Abstract
A wide range of species can be sown as cover crops during fallow periods to provide various ecosystem services. Plant establishment is a key stage, especially when sowing occurs in summer with high soil temperatures and low water availability. The aim of this study was to determine the response of germination to temperature and water potential for diverse cover crop species. Based on these characteristics, we developed contrasting functional groups that group species with the same germination ability, which may be useful to adapt species choice to climatic sowing conditions. Germination of 36 different species from six botanical families was measured in the laboratory at eight temperatures ranging from 4.5–43°C and at four water potentials. Final germination percentages, germination rate, cardinal temperatures, base temperature and base water potential were calculated for each species. Optimal temperatures varied from 21.3–37.2°C, maximum temperatures at which the species could germinate varied from 27.7–43.0°C and base water potentials varied from -0.1 to -2.6 MPa. Most cover crops were adapted to summer sowing with a relatively high mean optimal temperature for germination, but some Fabaceae species were more sensitive to high temperatures. Species mainly from Poaceae and Brassicaceae were the most resistant to water deficit and germinated under a low base water potential. Species were classified, independent of family, according to their ability to germinate under a range of temperatures and according to their base water potential in order to group species by functional germination groups. These groups may help in choosing the most adapted cover crop species to sow based on climatic conditions in order to favor plant establishment and the services provided by cover crops during fallow periods. Our data can also be useful as germination parameters in crop models to simulate the emergence of cover crops under different pedoclimatic conditions and crop management practices.
Highlights
Diverse cover crop species are increasingly used in agriculture during fallow periods to provide various ecosystem services, such as catching nitrate to limit water pollution, increasing nitrogen available for the crop and protecting soils against erosion [1,2,3]
For Poaceae (Fig 2c and 2d), the largest differences between the two temperatures were observed for the two C4 species, Sorghum bicolor var. sudanense and Setaria italica, whose final germination percentages were much lower at 11.5°C, since they were reduced by 56% and 80%, respectively
Setaria italica and Polygonum fagopyrum were distinguished from other species in this study for their high Tb (7.8°C and 10.6°C, respectively), which was consistent with literature values (Tb-emerg = 10.9°C and 11.1°C, respectively [27,28])
Summary
Diverse cover crop species are increasingly used in agriculture during fallow periods to provide various ecosystem services, such as catching nitrate to limit water pollution, increasing nitrogen available for the crop and protecting soils against erosion [1,2,3]. These species can be sown as a sole crop (monoculture) or intercropped (species mixture) to provide the services [4,5]. If the species cannot germinate because of too high temperature and too low water potential in the seedbed, the plant cover will never be correctly established
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