Crop lodging

In this blog post I want to introduce the work that I, together with a number of colleagues, are carrying out on the phenomenon known as crop lodging. First I guess it is actually necessary to define what the word “lodging” means. In simple terms, lodging is the failure of crops due to stem breakage or uprooting during periods of high winds and/ or heavy rainfall. I need to make the point very firmly right at the start that it has got absolutely nothing at all to do with crop circles!  It does however have significant economic consequences, with yield losses in winter wheat resulting in costs to growers of the order of £100m in the UK in a high lodging season. Some pictures of lodging are given in figure 1 below.

Figure 2. Lodging in coral crops

Our work on this issue goes back in one form or another over a period of 30 years. It all began in in 1987 when I was an academic at the University of Nottingham. After the Great Storm of that year wreaked havoc with the tree stock in the south of the country, I still remember a colleague (Andrew Dawson) putting his head around the door of my office and saying “I have an idea for a research grant….”. This led to a grant from the Science Research Council to investigate the aerodynamics of urban trees – and we thoroughly enjoyed ourselves making measurements of the mechanical and aerodynamic properties of trees on and around the University campus, evolving an experimental technique that we named tree-twanging – pulling trees with a winch and then releasing them to measure the frequency of the oscillations. One of the less successful parts of that work was the initial development of a mechanical model of trees in high winds, which tried to represent trees in engineering terms. At the time this didn’t progress very far, but a few years later, in the early 1990s, I was approached by a colleague from the University School of Agriculture at the Sutton Bonnington Campus (Prof. Keith Scott) to help with a project that was investigating the lodging of winter wheat, and in particular to help supervise the PhD research of two students – John Griffin and Pete Berry. Perhaps the most challenging part of this work, both for me and staff and students at Sutton Bonnington was the need to learn to speak the vocabulary of anther discipline. This collaboration led to me doing some serious work on analytical model development that produced a reasonably robust description of the mechanical behavior of plants, and in particular winter wheat, in high winds and heavy rainfall. 

The next phase of this work began in 1998, when we (myself and colleagues at Sutton Bonnington and ADAS) obtained a grant from the Biology and Biotechology Research Council (BBSRC) to investigate lodging of winter wheat in some detail, to identify those plant characteristics that resulted in an increase in lodging risk. This date also coincided with my move from Nottingham to the University of Birmingham.  This work involved an extensive series of field trials at ADAS to measure characteristics of plants relevant to the lodging process, and we at Birmingham were responsible for developing a model of the lodging process and for carrying out experiments to calibrate the model. By this time (Dr.) Pete Berry was working for ADAS, so the collaboration with him thus continued. The Research Fellow appointed at Birmingham for this work was Dr. Mark Sterling, who had recently graduated from there with a PhD in open channel flow. We built the lodging model on the basis of the earlier modeling work, but needed a variety of aerodynamic information to calibrate this. Normally in engineering terms, this would have been obtained through wind tunnel tests – it is however not easy to put a representative section of a wheat field into a wind tunnel. The solution was to take a wind tunnel into the field – see the picture below. This proved to be more than a little challenging, but during the course of the experiments we were able to obtain the very first video footage of lodging actually taking place – this usually occurs in high winds and heavy rain and more often than not in the middle of the night, so the use of a portable wind tunnel, difficult as it was, was actually the most straightforward way of doing this. I am told by Mark that fixing strain gauges to wheat stems in the field to measure the displacement was one of the most entertaining tasks that he has ever been faced with.

Overall the project was very successful and enabled us to learn a great deal about the mechanics of root and stem lodging, to provide solid scientific information that cut through much of the hearsay that was around in the industry at the time about lodging, and to provide robust agronomical advice for farmers for techniques to avoid lodging. The collaboration between the University and ADAS was vital in this regard.

Over the next few years, work continued at a lower level, with the production of a few collaborative review papers, and the application of the lodging model to barley. However by the start of the current decade it was becoming clear that the model as it stood, whilst perfectly acceptable for wheat crops where the plants were essentially isolated throughout the growing season, was not really applicable to a range of crops for which, late in their growing season, individual plants interlocked to produce a much denser canopy. Thus we (myself, Pete Berry and Mark Sterling, by now the Head of Civil Engineering at Birmingham and thus my boss) began work on the development of a generalized lodging model that could allow for plant interlocking. Whilst the modeling was quite complex, it resulted in the relatively simple pictorial representation shown below in figure 2, where regions of stem lodging and root lodging were defined in terms of the daily rainfall rate and the hourly wind speed. The various velocities and rainfalls shown on this figure are all (rather complex) functions of plant and soil parameters and can, once the model is calibrated, be fairly easily specified. In principle this graph can be used with a representation of wind and rainfall probabilities to determine the risk of lodging occurring for any set of plant and soil parameters, and mitigation methods taken if this risk is deemed to be too high. In the peer review process, one of the reviewers of the paper acknowledged the elegance of the model, but made the comment that it would never find a practical outcome. We were to prove him wrong!

Figure 2. Lodging regions in the rainfall / windspeed plane

Over the last few years the work on lodging has grown very significantly, and we now have three projects underway. The first was funded by Teagasc in Ireland, to investigate methods to reduce oat lodging. We used the model described above and the work included a series of experiments in Ireland to measure, the behavior of oats in high winds.. The second project was funded by BBSRC under the SARIC (Sustainable Agriculture Research and Innovation Club) scheme, with myself and Mark, working again with Pete at ADAS. This used the same set of techniques to investigate the lodging of Oil Seed Rape. The unique aspect of this project however was a collaboration with Dr. Alan Blackburn and his colleagues at the University of Lancaster who are experts in Earth Observation and Remote Sensing, and the local modeling of lodging is being embedded in a much wider scheme to integrate spatial, topographic and meteorological data sets to predict the risk of lodging for individual crops and fields, and to identify those soil, plant and weather characteristics that cause lodging. The final project was also funded by BBSRC, but this time through the Global Challenges Research Fund which directs research funds to the problems of developing countries. We used a similar approach to the SARIC project, but this time directed towards maize and rice, working again with ADAS and Lancaster University, and also with colleagues at the Chinese Agricultural University and with CIMYTT in Mexico, who work in a large range of countries in the developing world.  The potential significance of this project is huge – lodging causes yield losses of up to 40% in rice and maize, reduces grain quality, increases time to harvest, increases grain drying costs and increases health damaging micro-organisms on grain. It is estimated that lodging in rice and maize reduces crop production in China and Mexico alone by $1500 million per year. 

All this research has all developed from a chance conversation and some early blue-sky research on trees over 30 years ago – and now has the possibility of producing results that will have a major effect on crop productivity around the world. In these days when funding for such fundamental research is under increasing pressure, this is perhaps worth remembering. But for now, these are exciting times – watch this space for future updates. 

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