Abstract: A portable grain bin comprises a wheeled frame in which the wheels are movable relative to the frame to sit the frame on the ground and thereby transfer the load of material in the bin to the ground. The bin is grossly asymmetric with a bottom discharge much closer to one end than to other. The bottom wall nearest the bottom discharge is very steep. The bottom wall opposite the bottom discharge is relatively shallow but still exceeds a normal angle of repose of grain placed in the bin. The bottom discharge includes an opening spanned by a series of stationary slats and a movable member comprising a frame having a series of complementary slats which selectively align with or are offset from the stationary slats. The grain bin is used with a batch type grain dryer to provide surge capacity in a harvesting operation.