Question

it is important to have a very good contact between the lower end of a lightening conductor and earth

Answer 1

Earth is not good conductor of electricity like metals. However, it conducts the electricity to very low extent ( very less), as resistivity of the earth is quite high. 
In fact, conductivity of earth depends upon the type of soil present at that place. for example, if the soil at some place is full of moisture, it would better conduct electricity  in comparison to the dry soil at other place.

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Answer 2

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yes it is important to have a very good contact with win the lower end of lightning conductor and the earth because it is providing a safe and easy passage for following electric charge when lightning occurs and Thursday appliances can save from the the damaging effect of lightning.

@Fruti06