Controlle Release Fertilizers on Onions, 1999.doc

? Malheur Experiment Station Oregon State University Controlled Release Fertilizers on Onions, 1999 Lynn Jensen OSU Malheur County Extension Office Lamont Sanders OSU Malheur Experiment Station Ontario, Oregon Introduction Controlled release fertilizers have been used for many years, beginning with the sulfur coated ureas. The early sulfur coated materials did not always give a uniform response, because the coating sometimes would crack or the coating would be of uneven thickness, allowing the fertilizer granules to break down at different times. However, newer generation of controlled release fertilizers have resin coats that better control the release of the fertilizer. Although controlled release fertilizers are generally 3 to 4 times more expensive than traditional materials, there are some possible advantages to using them, particularly in furrow irrigated, high value crops such as onions. One advantage is the possibility of applying all of the fertilizer in the fall when the beds are formed. Since controlled release fertilizers generally do not release nitrogen under cool fall or winter conditions, the nitrogen would not leach with the winter moisture. Most fertilizer nitrogen is applied in two or three sidedress applications, plus a small amount is applied in the fall when the field is bedded. A one-time application would save the cost of the sidedress applications. Finally, onions are irrigated heavily and nitrogen easily can be leached, requiring the application of more nitrogen than the crop actually requires. Controlled release fertilizers could match the fertilizer application more closely with the amount actually needed for plant growth. Materials and Methods The treatment and application data are included in Table 1. The controlled release treatments were fixed at 65 and 80 percent of the standard commercial application rate for the area. Table 1. Material and application data for the controlled release fertilizer trial, Ontario, Ore