Herbicides and Plant Physiology. Andrew H. Cobb. Читать онлайн. Newlib. NEWLIB.NET

Автор: Andrew H. Cobb
Издательство: John Wiley & Sons Limited
Серия:
Жанр произведения: Биология
Год издания: 0
isbn: 9781119157700
Скачать книгу
Scentless mayweed 15,000–19,000 Echinochloa crus‐galli Barnyard grass 2000–40,000 Chamaenerion angustifolium Rosebay willowherb 80,000 Eleusine indica Goose grass 50,000–135,000 Digitaria sanguinalis Large crabgrass 2000–150,000 Chenopodium album Fat hen 13,000–500,000 Triticum aestivum Wheat 90–100 Schematic illustration of some methods of weed seed dispersal with their estimated range in metres.

      Source: Liebman, M., Mohler, C.L. and Staver, C.P. (2001) Ecological Management of Agricultural Weeds. Cambridge University Press. Reproduced with permission of Cambridge University Press.

       1.5.7 Dormancy and duration of viability

      The length of time that seeds of individual species of weed remain viable in soil varies considerably. The nature of the research involved in collecting such data means that few comprehensive studies have been carried out, but those that have (see Toole and Brown, 1946, for a 39 year study!) show that although seeds of many species are viable for less than a decade, some species can survive for in excess of 80 years (examples include poppy and fat hen). Evidence from soils collected during archaeological excavations reveals seeds of certain species germinating after burial for 100–600 (and maybe even up to 1700!) years (Ødum, 1965).

      Dormancy in weed seeds allows for germination to be delayed until conditions are favourable. This dormancy may be innate and contributes to the periodicity of germination, as illustrated in Figure 1.1. In addition, dormancy may be induced or enforced in non‐dormant seeds if environmental conditions are unfavourable. This ensures that the weed seed germinates when conditions are most conducive to seedling survival.

Schematic illustration of factors affecting the soil seed population.

      Source: Grundy, A.C. and Jones, N.E. (2002) What is the weed seed bank? In: Naylor, R.E.L. (ed.) Weed Management Handbook, 9th edn. Oxford: Blackwell Publishing/BCPC. Reproduced with permission of John Wiley & Sons.

       1.5.8 Plasticity of weed growth

      The ability of a weed species to make rapid phenotypic adjustment to environmental change (acclimation) may offer a considerable strategic advantage to the weed in an arable context. An example of the consequence of such plasticity is environmental sensing by fat hen (Chenopodium album). This important weed can respond to canopy shade by undergoing rapid stem (internode) elongation, although the plant is invariably shorter if growing in full sun. Similarly, many species can undergo sun–shade leaf transitions for maximum light interception (Patterson, 1985).

       1.5.9 Photosynthetic pathways

      Returning to the interaction between crop and weed, it is therefore apparent that, depending on climate, light to severe competition may be predicted. For example, a temperate C3 crop may not compete well with a C4 weed (e.g. sugar beet, Beta vulgaris, and redroot pigweed, Amaranthus retroflexus) and a C4 crop might be predicted to outgrow some C3 weeds (e.g. maize, Zea mays, and fat hen, Chenopodium album). Less competition is then predicted between C3 crop and C3 weeds in temperate conditions, with respect to photosynthesis alone.