Determination of crop dynamic and aerodynamic parameters for lodging prediction
Introduction
Lodging is the permanent displacement of crop stems from their (original) vertical position, due to a combination of high winds and heavy rain, and can result in significant crop yield reductions (Berry et al. (2000)). The phenomenon affects a wide range of crops – wheat, barley, rice, oats, maize, oilseed rape etc., and is a problem of significant concern in many countries around the world. There are two basic failure modes – stem lodging (failure at some point of the stem above the ground) and root lodging (failure at the root/soil interface). These two lodging mechanisms are illustrated in Fig. 1 for the three crops with which this paper is mainly concerned - oats (Avena sativa), maize (Zea mays) and oilseed rape (OSR, Brassica napus). Whilst the primary loading on the plants that causes lodging to occur is the wind, heavy rainfall can affect the soil conditions and increase the likelihood of root lodging.
The costs of lodging can be considerable. For example, in the UK it is estimated that as a direct result of lodging in OSR, yield is reduced by ~46% resulting in losses of ~£120 million per year (Kendall et al., 2017). Stem lodging of maize accounts for worldwide yield losses of up to 20% (Flint-Garcia et al., 2003), whilst a further 20% reduction in yield can be attributed to root lodging. The costs incurred by lodging arise as a direct consequence of yield loss and indirectly from reduced grain quality, increased drying, increased susceptibility to plant pathogens and pests, and the increased difficulties associated with harvesting (Crook and Ennos, 1993; Berry et al., 2003, 2004; Berry and Spink, 2012; Sterling et al., 2018). Furthermore, the effects of crop lodging can directly and indirectly impact on a number of the United Nations Sustainable Development Goals (United Nations, 2019), in particular: no poverty, zero hunger, good health and well-being, and responsible consumption and production. Some researchers have suggested that climate change may exacerbate the issue in certain parts of the world (Challinor et al., 2010; Mohammadi et al., 2020), particularly through heavier rain fall increasing the susceptibility of crops to root lodging.
Whilst much of the basic work in this area has been carried out by agronomists and plant scientists, some experimental work looking at tree behaviour in high winds from an engineering perspective has been carried out both by one of the author and his co-workers (Baker and Bell, 1992; Roodbaraky et al., 1994) for urban trees, and by Boldes and his colleagues in Argentina (Boldes et al., 2001, 2002, 2003) for forest trees and shelterbelts. Computational studies of flows within canopies are also reported by Hiraoka (1993) and Hiraoka and Ohashi (2008). More recently Rhee and Lombardo (2018) have begun to consider tree and crop failure as indicators of the strength of tornadoes.
Over the last two decades, research has been carried out by some of the authors to understand the mechanisms of lodging and, in doing so, to enable the best application of remedial measures/interventional (management) approaches. As a result of this work, a mechanical model of the lodging process was developed in which a single plant is represented as a damped harmonic oscillator (Baker, 1995; Baker et al., 1998; Berry et al., 2006). Applying a representative wind gust, it was possible in this model to calculate the wind-induced bending moment at the base of the plant, which was compared with the stem failure moment and the failure moment of the root plate. An improved model was subsequently developed (Baker et al., 2014) which was generalised for any plant type and enabled canopy interactions with the environment to be taken into account. The model allows for consideration of both individual plants and crops with interlocked canopies, such as OSR. In addition, a more complex, stochastic, representation of the wind was used. For crops that oscillate as isolated plants (e.g., wheat), the generalised model reduces to that described in Baker (1995). The model has been used in a number of linked multi-disciplinary investigations to study the lodging of a variety of crops around the world, based on a range of aerodynamic, climate and agronomic studies, with a view to incorporating of the results into a GIS framework that can be used to identify crops at risk of lodging, or, conversely, the development of more risk resistant crops (Berry et al., 2019).
In order to apply the new model, a variety of aerodynamic and plant related parameters are required. The focus of the current paper is to present a viable methodology for determining these parameters using in-situ measurements of wind over the crop canopy and the corresponding wind-induced displacement of the crop. Section 2 of the paper briefly outlines the generalised lodging model and how it is parameterised. Section 3 outlines the methodology of the field experiments undertaken on oats, maize and OSR. Experimental results are set out and discussed in section 4 and some concluding remarks are made in section 5.
Section snippets
The generalised lodging model
As noted above, the authors have developed a model of the lodging process that can predict, for specific wind and rain conditions, the probability of root and stem lodging. This will not be described in detail here, and the reader is referred to Baker et al. (2014) for further details. Here it is sufficient to say that a mechanical analysis of individual plants or an interlocked canopy of multiple plants, assuming the crop can be represented by point masses at the top of weightless, elastic
Experimental set-up
The experiments reported below were undertaken at various farm locations in the UK and the Republic of Ireland (Table 1). The primary objective of these experiments was to observe the effects of wind and rain on the motion of three specific crops, namely oats, maize and OSR, selected because of differences in their canopy morphologies which leads to variations in canopy interlocking. Wind conditions and plant displacement were simultaneously measured. The experiments were conducted after
Canopy top flow parameters
In this section and subsequent sections relevant parameters have been averaged over 17, 20 minute datasets for maize and 18, ten minute datasets for OSR. Table 2 shows average values across all the datasets at crop height of where is the standard deviation of the velocity component i and is the friction velocity given by ; , the turbulence intensity of the velocity component i (); and /h, the integral length scales of the velocity component i normalised by crop height h
Conclusions
From what has been set out above, the following major conclusions can be drawn.
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The experimental methodologies adopted have been shown to be robust and consistent dynamic and aerodynamic parameter values have been derived. The spread of data for the biological systems studied here is large in comparison to normal wind engineering expectations.
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Whilst the measurements for oats and maize show strong peaks in the displacement spectra at the natural frequency, the experimental data for the
Dedication
This paper is dedicated to one of the authors, John Finnan, who died in an aircraft accident during the course of the research. John’s expertise and input was instrumental for the agricultural elements of the research on oats. However, John also had an uncanny knack of delivering a constructive and well-timed challenge on the wind engineering aspects of the research, thereby ensuring that those authors who claim to profess such expertise reflected long and hard on how their message could be
CRediT authorship contribution statement
G.M.D. Joseph: Methodology, Software, Formal analysis, Investigation, Data curation, Writing - original draft. M. Mohammadi: Methodology, Investigation, Formal analysis. M. Sterling: Conceptualization, Methodology, Resources, Data curation, Funding acquisition. C.J. Baker: Conceptualization, Methodology, Formal analysis, Writing - original draft, Funding acquisition, Writing - review & editing. S.G. Gillmeier: Software. D. Soper: Methodology, Investigation. M. Jesson: Methodology,
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This study was made possible by funding grants from the British Biology and Biosciences Research Council Global Challenges Research Fund (GCRF BB/P023282), Sustainable Agriculture Research and Innovation Club (SARIC BB/P004555) fund and Teagasc (Walsh Fellowship) the Agricultural and Food Development Authority of the Republic of Ireland.
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