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Fluid Journal : Fall 2012
03 The Fluid Journal Fall 2012 45 percent nitrate, and 20 percent water (eutectic point), the resulting solution contains 32 percent N with a salt-out temperature of 32oF (Figure 2). At this ratio, about 50 percent of the N in UAN is present as urea-N and 50 percent as ammonium nitrate-N. As a result UAN provides about 25 percent of total N as nitrate-N, 25 percent as ammonium-N, and 50 percent as ammonium forming Urea-N. The principle of eutectic solutions is the backbone of the N solution industry (and interestingly enough, the backbone of the fluid phosphate industry as well). Salt-out temperature is the temperature at which the concentration of salts in solution exceeds the solubility of those salts at a specific temperature and those salts begin to crystallize ('come out' of solution). Table 1 provides typical compositions and characteristics of the most common grades of UAN solution found in the market. Both the salt-out temperature and the density of UAN increase as the nutrient content increases. Notice that UAN contains a remarkably small amount of water with 28 percent UAN containing 30 percent water (wt/wt), but 32 percent UAN contains only 20 percent water- -or about one quart of water per gallon of 32 percent UAN! These numbers may vary slightly from one manufacturer to another, but will be relatively close. Popularity increases There are many reasons the popularity of UAN has continued its steady increase over the years. While advantages of dry fertilizers and ammonia generally center on the purchase price of needed N, there are many other aspects of overall crop production management that influence the final applied fertilizer cost and overall profitability. Safety issues. While direct- applied ammonia dominated the U.S. fertilizer N marketplace through the 1970s and into the 1980s, its popularity has gradually declined in the decades since. Part of this loss of direct-applied ammonia market share is due to safety and liability issues that result in the need for strict safety precautions when handling and using this product. Dry fertilizer N sources tend to absorb moisture during storage, which may result in some caking problems. At the same time, whenever dry fertilizer is handled, some loss of product quality occurs as "fines" develop, which may lead to dust problems and bridging in application equipment. Handling, storage, and application of UAN, in comparison, are much safer and simpler than other N sources. UAN has a long shelf life, does not absorb moisture or suffer loss of product quality in storage, and does not require high pressure tanks and plumbing for storage and application. Also, there are many more equipment options for non-pressure UAN application than other N sources. Logistics. Tendering UAN is easy and convenient. It is much easier and more logistically efficient to pump UAN as compared to shoveling or using an auger or belt conveyor. Easily blended with many secondary and micronutrients, UAN can be mixed with many other fluid fertilizer products to fill a 'prescription' of nutrient needs for efficient crop production. And unlike blending of several dry fertilizer products with urea, fluid blends of UAN with other fertilizer products are homogeneous, each drop has the same analysis and does not segregate. Dry blends of urea with other dry fertilizer products may be uniformly mixed at the local blend plant, but they begin to 'unmix' and segregate as they are transported, handled, and applied. Pesticides of many types can be included in a simultaneous application to fields, including pesticides in a single application. The practice of combining UAN with certain pesticides (especially herbicides) in a simultaneous application eliminates a trip across the field, which greatly reduces application costs. Additionally, depending on specific field and weather conditions, these combined applications potentially increase yield potential by providing for more timely fertilizer and/or pesticide applications, as well as other time-critical management practices affecting the crop. Uniformity/accuracy. It is much easier to calibrate equipment to uniformly apply UAN via fluid applicators as compared to other types of fertilizer materials. Additionally, it is also much easier to accurately regulate the desired rates Table 2. Corn Yield and N Recovery Increased By Split Applications of UAN G. Randall, Univ. of Minnesota Fall Ammonia Spring Preplant At Planting Sidedress Yield N Recovery Lbs N/A Bu/A % 0 0 0 0 118 --- 100 + N-Serve 0 0 0 167 63 80 + N-Serve 0 0 0 169 60 0 100 NH3 0 0 164 60 0 100 UAN b'cast 0 0 163 59 0 0 40 UAN dribble 60 UAN coulter 175 73 0 0 40 UAN b'cast 60 UAN coulter 177 73 Table 1. Typical Composition and Characteristics of UAN Solutions 28% N 30% N 32% N Composition Typical Weight Percentage Of UAN Solutions Urea 39.4 42.2 45 Ammonium Nitrate 30.6 32.8 35 Water 30.0 25 20 Characteristics Typical Characteristics of UAN Solutions pH 7.0-7.5 7.0-7.5 7.0-7.5 Density (60o F) 10.67 lbs/gal 10.87 lbs/gal 11.06 lbs/gal Salt-out Temperature ~0o F ~16o F ~32o F
Late Spring 2012