In a case of Yored b'Reshus, the owner of the field consented and thereby obligated himself to pay.

In Yored she'Lo b'Reshus, someone who planted a field that doesn't belong to him may demand compensation from the owner even though he was not requested to plant, provided that the field is fit for planting. The Chiyuv seems to be based on the Halachah of Neheneh (one must pay someone from whom he benefits).

Tosfos in Kesuvos 107b and Bava Kama 58a are troubled by why the owner has to pay since he never asked the worker to plant. According to the Pnei Yehoshua, Tosfos offers two answers.

The first answer is that the beneficiary of work is Chayav to compensate a worker any time there is an Umdena d'Muchach (a likelihood) that he is pleased with the work done on his behalf. Someone who warded off a thief from breaking into a store is entitled to compensation from the owner for his efforts. Similarly, the owner of an empty plot of land must pay someone who built a house there if the property is now worth significantly more.

The second answer they suggest is that the owner is Chayav whenever there is a b'Ein of Shevach. That means that there is a visible product that has increased in value due to the worker's efforts, and not just a service provided. According to this approach, someone who warded off a thief from breaking into a store is not entitled to compensation for his efforts, but one who built a house is.

Rav Hershel Schachter noted that the Rema (CM 264:7) rules like the first answer, while the Birkas Shmuel (Nedarim 22) says that Rav Chaim of Brisk holds like the second answer, in accordance with Rav Chaim's opinion in his Chidushim on the Rambam, Hilchos Malveh v'Loveh.

Avraham Phillips