Browsing by Author "Earl, R."
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Item Open Access Developing strategies for spatially variable nitrogen application in cereals II: wheat(Elsevier , 2003-04) Welsh, J. P.; Wood, G. A.; Godwin, R. J.; Taylor, John C.; Earl, R.; Blackmore, S.; Knight, S. M.For precision agriculture to provide both economic and environmental benefits over conventional farm practice, management strategies must be developed to accommodate the spatial variability in crop performance that occurs within fields. Experiments were established in crops of winter barley (Hordeum vulgare L.) over three seasons. The aim of which was to evaluate a set of variable rate nitrogen strategies and examining the spatial variation in crop response to applied N. The optimum N application rate varied from 90 to in excess of 160 kg [N] ha−1 in different parts of the field, which supports the case for applying spatially variable rates of N. This, however, is highly dependent on seasonal variations, e.g. the quantity and distribution of rainfall and the effect that this has on soil moisture deficits and crop growth. Estimates of yield potential, produced from either historic yield data or shoot density maps derived from airborne digital photographic images, were used to divide experimental strips into management zones. These zones were then managed according to two N application strategies. The results from the historic yield approach, based on 3 yr of yield data, were inconsistent, and it was concluded that that this approach, which is currently the most practical commercial system, does not provide a suitable basis for varying N rates. The shoot density approach, however, offered considerably greater potential as it takes account of variation in the current crop. Using this approach, it was found that applying additional N to areas with a low shoot population and reducing N to areas with a high shoot population resulted in an average strategy benefit of up to 0·36 t ha−1 compared with standard farm practice.Item Open Access Developing Strategies for spatially variable nitrogen application in cereals, I: Winter barley(Elsevier , 2003-04) Welsh, J. P.; Wood, G. A.; Godwin, R. J.; Taylor, John C.; Earl, R.; Blackmore, S.; Knight, S. M.For precision agriculture to provide both economic and environmental benefits over conventional farm practice, management strategies must be developed to accommodate the spatial variability in crop performance that occurs within fields. Experiments were established in crops of winter barley (Hordeum vulgare L.) over three seasons. The aim of which was to evaluate a set of variable rate nitrogen strategies and examining the spatial variation in crop response to applied N. The optimum N application rate varied from 90 to in excess of 160 kg [N] ha−1 in different parts of the field, which supports the case for applying spatially variable rates of N. This, however, is highly dependent on seasonal variations, e.g. the quantity and distribution of rainfall and the effect that this has on soil moisture deficits and crop growth. Estimates of yield potential, produced from either historic yield data or shoot density maps derived from airborne digital photographic images, were used to divide experimental strips into management zones. These zones were then managed according to two N application strategies. The results from the historic yield approach, based on 3 yr of yield data, were inconsistent, and it was concluded that that this approach, which is currently the most practical commercial system, does not provide a suitable basis for varying N rates. The shoot density approach, however, offered considerably greater potential as it takes account of variation in the current crop. Using this approach, it was found that applying additional N to areas with a low shoot population and reducing N to areas with a high shoot population resulted in an average strategy benefit of up to 0·36 t ha−1 compared with standard farm practice.Item Open Access The development of techniques for assessing compactibility of field soils.(Cranfield University, 1995-07) Alexandrou, Athanassios; Earl, R.During the last five decades, effects of soil compaction on crop growth and yield have been of increasing concern due to the introduction of heavier agricultural machinery. Most researchers agree that, although a certain degree of compaction can be beneficial to crops, loading beyond this can be very detrimental and, therefore, soil compaction should be considered as an important factor which should be managed in crop production systems. The majority of work to date has been conducted using disturbed soil samples and hence not representative of field situations. The aim of this project was to investigate further the compactibility behaviour of field soils. Work was conducted in a soil bin as well as on field soils (sandy loam and clay ) in a range of climatic conditions. Techniques for assessing soil compactibility are proposed, based on the stress-strain (load-sinkage) characteristics of soil, soil strength prior to loading, and the mode and extent of soil deformation for a given loading situation. The determination of these soil characteristics proved somewhat cumbersome and time consuming and, therefore, the prediction of these variables from more easily determined soil properties (volumetric water content, initial dry bulk density, void ratio and degree of saturation) was investigated with promising results. In addition, a model is proposed which predicts the extent of deformation within the soil profile for a given loading situation.Item Open Access Real-time measures of canopy size as a basis for spatially varying nitrogen applications to winter wheat sown at different seed rates(Elsevier, 2003-04) Wood, G. A.; Welsh, J. P.; Godwin, R. J.; Taylor, John C.; Earl, R.; Knight, S. M.Experiments at two sites growing winter wheat show that in order to manage a wheat canopy more effectively, the use of specific remote sensing techniques both to monitor crop canopy expansion, and to determine variable nitrogen applications at key timings is required. Variations in seed rate were used to achieve a range of initial crop structures, and treatments were compared to standard farm practice. In the first year, the effect of varying seed rate (250, 350 and 450 seeds m−2) on crop structure, yield components and grain yield, was compared to the effects of underlying spatial variation. Plant populations increased up to the highest rate, but shoot and ear populations peaked at 350 seeds m−2. Compensation through an increased number of grains per ear and thousand grain weight resulted in the highest yield and gross margin at the lowest seed rate. In later experiments, the range of seed rates was extended to include 150 seeds m−2, each sown in 24 m wide strips split into 12 m wide halves. One half received a standard nitrogen dose of 200 kg [N] ha−1, the other a variable treatment based on near ‘real-time’ maps of crop growth. Both were split into three applications, targeted at mid-late tillering (early March), growth stages GS30-31 (mid April) and GS33 (mid May). At each timing, calibrated aerial digital photography was used to assess crop growth in terms of shoot population at tillering, and canopy green area index at GS30-31 and GS33. These were compared to current agronomic guidelines. Application rates were then varied below or above the planned amount where growth was above- or below-target, respectively. In the first field, total nitrogen doses in the variable treatments ranged from 188 to 243 kg [N] ha−1, which gave higher yields than the standards at all seed rates in the range 0·36–0·78 t ha−1 and gross margins of £17 to £60 ha−1. In the second field, variable treatments ranged from 135 to 197 kg [N] ha−1 that resulted in lower yields of −0·32 to +0·30 t ha−1. However, in three out of the four seed rates, variable treatments produced higher gross margins than the standard, which ranged from £2 to £20 ha−1. In both fields, the greatest benefits were obtained where the total amount of applied nitrogen was similar to the standard, but was applied variably rather than uniformly along the strips. Simple nitrogen balance calculations have shown that variable application of nitrogen can have an overall effect on reducing the nitrogen surplus by one-third.Item Open Access Soil factors and their influence on within-field crop variability II: spatial analysis and determination of management zones(Elsevier, 2003-04) Taylor, John C.; Wood, G. A.; Earl, R.; Godwin, R. J.Spatial variation of crop yields was examined in three trial cereal fields in England from 1994 through 1997. The fields were managed with uniform inputs but there were considerable differences in the spatial patterns and magnitudes of variation between fields and seasons. Up to 50% of the yield variation was within the tramline spacing distance (20â 24 m) and this appeared to relate to crop management practices rather than underlying soil factors. Longer-range variation generally increased up to field scale but was not constant between seasons. Longer-range variation was more apparent in dry years and was attributable to soil variation. Soil series differences coincided with yield differences in dry years when the soil series differences could be expected to create large differences in soilâ water relationships. Soil electrical conductivity, measured by electromagnetic induction (EMI), was investigated as a surrogate for detailed soil coring. Field zones created by EMI also coincided with yield differences and zones were similar to those delineated by soil series with expected differences in soilâ water relationships. The EMI observations were found to be a useful and cost-effective surrogate for representing soil variability in fields likely to create yield variations. Subdivision of fields into management zones using multi-variate K-means cluster analysis of historical yield and EMI observations formed an objective basis for targeting soil samples for nutrient analysis and development of site-specific application strategies. The appropriateness of site-specific management has to be assessed annually because magnitude and pattern of variation changes from season to season.Item Open Access Soil Factors and their Influence on Within-Field Crop Variability, I: Field Observation of Soil Variation(Elsevier Science B.V., Amsterdam, 2003-04-01T00:00:00Z) Earl, R.; Taylor, John C.; Wood, G. A.; Bradley, I.; James, Iain T.; Waine, Toby W.; Welsh, J. P.; Godwin, R. J.; Knight, S. M.A fundamental component of adopting the concept of precision farming in practice is the ability to measure spatial variation in soil factors and assess the influence of this on crop variability in order to apply appropriate management strategies. The aim of this study was to appraise potential methods for measuring spatial variability in soil type, nutrient status and physical properties in practical farming situations. Five fields that are representative of more than 30% of soils used for arable production in England and Wales were selected for use as case studies. Maps of soil type were generated from a conventional hand auger survey on a 100 m grid and the excavation of targeted soil profile pits. These were compared with those refined using a mechanised soil coring device and scans of electromagnetic inductance (EMI) carried out while the soil could reasonably be considered to be at, or near, field capacity moisture content. In addition, soil sampling for nutrient analyses was conducted on a 50 m grid to examine the spatial variation in nutrient status. Conventional methods for sampling soil were found to be appropriate for identifying soil types at specific locations within the field sites, however, they were time- consuming to perform which placed an economic and therefore a practical limitation on the sampling density possible. The resulting data were considered to be too sparse for demarcating soil type boundaries for use in the context of precision farming. The location of soil boundaries were refined by using the mechanised soil corer, however, the limitation of this was found to be the time required to analyse the soil cores produced. Maps of soil variation generated from EMI scans conducted at field capacity appear to reflect the underlying variation in soil type observed in maps generated using the mechanised soil corer. and, therefore, this approach has potential as a cost-effective, data- rich, surrogate for measures of soil variability. Results from analyses of soil samples for measurement of nutrient status indicated that whilst there was considerable variation in macro- and micro-nutrient levels in each field, with the exception of pH, these levels were above commonly accepted agronomic limits. Results did however demonstrate the potential for addressing variation in critical factors such as pH at specific locations, however, there is a need to develop protocols for targeting sampling in order to reduce costs.Item Open Access Soil incorporation of bio-solids into arable cropping(Cranfield University, 1999) Moseley, Peter; Earl, R."The application of bio-solids to established arable crops, using shallow injection techniques developed during this study, is feasible in environmental, economic,agronomic and engineering terms." Novel approaches to bio-solids disposal and recycling are required to compensate for expected increases in production, and to alleviate the extemal pressures exerted on the water company through legislation and increased public awareness of environmental issues. A review of previous work has identied bio-solids application to arable cropping as a promising benecial outlet for increased volumes of waste. From this doctoral study, in collaboration with a parallel fast track project, a improved, shallow injection system has been developed, based on soil mechanics theory and extensive laboratory and field testing. Environmental pollution, in terms of odour and ammonia emissions, may be signicantly reduced through the use of this system, when compared to other shallow injection or surface application methods. Nitrate leaching was found to be unaffected by the increased retention of valuable nutrients under field conditions prevailing during the study period, and no detrimental effect on agronomic performance has been identied following application to crops up to three months prior to harvest. Economically, a market exists for this technology, through the enhanced nutrient value of the bio-solids product. However, product quality, consistency and other enviromnental issues require solutions before the full economic benefits and market acceptance can be realised. Theoretically, the increased application "window of opportunity" has the potential to increase producers operating profits substantially (1.7%/yr, Anglian Water Services Region) through reduced inventory, storage and distribution costs. Maximisation of enviromnental benefits has been addressed in terms of implement control, by maintaining constant tine attitude to the soil, through a parallel linkage system. A analysis of the force system associated with the parallel lirkage system, in conjunction with the development of a model to predict tine depth, was used to examine ways of optimising the dynamic performance of the system. This work demonstrated that geometric changes to the parallel linkage are unlikely to affect dynamic performance. However, the use of frictionless linkage joints in conjunction with depth control skids was shown to improve dynamic performance signicantly and a novel multiple curve fitting technique was developed to improve the accuracy of the depth prediction model.