Following the teaching presented in the first Mishna in the perek (28a) that once a person lived or worked land for three years it is considered a ḥazaka – presumptive ownership – the Mishna on our daf suggests that there are times when this ḥazaka will not apply.
The Tanna Kamma of our Mishna teaches that Israel is divided into three parts for the purpose of ḥazaka – Judea (the southern part of the country), ever ha-yarden (the East Bank of the Jordan River) and the Galilee (the northern part of the country). Since travel between these areas was difficult, someone who lived or worked the land in one area would only get a ḥazaka in the field if the claimant had been with him in that area during that time. If the claimant was in one of the other areas, it is possible that he never found out that someone was working his land, and he had no reason – and no way – to object. Rabbi Yehuda says that the three year rule was made so that someone who was a great distance away – in Aspamya (Spain) – would hear about the person who moved onto his land and would have time to raise an objection.
According to Rav Hai Gaon, Rabbi Yehuda does not disagree with the Tanna Kamma, since according to the Gemara’s explanation the Tanna Kamma only suggests his ruling in a she’at ḥeirum – a time of danger when the borders were closed. Rabbi Yehuda is simply teaching that in normal times, even if the claimant is a great distance away, we assume that within three years he will have time to receive reports about his land and come to make a claim.
Many rishonim disagree and understand that Rabbi Yehuda disagrees with the Tanna Kamma on two points:
Three years is the standard determined by the Sages and it will establish ḥazaka in all cases, and
In an ordinary case, where the original owner is nearby and knows what is going on, even a shorter amount of time will serve as a ḥazaka since the original owner clearly knew about the activities on the field and did not object. Three years is only necessary when the original owner is far away.