Functional Group Editor

The functional group editor.

LAI

Leaf area index is a factor that indicates how many leaf (or photosynthetically active) surfaces are in a column extended from area of ground under the canopy diameter up through the canopy. Another way to think about LAI is to consider it a shade index, with a 0.0 LAI casting no shadow all day, a 1.0 LAI allows %50 of the daily radiation hit the ground under the canopy, a 3.0 LAI allows %15 of the radiation to reach the ground under the canopy.

Some crop max LAI values are:

Corn 5.0

Soybeans 7.0

Sorghum 5.0

Cotton 6.0

Winter Wheat 8.0

Spring Wheat 8.0

Oats 8.0

Alfalfa 6.0

Brome-Grass 9.0

Peanut 4.5

Tobacco 3.4

Annual Ryegrass 6.0

Energy to Biomass Conversion Factor

The energy to biomass conversion factor estimates the rate of conversion of photosynthetically available radiation to biomass. The units of the factor are grams pre kilojoule. The energy to biomass conversion factor could also be viewed as a maximum growth rate (if temperature were always optimum, water plentiful, and radiation available.)

Some crop Energy to Biomass Conversion Factors are:

Corn 1.75

Soybeans 0.8

Sorghum 1.75

Cotton 0.855

Winter Wheat 1.5

Spring Wheat 1.5

Oats 1.5

Alfalfa 1.0

Brome-Grass 1.25

Peanut 1.0

Tobacco 1.25

Annual Ryegrass 1.25

Base Temperature

The base temperature is the temperature when the functional group can begin growth.

Optimum Temperature

The optimum temperature is the temperature where the functional group suffers no stress to growth. The base temperature and the optimum temperature determine the growing range of the functional group. The range will be the base temperature, to the optimum temperature + the difference between the base and the optimum temperature, so optimum temperature could be inferred as the average of base temperature and the temperature where heat stress stops growth in the functional group.

Daily Turnover Rate as % Standing Crop

A simple estimation for turnover rate is to examine a no growth (dry soil, cold temperature, or hot temperature) day and see the % standing crop lost.

HUI Accumulation at Maturity

This is a measure of the accumulation of degrees of the average temperature in excess of the base temperature of the functional group at which time the functional group reaches maturity. After this point the functional group ceases to grow photosynthetically active leaves, and begins to grow reproductive structures.

HUI Accumulation at Leaf Drop

This is a measure of the accumulation of degrees of the average temperature in excess of the base temperature of the functional group after maturity when the functional group dies. It is best to estimate both of these values by observation of previous year's weather files.

Root Depth at Maximum Biomass (and a Maximum Biomass)

This value will be used to estimate the current rooting depth of the group, as a linear function of current biomass (e.g. if a 10kg plant has a rooting depth of 1 meter, the a similar plant at 5kg will have an estimated root depth of 0.5 meters.)

Canopy Height at Maximum Biomass

This value will be used to estimate the current canopy height of the group, as a linear function of current biomass (e.g. if a 10kg plant has a canopy height of 3 meters, the a similar plant at 5kg will have an estimated canopy height of 1.5 meters.)

Other views into the functional groups (while editing.)

During functional group editing, many aspects of the factors affecting growth can be viewed, and each will provide a popup graph of that aspect. Here is a short description of each view:

Daily Heat Accumulation: The heat accumulation graph will help determine appropriate values for Heat Accumulation at Seed Head, and at plant maturity (this provides a method to have a phenolgical halt to the plant growth.)
Daily PAR: Photsenthetically Available Radiation is the light that the plant can use for growth (it tends to be a bell curve centered at the Summer with dips for cloudy days)
Daily Turnover: Daily Turnover will show how much of the standing crop was lost and when.
Daily Temperature Stress: The Daily Temperature Stress graph helps to tune the optimum and base temperatures, so that the growth surges of the plant happen at the right time.
Daily Delta Growth: Daily Delta Growth is usefull for checking how the plant accumulated the standing crop (if someone is more familar with growth rates than with standing crop.)