A method for the assessment of the risk of wheat lodging

A model of the wheat canopy/root/soil system has been developed, which calculates the risk of stem and root lodging from crop parameters and soil characteristics. For a large number of wind speed and rainfall realisations the model determines whether or not stem lodging will occur by comparing the wind induced bending moment at the base of an individual shoot with the stem base failure moment. Similarly, whether or not root lodging will occur is ascertained by comparing the wind induced base bending moment of the whole plant with the plant's root failure moment. The overall probability of lodging is determined from the proportion of wind speed and rainfall realisations for which lodging is predicted to occur. For differently managed wheat crops the model correctly predicted lodging in 21 of the 30 lodged crops and nil lodging for 38 of the 42 standing crops. The model showed that both stem and root lodging may occur given suitable circumstances. The state of the crop was as important as the prevailing weather for influencing lodging risk. A relatively small number of crop parameters were of major importance in the lodging process. These include the shoot's centre of gravity height, natural frequency, stem base radius and failure yield stress, and the plant's shoot number, root plate diameter and structural rooting depth. In addition, the importance of soil, particularly clay content, in influencing anchorage was illustrated. Recommendations for further improvement of the model include improvement of the soil strength calculation. (C) 1998 Academic Press.