nitrogen <- rep(1:4,each=6)
block <- rep(1:2,each=3,times=4)
years <- rep(seq(2,8,3),times=8)

chlrfl <- c(3.8,5.3,5.9,3.9,5.4,4.3,5.2,5.6,5.4,6.0,6.1,6.2,
            6.0,5.6,7.8,7.0,6.4,7.8,6.8,8.6,8.5,7.9,8.6,8.4)

tg <- data.frame(nitrogen,block,years,chlrfl)
attach(tg)

nitrogen <- factor(nitrogen)
block <- factor(block)
years <- factor(years)

turfg.mod1 <- aov(chlrfl ~ block + nitrogen + block:nitrogen + years + years:nitrogen)
summary(turfg.mod1)

turfg.mod2 <-  aov(chlrfl ~ nitrogen*years + Error(block/nitrogen))
summary(turfg.mod2)

library(lme4)

turfg.mod3 <- lmer(chlrfl ~ nitrogen*years + (1|block/nitrogen))
summary(turfg.mod3)
anova(turfg.mod3)