Repaying neighbors with shemitah produce
Question
Before Shabbat I saw I was short on carrots, so I borrowed a few from my next-door neighbor. I just restocked with otzar beit din carrots. Can I "repay" my neighbor with these carrots that have kedushat shevi'it, or is it like repaying a debt with kedushat shevi'it produce?
Answer
It is best to avoid using shemitah carrots to repay debts (even social debts). However, since often neighbors with good relations do not keep a list what was borrowed and returned and will not sue their neighbor for failing to return three carrots, many posekim do not consider this an actual debt. Rather, it is more like a neighborly gift. This is why we are not concerned about the prohibition of ribbit, lending on interest, between neighbors and it is halachically permissible to return vegetables of different sizes.
If you want to be stringent, you have two options:
1. When giving back the carrots, state that it is a gift (this is also helpful for those who want to be stringent about ribbit).
2. When borrowing the carrots, note that you will be giving in return carrots with kedushat shevi'it. Then it is no longer a debt, rather a barter (which the Rambam permits).