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 nonlimiting 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 (θ 0.8-θ 0.2) or chronological times (t 0.8-t 0.2) 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 (θ 0.8-θ 0.2) and (t 0.8-t 0.2) 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 t 0.8-t 0.2 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.

Optimizing the establishment of bean and maize varieties in tropical environments

“…The three phases of S-shaped curves for both cumulative germination and emergence curves (lag phase, near-linear growth phase and the final asymptotic plateau phase) vary over the thermal tolerance range of any crop [16,22,49].…”

“…It is thus useful to know for each crop a temperature range that ensures minimum dispersion values or acceptable values from the farmer's point of view, rather than finding only a single temperature that minimizes dispersion. Also, in the case of dispersion, the relevance of this issue increases with both daily and annual variations in soil temperature [49].…”

“…Both germination and emergence dispersions (SdG and SdE, respectively) were assessed by the differences between the respective germination or emergence times necessary for 0.2Gf or 0.2Ef (t20) and 0.8Gf or 0.8Ef (t80) at each temperature tested [26,49]. Reasons for using chronological time instead of thermal time can be found in [16] or [49]. The option for these two percentiles was largely justified in the previous subsection (speed).…”

“…Plots of germination or emergence times versus temperature [51,52] suggested that, for all crops, both times were minimal along a fairly broad thermal range and increased toward the more extreme temperatures considered, regardless of the germination or emergence fraction. A polynomial function of even degree (2k, k ϵ ℕ) was proposed in [49] to model the relationship between Sd (either SdG or SdE, both expressed by t80−t20) and temperature (T):…”

“…The value of m.a.s. =1.05Sdmin was considered as the maximum acceptable spread [49]. Setting, in Eq.…”