EFFECT OF TEMPERATURE ON PHASIC DEVELOPMENT OF SPRING WHEAT IN NORTHERN CONDITIONS

The thermal response of spring wheat (Triticum aestivum L.) was examined using three cultivars grown in Finland. Field data was collected in 1977-88, Four different mathematical models were used to simulate the length of the development phases (sowing-to-heading, heading-to-yellow ripening and sowing-to-yellow ripening), and the accuracy of the models was compared. The thermal response of cvs. Heta and Kadett seems to be non-linear during the phase sowing-heading, while cv. Ruso reacts more linearly as temperature increases. For the other phases a linear model of response seems to be most accurate for all these cultivars. Mathematical simulation of the sowing-to-yellow ripening period was more accurate than for the other periods; its mean deviation with respect to the measured length of the phase (M(D)) was 2.7 days per year on average. Simulation of the sowing-to-heading period (M(D) = 3.3) was more accurate than for the heading-to-yellow ripening period (Mean(D) = 5.3). The results suggest improved means for the computation of development stage in crop growth models.