@idiosyncrasy
Most scholars that I am aware of believe there were three separate tithes given every three years, although a few believe the 3-year tithe took the place of the second tithe.
THE FIRST TITHE
Leviticus 27:30-33 defines this tithe as a tenth of crops and animals in herds and flocks.
Numbers 18 gives the ordinances, or instructions, for this tithe, and commands this tithe be taken to the Levites.
Purpose of this tithe: to support the Levitical Priesthood.
SECOND TITHE
Deuteronomy 14:22-27: aka The Festival Tithe - a tenth of crops, plus add to that the firstborn animals, and take to the yearly feasts.
Purpose of this tithe: “that thou mayest learn to fear the LORD thy God always”
THIRD TITHE
Deuteronomy 14:28-29: aka The Three-Year Tithe aka The Poor Tithe - a tenth of crops, kept at home, and invite the Levites, widows, orphans, stranger to eat.
Purpose of this tithe: to feed the poor.
It is important to understand that the Biblical tithe never came from income. It always came from assets (crops and animals). The farmers made their income by selling and/or barter exchanging their crops and animals but did not tithe from their income. Wage earners did not tithe.
The first tithe was NOT brought to the Temple. It was taken to the Levites who lived in the Levitical cities.
Nehemiah 10:37-38 (KJV)
37And that we should bring the firstfruits of our dough, and our offerings, and the fruit of all manner of trees, of wine and of oil, unto the priests, to the chambers of the house of our God; and the tithes of our ground unto the Levites, that the same Levites might have the tithes in all the cities of our tillage.
38And the priest the son of Aaron shall be with the Levites, when the Levites take tithes: and the Levites shall bring up the tithe of the tithes unto the house of our God, to the chambers, into the treasure house.
In Nehemiah 10:37 we learn that the firstfruits were taken to the temple for the priests, and the tithes were taken to the Levites who lived in the Levitical cities. Therefore, we see that firstfruits have nothing to do with the tithe.
In Nehemiah 10:38 we learn that the Levites would take a tithe of the tithe to the Temple. It is this tithe, the tithe from the Levites, that went to the storehouse, not the tithe from the people. This is important to remember when we study Malachi 3:10.