FATE OF SEEDS OF SOME ANNUAL WEEDS IN DIFFERENT DEPTHS OF CULTIVATED AND UNDISTURBED SOIL

Abstract

Summary. Freshly‐collected seeds of twenty species of annual weeds were uniformly mixed with 2.5, 7.5 or 15 cm of soil confined in cylinders sunk in the ground outdoors. The soil was either cultivated four times a year or left undisturbed, seedling emergence was recorded, and after 5 years the numbers of viable seeds remaining were determined. Total seedling emergence from seeds incorporated to 2·5, 7·5 and 15 cm amounted to 75, 65 and 54% respectively of those added when the soil was cultivated, and 58, 36 and 21% where it was left undisturbed. The corresponding numbers of viable seeds remaining after 5 years were 2·3, 4·0 and 7·7% respectively for cultivated soil, and 6·8, 16·5 and 31·6% of the seeds initially added and then not disturbed. Individual species varied in their responses to increasing depth of incorporation and to cultivation; these differences are discussed in relation to the dormancy characteritics of the seeds. Devenir des semences de quelques mauvaises herbes annuelles à différentes profondeur dans un sol cultivé et non cultivé