'Voluntarily' in the Bible

Jehoash said to the priests, “All the money for the dedicated things which is brought into the house of the Lord, in current money, both the money of each man’s assessment [for all those bound by vows], and all the money which any man’s heart prompts him to bring into the house (temple) of the Lord,

‘Then this shall be the sign [of these things] to you [Hezekiah]: this year you will eat what grows of itself, in the second year what springs up voluntarily, and in the third year sow and reap, plant vineyards, and eat their fruit.