Crop species have their own characteristic ‘window’ of development when yield is more vulnerable to stresses such as drought, nutrient deficiency, frost and heatwaves.
In wheat, for example, the most critical window is between stem elongation and a week after flowering. Grain number, the main component of yield, is determined in this window.
To determine the critical window for chickpea yield, the South Australian Research and Development Institute (SARDI) set up trials at Roseworthy (sowing date 7 June) and Turretfield (sowing dates 14 June and 9 July) in SA.
Crops of PBA Boundary and PBA Slasher were shaded for two weeks at different stages during the growing season.
Untreated controls yielded three tonnes per hectare and Figure 1 shows yields achieved by the shade-stressed crops.
The SARDI trials showed that the critical window for chickpeas starts at about 300 ‘degree-days’ before flowering and the most vulnerable stage for yield was found to be 200 ‘degree-days’ after flowering (Figure 1).
Figure 1 Yield of chickpeas in response to timing of stress.
Note: the yield is most severely reduced with stress about 200 to 300 degree days after flowering.
PBA Boundary is represented with circles and PBA Slasher with triangles.
Crops at Roseworthy are shown with black symbols, early-sowing crops at Turretfield are shown in red and late-sowing crops at Turretfield are shown in blue.
(Hollow red circles and triangles are not significantly different from the control.)
Degree-days are a calculation of time based on daily temperature and are necessary to account for the fact that crops develop faster at high temperatures. For the crop, one day at 15°C is not the same as a day at 10°C.
For example, if chickpeas are grown in conditions where the daily mean temperature is 15°C, the critical stage of 200 degree-days will be reached 13 days after flowering (200 ÷ 15 = 13). If chickpeas are grown in a warmer region or the crop was sown late with, for example, a daily mean temperature of 20°C, the crop will reach the 200-degree-days mark 10 days after flowering (200 ÷ 20 = 10).
Ensuring good growing conditions (sufficient supply of water and nutrients) and avoiding stress (such as frost and heat) during the critical window are essential for high-yielding chickpea crops.
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