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 date (20 September to 1 November), seed rate (500 and 250 seeds m(-2)) and residual soil nitrogen (116-46 kg ha(-1) in February). in all combinations with four spring treatments: none, one or two plant growth regulators (PGRs), or reduced and delayed applications of nitrogen. The separate and combined effects of all plant characters on lodging were estimated using a model to 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 lodging). Measurements in July showed that all plant characters were influenced by the husbandry treatments, most changes increasing the minimum wind speed at which the plant lodges. PGRs, reduced spring nitrogen and delayed sowing reduced shoot leverage by reducing the height at centre of gravity and increasing natural frequency Reduced spring nitrogen also reduced ear area. Delayed sowing, low residual nitrogen and reduced spring nitrogen increased stem strength by increasing both stem diameter and wall width. Soils with low residual nitrogen also increased material strength (failure yield stress) of the stem wall. Reduced seed rate increased stem diameter but reduced material strength slightly. Reducing seed rate also increased anchorage by increasing the spread and depth of the root plate. However, low seed rates also increased shoot number per plant, which partially counteracted the root plate 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 estimated that wheat must withstand gusts of up to 40 m s(-1) if it is to lodge only once every century. This study concludes that the best husbandry practices, which are compatible with high yields, could not achieve the structural specification to withstand such wind gusts. It is suggested that new genotypes are needed to achieve lodging-proof wheat crops, particularly to provide stronger basal internodes and a wider root plate per shoot. (C) 2000 Elsevier Science B.V. All rights reserved.