Onions require key nutrients during their growth in order to optimize yield and growth, such as light, water, minerals, oxygen, carbon dioxide, and a suitable temperature. These mandatory growth components must be available and in balance with others for optimum onion growth. In order for growers to know what nutrients their onion crops require, tests are completed to show the nutrient make-up of the soil and plant tissues. Soil tests determine what nutrients are already present in the soil and which nutrients need to be added. They also measure soil acidity and can highlight contaminants in the soil that require treatment. Onions need 16 elements to grow; and, while some are found naturally in water and air, others are supplied by the soil (Plant Tissue Analysis). Nitrogen (N) is one of the most common chemicals needed for optimal onion production. Because available forms of N (nitrate and ammonium) are rapidly lost from the soil, it is most efficient to apply N fertilizer in small increments as needed.

In addition to soil tests, tissue tests are also helpful tools for growers—they show the grower what kind and how much fertilizer to add to their crops. However, there are some limits to using this method. For example, if the crop has been sprayed with certain nutrients, the test will be inconclusive (Plant Analysis).

Root tissue analysis has been shown to be extremely useful on onions. With root tissue analysis, studies can be completed on the effects of fertilizer on onions as well as their nutrient levels.

There are many different ways to apply nutrients to a field of onions. The most commonly used are fertigation, foliar, and broadcast application of nutrients. Fertigation is the application of fertilizer through irrigation water—applying fertilizer in a liquid form is an easy, efficient application method and can also incorporate pesticide and fungicide. Spraying the leaves of plants with fertilizer is also an option. With this method, a grower must consider that leaves can only collect and utilize a small amount of nutrients at a time. The spraying method is extremely dependent on environmental factors. Banded application, where fertilizer is only placed beside the crop on fields, and broadcasting (using tractors and spreaders) are also options. Of all these options, fertigation is the quickest and most precise way to give growing onions nutrients.