The Mishnah now turns to the exceptions to the rule forbidding the harvesting of grain before the barley for the Omer offering is cut. The source of the prohibition, as mentioned, lies in the fact that the verse refers to the Omer offering - the barley reaped for the Omer - as "reishis ketzirchem", the beginning of your harvest, from which we learn that nothing else may be harvested before the barley reaped for the Omer. Nevertheless, that very same verse states: "When you come into the land... and you reap its harvest", and this doubled expression teaches the Sages that there are harvests permitted to an ordinary person, for purposes other than the needs of the Beis HaMikdash.
The essence of our Mishnah is this: barley that in any case does not meet the standards required for the Omer offering and is not fit to serve as the Omer barley may be harvested even at the outset. In the next Mishnah we will see further leniencies, derived from the word "ketzirchem" - your harvest: one who reaps not for his own needs but for some other reason, such as for the sake of a mitzvah, is likewise permitted.
It is worth noting that the first grain to ripen in Eretz Yisrael is generally barley, and barley is the type of grain used for the Omer. Even so, the leniencies of our Mishnah apply as well to wheat growing in those same types of fields in which barley may be harvested before the Omer barley is cut.
A fundamental point that must be clearly understood: although there are several leniencies regarding harvesting before the Omer offering is brought, there is no leniency whatsoever permitting the eating of chadash - this year's crop - before the Omer is waved and offered. The leniencies were stated with regard to harvesting alone, and not with regard to eating chadash before the Omer.
"Kotzrin beis hashelachin she'ba'amakim":
One may harvest grain growing in a beis hashelachin - a field irrigated by hand - located in the valleys. The idea is that irrigated fields require additional water, which shows that their basic growing conditions are inferior; they need extra human intervention, and therefore their grain is not of high quality and is not the choice grain that would be used for bringing the Omer offering. Since it would not have been used for the Omer in any case, it may be harvested early.
According to the version of the text before us, both conditions are required together: that it be a beis hashelachin, a field irrigated by hand rather than by rainwater, and that it be in a valley. It is worth noting that many of the Rishonim had other versions in which one condition alone suffices - either a beis hashelachin or a valley - and many of them ruled accordingly. But according to our Mishnah both are required, and therefore there is no permission to harvest in a valley that is not irrigated, or in an irrigated field that is not in a valley.
"Aval lo godshin":
Although it is permitted to actually harvest, that is, to detach the grain from the ground, one may not pile it into a stack. To understand this one must be familiar with the process of harvesting: first the grain is detached from the ground - this is the reaping, and it is for this that Shavuos is called "Chag HaKatzir", the Festival of the Harvest. Afterwards the grain is left in the sun throughout the summer so that it will dry out completely, for only properly dried grain can be put into storage and keep there over time.
The drying is not done by spreading the grain out on the ground, since then pests - ants, mice, rats and voles - would easily reach it. They would therefore heap it into a mound, usually in a conical shape, so that the grain does not lie on the ground and can dry in the sun without easy access for pests. This is the stacking.
Our Mishnah therefore establishes that while the reaping - the detaching from the ground - of this type of grain is permitted before the barley for the Omer offering is cut, the stacking is still forbidden, and the grain must be left unpiled. The reason for this is that it serves as a distinguishing sign: since the harvest is not being done in its usual manner, a person will remember that although this grain may be harvested and detached from the ground, it may not be eaten until after the Omer is brought. That distinguishing sign keeps the matter in mind, so that the grain will not be eaten by mistake before its time and contrary to halachah. This is a rabbinic law: at times the reaping is permitted, but the stacking is forbidden.
And if the question is asked: since the Sages are in any case decreeing that the work not be done in its usual manner, why not decree rabbinically that it not be harvested at all, so that one not come to eat it? The answer is that in a beis hashelachin, an irrigated field, leaving the grain in the ground longer than necessary is liable to ruin it - it needs to be detached from the ground, and if not it will become overripe. The Sages have concern for the money of Israel and do not wish to cause a financial loss, and therefore they permitted detaching it from the ground, while insisting that it not be eaten, since it is still chadash and forbidden.
The People of Jericho:
The Mishnah continues and tells of the Jewish farmers in Jericho:
"Anshei Yericho kotzrin b'ratzon chachamim" - they cut the grain from the ground with the full agreement and support of the Sages. Jericho is indeed a valley, and they had irrigated fields near the Jordan from which they could water their crops, so these were irrigated fields in a valley, where harvesting is permitted.
"V'godshin" - they even piled the grain they had cut into stacks, even though stacking is forbidden by rabbinic law.
"V'lo michu b'yadam chachamim" - even though they did not act properly, the Sages did not intervene and did not protest as they should have.
The reason for this, according to most opinions: this is a rabbinic law based on a remote concern. Cutting the grain early does not in itself lead a person to eat from the crop, and although the Sages preferred that they not stack it, once they did stack it the Sages did not enter into a confrontation with them and did not make an issue of it.
"Kol shel shachas... u'ma'achil labeheimah":
One who cuts for fodder, meaning that he detaches the grain from the ground for the purpose of destroying it rather than for human consumption, and feeds it to animals as fodder - his cutting is permitted. Shachas means grain that has not ripened, like wheat grass at the stage when the grain is only beginning to sprout on it and it is not yet fit for human consumption. This is not considered harvesting, since there is as yet no human food here, and therefore it is permitted even before the barley for the Omer offering has been cut.
It is worth emphasizing: cutting grain at the peak of its ripeness, when it is fit for human consumption, and giving it to an animal, is not shachas at all, since it is human food. Just as one who feeds his dog the leftovers from his table, or his horse carrots, sugar cubes and oats, is placing human food before them.
Before It Reaches a Third:
The question is until when the grain is still considered shachas. The Tannaim disagree about this:
"Amar Rabbi Yehudah: Eimasai? Bizman shehischil ad shelo heivi shelish" - the window of permission runs from the moment it begins to sprout until it reaches a third of its growth. Once it has reached a third there is already a problem, since it could be eaten by people as food in a pressing situation.
"Rabbi Shimon omer: Af yiktzor v'ya'achil af mishe'heivi shelish" - even after it has reached a third, if the cutting is for animal feed it is not a human harvest, and it is permitted. The only restriction in his view is cutting for human consumption.
It should be clarified that this does not refer to a third of the growth of the wheat grass, since wheat grass is not human food at all. It refers to the stage at which the wheat grass has already produced an ear of grain, and one can see the wheat kernels growing in it. From the appearance of the kernels until their full ripening a certain period of time passes, and the exact length of time makes no difference. If we assume for the sake of example that the process takes three weeks, then during the first third, while the kernels are emerging and growing, it is permitted to cut them and feed them to animals; beyond that, according to Rabbi Yehudah, they already have an aspect of human food and may not be cut.
It is worth noting that this is not the approach of the Bartenura. Although this measure of a third of growth - a third of the way toward being fit for eating - appears countless times throughout Shas in many contexts, and is always understood as described, here the Bartenura follows the explanation of the Ramban and understands that the intent is not the first third but the final third. In his words: "ad shelo heivi shelish acharon" - that is, as long as it has not reached the final third of its ripening it may be cut for animals. According to this, if the ripening of the kernels takes three weeks, even during the second third it is still permitted to cut and feed it to an animal, but not to people.
However, the halachah does not follow his view. The halachah follows the Rambam's ruling in the Yad, and as it is brought in the other places: the first third only, and that is all.