Being a farmer has always been hard work. Especially in the time of old when all farming had to be done by hand with only the help of animals.
After weeks and weeks of working the land and planting crops, one had to wait to see if the seeds would grow or not. Would Hashem send enough rain? Would there be enough sunshine? Prayer was a necessity, in the hope of guaranteeing the well-being of one's entire family. Finally, after many months of waiting, the farmer's harvested his wheat, but then he had to be careful not to cut the wheat in the corner of the field. Hashem commended that the corner be left for poor people to take from. This is called Peiya. The Halacha is that one may not leave two Peiyot in one field and none in a second one. However, one may leave as much or as little as he wants in every field. Consequently, the farmer has fulfilled his Torah-level obligation even if he left only a minuscule amount. If one had a vineyard then he couldn't pluck the unripe grapes, nor pick up those that fell to the ground. These too were left for the poor. The reason for these laws is that Hashem did not make the produce for the farmer alone, but for poor people as well. To emphasize that one is obligated to do these commandment the Pasuk says "I am Hashem, your God."
There are two other Mitzvot to farmers in Eretz Yisrael. Leket if you or your workers are working and one or two stalks fall to the ground then you may not pick them up. You must leave them there for the poor person to take. But if you drop three stalks then you may pick them up. Shikcha after cutting the stalks workers tie the stalks into bundles. You bring them to your barn and you leave them there, but if you overlook one of the bundles them you must leave that bundle in the field for the poor.