Improving the prediction of processing pea maturity based on the growing degree day approach

The heat-unit system, involving the sum of daily mean temperatures above a given base temperature, is used with processing pea (Pisum sativum L.) to p redict relative maturity during the growing season and to schedule planting dates based on average temperature data. The Quebec pea processing industr y uses a base temperature of 5 degrees C to compute growing-degree days (GD D) between sowing and maturity, This study was initiated to verify if the c urrent model, which uses a base temperature of 5 degrees C, can be improved to predict maturity in Quebec, Four pea cultivars, 'Bolero', 'Rally', 'Fla ir', and 'Kriter', were grown between 1985 and 1997 on an experimental farm in Quebec, For all cultivars, when using a limited number of years, a base temperature between 0.0 and 0.8 degrees C reduced the coefficient of varia tion (cv) as compared with 5.0 degrees C, indicating that the base temperat ure used commercially is probably not the most appropriate for Quebec clima tic conditions. The division of the developmental period into different sta ges (sowing until emergence, emergence until flowering, and flowering until maturity) was also investigated for some years, Use of base temperatures s pecific for each crop phase did not improve the prediction of maturity when compared with the use of an overall base temperature. All years for a give n cultivar were then used to determine the base temperature with the lowest cv for predicting the time from sowing to maturity. A base temperature fro m 0 to 5 degrees C was generally adequate for all cultivars, and a common b ase temperature of 3.0 degrees C was selected for all cultivars, For the ye ars and cultivars used in this study, the computation of GDD with a base te mperature of 3 degrees C gave an overall prediction of maturity of 2.0, 2.4 , 2.2, and 2.5 days based on the average of the absolute values of the diff erences for the cultivars Bolero, Rally, Flair, and Kriter, respectively.