Light extinction of wheat as affected by N fertilisation and plant parameters

Light absorption and light extinction of wheat (Triticum aestivum L.) are among the most important parameters affecting wheat growth and yield production. However, these properties are affected by plant and environmental factors. Despite wheat being an important food crop, there is not much information on these light parameters in wheat. Accordingly, light parameters were investigated in wheat plants in the present study in three field experiments under two distinct climatic conditions, a warm arid and semi-arid climate and a cool climate. The aims of the study were to determine how light absorption and light extinction of wheat are affected by: (1) planting date and plant genotype under arid and semi-arid conditions (Experiment I); and (2) N chemical fertilisation and plant genotype under arid and semi-arid conditions (Experiment II) and cool temperate conditions (Experiment III). Light absorption by the canopy was determined using a lightmeter and coefficients of extinction were calculated. Analyses of variance indicated significant effects of experimental treatments on light properties, wheat growth and yield production. There was a high rate of variability in light absorption, with a maximum of 59.27%, and light extinction coefficients were in the range 0.45–0.66. The experimental treatments resulted in high variability in the leaf area index (2.08–7.49), wheat biological yield (7831.1–22 515.96 kg ha–¹), grain yield (2481.3–9273.57 kg ha–¹) and harvest index (32.86–53.90%). The interaction between planting date and plant genotypes indicated that the responses of different wheat genotypes to planting date were highly variable, significantly affecting light absorption and light extinction by wheat. It is possible to make the optimum use of solar light and produce the highest rate of yield if the most efficient genotype (Line 14-C81, Pishvaz and Pishtaz) is planted on the right planting date (15 November) using the optimum rate of N chemical fertilisation (50, 100, 150 kg ha–¹).