Answer:
   
   There are four gifts given to the poor:
    1. In the third and sixth year of the sabbatical cycle, the second
       tithe is given to the poor. This is given after the priests' gift
       of approximately 2% and the levites' tithe which comes to 9.8%
       (10% of the 98% that remains). So, we are talking about 8.64% or
       so.
    2. Fallen stalks: stalks dropped by the harvesters in ones or twos
       may not be picked up, but must be left for the poor. (If three or
       more fall, they may be picked up)
    3. Forgotten sheaves: if one or two bundles are forgotten when the
       grain is brought in from the field, you may not go back to get
       them, they are left for the poor. (Again, if three are more are
       left, you may bring them in for threashing.) For vineyards, this
       not only includes overlooked bunches of grapes, but there is also
       a law against taking one or two grapes left behind when a bunch is
       picked.
    4. A corner of the field must be left for the poor. For this, there
       is no measure; the farmer's conscience is his guide.
       
   A couple of notes: We do not believe these numbers are rabbinic.
   Rather, they are part of an oral tradition that dates back to the
   giving of the law. Not every detail that God gave us is recorded in
   the Torah. In particular, measures for each law are rarely given in
   the text.
   
   Second, these laws are viewed as being tied to the sanctity of the
   land of Israel and sactifying the Jewish settlement of that land.
   Non-Jewish citizens of Biblical Israel were not expected to give any
   of these. Nor were Jews who resided outside of Israel.