The Effects of Seed Burial and Soil Disturbance on Emergence and Survival of Arable Weeds in Relation to Minimal Cultivation

Abstract

(1) Seeds of sixteen weed species (six grasses and ten herbs) were collected from arable field margins during 1977. Species included were Agrostis gigantea, Alopecurus myosuroides, Arrhenatherum elatius, Avena fatua, Bromus sterilis, Poa trivialis, Capsella bursa-pastoris, Galium aparine, Papaver rhoeas, Plantago major, Polygonum aviculare, Stellaria media, Tripleurospermum inodorum, Veronica arvensis, Veronica persica, and Viola arvensis. Seeds were sown in soil in pots or boxes at various depths, and either disturbed periodically or left undisturbed. Periodicity of emergence was recorded for each species. (2) Four patterns of emergence were recorded: (i) emergence in spring alone; (ii) predominantly in autumn; (iii) in both spring and autumn; (iv) emergence indifferent to season. Most of the grasses emerged predominantly in autumn whereas the main period of emergence for many of the dicotyledonous species was in spring. (3) Burial of small-seeded species both delayed and reduced seedling emergence as compared to surface-sown seed. In contrast germination and emergence of the larger-seeded species was increased by burial. Soil disturbance increased the total number of seedlings which emerged, but in general it did not alter the relative periodicity of germination, nor was emergence promoted by cultivation at times outside the period of natural emergence. (4) The number of viable but ungerminated seeds which remained after 2 years varied between species. It was least for surface sown seed and greatest for buried undisturbed seed. Most frequent were A. myosuroides, Viola arvensis, P. rhoeas and P. aviculare. No seeds of A. elatius, B. sterilis or G. aparine remained after 12 months. (5) Relatively few species emerged from below 50 mm with the exception of several large-seeded species. These species generally failed to establish from seed on the soil surface. (6) The results are discussed in relation to the use of minimal cultivations for cereal production. It is concluded that the majority of annual grass-weeds, despite having little innate dormancy, will continue to be encouraged by current agronomic practices. In contrast, many annual dicotyledonous species will decline in importance, partly as a result of their susceptibility to herbicides and partly because their periodicity of germination does not coincide with the establishment phase of autumn-sown cereals.