A trench closing sensor adapted to mount to an agricultural implement to detect whether a seed trench is sufficiently closed with soil to ensure good seed to soil contact. The trench closing sensor may also detect the amount of compaction of the soil over the seed within the seed trench. The trench closing sensor may be in the form of a seed firmer from which a drag wire extends. As the open seed trench and drag wire are covered with soil, instrumentation measures or detects whether the seed trench is being adequately closed with soil by measuring the amount of force required to pull the wire through the soil or by measuring the amount of strain, pulling force or tension in the wire or by measuring the amount of soil pressure acting on the wire. The trench closing sensor may include other sensors for detecting soil characteristics.