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 r ealisations the model determines whether or not stem lodging will occu r by comparing the wind induced bending moment at the base of an indiv idual shoot with the stem base failure moment. Similarly, whether or n ot root lodging will occur is ascertained by comparing the wind induce d base bending moment of the whole plant with the plant's root failure moment. The overall probability of lodging is determined from the pro portion of wind speed and rainfall realisations for which lodging is p redicted to occur. For differently managed wheat crops the model corre ctly predicted lodging in 21 of the 30 lodged crops and nil lodging fo r 38 of the 42 standing crops. The model showed that both stem and roo t lodging may occur given suitable circumstances. The state of the cro p was as important as the prevailing weather for influencing lodging r isk. A relatively small number of crop parameters were of major import ance in the lodging process. These include the shoot's centre of gravi ty height, natural frequency, stem base radius and failure yield stres s, and the plant's shoot number, root plate diameter and structural ro oting depth. In addition, the importance of soil, particularly clay co ntent, in influencing anchorage was illustrated. Recommendations for f urther improvement of the model include improvement of the soil streng th calculation. (C) 1998 Academic Press.