Is this movie autobiographical?

Yes, it was partly autobiographical:

http://www.joo2joo.org/a_hard_look_at_life_on_the_kibbutz

Shaul's fictional movie, "Sweet Mud," based on his childhood in the village and memories of his mother's long battle with mental illness there, paints an unflattering picture of life on the kibbutz in the 1970s.

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Shaul said the movie tracks fairly closely his childhood experiences. His own father died while Shaul was an infant, and his mother, Tzipora, would battle depression for years as she raised him and two brothers, he said. She died of liver problems in 1983, when Shaul was 12.

The director said he realized the depth of his mother's anguish when he unearthed a box of yellowed letters and diaries six years ago; her writings revealed someone confused, depressed and deeply bitter toward the kibbutz. Shaul, then with two films under his belt, began to develop ideas for "Sweet Mud."

"Making the film was not only closing a circle in my relationship with my mother," he said. "It was closing a circle in my relationship with the people in the kibbutz and finally understanding them."

It is not the first time Shaul has turned family experiences into a film project. His first movie, a 1999 comedy called "Operation Grandma," was inspired when he and his brothers were put in charge of their grandmother's funeral. The movie is a cult favorite here. His second film, "Sima Vaknin, Witch," a comedy released in 2003, offers a satirical look at Israeli society.

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For Shaul, who after his mother's death remained at Kissufim until he was old enough for army service, the kibbutz ideal of selflessness was bound to clash with the needs and frailties of ordinary people...