Vaisesika Sūtra 8.2.05

भूयस्त्वाद् गन्धवत्त्वाच्च पृथिवी गन्धज्ञाने प्रकृतिः ॥५॥

bhūyastvād gandhavatvācca pṛthivī gandhajñāne prakṛtiḥ ॥5॥

[भूयस्त्वात् (bhūyastvāt) - from predominance; गन्धवत्त्वात् (gandhavatvāt) - from possessing smell; च (ca) - and; पृथिवी (pṛthivī) - earth; गन्धज्ञाने (gandhajñāne) - in the cognition of smell; प्रकृतिः (prakṛtiḥ) - the substratum;]

Because of its predominance and possession of smell, earth is the substratum for the cognition of smell.