Document RpgbKRnx11kLbn5RoK07EYOwk

126 GHAPTER 8 ' R. J. Downs, S. 6. Hendricks wd H. A. Borthwick: Fhotoreversible control of elongation of pinto fawna *nd other plants under-normal conditions of growth (Botanical Gazette, Vot. 118, 1957, p. 199). - 44 S. B.' Hendricks:and Hi A.Borthwick: Control of Plant Growth by light (Environmental Control qf Plant Growth, edited by L:T. Evans,:AcMemiePress,;1963). . W. 8. Hfflmm: The Physiology cf Flowering (Holt,.Rinehart, 'and Winston, New York, 1962). ' * It Van Der Veen' and G: Meijer: Light and Plant,Growth (Philips Technical library, Philips Research Laboratories, Eind hoven, The Netherlands, 1959). n R. B. Withrow: Photoperiodiem and Related Phenomena.in ^ >1965 Guide And Data Book Plante and Animate (American Association for the Advancement u F.' w.` Wentr*Bxperinwttal Control of Plaint Growth.' (7he Ronald Press Company, New York, 1957).' ' ** A. Jaffe: An evaluation of controlled-temperature environ, meats for plant growth investigations (Nature, VqL-1043, 1962). " R. N. Morse and L. T. Evans: Design and development of ceres (Journal ofApicultuml Engineering Research, VoL 7, 1962). " C. S. French, W. M. Hieaey, and H. W. Milner: CO% Control for Plant Growth Chamber (Carnegie Institution of Washington, Year Book, 19S8,p. 352). P._Garistrs: Climatic Control of PhbtosvnthA* ?--- j,'..-? < CHAPTER 9 PHYSIOLOGICAL FACTORS IN DRYING AND STORING FARM CROPS Factors That Determine Safe Storage, Moisture Measurement, Drying Theory, Drying of Specific Crops ODERN man has learned to store crops in great quanti species of molds. The respiration of the microflora, as well as M ties under more critical conditions, with a very low an increased respiration of the grain itself, due to high mois percentage of storage loss, and at a very low cost relative toture content, produces heat and more moisture to further com the value of the commodity. Stored crops are living material plicate the problem. Such self-heating of forage crops stored found in various stages of dormancy. The object of storage is to TT,ainfft'n this dormancy to tire greatest degree and to fwimmiitfr any changes that may occur with time. Stored crops are subject to respiration or reaction with atmospheric oxygen to produce heat, water, and carbon dioxide. Carbohydrate and fats are most subject to this type of change. Crop materials such as grain are inhabited by various micro at too high a moisture content can result in uncontrolled tem perature rise to the point of ignition and spontaneous com bustion. Very low moisture (loss than 11 -percent) grain is not as attractive to insects as higher moisture grain; however, insects can also be controlled by the use of insecticide chemicals. Table 1 lists moisture levels for safe storage ofseveral crops. organisms, including molds and yeasts. Under certain condi tions these organisms thrive by breaking down the grain as-a Temperature growth media and producing further heat, water, and'carbon For safe long-term storage of grain, temperatures in .the dioxide through their, respiration process. Their contribution 40-50 F range are considered most desirable. At this tem to the total respiration rate of the total mass is usually greater perature the respiration rate is low'if the moisture content of than that of the crop itself. the grain is also at a safe level. Insect activity is also reduced, Chemical changes other than respiration also occur, fre^ since most insect species are unable to reproduce at tem quently aided by enzymes, the organic catalysts. Some of the peratures below 50 F. Lower storage temperatures near 0 F common reactions that occur include the change of starches to will apparently preserve grain indefinitely, even at high mois sugars, fermentation, as well as protein changes to amino ture contents; however, no practical means of .maintaining acids and other forms. These changes are not generally con such a temperature in large storages has been demonstrated sidered desirable in the uncontrolled state. Not tiie least hazard to stored grain is insect damage. Cer to date. Higher temperatures generally increase the rate'of all tain species of insects do significant damage to our grain chemical reactions; however, enzymic reactions may be supply in spite of the availability of control measures. stopped at extremely high temperatures, near.200 F. The A good general reference on the subject of grain storage is a respiration rate of stored products generally increases with monograph edited by Anderson and Alcock1 - who have increasing temperature until the temperature is high enough brought together the reviews of several specialists who have in to kill the microflora whose respiration is helping to produce turn summarized the work of many original investigators on the subject of grain storage. the heat. A description of the design and operation of crop driers can Oxygen Supply be found in Chapter- 32 of the 19&4 Guide And Data Book. As indicated previously, much of the deterioration of high FACTORS THAT DETERMINE SAFE STORAGE moisture grain stored at ordinary ambient temperatures is caused by respiration processes which require oxygen. If Moisture Content High moisture grain deteriorates from several causes, most of them connected with the fact that higher moisture content results in a high equilibrium .relative humidity (above 70 percent) of the inter-seed air in the grain. This condition encourages the growth of microflora, particularly the aerobic' oxygen is excluded from a grain storage, the oxidative respira tion of the grain and the aerobic microflora will cease, much as combustion ceases when oxygen is no longer supplied. This can be accomplished in a practical way by placing the grain in a gas-tight structure. It should be emphasized that not alldeteriorative changes are haJted by lack of oxygeh'if tempera ture and moisture content are high. Certain chemical-changes . Tt* seaenl reapouibttitjr for thit chapter is uaigaed to tiw A8KRAE-ASAE iBttTKxwty Commit*** oa Pbot ad Animal- Ptysiolofy.- This tnteraocietjr Ccmaittse eoossta of ASHRAE TC 1.5 and Committee C-18 of the Ameheu of Axrieoltur*)'Engineers. - and anaerobic fermentation proceed in the absence of oxygen. These are the changes that carry out the eristiing prooera in high moisture grain and forage crops and give,them:their 127