Seed Storage :: Storage factors
Factors influencing seed storage
2. Abiotic factors
Seed factors :
Micro biotic – short lived
Initial seed quality
Effect of provenance: The place where the seed crop was produced greately influences the storability. (e.g.) Red clover seeds grown in Canada stored for 4 years with 80% germination whereas seeds grown in England and Newzealand stored only for 3 years with 80% germination. This is due to different climatic conditions and soil types prevailing in different places.
Effect of weather
Pre harvest sanitation spray
Seed moisture content
Generally if the seed moisture content increases storage life decreases. If seeds are kept at high moisture content the losses could be very rapid due to mould growth very low moisture content below 4% may also damage seeds due to extreme desiccation or cause hard seededness in some crops.
Since the life of a seed largely revolves around its moisture content it is necessary to dry seeds to safe moisture contents. The sage moisture content however depends upon storage length, type of storage structure, kind / variety of seed type of packing material used. For cereals in ordinary storage conditions for 12-18 months, seed drying up to 10% moisture content appears quite satisfactory. However, for storage in sealed containers, drying upto 5-8 % moisture content depending upon particular kind may be necessary.
Harringtons thumb rule on seed moisture content :
Orthodox – the seeds able to tolerate moisture loss and less seed moisture favours the storage. i.e. decreased moisture increased storage period. Eg. Rice, sorghum , and most of the cultivated species.
Recalcitrant – just opposite to the orthodox. Seeds not able to tolerate moisture loss. Required high moisture for viability maintenance.
Microflora, Insects and Mites
Abiotic factors :
Relative humidity is the amount of H2O present in the air at a given temperature in proportion to its maximum water holding capacity. Relative Humidity and temperature are the most important factors determining the storage life of seeds. Seeds attain a specific and characteristic moisture content when subjected to given levels of atmospheric humidities. This characteristic moisture content called equilibrium moisture content.
Equilibrium moisture content for a particular kind of seed at a given Relative Humidity tends to increase as temperature decreases. Thus the maintenance of seed moisture content during storage is a function of relative humidity and to a lesser extent of temperature. At equilibrium moisture content there is no net gain or loss in seed moisture content.
Temperature also plays an important role in life of seed. Insects and moulds increase as temperature increases. The higher the moisture content of the seeds the more they are adversely affected by temperature. Decreasing temperature and seed moisture is an effective means of maintaining seed quality in storage. The following thumb rules by Harrington are useful measures for assessing the effect of moisture and temperature on seed storage. These rules are as follows.
1. For every decrease of 1% seed moisture content the life of the seed doubles. This rule is applicable between moisture content of 5-14%.
3. Good seed storage is achieved when the % of relative humidity in storage environment and the storage temperature in degrees Fahrenheit add upto one hundred but the contribution from temperature should not exceed 50 oF.
Roberts (1972) developed formulae to describe the relationship between temperature seed m.c. and period of viability. From these relationships it was possible to construct a seed viability nomograph. These nomograph are helpful in predicting the retention of seed viability indefined storage environment for a particular period or to determine combinations of temperature and moisture content which will ensure the retention of a desired level of seed viability for specific period.
Gas during storage
Increase in O2 pressure decrease the period of viability
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