Three factor bar graph in R

 

p_nitrate =ggplot(data=mean_soil ,aes(x=Depth, y=nitrate ,
                                      fill=factor(Fertilizer.type) )) +  theme_bw() +
  geom_bar(width=pos,position=position_dodge(pos),stat="identity")+
  geom_errorbar(aes(ymin=mean_soil$nitrate -sd_soil$nitrate ,ymax=mean_soil$nitrate +sd_soil$nitrate ),
                width=pos/2,
                position=position_dodge(pos))+
  #geom_line(aes(color = Fertilizer.type), position = position_dodge(width = 1))+
  xlab("Soil depths") +
  ylab(labs$nitrate )+
  scale_fill_manual(values=c("red", "blue", "green","grey", "yellow"))+
  s.theme1+ # add x and y axis theme here
  s.theme2+ # add-legend theme here
  facet +    # third factor
  facect.t + # facet adjustment
  scale_y_continuous(limits = c(0, 1.5), breaks = seq(0, 15, by = 0.3))+
  theme(legend.position = "top")+ # facet adjustment
  labs(fill = "Fertilizer type") # correct legend title
p_nitrate  
ggsave("soil_nitrate .png", width = 20, height =10)