Crop rotation and weed flora, with special reference to the nutrient and light demand of Equisetum arvense L.
1997
Andersson, T.N. (SLU, Uppsala (Sweden). Inst. foer Vaextodlingslaera)
This thesis focuses on (1) the effects of varied crop rotations on the weed flora and (2) the response of Equisetum arvense (field horsetail) to light, nitrogen (N) and potassium (K). Three 6-year crop rotations were etablished at three sites in southern Sweden in the mid-1960s. All crops were present each year. The rotations had either a grass ley, a legume-grass ley or spring wheat followed by a repeatedly harrowed fallow. The leys of the fallow were followed by winter turnip rape, winter wheat, oats and barley. Ley plants were undersown in barley. No herbicides were used in the study year (1994). Nutrients were given at standard rates, except N which was applied at four rates, from very low rates to conventional rates. Individuals of each weed species were counted. Crop biomass and light intensity in crop stand were measured in one site. No specific weed problem related to crop rotation had developed. While differences in the weed flora were apparent between the sites and in the various types of crops they were small between the rotations. Total weed biomass was, however, largest in the grass ley rotation. The relationship between weed biomass and N was inconsistent. Equisetum arvense was characteristic of low-N plots at one site. Two hydroponic culture studies showed that when provided with an unrestricted N supply this species hasa low relative growth rate, a low nitrogen demand and a high K demand. Even at low light intensities, vigorous rhizome growth was initiated soon after planting, whereas shoot elongation was weak and depended on resources stored in the rhizomes. Thus, although Equisetum arvense is adapted to sunny habitats, it can tolerate short periods of low light intensities. However, growth was considerably suppressed by a dense crop stand.
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