This is a fast deck, that can quickly put 10+ lands on field by turn 5. The low land count is because you can easily go through your entire deck after just 7 turns of combo. Once combo is set up, playing a land can trigger a long cycle of come-into-play effects. Specifically, the combo is:

1) Play a land
2) Place +1/+1 counter on elemental
3) Play an elemental
4) Scry (if not a land, place at bottom of deck)
5) Land enters the field, triggering #2

Loop stops when you can no longer play an elemental. If two copies of risen reef are in play, then it creates a double #5,  potentially putting twice the number of lands each round.