The effects of length of growing season and plant population density on the growth of leafy forage brassicas
Compton, Ian James
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Experiments were carried out over three years to investigate the growth and development of leafy forage brassicas. The varieties used were Lair rape, Maris Kestrel kale and a line of Raphanobrassica developed at the Scottish Plant Breeding Station. Length of growing season was varied by utilising several sowing dates and a series of harvest dates, and in 1980 plant population density was also a treatment. A separate, smaller experiment in 1979 investigated plant population effects over a single length of growing season..Length of growing season was found to be the most important determining factor of total yield potential. A linear relationship between total yield and length of growing season was found, which could be applied to all three varieties in all three seasons. Most of the response of total yield was in the stem fraction, with leaf and petiole yield showing less variation. Plant population density had a smaller effect on yield, most pronounced early in the season and in the lower range (13 -39 m -2) . The stem fraction again showed the greatest response.Raphanobrassica tended to have the greatest final leaf and petiole yields, and the lowest stem yields, whilst Lair had the lowest leaf and petiole yields and greatest stem yields . The final total yields of all three varieties were similar. Lair had the fastest early growth, whilst Maris Kestrel had a lower initial growth rate but was more persistent in growth later in the season. Raphanobrassica followed an intermediate pattern.Further growth analysis of the 1980 results demonstrated a maximum LAI, similar for all three varieties. There was little varietal difference in LAR throughout the season, but Lair had the greatest SLA and lowest LWR, whilst Raphanobrassica had the lowest SLA and greatest LWR.Raphanobrassica showed a tendency for flowering from sowings earlier than late June in the main experiments, and this was further investigated by two small flowering experiments. The results suggested a response to both temperature and daylength, with cold treatment and long daylength inducing full flowering, but long daylength in the absence of cold treatment only partial flowering of the crop.