The Chinuch states that there is a positive commandment which forbids plowing on Shemitah. It is written [Shmos 34:21]: From plowing and harvesting you shall desist.

The Minchas Chinuch (112) asks that if so, women should be exempt from this mitzvah, and they should be permitted to plow on shemitah because it is a positive commandment that has a time element to it and the principle is that women are exempt from any positive mitzvah which is governed by time?

He answers that women are obligated in this mitzvah because that rule is applicable only regarding a positive mitzvah that is incumbent on the body of the person and not a mitzvah like shemitah, which is a mitzvah that is dependent on the land (mitzvos hateluyos ba’aretz). This can be better understood based upon our Gemora which says that the shemitah prohibition is on account of the ground.

Proof to this distinction is cited from the Ritva in Kiddushin (29a). The Gemora rules, based on a Scriptural verse that women are not obligated to perform a circumcision on their sons. Tosfos asks: Why is a verse necessary; circumcision is a positive mitzvah which is governed by time since the mitzvah can only be performed by day, and women are exempt? The Ritva answers: Any mitzvah which is not related to the person themselves; this principle does not apply. The mitzvah of milah is to perform the circumcision on the son and therefore women would be obligated if not for the special verse teaching us otherwise.