How to Calculate Crop Growth

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Crop growth rate is a measure of the increase in size, mass or number of crops over a period of time. The increase can be plotted as a logarithmic or exponential curve in many cases. The absolute growth rate is the slope of the curve. Relative growth rate is the slope of a curve that represents logarithmic growth over a period of time. An exponential growth rate is not sustainable over time. The curve typically flattens out, representing a saturation in growth at a certain point in time. The crop growth rate calculation is dependent on the values of NAR (Net Assimilation Rate) and LAI (Leaf Area Index) of the crop.

Plot the absolute and relative growth of the crop over the same period of time. Calculate AGR (Absolute Growth Rate) by measuring the slope of the absolute growth curve. Calculate RGR (Relative Growth Rate) by measuring the slope of the relative growth curve.

Calculate the LAR (Leaf Area Ratio) with the following formula:

LAR over the life of the crop = final leaf area / final plant dry weight

This value represents the efficiency of a particular leaf area.

Calculate the NAR (Net Assimilation Ratio) with the following formula:

NAR = RGR / LAR

This value represents the efficiency of production.

Use the values generated in Steps 1 to 3 to calculate the CGR (Crop Growth Rate) with the following formula:

CGR = NAR * LAI

The crop growth rate is the efficiency of the complete crop over a specific soil area.

Tips

• Herbaceous plants have a higher crop growth rate than woody plants.