How does the quantity of salt change after the steaming stage when cooking pulao? When making pulao1, I taste the salt in the broth before the steaming stage (also called dum). At this time, the saltiness is just right. But after the rice has finished steaming, it is less salty than before. 

Why does this happen? What is the effect of steaming on the saltiness of cooked rice?

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1 Pulao is a very popular rice dish on the Indian subcontinent and Middle Eastern countries in which rice is cooked in a seasoned broth. The broth may contain cooked onion, garlic, ginger along with spices. It may also contain meat, fish or vegetables. It is sometimes also called rice pilaf.
Dum is the steaming stage of the cooking. This is the stage where rice absorb water and the flavor. From my experience and what all our generations have been told on how to cook pulao/rice, you taste the water/broth just after adding rice. It should be a bit saltier than what you would normally like. This way the saltiness in rice will be just right when you finish the cooking. 



EDIT (with the comments from Stephie):

Rice absorbs water and with the water, some of the salt.

In the beginning, you are tasting the water : salt ratio. After cooking, you are tasting the (water + rice) : salt ratio which means you are getting something that tastes less salty.