Factors influencing seed storage

Biotic factors:

a. Factors related to seed

2. Abiotic factors

Seed factors :

Genetic factors

The storage is influenced by the genetic make up of the seed. Some kinds are naturally short lived (e.g) onion, soybeans, ground nut etc., Based on the genetic make up seeds are classified into

Micro biotic – short lived
Meso biotic-   medium  lived
Macro biotic – long lived

Initial seed quality

Barton (1941) found that the seeds of high initial viability are much more resistant to unfavourable storage environmental conditions than low  viable seed. Once seed start to deteriorate it proceeds rapidly. The seed which injured mechanically suffered a lot and loses its viability and vigour very quickly.  Generally small seeds escape injury whereas large seeds are more likely to be extensively damaged (e.g) bean, lima-bean and soybean. Spherical seeds usually give more protection than flat or irregularly shaped seeds

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

Fluctuating temperature during seed formation and maturity will affect seed storage. Pre-harvest rain may also affect the viability.

Pre harvest sanitation spray

In pulses, insect infestation comes from field (e.g.) bruchids.

Seed moisture content 

Most important factor influence the storability. The amount of moisture in the seeds is the most important factor influencing seed viability during storage.

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 :

For every one per cent decrease in seed moisture content the life of seed will be doubled. This is again hold good between 4- 12 C. Based on the tolerance and susceptibility of seeds towards moisture loss seeds are classified into

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

The activity of all these organisms can lead to damage resulting in loss of viability.The microflora activity is controlled by Relative Humidity temperature and Moisture Content of seed.
Treated seeds with fungicides can be stored for longer periods. Fumigation to control insects will also help in longer period of stroage.
Fumigants - (e.g) methyl bromide, hydrogen cyanide, ethyline dichloride, carbon tetra chloride, carbon disulphide and napthalene and aluminimum phosphine.

Abiotic factors :

Relative humidity

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

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%.
2. For every decrease of 5oC in storage temperature the life of the seed doubles. This rules applies between 0oC to 50oC.

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.

Nomograph

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
N2 and CO2 atmosphere will increase the storage life of seeds.