See Dixondale Farm’s links below -extracted from their web page–and in the footer.

  • Start plants out and establish root systems with our exclusive Dixondale Farms Onion Special 10-20-10 fertilizer.*
  • Perform pre-emergent weed control at planting time with Treflan Herbicide Granules.*
  • Boost nitrogen levels with Ammonium Sulfate three weeks after planting for more rings and larger bulbs.
  • Use Mancozeb Fungicide with Zinc to control moisture-related issues.

From Dixondale Newsletter 3/28/19

The Importance of Nitrogen in Your Onion Crop

Your soil is the storage vehicle for the nutrients for your onion crop. Replenishing the soil with these essential nutrients is critical to having success. With all the rain that has fallen across most of the country your soil has lost lots of these nutrients due to leeching. Specifically, Nitrogen is the most common nutrient that is easily leeched from the soil by excessive rainfall.

The easiest way to determine if the onion plant has enough Nitrogen available is to look at the leaves. Plants that are lacking Nitrogen have a pale green to yellow appearance. If the tops are stunted and not growing also indicates a lack of this essential nutrient. Applying adequate Nitrogen to the plant not only greens the foliage but also increases the length of the leaves. It also enhances efficient uptake and utilization of other nutrients especially phosphorous and potassium, as well as increasing the number of leaves. Remember that each leaf translates in to another ring of onion so the more leaves you have, the larger the bulb will be.

Applying Ammonium Sulfate (21-0-0) or a similar source of Nitrogen at a rate of 1 cup per 10 feet will be adequate to generate a response in your onion crop. If you use another source of Nitrogen such as Urea (40-0-0), adjust the application based on the first number of the analysis. Each application will give your crop approximately 40 actual lbs of Nitrogen. After your plants recover, continue applying Nitrogen every three weeks at a rate of 1 cup per 20 feet to maintain adequate Nitrogen levels.

The amount of Nitrogen already in your soil depends on what was planted in the soil previously. Grain or corn will provide approximately 50 lbs of Nitrogen if it was planted previously in the same location that you are now planting onions. Most row crops such as beans, peas, and potatoes will not provide any Nitrogen the next year. Getting a soil sample will provide you with your starting point.

Total Nitrogen needed is in the range of 150-160 pounds of Nitrogen so in this case it is presumed that your soil already has around 28-58 units of Nitrogen to begin with.

Calculation of N application rate. (lb N per acre)

N requirement: 160
Soil test N: -44
Previous crop: +25
Irrigation water: -10
N rate to apply: 131 lbs N per acre

If you’re fertilizing less than an acre, see how to calculate your rate on a square foot basis.

In this case on a per acre basis, approximately 625 pounds of Ammonium Sulfate is required as a general rule of thumb. This will produce units of actual Nitrogen (625 X 21% Nitrogen content of Ammonium Sulfate).

Once the onions begin to swell at the bulb, you will need to stop any additional applications of Nitrogen. Applying Nitrogen late in the growing season will produce what is called “thick necks”. This will reduce the shelf life of the onions in storage. Onions with thin necks store better than onions with thick diameters.

Print Friendly, PDF & Email