Seed size, substrate granulometry and sowing depth in seed and seedling vigor of two weeds

Weeds produce a large quantity of seed, which generate several generations during the crop cycle. Their biological characteristics, such as seed and seedling vigor, allow weeds to persist in unfavorable environments. The objective of this study was to obtain information on Amaranthus hybridus L. (pigweed) and Malva parviflora L. (cheeseweed) seed vigor using physiological cold test, accelerated aging and standard germination in light and darkness and on seedling vigor using a physical test, emergence and root growth in substrates with different granulometries and two seeding depths in function of seed size. The combination of species, seed size, and physiological test constituted one treatment with four replications with 25 seeds. In physical tests, the combination species, seed size, substrate granulometry and sowing depth constituted one treatment with four replications of five seeds. Multiple ANOVAs and the Tukey test of comparison of means (p≤0.01) were performed with data of all trials. Both sizes of amaranth seed were 100 % viable and cheeseweed seed was 80 % viable. After the cold and accelerated aging tests, germination percentages were lower than those of standard germination and higher in amaranth than in cheeseweed (p≤0.01). There were no differences between seed sizes within species. Emergence percentage of shoots from large seeds sown 1 cm deep in the medium and coarse granulometries was higher than that from seeds sown in fine substrate 2 cm deep (p≤0.01). Considering all the factors, final root lengths were similar. Cheeseweed seedlings from large seeds took longer to deplete their reserves than small seeds and amaranth seeds of both sizes. Amaranth was more vigorous than cheeseweed.