What's it mean? 她们不时抖动着屁股**摔去根须上**的泥巴。

[艾墨本]

我走到了一棵有着茂盛树叶的树下，田里的棉花已被收起，几个包着头巾的女人正将棉秆拔出来，她们不时抖动着屁股摔去根须上的泥巴。

 

This is taken from the first chapter of 活着.

 

Can someone help me understand what it means here? Based on context I'm assuming something like "shake off the dirt," but then what does 根须上 mean?

 

Thank you,

艾墨本

[Publius]

棉秆根须上的泥巴

[艾墨本]

ah, got it. The construction still seems weird to say shake off the dirt that was on the roots of the cotton as opposed to shake off the dirt that was on their butts. 

[Publius]

Yeah, I agree with you. "我走到了一棵有着茂盛树叶的树下" <-- this also sounds somewhat unnatural to me. But who am I to criticize a successful writer.