How can poor farming methods lead to overpopulation?

It doesn't it can't. There is no corralation between poor farming methods "LEADING" to overpopulation. In an agriarian society more of the population is involved with farming which leads to more people being needed. But the reverse is not true. There is no documented case were Poor farming led to Overpopulation. At one point in time a large percentage of the US population was involved with farming. Farming methods improved dramatically, and the population not only grew, but a much lower percentage of people was/is needed to produce more food than before. Same principle holds true throught the world. Even in china where there is a lot of manual labor in Agriculture it is still a small percentage of the population. China is improving it's farming methods and becoming more "mechanical" yet the OVERALL population of China has zero to do with their farming methods. That is precisely why China has a National 1 child law. Overpopulation is caused by indiscriminate sex all the time, it has nothing to do with poor or good farming methods. .

Second pretty much has it -- but an odd corollary is that underpopulation is just as bad. If everyone in a community has to work as much as possible just to provide adequate food, there will never be any sort of progress possible. Only when there are enough extra people that can do something besides scrape potatoes out of the dirt (and enough potatoes of course) will there be someone to build better huts, or an improved water supply, or any of the things that turn a society from a subsistence-living group to a real civilization.

Because there would be less food to eat, so instead of eating food, people would occupy the now vacant time slot by getting it on. At least, that's the only logical explanation I can come up with.

Where did the question come from....It seems to be off somewhat. If I were you, I'd recheck the source........

Low-technology farming is labor intensive. Higher-technology farming is not labor intensive. Low-tech farming leads to huge families and high populations.