Bava Batra 27 - July 22, 16 Tamuz

Ulla ruled that one does not bring bikurim from a fruit tree growing within sixteen cubits of a neighboring field as it is "stealing" nutrients from the neighbor's soil. From where does Ulla derive the number sixteen? Four sources are brought to contradict Ulla's amount of sixteen cubits, but all the sources are explained also according to Ulla. If sixteen cubits is the proper amount, why does the Mishna rule that a tree needs to be distanced twenty-five cubits from a pit? The issue there is not the same as Ulla is relating to sapping the soil of nutrients, while the issue with the pit is the roots destroying the pit's wall, which can happen even if the roots are not absorbing nutrients. Rabbi Yochanan's opinion on the issue has two versions - either agreeing or disagreeing with Ulla. When can a neighbor cut the trees leaning over into their property? What about trees jutting out into the public domain?