R’ Yehuda says that originally when bais din uprooted the kilayim they threw the vegetation before the owners. Later as the situation became worse they threw the vegetation on the public roads and still later as it got even worse they made the whole field hefker.

Shikalim 1:3

On the 15^th day of Adar moneychangers would sit in all the cities to be able to change money for the shikalim. On the 25^th they sat in the Bais Hamikdash. On that day bais din would start taking collateral from the people who did not pay.

We take collateral from leviim, yisraalim, proselytes, and freed slaves. Women, slaves, and children are not obligated. If a father started giving for his son, he should not stop.

We do not force cohanim even though they are obligated to give, so as to keep the peace.