Estimating base temperature and thermal time requirement for chickpea (Cicer arietinum L.) emergence

Abstract

In order to reach different growth stages, crops have a certain thermal time requirement, which includes mean ambient temperature and developmental base temperature (Tb). Calculating Tb allows estimating growing degree days (GDD) more precisely. This work aimed to determine the Tb and GDD required for cv. Norteño chickpea (Cicer arietinum L.) sowing-emergence stage. Pot and field trials were conducted to obtain and validate data. From July to December 2016, 15 pots were planted on each date, and 5 seeds per pot. In the field, they were planted on 6/4 and 6/19 of 2015, 4/15, 5/23, 6/14, 7/7, and 8/5 of 2016 in plots following a completely randomized design with 4 replications. Phenological records were kept daily. To estimate Tb, mathematical formulae of classical statistical methods were used: the coefficient of variation in GDD (CVGDD), the regression coefficient (RC), and the lowest standard deviation (SDGDD). Tb amounted to 3.75, 3.92, and 4.79°C, and GDD values for the sowing-emergence stage were 137.26, 135.57, and 126.93°C/d, respectively, as obtained with the CVGDD, RC and SDGDD methods. In order to validate these data, the refined index of agreement, the root mean square error, and the coefficient of determination were calculated. The parameters considered showed that the methods were adequate to predict the emergency, with SDGDD being the most accurate at estimating Tb and GDD, which turned out to be 4.79°C and 126.93°C/d, respectively.