Growth of field horsetail (Equisetum arvense) under low light and low nitrogen conditions

Field horsetail was grown from rhizome segments for 28 and 52 d under 35, 60, 120, 170, and 320 mu mol m(-2) s(-1) photosynthetic photon flux (PPF) and four continuous nitrogen (N) supply rates corresponding to a total of 1 to 6 tg N ha(-1) 28 d after planting (DAP) and 6 to 41 kg N ha(-1) 52 DAP. There was no response to the supply of N in the first growth period, probably due to the mobilization of nitrogen available in the planted rhizomes, and only dry weight (DW) of new belowground production, mostly roots, responded to increased light. Rhizomes were produced during the latter part of the 52-d period. Requirements for light and N during the 52-d period were low, because total new tissue production was only reduced at the lowest levels of light (35 mu mol m(-2) s(-1) PPF) and the two lowest N supply rates (6 and 18 kg N ha(-1)). The ratio of shoot DW to belowground organ DW increased only as the N supply increased. Shoot height response to an increased N supply was also small. Field horsetail can therefore be considered tolerant of low levels of N but will be overtopped by fast-growing species when competing for increased supplies of N. Both an increase in N supply and a reduction in light increased the reduction of DW of the planted rhizomes, whereas tuber production was favored by low N supply and high light intensities. Field horsetail can tolerate low levels of N but is not likely to be competitive in a dense crop stand.