Complex sentence: A player can never begin a sowing from "Uur" pits, and relay-sowing does not apply to "Uur" pits: as a consequence, the content of "Uur" pits tends to grow over time.
Split into simpler sentences: A player can never begin a sowing from "Uur" pits, and relay-sowing does not apply to "Uur" pits. Consequently, the content of "Uur" pits tends to grow over time.