Parshas Behar begins with the halachos of Shmittah. There are several mitzvos assei and lo sassei associated with shmittas karka. Some of the mitzvos assei are that one must be mafkir (disown) his produce. Not plowing the land is actually prohibited as an assei. Planting and harvesting are prohibited as lo sassei. The Chinuch in mitzvah 84 says that both men and women are obligated in the mitzvos assei and lo sassei of Shmittah.
In mitzvah 112 the Minchas Chinuch asks why women are not exempt from the mitzvos assei, since they are mitzvos assei she’hazman grama (time sensitive). While some Rishonim opine that when there is a mitzvos lo sassei associated with the mitzvas assei, women will be obligated, Tosfos in Kiddushin 34a says that women would still be exempt. It is then necessary to explain in Tosfos’s opinion why women are obligated in the mitzvos assei of Shmittah.
In mitzvah 84 the Minchas Chinuch suggests a reason why women would be obligated in the mitzvah of being mafkir one’s produce. He discusses whether the obligation is upon the owner to actually make the produce ownerless, or whether Hashem renders it ownerless regardless of the owner’s consent and actions.
He explains that if Hashem renders the produce ownerless automatically then we can understand why women are obligated in that mitzvah, namely because there is nothing for them to actually do. However, if the obligation is for the owner to disown the produce we need to explain why women are obligated.
The Minchas Chinuch (mitzvah 112:3) suggests an answer that explains why women are obligated in all of the mitzvos assei of Shmittah. The Rishonim, in Kiddushin 29a, ask why the Torah feels the need to write a pasuk exempting a woman from the obligation to perform the mitzvah of bris milah on her son. After all, she should obviously be exempt since it is a mitzvas assei she’hazman grama? The Ramban and the Ritvah answer that women are only exempt from mitzvos assei she’hazman grama on mitzvos that pertain to themselves. But when the mitzvah requires them to do something for someone else, they are not exempt. Therefore without their exemption from the pasuk, a woman would be obligated to perform (or according to the opinion that a woman may not perform a bris milah – arrange) a bris milah on her son.
The Minchas Chinuch understands the Ritvah’s answer to mean that mitzvos can be classified into two categories; those that are obligations on the individual to perform, and those that require that a certain situation take place (in other terms, a mitzvah on the gavra to perform or for something to occur to a cheftza). The Minchas Chinuch explains that the mitzvah on the parents to perform a bris milah on their son is not a mitzvah that obligates a person to perform a certain act; rather the mitzvah requires that a certain situation is accomplished – namely that their son should have a bris milah. Regarding these types of mitzvos women are not exempt, even if it is a mitzvas assei she’hazman grama. Therefore, if the Torah did not write a pasuk that exempted women, they would be obligated to ensure that a bris milah was performed on their son.
Similarly, says the Minchas Chinuch, women are not exempt from the mitzvah of Shmittah since its essence is to ensure that the land observes a sheveisa. It is not a mitzvah that obligates them to perform a specific action per se; rather the mitzvah requires that a certain situation is arranged, namely that the land observes a rest. Therefore, women are obligated to keep this mitzvah.