重命名beanplot中的x轴标签

Question

我正在使用以下代码使用beanplot函数：

library(beanplot)
beanplot(Grainyield~Year*Tmnt,las = 2, 
     data = maize,
     xlab = "Factors Year.Water Treatment ", 
     ylab = "Yield [kg/ha]", 
     col  = list("yellow", "orange", "green", "blue"))

legend("bottomleft", 
   bty="n",
   c("2008","2009","2010","2011"),
   fill = c("yellow", "orange", "green", "blue"))

x轴标签不正确，我尝试使用以下代码格式化x轴标签，但是我一直收到错误消息：

axis(1, at=2008.1:2011.6, 
labels=c[1,1,1,1,2,2,2,2,3,3,3,3,4,4,4,4,5,5,5,5,6,6,6,6])

有什么建议吗？