The public fields were usually rented out by government administrators.
Managing the public fields was a lucrative job, with ample opportunity for manipulation. Especially in disaster years, out of a thousand acres of public land, only more than ten might suffer from floods. Yet, the managing officials might report that a hundred acres of good land were affected.
The government would send people to check.
At that time, a little bribe could make the inspectors help to falsely report the disaster.
If the inspectors couldn't be bribed, there were other methods.
One only had to collude with the local field protectors and spokesmen. By leading the inspectors through the genuinely affected fields a couple of times, they could easily be deceived.
This year, there was no need to lie about the disaster at all, as the locust plague devastated indiscriminately, attacking all the crops within the fields.
The public fields of the government were exempt from rent.