This spring returns the shutter assembly on the fertilizer spreader to its closed position after the metering cycle ends. It provides the closing force that holds the shutter against its seat, preventing unintended material flow when the metering mechanism is not actuated. A fatigued spring can allow the shutter to remain partially open, leading to over-application or dribbling at the start of the next pass. The spring is designed to match the original free length and rate, so the shutter opens fully when the actuator pulls and closes completely when the actuator releases.