Modeling the spread of germination of four Mediterranean crops at different temperatures

Abstract

Minimizing the dispersion of germination across time allows greater uniformity during crop development. The aim of this paper was to model the spread of germination, under non-limiting water conditions and as a function of temperature, of four Mediterranean crops: pea (Pisum sativum L.), broad bean (Vicia faba L.), corn (Zea mays L.) and sorghum (Sorghum vulgare L.). Experiments were performed using a thermogradient plate. Four temperature ranges suitable for the thermal responses of each crop were used. Dispersion was expressed as standard deviation (σ) of the frequency distribution of thermal times in the population, modeled by a probit regression and by differences between both accumulated temperatures above the base temperature (0.8–0.2) or chronological times (t0.8-t0.2) required to reach 0.2 and 0.8 of final germination. Estimates of σ were obtained both within thermal ranges defined by applying the plateau-shaped model to the rate vs. temperature relationship and at single temperatures. The differences (0.8–0.2) and (t0.8-t0.2) were evaluated for each temperature. Reference values were successfully assigned to the germination dispersion of each crop, either to the different thermal ranges used or to single temperatures. Furthermore, a thermal range ensuring minimum values of dispersion was obtained for each crop using a polynomial equation to model the variation of t0.8-t0.2 on the set of temperatures used. The dimension of this thermal range was larger for winter than for summer crops. Crop competitiveness depends on the indicators used to assess dispersion. The results allow farmers to choose between different crops and thus optimize germination.