Optimizing germination of seven Mediterranean crops
Andrade, José A. | Cadima, Jorge | Abreu, Francisco G.
Crop establishment is a major factor determining crop productivity. Successful crop establishment requires generalized, fast and concentrated germination. Final germination counts (size), speed and spread depend on soil temperature and moisture. This work seeks to determine, under non-limiting water conditions, optimal temperature ranges for the germination of seven common Mediterranean crops, viz., pea (Pisum sativum L.), lupine (Lupinus luteus L.), chickpea (Cicer arietinum L.), broad bean (Vicia faba L.), sunflower (Helianthus annuus L.), corn (Zea mays L.) and sorghum (Sorghum bicolor (L.) Moench). Experiments used a thermogradient plate, with temperatures monitored by Cu-CuNi thermocouples. Thermal ranges [Tₒ₁ˢᶻ, Tₒ₂ˢᶻ] along which germination counts are nearly maximized were identified by the successful use of a flattened bell curve function. Thermal ranges [Tₒ₁ˢᵖ, Tₒ₂ˢᵖ], where germination speed is maximized, were defined using the plateau-shaped model for rate of germination vs. temperature relationship. Ranges [Tₒ₁ˢᵈ, Tₒ₂ˢᵈ], along which dispersion is nearly minimized, were successfully identified using even-degree polynomials. The intersection of these three thermal ranges provided an optimal temperature range (OTRG) for the germination of each crop. In most cases, OTRG begins at the lowest temperature that guarantees a maximum germination rate (Tₒ₁ˢᵖ) and ends at the maximum temperature that ensures minimal dispersion (Tₒ₂ˢᵈ). The endpoints and length of the OTRG were found to be crop-dependent. For each crop, OTRG also depended on the fraction of germinated seeds and on the level of dispersion that is considered acceptable. The results allow farmers to choose between different crops and to optimize their germinations.
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