The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
J. A. Cornell - One of the best experts on this subject based on the ideXlab platform.
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Error Sources Affecting Variable Rate Application of Nitrogen Fertilizer
Precision Agriculture, 2004Co-Authors: C. W. Chan, J. K. Schueller, W. M. Miller, J. D. Whitney, J. A. CornellAbstract:The accuracy and interaction among global positioning system (GPS) horizontal accuracy, differential GPS (DGPS) sampling frequencies and machine delay times of a hypothetical Variable Rate applicator for nitrogen (N) fertilizer Application based on an Application map in Florida citrus were studied. Parameters studied included: five GPS horizontal accuracy levels, two levels of DGPS horizontal accuracy, two DGPS sampling frequencies and two machine delay times. Two integRated models were developed which documented the effects of the parameters. Machine delay time was the most important factor and GPS horizontal accuracy was the second most important.
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error sources on yield based fertilizer Variable Rate Application maps
Precision Agriculture, 2002Co-Authors: C. W. Chan, J. K. Schueller, W. M. Miller, J. D. Whitney, T A Wheaton, J. A. CornellAbstract:Spatially-Variable Application of inputs to agricultural fields is dependent upon accuracy of the input Variables. The effects of boundary determination, interpolation method, and GPS location errors were studied for determining a Variable Rate nitrogen Application map based upon yield maps of a 3.6 ha Florida citrus block. A general linear model for the mean absolute error approximated the error effects.
W. M. Miller - One of the best experts on this subject based on the ideXlab platform.
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Variable Rate nitrogen Application in florida citrus based on ultrasonically sensed tree size
Applied Engineering in Agriculture, 2005Co-Authors: Qamar U Zaman, Arnold W Schumann, W. M. MillerAbstract:Most Florida citrus groves are still managed as large contiguous uniform blocks, despite significant variation in fruit yield and tree canopy size. Site-specific grove management by Variable Rate delivery of inputs such as fertilizers on a tree size basis could improve horticultural profitability and environmental protection. Tree canopy sizes were measured real-time in a typical 17-ha Valencia grove with an automated ultrasonic sensor system equipped with Differential Global Positioning System (DGPS). Prescription maps for Variable Application of nitrogen fertilizer were geneRated from ultrasonically scanned tree sizes on a single tree basis using ArcView GIS and Midtech Fieldware. Leaf samples from trees with different canopy sizes, which had been fertilized at a conventional uniform Rate of 270 kg N/ha/y, were analyzed for nitrogen concentration. Analysis of 2980 tree spaces in the grove showed a skewed size distribution, with 62% in the 0- to 100-m3/tree volume classes and a median volume of 79 m3/tree. The tree volumes ranged from 0 to 240 m3/tree. Regression analysis showed that trees with excess leaf nitrogen (>3%) had canopies less than 100 m3. These trees receiving excess nitrogen are likely to have lower fruit yields and quality, and wasted fertilizer nitRates may leach beyond the root zone to groundwater. In order to rectify the excess fertilization of smaller trees, a granular fertilizer spreader with hydraulically powered split-chain outputs controlled with a MidTech Legacy 6000 controller was used for Variable Rate Application of nitrogen in one-half of the grove. A 38% to 40% saving in granular fertilizer cost was achieved for this grove when Variable N Rates were implemented on a per-tree basis ranging from 135 to 270 kg N/ha/y.
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Error Sources Affecting Variable Rate Application of Nitrogen Fertilizer
Precision Agriculture, 2004Co-Authors: C. W. Chan, J. K. Schueller, W. M. Miller, J. D. Whitney, J. A. CornellAbstract:The accuracy and interaction among global positioning system (GPS) horizontal accuracy, differential GPS (DGPS) sampling frequencies and machine delay times of a hypothetical Variable Rate applicator for nitrogen (N) fertilizer Application based on an Application map in Florida citrus were studied. Parameters studied included: five GPS horizontal accuracy levels, two levels of DGPS horizontal accuracy, two DGPS sampling frequencies and two machine delay times. Two integRated models were developed which documented the effects of the parameters. Machine delay time was the most important factor and GPS horizontal accuracy was the second most important.
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error sources on yield based fertilizer Variable Rate Application maps
Precision Agriculture, 2002Co-Authors: C. W. Chan, J. K. Schueller, W. M. Miller, J. D. Whitney, T A Wheaton, J. A. CornellAbstract:Spatially-Variable Application of inputs to agricultural fields is dependent upon accuracy of the input Variables. The effects of boundary determination, interpolation method, and GPS location errors were studied for determining a Variable Rate nitrogen Application map based upon yield maps of a 3.6 ha Florida citrus block. A general linear model for the mean absolute error approximated the error effects.
Mohammadreza Maleki - One of the best experts on this subject based on the ideXlab platform.
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optimisation of soil vis nir sensor based Variable Rate Application system of soil phosphorus
Soil & Tillage Research, 2007Co-Authors: Mohammadreza Maleki, A M Mouazen, Herman Ramon, J De BaerdemaekerAbstract:Abstract Uniform phosphorous fertilisation has economical, ecological and agronomical shortcomings. This study was undertaken to optimise the Variable Rate (VR) elemental P Application using a previously developed on-the-go visible (VIS) and near infrared (NIR) soil sensor. This VIS–NIR sensor consists of a chisel unit, to which the optical unit to detect soil extractable phosphorous (P-ext) was attached. A mobile, fibre-type VIS–NIR spectrophotometer (Zeiss Corona 45 visnir, Germany ) with a measurement range between 305 and 1711 nm was used to measure soil spectra in reflectance mode. On-the-go measurement of soil spectra was carried out in two fields (A and B) situated near Leuven in Belgium. From the spectra, P-ext was calculated in soil and subsequently the required elemental P was determined. Different averaging windows (AW) of the predicted P-ext from successive spectra (2–22) and five recommendation classification intervals (RCI) of elemental P of 20, 10, 5, 2 and 1 kg ha −1 were assigned and tested. The VR of elemental P was compared with uniform Rate (UR) Application. Results showed that among the five RCIs, the minimum elemental P Application Rate was for interval of 5 kg ha −1 , with small differences of among the different RCIs. In the fields under study, the amount of elemental P fertiliser according to the VR approach was higher than the UR Application with an extra elemental P of 4 and 2.38 kg ha −1 for fields A and B, respectively. However, this higher elemental P fertiliser recommendation of VR is only valid when an equal number of samples (1200 in field A and 660 in field B) is considered for both VR and UR methods. Larger amounts of elemental P fertiliser were needed for plots and/or fields having higher variation in measured P-ext. The results also showed that in both fields the Application Rate decreased with larger AWs. Averaging of less than five P-ext successive values was not a proper choice with any RCIs due to the large deviation between the target and classified elemental P into the different RCIs. The combination of RCI 5 and AW between 10 and 15 is recommended to provide a good matching between uniform and applied elemental P at low cost.
S B Mahajanashetti - One of the best experts on this subject based on the ideXlab platform.
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evaluating the returns to Variable Rate nitrogen Application
Social Science Research Network, 2001Co-Authors: Roland K Roberts, Burton C English, S B MahajanashettiAbstract:Potential benefits of Variable Rate nitrogen Application are illustRated and information needs identified. Lower costs of precision farming services, higher crop prices, and greater divergence in yield response potentials across management zones reduce the spatial variability required for profitable Variable Rate Application. Information needs include identification and measurement of management zones within a field and estimation of management zone yield response functions, crop and input prices, and the cost of precision farming services.
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economic and environmental benefits of Variable Rate Application of nitrogen to corn fields role of variability and weather
1999 Annual meeting August 8-11 Nashville TN, 1999Co-Authors: Burton C English, S B Mahajanashetti, Roland K RobertsAbstract:The use of meta-response functions based on EPIC-geneRated data resulted in comparisons between Variable (VRAT) and uniform Rate Application technologies for 36 simulated fields. VRAT was more profitable and less nitrogen was lost to the environment in most cases. When spatial variability was small, uniform Rate Application techniques were adopted. However, when nitrogen use is restricted, VRAT is used on all simulated fields.
Arnold W Schumann - One of the best experts on this subject based on the ideXlab platform.
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precise placement and Variable Rate fertilizer Application technologies for horticultural crops
Horttechnology, 2010Co-Authors: Arnold W SchumannAbstract:Fertilizer spreaders capable of Variable Rate Application are increasingly important for enhancing nutrient management in horticultural crops because they improve placement and increase nutrient uptake efficiency. Matching applied fertilizer to fertilizer requirements represents a significant input cost saving for the grower and a reduction in potential pollutant loading to ground and surface water. Variable Rate fertilization (VRF) is a precision agriculture technology made possible by embedded high-speed computers, accuRate Global Positioning System (GPS) receivers, Geographic Information Systems (GIS), remote sensing, yield or soil maps, actuators, and electronic sensors capable of measuring and even forecasting crop properties in real time. For tree crops like Florida citrus (Citrus spp.), the most important function of the VRF spreader is to detect and avoid fertilizing spaces of the orchard not occupied by trees. Treeless spaces are becoming more common in Florida as diseases such as citrus greening (Candidatus Liberibacter asiaticus) and canker (Xanthomonas axonopodis) cause the removal of thousands of trees every year. VRF works best under those conditions. Because VRF exploits crop and soil variability, it has no value in a perfectly uniform field. VRF enables smaller trees including resets to be fertilized at lower, most appropriate Rates, thus minimizing any excess Application. This article examines the existing knowledge on using precision agriculture and Variable Rate technology to keep water and nutrients in the root zone of horticultural crops, thus facilitating maximum uptake efficiency.
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nutrient management zones for citrus based on variation in soil properties and tree performance
Precision Agriculture, 2006Co-Authors: Arnold W SchumannAbstract:Site-specific soil management can improve profitability and environmental protection of citrus groves having large spatial variation in soil and tree characteristics. The objectives of this study were to identify soil factors causing tree performance decline in a Variable citrus grove, and to develop soil-specific management zones based on easily measured soil/tree parameters for Variable Rate Applications of appropriate soil amendments. Selected soil properties at six profile depths (0–1.5 m), water table depth, ground conductivity, leaf chlorophyll index, leaf nutrients and normalized difference vegetation index were compared at 50 control points in a highly Variable 45-ha citrus grove. Regression analysis indicated that 90% of spatial variation in tree growth, assessed by NDVI, was explained by average soil profile properties of organic matter, color, near-infrared reflectance, soil solution electrical conductivity, ground conductivity and water table depth. Regression results also showed that soil samples at the surface only (0–150 mm) explained 78% of NDVI variability with NIR and DTPA-extractable Fe. Excessive available copper in low soil organic matter areas of the grove apparently induced Fe deficiency, causing chlorotic foliage disorders and stunted tree growth. The semivariograms of selected Variables showed a strong spatial dependence with large ranges (varied from 230 m to 255 m). This grove can be divided into different management zones on the basis of easily measured NDVI and/or soil organic matter for Variable Rate Application of dolomite and chelated iron to improve tree performance.
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Variable Rate nitrogen Application in florida citrus based on ultrasonically sensed tree size
Applied Engineering in Agriculture, 2005Co-Authors: Qamar U Zaman, Arnold W Schumann, W. M. MillerAbstract:Most Florida citrus groves are still managed as large contiguous uniform blocks, despite significant variation in fruit yield and tree canopy size. Site-specific grove management by Variable Rate delivery of inputs such as fertilizers on a tree size basis could improve horticultural profitability and environmental protection. Tree canopy sizes were measured real-time in a typical 17-ha Valencia grove with an automated ultrasonic sensor system equipped with Differential Global Positioning System (DGPS). Prescription maps for Variable Application of nitrogen fertilizer were geneRated from ultrasonically scanned tree sizes on a single tree basis using ArcView GIS and Midtech Fieldware. Leaf samples from trees with different canopy sizes, which had been fertilized at a conventional uniform Rate of 270 kg N/ha/y, were analyzed for nitrogen concentration. Analysis of 2980 tree spaces in the grove showed a skewed size distribution, with 62% in the 0- to 100-m3/tree volume classes and a median volume of 79 m3/tree. The tree volumes ranged from 0 to 240 m3/tree. Regression analysis showed that trees with excess leaf nitrogen (>3%) had canopies less than 100 m3. These trees receiving excess nitrogen are likely to have lower fruit yields and quality, and wasted fertilizer nitRates may leach beyond the root zone to groundwater. In order to rectify the excess fertilization of smaller trees, a granular fertilizer spreader with hydraulically powered split-chain outputs controlled with a MidTech Legacy 6000 controller was used for Variable Rate Application of nitrogen in one-half of the grove. A 38% to 40% saving in granular fertilizer cost was achieved for this grove when Variable N Rates were implemented on a per-tree basis ranging from 135 to 270 kg N/ha/y.
