Sarah Smarsh’s memoir, “Heartland,” opens with a perplexing ode to an imaginary baby. “I’m glad you never ended up as a physical reality in my life. But we talked for so many years that I don’t guess I’ll ever stop talking to you.” Throughout the book an apparition of the author’s unborn child pops into the prose like Ally McBeal’s Baby Cha-Cha, inducing the otherwise sage Smarsh to write in the inexorably sentimental second person.Smarsh escaped poverty, she believes, because, unlike her mother, grandmother and great-grandmother, she didn’t become a teenage mom. In part, she says, this was because she was among the first generation of her family to have at least one constant home, dating to when her maternal grandmother, Betty, married her seventh husband, Arnie. (By contrast, Smarsh’s mom, Jeannie, moved 48 times before starting high school.) Such is the reality of poverty. The memoir flickers to life at that home, a humble farmhouse on 160 acres of wheat fields outside Wichita.