Why was agriculture more conducive to slavery in U.S. South than the North?

Question

The most common explanation I hear for why there was more slavery in the South than the North in is that farming was more profitable in the South due to climate, soil quality etc. and the North had more industry.

This explanation seems slightly anachronistic to me because the divide between Southern slave states and Northern free states was already evident by the time of the Constitutional Convention in 1787. At the time, my understanding is that both the North and South were agrarian economies (most people date the start of U.S. industrialization to the 1820s).

So, if both economies were based on agriculture, why were slaves common in one, and not the other?

Answer 1

For our purposes, there are two types of agriculture: Subsistence (food) agriculture and cash crop agriculture. The farming in the North focused on foodstuffs (corn, wheat, vegetables, etc.). The farming in the South focused on higher value cash crops, cotton, indigo, sugar, etc.

Under a subsistence economy focused on food, you don't want slaves, because they represent more mouths to feed. You want to use your farmland to grow food for your own family, not for a bunch of other people. This was true in the North, where the climate permitted people to grow only enough food for themselves (and a little extra for trade), but not for "export." Later, machines such as tractors enabled 1 person to grow food for 30-40, but those are cheaper than slaves. Enough said.

It was different in the South. Cash crops such as cotton or sugar are more valuable than food, but such crops grow best in warmer, southern latitudes. So you could employ slaves to grow these crops, sell them abroad, use the money to buy food for them and for yourself, and still make a profit. Many cash crops do not lend themselves well to mechanization, which is why slavery can be profitable.

Essentially, "agriculture" was more profitable in the South than in the North, and that's why northerners were more eager to "industrialize," while the South preferred to remain "agricultural" for longer.

Answer 2

Though not properly sourced it could provide keywords to help in the search.

From early on people coming to North America from Europe found that the warm weather of the lower latitudes offered several new diseases they were not familiar with. Later on people who signed on as indentured servants, 3 or so years of work to gain their freedom in the new world, were at risk for their first year or so. Their possible survival became known as "seasoning" that is, getting over the transition to the new climate. Often a bout of disease could make them unsuitable for hard labor anymore.

People originally from the lower latitudes, say Africans, had this problem beat already. The trade offs were overcome and total slavery was taken over recruiting European indentured servants. Source is a book described on The John Bachelor Show