Siman 328

One who receives a field from his fellow and it did not produce fruit, if it contains enough to produce two se'ah beyond the expenses, the contractor is obligated to attend to it and cannot withdraw, because he wrote thus to the owner of the land: "I will stand and sow and reap and set up a stack before you and you shall take your portion." The sages estimated that the setting up of a stack is in two se'ah, and from this shall also be the portion of the land owner. There is no difference between a large field and a small one, and even if he did not write thus, it is as if it were written, for anyone who receives does so according to the local custom. Therefore, if there is some other custom in this place, they shall act according to their custom. This applies specifically when they performed a kinyan, for if not so, a worker may retract even in the middle of the day. Regarding one who receives an orchard of trees, it is not explained in the Gemara, and they shall act according to the assessment of experts whether it is worth tending to this or not; and so too with gardens of vegetables. And some say that he is always obligated to tend to it [Chavat Yair]. And if there is some custom in this, they shall act according to their custom. All this is only regarding a kablanut arrangement, but regarding a chakirut arrangement this is not relevant, for even if it produced nothing, he must pay his chakirut if it is not a regional disaster, as I wrote in siman 322 [Tur].

If he did not work it at all, but rather left it entirely or partially fallow, they assess it for how much it was fit to produce, and he gives him his portion that would have reached him according to their agreement. Even if he did not write this for him and did not stipulate thus with him, nevertheless he must pay him according to this value, and he may pay him in money or in produce. In a case of leasing, an assessment is not necessary, for whatever he stipulated he must give him in produce [it appears to me]. See what I wrote in siman 322. If he stipulated with him, "If I leave it fallow and do not work it, I will pay you a thousand zuz," this is an asmachta and he only gives him according to what it was fit to produce alone, as I wrote regarding the laws of asmachta in siman 207; see there. If he left it fallow and there was a regional plague where all the fields were stricken with blight, nevertheless the renter must pay him, even if it is a sharecropping arrangement, because he can say, "Had you sown it, it would have been fulfilled for me: 'They shall not be ashamed in the evil time, etc.'" And even though he did not stipulate with him that he should sow it, but rather took it in sharecropping without specification, for a sharecropping arrangement without specification is for sowing [it appears to me].