## Example of leaf appearance calculation
library(lattice)

## Phyllochron for maize 25-55 degree days (ave. 40)

phyll <- 40

T.b <- 8 ## Base temperature

cmi <- read.table("cmiWet-1990.txt", header=TRUE)

class(cmi)

dim(cmi)

## Temperature is in Fahrenheit
TempC <- (cmi$Temp - 32) * 5/9

## Coding exercise to calculate GDD
res.col <- numeric(length(TempC))

for(i in 1:length(TempC)){

  tmp <- TempC[i] - T.b

  if(tmp < 0){
    res.col[i] <- 0
  }else{
    res.col[i] <- tmp
  }
}

plot(res.col)

TTcum <- cumsum(res.col)

doy <- seq(from = 1, to = 365, by = 1)

xyplot(TTcum ~ doy,
       type = "l",
       ylab = "Cummulative Thermal Time",
       xlab = "Day of the Year")

## How do we calculate the number of leaves?

## First select a range of values plausible for leaf production

## Day of crop emergence and tasseling

day1 <- 110 ## Apr 20
dayn <- 195 ## July 14

TTcum.sub <- TTcum[day1:dayn] - 258
LeafProd <- TTcum.sub %/% 40

xyplot(LeafProd ~ day1:dayn, type = "l")

# Maize produces 16-23 leaves (Hay & Porter, 2006)
# Could up to 30 leaves under the right conditions