Boyd, A. H.

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Mississippi State University Scholars Junction Proceedings of the Short Course for Seedsmen MAFES (Mississippi Agricultural and Foresty Experiment Station) 4-1-1975 Bulk Seed Storage, Drying and Aeration A. H. Boyd Follow this and additional works at: https://scholarsjunction.msstate.edu/seedsmen-short-course Recommended Citation Boyd, A. H., "Bulk Seed Storage, Drying and Aeration" (1975). Proceedings of the Short Course for Seedsmen. 298. https://scholarsjunction.msstate.edu/seedsmen-short-course/298 This Article is brought to you for free and open access by the MAFES (Mississippi Agricultural and Foresty Experiment Station) at Scholars Junction. It has been accepted for inclusion in Proceedings of the Short Course for Seedsmen by an authorized administrator of Scholars Junction. For more information, please contact scholcomm@msstate.libanswers.com. BULK SEED STORAGE, DRYING AND AERATION A.H. Boydl/ To meet the demands of the ever-increas i ng market for quality seed, many seedsmen have found it necessary to expand and modify their operations. To keep a seed processing plant operating, it is necessary to have adequate seeds in storage either on the premises or on the farm where they were produced. However, our storage, drying and aeration problems do not neces-sarily begin when we load the seed into the storage facility. Quite often we 11 Store11 seed in the fields when weather conditions prevent a timely harvest. It has been demonstrated that soybeans which have been damaged, mechani cally or by weather, deteriorate much faster in storage than those which were harvested early with little or no weather damage. Part of this effect is the presence of more fungi on weather damaged seeds . Mechanically damaged seeds are more sus-ceptible to storage fungi than undamaged seeds. As harvesting equipment gets larger, farms get larger, and the harvest season shorter, there is more and more pressure on the drying and storage faci l ities. This creates a greater tendency for farmers to have storage on their own farms. The presence of storage and dry-ing bins on the farm give the farmer-seedsman more f lexibi l ity in his choice at the market , but at the same time create management problems and add the risk of seed losing value because of improper handling. 25 Adaptations of existing equipment may be as varied as the me-chanical drying and storage ingenuity of the seedsman and the dictates of hts extsting equtpment. In some cases batch drying has been used in combination with dryer bins quite effectively . Since most of these dryers are designed for grain, a temperature rise of 90 to as much as 150F i s common. With a limitation of llOF air temperature for drying seed, the farmers must be limited to a 30-50F temperature rise to effectively dry seeds. The drying rate will be slower at the lower temperature than 1t would have been under grain drying conditions. The most common farm installations are large f lat bottom bins, Generally, the greatest problem with such installations is the tendency of the seedsman to fill the bin completely rather than fill it to the level where effective drying can take place . Such bins almost always can store much more than they can effectively dry. Figure 1 shows the relation of horse power to depth of seed and air flow in a typical soy-bean storage and drying bin. Note that as the depth of seed increases, the a1r flow i'n cubic feet per minute per bushel decreases rapidly un-til a point is reached where the air flow approaches zero . Bin drying can 11Dr. Boyd is an Assistant Agronomist at the Noble Pace Seed Tech-nology Laboratory, Mississippi Agricultural and Forestry Experiment Sta-tion, Mississfppi, State University. 26 -cu 16 ..c "' :::J c:o ' ::E: 14 L&.. u c: -~ 0 12 -L&.. ~ - 10 < 0 0 NOTE : Exact curve will vary s lightly with manufacturer's fan design. ~20H.P. 1 2 3 4 5 6 7 8 9 10 Depth of Fi ll in Feet 1000 2000 3000 4000 Capacity in Bushels Figure 1. Estimated air flow in cfm/bu. vs. seed depth for a 27 foot diameter drying bin of soybeans with 10 hp and 20 hp centrifugal fans . 11 5000 12 be an economical and effective method of drying but when a high side-wall bin is almost completely full, about all you can expect out of drying fans of any practical size is a good job of aeration or tem-perature adj ustment but not a good job of drying. 27 As we can eas ily observe as we travel, almost anything is mecha-nically possible in the way of modification or construction of drying, storage and aeration facilities. Facilities are only limited by the imagination of the designers and the economics of construction. If one will carefu lly observe seed drying facilities, it soon becomes ob-vious that facilities are not the ultimate answer to the question . The man operating the drying facility and making the decisions must understand the problem; he must understand the principles of drying and storage, the relationships of drying fronts, air flow, temperature, moisture evaporation and heat transfer as well as the mechanics of air movement and seed conveying. One important point to remember i s that there is no magic moisture content for bulk storage of seed . The equilibrium moi sture content of a seed at a given relati've humidity changes somewhat with change in temperature . Seed reach a lower moisture content at a given relative humidity at a higher temperature, but the same seed will reach a higher moisture content at the same relative humidity at a lower temperature. Figure 2 gives an example of the equilibrium moi sture content of soy-beans at 40 , 82, and 92 F. Continuing with soybeans as an example, let us relate this diffe-rence in equilibrium moisture content at varying temperatures to the conditions as they exist in the field. Figure 3 shows average tempera-tures at Mississippi State, Mississippi and the maturity date of four varieties of soybeans to indicate the date and average temperature when harvest and storage is likely to begin. We generally assume that when seed are in equilibrium with 60% re-lative humidity they are quite safe for short term seed storage and reasonably safe even at equilibrium with 65% relative humidity. Figure 4 shows the equi librium moisture content at varying temperatures in re-lation to the varieties and average temperature at harvest. For example the Hill vartety soybeans harvested early in September will be quite warm and the 65% relatfve humidity equilibrium point is about 11%. If we store at the usually assumed safe storage moisture content of 12% with temperatures in this range we may encounter rapid deterioration of seed quality. Couple this situation with the occurence of green weed seed and plant parts in the early harvested crop and it is easy to understand how farmers often get tnto trouble with seed that are harvested in warm weather . figure 5 shows similar data for corn · but with the average tempera-ture at harvest time at various l ocations throughout the U.S. Notice that the equilibrium moisture content for corn at a given condition is htgher than for soybeans . This difference is due primarily to the dif-ferences tn chemical compositton of corn as compared to that of soybeans. Figure 2. Equilibrium moisture content of soybeans under different temperature conditions. N CXl I 35 -. co . 3 ~ 30 ......... .fj c: Q) .fj c: 0 u 25t /;82°F Q) s.. :;:, .fj VI ·~ 0 ~ E 20 :;:, ·~ s.. ..0 ·~ r-.,... :;:, CT UJ 15 10 5 0 10 20 30 40 ~o Gb lo a1o 9b 10b Relative Humidity (%) ~ .. ..... s::: C1l ..... s::: 0 u C1l s.. :::J ., ~') ·-0 ~ E :::J •.-s.. .Ll .,_. ,_.. •.-:::J CT ...., 29 18 17 16 15 14 13 s.. C1l .Ll ~ > 12 0 z . ~ .. 0 s.. 0 11 , u •.-.s::: u 0 s.. .Ll C1l VI .Ll s::: 0 C1l ..... ~ u 0 10 30 40 50 60 70 80 Ai r and Grain Temperature , °F Figure 3. Effect of air and grain temperature and equilibrium rel ative humidity on the safe storage moisture content of shelled corn. 90 30 18 0 N &.n N ....... ....... N . . . . ~ ~ ~ ~ u u u 0 0 0 ~ .. ~ ~ 1 V) s::: QJ QJ !... ..-~ !... ,.... s::: 0 •r-0 u.. :X: u QJ s... ::3 ~ V) ..... 0 ::E E ::3 •r-s... ~ ..... ..... ..... ::3 C1' LU lOL--------L----~~---L----~----~~~~--~--~~--· 30 40 50 60 70 80 90 Air & Grain Temperature, °F Figure 4. Effect of air and grain temperature and equilibrium relative humidity on the safe storage moisture content of soybeans. Seasonal Temperatures At Mississippi State, MS 80 La.. 0 Q) s... 70 :;:::, Hi 11 ~ , s... Forrest Q) 1o c. m 60 ~Ql/ Lee 68 1-Q) ~ Bragg C'l ~k , ~J' s... Q) 50 "',() > <: ~ n,~. E 00" Q) 1- 40 C'l c: 0 ...J 30 20 ._ __ _. ____ ~----~--~----~----~--_.--~ Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. MONTH Figure 5. Expected average temperature and harvest dates at Mississippi State, MS . 31 32 Moisture Migration Another phenomenon that is even more important in bulk seed stor-age, as compared to grain storage, is moisture migration. Differences in temperature between the outside and inside of a storage bin cause convection currents to flow inside the bin. Even if your seed are within a safe equilibrium moisture content and temperature condition, very cold outside temperatures can cause condensation or "sweating" around the top and sides of the seed mass (Figure 6). After the seed are cool, a subsequent period of warm weather can cause warm air cur-re~ts to rise alongside the bin with cool air settling through the cellter thus causi'ng a high moisture zone to form in the center bottom of the seed mass (Figure 7). Several changes in the weather can create hot spots in the seed which may not be detected until the bin is unloaded. Even more care is necessary to prevent such a condition in seed storage than in grain since i't has been shown by several investigators that germi nation and vigor decreases drastically long before a reduction of one commercial grain grade is noticed. Moisture migration due to convection currents can be prevented by timely aeration. Some good rules of thumb for aeration are: 1. When the average outside temperature differs more than 20F from the temperature of the seed in the bin, the aeration fans should be turned on and the temperature adjusted. 2. When a temperature rise of SF at any spot inside a bin is detected, the bin should be aerated regardless of weather conditions. 3. An air flow of about 0.1 cfm/bu is adequate for aeration purposes. The ultimate key to mai.ntaining high quality in our stored seed is stil l the man who is responsible for them. The greater his know-ledge of the many factors that affect changes in seed quality the more likely he is to recognize the conditions that can cause trouble and have self confidence enough to correct the conditions. IS WARMED Figure 6. Moisture migration caused by col d outside conditions when the seed mass is warm. 33 SEED SURFACE 34 WARM AIR (/') LU (/') -0:: 0:: -~ Figure 7. SEED SURFACE Moisture migration caused by warm outside conditions when the seed mass is cold . 

Bulk Seed Storage, Drying and Aeration

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Bulk Seed Storage, Drying and Aeration

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