The interrelation between growth and development of wheat as influenced by temperature, light and nitrogen

Development was studied in wheat, mainly the subtropical varieties Hindi and Baladi. Leaf emergence was faster and the relation shoot/root decreased as temperature increased from 10° to 30°C. After transfer from low night temperature to higher temperatures for daily illumination, the root system was slower than aerial parts in reaching ambient temperature, causing damage to the plant. Warm water circulating slowly through the soil for a few minutes could avoid this. Stem elongation was most favoured at 10°-20°C in the night. Higher night temperatures gave fewer tillers and more leaves. Spikes developed sooner with 10°C than with 27°C at night and later with constant day-night temperatures.

Increase of daylength (8-24 h) increased stem length and decreased tiller number, and leaf number and area. Production of dry matter was highest with 16-20 h and was less with continuous light. Increasing intensities of extra illumination after normal daylight in the greenhouse increased stem length, decreased tillering, leaf formation and leaf area, and accelerated reproduction. Increase in normal illumination suppressed stem elongation, but increased number of tillers and leaves. White and red supplementary light for 3 weeks induced early flowering. Intense red light for 16 h accelerated spike initiation. The relation root/top increased with intensity.

Influence of N depended on light intensity. Low rate of N increased root/shoot ratio independently of light intensity. The relation C/N in the plant depended on N rate, photoperiod and night temperature. Early flowering usually accompanied a high C/N ratio. The relation of dry matter in heads to that in stems and leaves decreased with increasing N in both SD and LD. The absolute quantity of N in heads or stems, however, increased with high N and was mostly smaller in SD than LD.