On-Farm Grain Drying Methods
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DIVISION OF AGRICULTURE RESEARCH & EXTENSION UJA--University of Arkansas System Agriculture and Natural Resources FSA1072 OnFarm Grain Drying Methods grain production more attractive Sammy Sadaka, Introduction resulting in more producers and Ph.D., P.E. When grain is harvested from the more production. This increased sup Assistant Professor field, it contains dry matter and water. ply is associated with a larger grain Extension Engineer While water is necessary for price swing between harvest and plant growth and grain production, nonharvest periods. Therefore, in Karl VanDevender, excess moisture after grain maturity addition to more control of harvest can lead to storagerelated problems. timing, there are potential economic Ph.D., P.E. Grain moisture content is expressed advantages to onfarm drying and Professor Extension as a percent of the grain weight. storage. Accordingly, several Arkansas Engineer For example, 100 pounds of 13% producers indicated their interest in moisture content rice contains 13 exploring the possible techniques of Griffiths Atungulu, Ph.D. pounds of water and 87 pounds of dry onfarm grain drying and storage. Assistant Professor matter rice. Grain moisture con This fact sheet provides an overview Grain Processing tent and temperature play a key role of the basics of onfarm grain drying Engineering in determining safe storage life (see and storage methods. https://www.uaex.uada.edu/publications/ pdf/FSA1058.pdf). As a ru le, dryer grain and cooler temperatures increase safe Grain Drying Basics storage durations. In contrast, wetter grain and warmer tempera Storage Moisture Content tures increase the potential for pests, The first step in drying grain is insects, mold and fungi to reduce determining the desired, or target, grain quality and market value. grain moisture content level. Under Therefore, the primary objective of drying grain reduces safe storage grain drying and storage is to manage time, increases the potential for qual the temperature and moisture of the ity losses and increases the likelihood air around the grain to minimize of high moisture price dockages grain quality and market value losses upon sale. Over drying grain reduces while holding grain for better market income due to increased drying costs. opportunities. Maintaining grain qual In addition, since grain is usually sold ity requires drying the grain to safe on a weight basis, one of the expenses moisture content levels after harvest involved in drying grain is the “cost” followed by lowering and maintaining of the weight loss that occurs during the grain temperature within a few the drying process. This weight loss degrees of ambient air temperatures. by drying is referred to as “shrink” Arkansas Is and is expressed as a percentage of Our Campus Traditionally, onfarm grain the original quantity before it is dried. drying and storage has seen limited Shrinkage should be considered to use in Arkansas. However, recent accurately determine the total cost of changes in agricultural markets and mechanical drying. Shrinkage tables Visit our web site at: s .uada technological advances have made provide bushel weights for various http ://www.uaex .edu University of Arkansas, United States Department of Agriculture, and County Governments Cooperating moisture content levels of grains (see https://www. uaex.uada.edu/publications/pdf/FSA1078.pdf). When Temperature and Humidity choosing the desired target moisture content, safe As indicated earlier, air temperature and humid storage time, grain shrinkage and buyer’s require ity determine EMC level and thus the drying capacity ments should be considered. of the air around the grain. Since ambient air temper atures and humidities fluctuate over time, the EMC Grain conditioning by drying and cooling to target and drying potential of air also fluctuates. Therefore, ranges should begin immediately after harvest. If in drying systems that use ambient air (with or with possible, avoid leaving grain in carts and buggies for out low levels of supplemental heat), air temperature more than a few hours or overnight. As indicated and humidity should be monitored and used to deter earlier, grain temperature and moisture content dic mine when the drying system should be operated. If tate how quickly grain quality and market value are mismanaged, drying opportunities could be missed or reduced. Drying and cooling freshly harvested grain moisture could be added back to the grain environ will delay spoilage and must begin within 24 hours ment increasing storage risks and wasting the energy and preferably within 12 hours after the harvest. to run fans again to redry. The ability to heat drying air increases the oppor Equilibrium Moisture Content tunities to dry grain and provides more control over the grain drying and storage process. If the EMC of The moisture in grain creates vapor pressure. ambient air will result in grain drying, adding heat In a like manner, the moisture in the air around the will reduce drying time and lower the final grain grain also creates vapor pressure. Moisture moves moisture content. The reduced drying time is usually from areas of high vapor pressure to areas of low desirable. However, if mismanaged, there is an vapor pressure. This moisture movement continues increased risk of over drying grain. There is also until the vapor pressures in the grain and air are energy cost to run fans and heaters. If the EMC of equal. The point at which vapor pressure in grain ambient air will not result in grain drying, adding and air are equal is called the Equilibrium Moisture heat can provide drying that otherwise would not Content (EMC). The EMC is dependent on three fac take place. As a result, the decisions of what type of tors: air temperature, air relative humidity around grain drying/storage system to install and when to the grain and grain type. EMC values for grain run fans and/or heaters become a process of balancing decreases as air humidity decreases or air temperature risks and economic inputs. increases (see https://www.uaex.uada.edu/publications /pdf/FSA1074.pdf). Thus, grain drying will occur For manually controlled systems, the temperature as long as the EMC is less than the current grain for determining EMC should be an average tempera moisture content. If the EMC is greater than current ture over the drying period. The relative humidity grain moisture content, drying will not occur. Instead, should be the average expected during the drying additional water will be added to the grain bin. Water period. However, several companies make automated will increase the potential for mold and needs to be grain drying controls which measure grain moisture, removed as soon as possible. air temperature and air humidity. These automated controls can take much of the “guesswork” out of grain drying. Temperature can be read with a ther mometer in the plenum or on the farm. Ideally, KEY CONCEPTS temperature and relative humidity should be mea l Moisture moves from high to low vapor sured on farm, but local weather information has pressure areas. been used in the decisionmaking process with acceptable results. l Grain drying occurs when the vapor pressure in the grain is greater than the vapor Evaporating moisture from grain requires energy pressure of the air surrounding the grain. in the form of heat. In general, it takes 1,100 BTUs of heat to vaporize one pound of water at 100% effi ciency. Heat energy can be supplied by the natural heat content of air or by supplemental heating. The If the current air conditions will not result in amount of moisture that air can absorb and transport grain drying, the easiest way to adjust EMC is by as it moves through the grain column is dependent heating the air. Heating air lowers the air relative primarily on EMC along with some influences from humidity and thus lowers the EMC and decreases air velocity, the distance the air travels and grain drying times. As a result, after heating air the new moisture content. As air moves through the grain relative humidity must be measured or calculated column, it absorbs moisture and thereby loses some before determining the new EMC. or all of its drying capabilities. grain to a certain moisture content and then harvest Grain Drying Options and dry further or market the grain at harvest. The Grain drying strategies can be divided into the disadvantage with this method is the reduced control following approaches: field drying, natural air drying, of the drying process and potential exposure to low temp drying, high temperature drying, and com weather and pests which causes damage. In addition, bination or dryeration. Allowing the grain to dry in over drying grain usually increases shatter and the field is the most widely used method. In many losses during harvest. Field drying should be used to cases, partial field drying is often used in conjunction manage grain moisture at the time of harvest. The with postharvest drying to reach target storage time of year grain reaches maturity and the weather moisture content. Natural air/low temp grain drying conditions can have a major impact on how quickly is best described as filling or partially filling bins the grain will dry to a moisture content acceptable with freshly harvested grain, then running fans to for storage or sale. force air through the bins until the desired moisture content is achieved. High temperature drying is either conducted in the bin or within a pass dryer. Natural Air Drying Air is heated to high temperatures and forced Natural air drying is the most common onfarm through the grain until the grain dries. Combination drying method in Arkansas. It refers to the process and dryeration is done by partially drying grain with in which grain bins are filled or partially filled with high temperature dryers, and then the remainder grain and then natural air is moved through the of the drying process is done with low temperature grain with fans (Figure 2).