Controlling plant form through husbandry to minimise lodging in wheat

Plant characters which affect lodging in winter wheat (Triticum aestivum L. ) were investigated through husbandry-change experiments at ADAS Rosemaund near Hereford (UK) over three seasons (1994-1996). Treatments were sowing d ate (20 September to 1 November), seed rate (500 and 250 seeds m(-2)) and r esidual soil nitrogen (116-46 kg ha(-1) in February). in all combinations w ith four spring treatments: none, one or two plant growth regulators (PGRs) , or reduced and delayed applications of nitrogen. The separate and combine d effects of all plant characters on lodging were estimated using a model t o calculate the minimum wind speed at which a shoot's leverage would exceed the strength of its stem base (stem lodging), and at which the leverage of all the shoots on a plant would exceed its anchorage strength (root lodgin g). Measurements in July showed that all plant characters were influenced by th e husbandry treatments, most changes increasing the minimum wind speed at w hich the plant lodges. PGRs, reduced spring nitrogen and delayed sowing red uced shoot leverage by reducing the height at centre of gravity and increas ing natural frequency Reduced spring nitrogen also reduced ear area. Delaye d sowing, low residual nitrogen and reduced spring nitrogen increased stem strength by increasing both stem diameter and wall width. Soils with low re sidual nitrogen also increased material strength (failure yield stress) of the stem wall. Reduced seed rate increased stem diameter but reduced materi al strength slightly. Reducing seed rate also increased anchorage by increa sing the spread and depth of the root plate. However, low seed rates also i ncreased shoot number per plant, which partially counteracted the root plat e effect. The most robust plants grown in this study were calculated to require gust speeds of 26-28 m s(-1) to cause stem and anchorage failure. It was estimat ed that wheat must withstand gusts of up to 40 m s(-1) if it is to lodge on ly once every century. This study concludes that the best husbandry practic es, which are compatible with high yields, could not achieve the structural specification to withstand such wind gusts. It is suggested that new genot ypes are needed to achieve lodging-proof wheat crops, particularly to provi de stronger basal internodes and a wider root plate per shoot. (C) 2000 Els evier Science B.V. All rights reserved.