/ PRINCIPLES AND PRACTICES OF SEED STORAGE \ - f • UNITED STATES AGRICULTURE PREPARED BY DEPARTMENT OF HANDBOOK SCIENCE AND M AGRICULTURE NUMBER 506 EDUCATION ADMINISTRATION PRINCIPLES AND PRACTICES OF SEED STORAGE By Oren L. Justice and Louis N. Bass NAL BIcT^*'''"^' ^S^îcultural Library 10301 Baltimore Blvd Beltsville, MD 20705-2351 Agriculture Handbook No. 506 On January 24, 1978, four USDA agencies—Agricultural Research Service (ARS), Cooperative State Research Service (CSRS), Extension Service (ES), and the National Agricultural Library (NAL)—merged to become a new organization, the Science and Education Administration (SEA), U.S. Department of Agriculture. This publication was prepared by the Science and Education Admin- istration's Federal Research staff, which was formerly the Agricultural Research Service. Library of Congress Catalog Card No. 78-600015 Washington, D.C. Issued April 1978 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 STOCK NUMBER 001-000-03653-0 This publication reports research involving pesticides. It does not contain recommendations for their use, nor does it imply that the uses discussed here have been registered. All uses of pesti- cides must be registered by appropriate State and/or Federal agencies before they can be recommended. CAUTION: Pesticides can be injurious to humans, domestic animals, beneficial insects, desirable plants, and fish or other wildlife—if they are not handled or applied properly. Use all pesticides selectively and carefully. Follow recommended prac- tices for the disposal of surplus pesticides and pesticide contain ers. ¿/4ep44á<s¿ai4^a^ FOLLOW THE LABKL U.S. DffAXTMENT OF AORICUITUIIE Trade names are used in this publication solely to provide specific information. Mention of a trade name does not constitute a warranty or an endorsement of the product by the U.S. Depart- ment of Agriculture to the exclusion of other products not mentioned. CONTENTS Page Introduction 1 Purpose and significance of safe seed storage 1 The seed, a fragile, living organism 2 From harvest to sowing 4 Decline and death of seeds 5 Scope of publication 6 Seed factors that affect storage life 7 Genetic effects 7 Variation among species 7 Variation among cultivars 8 Generalizations 8 Preharvest effects 9 How seeds are affected 9 Effect of provenance 10 Effect of weather 10 Seed structure and composition 11 Hard seeds 13 Seed maturity 17 Relationship of maturity to storability 17 Grass seeds 17 Other field crop seeds 18 Vegetable seeds 18 Seed size 19 Seed dormancy 20 Relationship of dormancy to storage 20 Dissipation of dormancy 20 Dormancy and lifespan 21 Moisture content 21 Mechanical damage 22 Awareness of seed damage 22 Vulnerability of some seeds to damage 23 Response of seeds to storage conditions 24 Possible involvement of genetics 24 Vigor 25 Effects of storage environment on seed longevity 26 Temperature 26 Temperatures above freezing 26 Temperatures below freezing 30 Seed moisture content and relative humidity 35 Direct effect of moisture on seed deterioration 35 Relationship between relative humidity and seed moisture content 38 Rate of moisture absorption and movement 48 Effect of extreme desiccation on viability and vigor 50 Interrelationship of temperature, seed moisture content, and storage life __ 52 III Page Effects of storage environment on seed longevity—Continued Vacuum and gas storage 57 Barley 57 Corn 57 Flower seeds 62 Grasses 62 Legumes 63 Oilseeds 63 Rice 63 Sorghum 64 Vegetable seeds 64 Wheat 64 Confirmation studies at the National Seed Storage Laboratory 65 Illumination 77 Respiration and heating 78 Depletion of food reserves 78 Respiration products that retard this process 79 Release of heat in respiration 79 Measurement of respiration 79 Some factors affecting respiration 80 Preservatives for reducing respiration . 80 Conclusion 81 Effects of pests and chemicals on seed deterioration in storage 81 Storage fungi 81 Control of fungal deterioration 87 Insects 88 Rodents 89 Fungicides and fumigants 89 Changes associated with seed deterioration 91 Biochemical changes 91 Germination and vigor 92 Yield 93 Cytological changes 94 How seeds are dried 95 Characteristics of water 95 Principles of drying 9g Methods of drying seeds 96 Natural drying 9g Sun drying 97 Artificial drying 97 Factors to consider in selecting a dryer system IO9 Drying seeds with desiccants 123 Seed storage structures 123 Basic features of storage structures 124 Protection from water I24 Protection from contamination 124 Protection from rodents 124 Protection from insects 124 Protection from fungi 125 Protection from fire 125 Types of storage structures 126 Farm storage 126 Country elevator storage 126 Seed processor storage 126 IV Page Seed storage structures—Continued Types of storage structures—Continued Retail storage 127 Research storage 127 Germ plasm storage 127 Constructing controlled atmosphere seed storage facilities 129 Controlling temperature 133 Refrigeration 133 Heat load 134 Refrigeration agent 134 Liquid refrigerants 135 Typical mechanical refrigeration system 135 Condensing units 136 System capacity 136 Compressor capacity 136 Controlling humidity 136 Moisture movement between air and materials 137 Refrigeration-type humidity control systems 138 Desiccant-type humidity control systems 138 Common-sense practices 141 Ventilation 141 Stacking seed bags 141 Removing seeds from controlled storage 141 Warehouse cleanliness 142 Packaging and packaging materials 142 Requirements of different situations 142 Types of packages 142 How packages are filled . 143 How containers are presented to the filler 143 Weighing and measuring devices 144 How containers are closed 144 Packaging field seeds 145 Packaging vegetable and flower seeds 146 Package labeling 147 Porous packaging materials 147 Moistureproof materials 148 Moistureproof storage 148 Response of different crop seeds to moistureproof storage 148 Safe moisture levels for sealed storage 158 Moisture-resistant materials 159 Testing moisture vapor transmission of flexible materials 163 Moisture-barrier storage 164 Use of desiccants in sealed containers 168 Monitoring seed storage environment and seed condition 169 Germination and viability 169 Seed vigor 170 Seed moisture content 170 Fungi and bacteria 171 Relative humidity 171 Temperature 172 Storability of seed lots 172 Detection and identification of fungi and insects 174 Some practical information for storing and transporting seeds at ambient conditions 174 E xamples of storability of different plant species 174 V Page Some practical information for storing and transporting seeds at ambient conditions—Continued Climatological data pertinent to seed storage 182 Relation of storage conditions to intended storage periods 183 Care of seeds in transit 194 Storage principles applicable to in-transit seeds 194 Historical background 194 Some hazards to be avoided 195 General recommendations 196 Theories regarding seed deterioration 197 Changes in protein structure 197 Depletion of food reserves 197 Development of fat acidity 198 Enzymatic activity 198 Chromosomal changes . 199 Membrane damage 200 Respiration 200 Summary 201 Old and ancient seeds 201 Maximum known survival of crop seeds 202 Maximum known survival of primarily weed and native plant seeds 202 Seeds stored dry 202 Buried seed experiments 209 Circumstantial evidence of long lifespans of seeds 210 Seeds in soil disturbed by digging graves 210 Seeds in soil under forests of known age 211 Seeds frozen in arctic tundra 211 Canna seeds in burial mound 212 Indian lotus seeds buried in former lakebed 212 Life in mummified seeds 213 Glossary 217 Vernacular and botanical-zoological name equivalents 228 Conversion tables for temperatures and measures 240 Temperature conversion 240 Measures of weight 243 Measures of length 243 Measures of area 243 Measures of volume 244 Measures of capacity 244 Literature cited 244 Index 275 VI PRINCIPLES AND PRACTICES OF SEED STORAGE By OREN L. JUSTICE i and Louis N. BASS2 INTRODUCTION Purpose and Significance of Safe Seed Storage The principal purpose of storing seeds of economic plants is to preserve planting stocks from one season until the next. Prehistoric man learned the necessity of this practice and developed methods of storing small quantities of seeds for his future use. As agriculture developed, man expanded his knowledge regarding both the require- ments of seed for maintenance of viability and methods of providing suitable storage conditions. In 1832, Aug. Pyr. de Candolle of France included a chapter on seed preservation in his book "Physiologie Végétale." He pointed out that the vitality of seeds would be prolonged if stored under conditions to protect them from heat, moisture, and oxygen. About the same time, other authors suggested the use of tar-coated wooden boxes and iron tanks capable of being sealed with stopcocks for drawing off the seeds as desired. Although the storage of seed stocks for planting the following season remains the most important reason for storing seeds, farmers and seedsmen have found it advantageous to carry over seeds for 2 or more years. This practice results in accumulating supplies of desired genetic stocks for use in years following periods of low production. Many kinds of seeds—mostly vegetable, flower, and forage seeds—move rather freely in world commerce. Many of these seed lots are not used the ñrst year after production. With increased knowledge and technology of plant genetics and plant breeding, the necessity