APPLICATION density. MATCHING SPRAY APPLICATIONS TO CANOPY CHARACTERISTICS IN CEREAL CROPS Paul Miller Andrew Lane and Helen Wheeler from Silsoe Research Institute Wrest Park Silsoe Bedford MK 45 4HS UK describes a ldquo;precision farmingrdquo; approach such materials by matching the characteristics of a delivered spray to those of the target crop canopy. The simplest form of such a relationship may be to adjust the volume application rate of a given tank mix of chemicals to the local value of leaf area or vegetative index in given parts of a field. However considerable research and practical development has been directed at defining other physical characteristics of a spray that influence both retention and efficacy of an application including droplet size distribution trajectory angle of the spray velocities of droplets within the spray and air conditions associated with the spray delivery.It may therefore be appropriate to adjust other factors controlling spray delivery to improve performance in given crop canopy conditions. The work described here has the main objective of linking spray applications to crop canopy characteristics so as to make recommendations relating to the improved use of fungicides and similar chemical sprays. 100 or 200 l/ha fine or medium vertical or 45deg; backwards The potential advantages There is now substantial evidence to indicate that in many arable crop situations improvements in both the financial and environmental aspects of crop production could be achieved by the appropriate management of spatial variability.The development of such ldquo;Precision Farmingrdquo; approaches has been made potentially viable by technological developments relating to l field-scale location systems where the development of methods based on optical reflectance radio systems and most significantly satellite navigation (e.g. the Global Positioning System) has enabled location to be determined to typically better than plusmn;2.0 m at an acceptable cost; l robust and relatively low cost computer systems for data collection manipulation and control that can be incorporated into or mounted along side existing systems used with field-based agricultural equipment; l appropriate sensor systems that enable a range of physical parameters to be measured such as the grain flow rate into the tank on a combine harvester for yield mapping or soil electromagnetic inductance to show differences in structure composition and moisture holding capacity across a field.For plant protection products such as fungicides that have a mode of action that is primarily associated with the surface of leaves then there may be scope to optimise the use of Figure 1. Map showing vegetative index measured in the winter wheat crop and divided into areas of high and low crop canopy 100 Pesticide Outlook ndash; June 2001 This journal is copy; The Royal Society of Chemistry 2001 Field studies Experiments were conducted on two fields in crops of spring and winter wheat using spectral reflectance measurements as a measure of crop canopy density.Measurements of vegetative index across each field were made using radiometers mounted on a spray boom at a spacing of approximately 4 m and a height of 1.5 m above the crop. An arrangement for recording the output from the radiometers into a portable computer was devised such that vegetative index could be calculated and tagged with position in the field from a GPS system also connected to the computer. By driving along tramlines at a speed of about 10 km/h before the crop had reached growth stage 32 data from which a vegetation index map could be plotted was obtained. The contours between areas of different vegetative index were smoothed in a computer mapping program and the field area was then divided into approximately two equal areas on the basis of the measured vegetative index (see Figure 1).Application plots were then laid out randomly in both areas of high and low crop canopy density. Randomised replicated plots each 10 m by 20 m were laid out to enable the following application variables to be investigated l spray volume rate l spray quality l angle of delivery Applications were made are both growth stage 32 and 39. DOI 10.1039/b104594f Results The measured spray deposits for the main treatment effects are shown in Figure 2. The differences in deposit level between areas of high and low crop canopy density are small. It was expected that deposit levels per unit of plant weight would be higher where the crop density was lower but this was not the case (Figure 2a).The results however did show some important and expected trends namely:- l spray deposits tended to increase when using a fine rather than a medium quality spray (Figure 2b) with the largest increase at the earlier growth stage l using the lower volume application rate (100 l/ha) gave substantially higher deposits than the conventional volume rate (200 l/ha) again with the largest difference at the earlier growth stage (Figure 2c) l angling the delivery of the spray also increased the level of deposit at the earlier growth stage as expected (Figure 2d) Figure 2 Spray deposits for different treatments. (a) The effect of canopy density (b) The effect of spray quality (c) The effect of volume application rate APPLICATION l penetration into the canopy was much greater for the smaller canopy condition at the earlier growth stage (Figure 2e) l It is very noticeable that deposit levels per unit of plant weight are consistently higher at the earlier growth stage.This reflects the changes in canopy size between the two growth stages and the fact that no changes were made to the application to account for this increasing canopy size Whereas Figure 2 gives the mean deposit levels for the main treatment effects a statistical analysis of the results indicates that the interactions between the experimental variables may be important. This is to be expected since for example it is likely that angling the spray delivery will have a larger effect on deposition when treating a relatively low canopy density at an early stage of growth compared with a more dense and well established canopy condition.(d) The effect of angled delivery (e) The penetration of spray into the canopy at the two growth stages Pesticide Outlook ndash; June 2001 101 APPLICATION Implications from the results Although the differences between deposit levels in the areas of high and low canopy density within a given field were small differences between the two growth stages were consistent and much larger. This result suggests that there is scope to improve application performance by matching spray delivery parameters to crop canopy structure and that changes should initially account for the effects of growth stage. Any strategy that aims at matching spray application to crop canopy structure requires a robust method of defining the canopy characteristics.Methods based on spectral reflectance measurements are being developed commercially to control the application of nitrogen fertilisers and are likely to be effective at early stages of growth but less discriminatory when the canopy is fully developed. The approach taken in the work reported here was to sense canopy characteristics at an early stage of growth when there was a high level of confidence in the sensor system being able to discriminate between differences in different parts of a field. However this strategy has an important weakness in that changes in canopy structure between sensing and treatment may be important and are not accounted for.Improved methods of sensing canopy structure may therefore be required. One approach that could be used to account for crop growth stage could be the use of growth rate keys with established relationships between the canopy and defined growth stage for the major cereal and/or oilseed varieties. Such an approach could then be implemented easily and at a relatively low cost. The results attained in the work are also dependent upon the fields used for the study. Although there was variation in these fields more information is needed on the range of variation in crop canopy conditions across a field. It is possible that larger variations in soil type aspect or drainage will give larger differences in canopy structure then those observed in this work and that the scope for spatially varying application parameters is greater.SILSOE RESEARCH INSTITUTE (SRI) SRI is the only research centre in the UK dedicated to the application of engineering and physical sciences to a wide range of biological systems and processes including applications in the food processing industry. SRIrsquo;s remit was to develop the mechanisation of UK agriculture but over the last 20 years there has been a strong move towards topics with a process engineering modelling and optimisation or environmental objective. Science groups l Environment l Biomaterials Group l Livestock Engineering l Mathematics amp; Decision Systems l Soil Science l Image Analysis l Chemical Applications l Heat amp; Mass Flow l International Development l Robotics amp; Automation Of particular interest to readers of Pesticide Outlook will be the Chemical Applications Group which has extensive experience of research on pesticide application systems and how the behaviour of sprays from nozzle to target influences losses to drift.For further information Silsoe Research Institute Wrest Park Silsoe Bedford MK45 4HS UK. (http://www.sri.bbsrc.ac.uk) 102 Pesticide Outlook ndash; June 2001 This study shows the importance and potential for adjusting a number of parameters defining spray application other than volume and/or dose rates. The ability to adjust volume rate spray quality and the delivery angle of sprays is likely to provide opportunities for increased deposition improved targeting within the canopy and optimised pesticide use.Acknowledgements The main part of the project work was funded by the Home- Grown Cereals Authority The Ministry of Agriculture Fisheries and Food funded aspects of the original work on sensing crop canopy characteristics. Thanks are also due to colleagues from Silsoe Research Institute Tom Robinson (Novartis Crop Protection Ltd) and Ben Freer (Morley Research Centre). References Miller P. C. H; Lane A. G; Wheeler H. C. (2000) Matching the application of fungicides to crop canopy characteristics. Proceedings The BCPC Conference ndash; Pests and Diseases 629ndash;636. Miller P. C. H; Paice M. E. R. (1998) Patch spraying approaches to optimise the use of herbicides applied to arable crops. Journal of the Royal Agricultural Society of England 159 70ndash;81. Paul Miller is an agricultural engineering graduate who joined what is now Silsoe Research Institute in 1971 and following research work relating to the sugar beet crop and grain drying was appointed to lead the Chemical Application Group in 1984. His research interests cover most aspects of agricultural chemical application particularly spray drift nozzle performance and sprayer control. In 2000 Paul was appointed to the post of Project Director and Head of Process Engineering Division that includes the Chemical Application Group. He is a Visiting Professor of Cranfield University and a Senior Research Fellow with the Home-Grown Cereals Authority with interests relating to precision farming approaches.
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