesium were tested for their effect on pickle yield and color including gypsum and dolomitic limestone preplant; potassium magnesium sulfate preplant and foliar; ammonium sulfate preplant and sidedress; magnesium sulfate sidress and foliar, elemental sulfur foliar, and ammonium sulfate nitrate preplant.
Color and L:D data was recorded from 3A and 3B pickle grades. Fruit color was impacted by N and differed by variety. In Expedition there was an increase in chlorophyll as nitrogen increased. This effect was not seen in Vlaspik. Treatments with ammonium sulfate were more highly colored that those using UAN. Yield was not increased in either variety past the 120 lbs/a rate. Pickle length did not vary with N rate. There were no significant differences in yield or color between sulfur (S) or magnesium (Mg) treatments.
This research has shown that increasing nitrogen can improve pickle color; however, this effect is variety dependent. There may be critical N rates for varieties to achieve highest color. However, this needs to be balanced with potential for producing too much foliage and increasing the potential for disease incidence. The addition of ammonium sulfate as part of the nitrogen source was shown to increase the amount of dark colored areas in pickle fruits. Additional nitrogen above 120 lbs per acre, while improving color, did not improve yield. By including a portion of the nitrogen source as ammonium sulfate, the same color improvement may be obtained without using higher total nitrogen rates.
There was an indication that ammonium sulfate produced more highly colored pickles in two studies but not in the third. Use of ammonium sulfate preplant did not have the same effect as when used as a sidedressing. Ammonium sulfate also had a significant effect on pickle length. This effect may be from the sulfur content and the specific balance between sulfur and nitrogen. Results suggest that N:S balance is important for color in some pickle varieties.
Adding additional magnesium or sulfur in other forms (other than ammonium sulfate) was not advantageous.