How much are Tzemed Kerem and Bas?
Rashi: It is the size of a field that one works in a day with Tzemed Bakar (yoked cattle). Bas is three Sa'im (the volume of 432 eggs).
What is the significance of 10 Tzimdei Kerem producing one Bas?
Rashi: Due to hunger, residents of the houses will be exiled, and no one dwells in them. This is Midah k'Neged Midah for making the fields close to each other, and stealing Hashem's portion in Ma'aser of the land 1 .
Radak: This is Midah k'Neged Midah for stealing fields of Aniyim - there will be a curse in the produce.
What is "Zera Chomer"?
Rashi: It is a Beis Kor, a field in which one sows 30 Sa'im of grain 1 ]. It will yield only three Sa'im.
Malbim: It is seed proper to produce 30 Sa'im; it will produce only a 10th of this. Their fields will be too small to produce enough food. The Navi mocks them - it would have helped more to steal fields 2 !