This form of dormancy is Exogenous because it is related to the physical properties of the seed coat. There are three factors that are responsible for exogenous dormancy. The impermeability of seed coats to water is typical of genetic and environmental conditions. Some varieties may be naturally inherent to dormancy, as a means of survival and this is often true in clovers. Environmental conditions such as the weather and soil conditions during the final stages of maturation can influence hard seed content. Seed coats can be selective to permitting the entry of water, but not oxygen. Without a movement of both, the seed will not imbibe water sufficiently. Also mechanical restriction, whereby the seed coat is too hard to be ruptured, and scarification or complete removal of the seed coat is necessary for germination to take place.
Exogenous dormancy is broken very often by piercing the seed coat either with a pin, or a scalpel or scratching it with sand paper. Chemical scarification is also an option where the seed is exposed Sulfuric acid; we tend to not use this method because it can affect the germination.
To date 8% of the pea germinations have had 1% – 5% hard seeds, and two samples had 8% and 15% which is very unusual. The good news is that in all cases the grade was not affected. These samples are mostly from Southern Alberta with a few coming in from Central Alberta.
The incidence of hard seed in lentils is much higher, 43% of the lentil germinations were affected this year, with 1% – 5%. Again the grade was not affected.
The lentils were all grown in Southern Alberta; it might be interesting to observe the nitrogen levels in the soil and a possible correlation with high early season rain falls in those areas where the lentils and peas where grown as lower N levels have been shown to increase dormancy.