Nitrogen, Sulfur, and Magnesium on Once-Over Harvested Pickling Cucumbers

Gordon Johnson, Extension Vegetable & Fruit Specialist;

Three years of research were conducted from 2011-2013 on the effect of fertility programs on pickling cucumber yield and quality. Processors were concerned that fruits were not as well colored in Eastern and Southern production compared to the Midwest and North Central states.

With three years of results, it has been shown that increasing nitrogen (N) beyond a rate of 80 lbs/acre for a once-over harvest crop does not improve yield and high N rates may decrease yield or delay maturity.

Color of pickles was regulated largely by N rate: the higher the rate, the more green color on the pickles. This was an interesting result as it was thought that extra N might cause added leaf cover and therefore more shade resulting in lighter fruit, but the opposite effect occurred. Treatments with additional sulfur when added as ammonium sulfate had darker pickles in some trials but not in others.

Higher nitrogen can improve pickle color; however, this effect is variety dependent. The variety ‘Expedition’ responded to N more than the variety ‘Vlaspik’. There may be critical N rates for varieties to achieve highest color. However, this needs to be balanced with potential for delaying flowering and fruit set, excessive foliage production, and increasing the potential for disease incidence. Nitrogen sources did not vary in their effect on yield but they did vary in their effect on fruit color. We tested ammonium sulfate, urea, UAN solution and UAN solution with sulfur. The addition of ammonium sulfate as part of the nitrogen source was shown to increase the amount of dark colored areas in pickle fruits in some trials but not in others. By including a portion of the nitrogen source as ammonium sulfate, the same color improvement may be obtained without using higher total nitrogen rates but this effect is not consistent enough to be a general recommendation.

The use of sulfur sources with nitrogen or nitrogen fertilizers that contained sulfur did not improve yield when compared to straight nitrogen sources. There was an indication that ammonium sulfate produced more highly colored pickles in two studies but not in four others. Use of ammonium sulfate preplant did not have the same effect as when used as a sidedressing. Pickle length was influenced by nitrogen source in two trials where ammonium sulfate treatments had longer pickles. This effect may be from the sulfur content and the specific balance between sulfur and nitrogen in some soils and the sulfur:nitrogen balance may be important for pickle color and may be an issue on our light textured (sandy) soils. Trials showed that adding additional sulfur or magnesium as foliar applications had no effect on yield or quality of pickles.

In 2013, trials were expanded to include lower N rates and different at-plant and sidedress N applications. It is clear that modest amounts of nitrogen are needed to grow a pickle crop in Delaware loamy sand soils. Depending on the nitrogen release in the soil from previous crop residue, as little as 60 lbs of N may be needed to grow a high yielding crop when the majority is applied as a sidedressing at 3 weeks after planting and no more than 90 lbs/a N is recommended for a once-over machine harvest. While adding a sulfur containing nitrogen fertilizer such as ammonium sulfate may be beneficial from a quality standpoint, there was no effect on yield in our trials.

Use of NDVI to predict N needs was not successful in pickling cucumbers and therefore variable rate N application to pickles is not recommended at this time. Because the crop is quick growing and has low relative N needs, any variation in application that could be imposed would be minimal and of limited cost savings.