While discussing situations where the husband gives his wife a divorce that is conditional on some event taking place (e.g., that a monetary payment will be made), the Gemara brings other situations where a conditional agreement is made and it is not clear whether the condition was fulfilled.
One example is a case where the owner of a field offered his sharecropper an increase in the percentage that he will get from the produce if the sharecropper put more effort into tending the field. Specifically, he told him that while most sharecroppers receive a quarter of the profits and water the field three times a year, he is willing to offer one third of the profits if he agrees to water the field four times a year. What if the sharecropper agrees to this arrangement, waters the field three times, and then discovers that rainfall has made it unnecessary to water the field a fourth time. Do we consider him to have fulfilled his agreement or not?
Rabbah rules that there was no need to water the field, so he is credited as though he did it and he receives the larger payment; Rav Yosef says that even though he agreed to water the field, he did not get to do so, and he should only receive the normal payment of a sharecropper.
The case discussed in the Gemara is one where the crops were not watered on a regular basis, and most of the water that they need to grow comes from rain and water sources deep in the ground. Nevertheless, such fields were watered a number of times a year – particularly in Bavel where the seasons were often dry ones – at critical times when the plants were putting down roots, until such times as the plant had developed an established root system. An additional watering, if done at the right time, may significantly improve the health of the plants and ultimately produce a larger harvest. It is therefore understandable that the owner’s interest would be to offer a larger percentage of the profit to the sharecropper, knowing that the increased harvest will more than cover the extra payment.