John P. Fulton

PERFORMANCE ASSESSMENT AND MODEL DEVELOPMENT OF A VARIABLE–RATE, SPINNER–DISC FERTILIZER APPLICATOR

The popularity of spinner spreaders for application of granular fertilizers and agricultural lime, along with increased interests in variable–rate technology (VRT), has raised concern about application accuracy and distribution of these spreaders. This investigation was undertaken to assess the application distribution of a VRT spinner fertilizer spreader. Application distribution was assessed using a matrix of collection pans and following test procedures outlined in ASAE Standard S341.2. Uniform and variable–rate tests were performed to characterize the application variability of the spreader and to test the effect of rate changes via GPS control. Uniform and variable–rate application models were developed from the collected data. A sigmoidal function was used to describe increasing application rate changes, while a linear function described decreasing rate changes. Average transverse distribution patterns were used to model both high and low application rates. The resulting models were then compared to the actual distributions. The model was found to do a good job of characterizing uniform and variable–rate application patterns and therefore may be suitable for simulating variable–rate application errors.

EVALUATING THE SENSITIVITY OF AN UNMANNED THERMAL INFRARED AERIAL SYSTEM TO DETECT WATER STRESS IN A COTTON CANOPY

Airborne thermal infrared (TIR) imagery is a promising and innovative tool for assessing canopy response to a range of stressors. However, the expense associated with acquiring imagery for agricultural management is often cost-prohibitive. The objective of this study was to evaluate a less expensive system, an unmanned airvehicle (UAV) equipped with a TIR sensor, for detecting cotton (Gossypium hirsutum L.) response to irrigation and crop residue management. The experimental site was located on a 6.1 ha field in the Tennessee Valley Research and Extension Center located in Belle Mina, Alabama, where landscapes are gently rolling and soils are highly weathered Rhodic Paleudults. Treatments consisted of irrigation (dryland or subsurface drip irrigation) and crop residue cover (no cover or winter wheat (Triticum aestivum L.)). TIR (7 to 14 µm) imagery was acquired on 18 July 2006 at an altitude of 90 m and spatial resolution of 0.5 m. Coincident with image acquisition, ground truth data consisting of soil water content (0-25 cm), stomatal conductance, and canopy cover were measured within a 1 m radius of each sample location. All sample locations were georeferenced using a real-time kinematic (RTK) GPS survey unit. Analysis of sample locations acquired in multiple flight lines was used to assess the stability and repeatability of the UAV system during an acquisition. Compared to field measurements of stomatal conductance with CVs ranging from 2% to 75%, variability in TIR emittance (CV < 40%) was within the observed tolerance of ground truth measurements of stomatal conductance. Significant differences in canopy cover and stomatal conductance across irrigation treatments allowed testing of the sensitivity of the UAV system. A negative correlation was observed between TIR emittance and stomatal conductance (r = -0.48) and canopy closure (r = -0.44), indicating increasing canopy stress as stomatal conductance and canopy closure decreased. TIR emittance exhibited greater sensitivity to canopy response compared to ground truth measurements, differentiating between irrigation and crop residue cover treatments. TIR imagery acquired with a low-altitude UAV can be used as a tool to manage within-season canopy stress.

Distribution pattern variability of granular VRT applicators

Granular applicators equipped with variable-rate technology (VRT) have gained popularity in recent years as a result of increased interest in variable-rate application. The purpose of this investigation was to characterize distribution patterns at varying rates for different granular applicators. Uniform-rate (UR) tests were conducted to assess the accuracy of variable-rate application from four granular applicators: two spinner-disc spreaders (A and B), and two pneumatic applicators (C and D). Pattern results indicated a consistent triangular pattern for spinner spreader B and consistent patterns for the pneumatic applicators (C and D). However, applicator D produced pattern variations at the center and right side. Simulated overlap analysis generated CVs <20% for applicators B and C. Applicator A performed well at the two lower rates (CVs <19%) but not at the highest rate (CV = 27%). Pattern unevenness for applicator D produced CVs between 25% and 34%. The spinner-disc spreaders over-applied, while the pneumatic applicators under-applied at the margins, suggesting an adjustment to the effective swath spacing or spinner-disc speed is needed to improve application accuracy. Further, overlap plots indicated pattern variability even when acceptable CVs were attained for applicators B and C. Therefore, it is recommended that CVs accompany simulated overlap pattern plots to ensure proper calibration of VRT equipment. Swath spacing analysis indicated that three of the four applicator spacings could be changed from the recommended value to improve application uniformity. Pattern comparisons showed that pattern shifts occurred for applicator A (P = 0.0092) with increasing application rate but not for applicators B, C, and D. These results demonstrate potential application errors with VRT and the need for proper calibration to maintain acceptable performance. Further, this investigation demonstrates the need for a VRT equipment testing standard.

An overview of current and potential applications of thermal remote sensing in precision agriculture

Abstract Precision agriculture (PA) utilizes tools and technologies to identify in-field soil and crop variability for improving farming practices and optimizing agronomic inputs. Traditionally, optical remote sensing (RS) that utilizes visible light and infrared regions of the electromagnetic spectrum has been used as an integral part of PA for crop and soil monitoring. Optical RS, however, is slow in differentiating stress levels in crops until visual symptoms become noticeable. Surface temperature is considered to be a rapid response variable that can indicate crop stresses prior to their visual symptoms. By measuring estimates of surface temperature, thermal RS has been found to be a promising tool for PA. Compared to optical RS, applications of thermal RS for PA have been limited. Until recently (i.e., before the advancement of low cost RS platforms such as unmanned aerial systems (UAVs)), the availability of high resolution thermal images was limited due to high acquisition costs. Given recent developments in UAVs, thermal images with high spatial and temporal resolutions have become available at a low cost, which has increased opportunities to understand in-field variability of crop and soil conditions useful for various agronomic decision-making. Before thermal RS is adopted as a routine tool for crop and environmental monitoring, there is a need to understand its current and potential applications as well as issues and concerns. This review focuses on current and potential applications of thermal RS in PA as well as some concerns relating to its application. The application areas of thermal RS in agriculture discussed here include irrigation scheduling, drought monitoring, crop disease detection, and mapping of soil properties, residues and tillage, field tiles, and crop maturity and yield. Some of the issues related to its application include spatial and temporal resolution, atmospheric conditions, and crop growth stages.

Compaction of poultry litter.

Poultry litter, a combination of accumulated chicken manure, feathers and bedding materials, is a potential feedstock for bioenergy and other value-added applications. The use of this waste product has been historically limited to within few miles of the place of generation because of its inherent low density. Compaction is one possible way to enhance the storage and transportation of the litter. This study therefore investigates the effect of moisture content (19.8-70.7%, d.b.) and pressure (0.8-8.4 MPa) on the compaction characteristics of poultry litter. Results obtained showed that the initial density of densified poultry litter, energy required for compaction and the strength of the densified material after 2 months of storage were significantly (P<0.05) affected by moisture content and pressure applied during compaction. The density of the compacted material was only affected by pressure applied during compaction after 2 months of storage. The specific energy required to produce the densified material varied from 0.25 to 2.00 kJ/kg and was significantly less than the energy required to produce pellets from biological materials. The results obtained from the study can be used for the economical design of on-farm compaction equipment for poultry litter.

Real-Time Pressure and Flow Dynamics Due to Boom Section and Individual Nozzle Control on Agricultural Sprayers

Most modern spray controllers when coupled with a differential global positioning system (DGPS) receiver can provide automatic section or swath (boom section or nozzle) control capabilities that minimize overlap and application into undesirable areas. This technology can improve application accuracy of pesticides and fertilizers, thereby reducing the number of inputs while promoting environmental stewardship. However, dynamic system response for sprayer boom operation, which includes cycling or using auto-swath technology, has not been investigated. Therefore, a study was conducted to develop a methodology and subsequently perform experiments to evaluate tip pressure and system flow variations on a typical agricultural sprayer equipped with a controller that provided both boom section and nozzle control. To quantify flow dynamics during boom section or nozzle control, a testing protocol was established that included three simulation patterns under both flow compensation and no-compensation modes achieved via the spray controller. Overall system flow rate and nozzle tip pressure at ten boom locations were recorded and analyzed to quantify pressure and flow variations. Results indicated that the test methodology generated sufficient data to analyze nozzle tip pressure and system flow rate changes. The tip pressure for the compensated section control tests varied between 6.7% and 20.0%, which equated to an increase of 3.7% to 10.6% in tip flow rate. The pressure stabilization time when turning boom sections and nozzles off approached 25.2 s but only approached 15.6 s when turning them back on for the flow compensation tests. Although extended periods were required for the tip pressure to stabilize, the system flow rate typically stabilized in less than 7 s. The tip flow rate was consistently higher (up to 10.6%) than the target flow rate, indicating that system flow did not truly represent tip flow during section control. The no-compensation tests exhibited tip pressure increases up to 35.7% during boom and nozzle control, which equated to an 18.2% increase in tip flow. Therefore, flow compensation over no-compensation had better control of tip flow rate. A consistent difference existed in dynamic pressure response between boom section and nozzle control. Increased tip pressure and delayed pressure stabilization times indicated that application variability can occur when manually turning sections on and off or implementing auto-swath technology, but further testing is needed to better understand the effect on application accuracy of agricultural sprayers.

Grain Yield Monitor Flow Sensor Accuracy for Simulated Varying Field Slopes

Yield monitors have become vital reference tools for grain growers in making informed management decisions in their cropping operations. The cornerstone of a yield monitor system is the mass flow sensor, used to calculate the mass flow rate of clean grain through a combine. This investigation was initiated to examine the influence of varying field slopes (both roll and pitch) on accuracy levels of a mass flow sensor for a commercially available yield monitor system. A laboratory test stand consisting of a combine clean grain elevator mounted on a gimbal fixture was used to simulate varying field slopes normally experienced during field operation of a combine. Results indicated that slope affected mass flow sensor response. Combine pitch had a greater effect than roll on mass flow measurements. While errors were observed during roll tests (-3.45% to 3.46%), they were considered small and were impractical to correct using predictive approaches. Pitch tests generated higher errors (-6.41% to 5.50%) with discernable linear trends indicating that mass flow was underestimated during aft operating conditions and overestimated during forward rotations. This trend suggests gravitational acceleration of the mass flow sensor during combine pitch may cause these errors. The use of a predictive linear model, to correct flow rates for slope, greatly decreased the overall error for the pitch results.

Rate Response Assessment from Various Granular VRT Applicators

Variable-rate technology (VRT) adds complexity to application equipment, thereby confounding the assessment of applicator performance. The intent of this investigation was to assess the rate response of various VRT granular applicators: two spinner spreaders (A and B), and two pneumatic applicators (C and D). Variable-rate (VR) tests were conducted to quantify the rate response characteristics (delay and transition times) for the applicators. A sigmoidal function was used to model the rate response for five of the six tests. Applicator A exhibited a linear response during decreasing rate changes. Results indicated that only applicator B demonstrated consistent delay and transition times, enabling the use of a single “look-ahead” time for rate response time correction. Contouring of prescription maps increased the transition times for applicator D by enlarging the adjustment area between management zones. Rate changes were quicker for the two newer VR control systems, signifying advancement in hydraulic control valve technology. This research illustrates the need for standard testing protocols for VRT systems to help guide VRT software developers, equipment manufacturers, and end users.

COMBINE YIELD MONITOR TEST FACILITY DEVELOPMENT AND INITIAL MONITORING TEST

The Yield Monitor Test Facility’s performance under static grain flow was very good. First, the grain metering system accurately meters grain at varying flow rates to the clean grain elevator over the prescribed time interval. Second, the weigh scale system appears to be very accurate in measuring the accumulated mass flow in the system. However, grain stream dynamics, tank vibration, and load cell sensitivity confounds attempts to measure instantaneous grain flow at low rates of 1 to 4 kg/s. Third, the commercially available yield monitor flow sensor demonstrated excellent accuracy across a wide range of static flow rates from 1.3 to 21.1 kg/s. Percent differences in accumulated mass flow for the yield monitor and the weigh scale were less than 1% at calibration flow rates and approximately 3% for extreme flow rates. Instantaneous mass flow rate variation was observed to be approximately 8% at the mean calibration flow rate.

Simulation of fixed- and variable-rate application of granular materials

Research has shown that application errors exist with variable–rate technology (VRT) systems. Consequently, using prescription maps for economic and agronomic analyses can generate misleading results. The intent of this article was to develop and validate a spatial data model for generating “as–applied” maps to support the advancement of precision agriculture practices. Previous research modified ASAE Standard S341.2 to include a 2–D matrix of collection pans to assess fixed–rate and variable–rate (VR) deposition of granular fertilizers and agricultural lime from a spinner disc spreader. The “as–applied” spatial data model uses GIS functionality to generate “as–applied” surfaces by merging distribution patterns and a spatial field application file (FAF) into an “as–applied” surface representing the actual distribution of granular fertilizer or agricultural lime across a field. To validate the “as–applied” spatial data model, field studies were conducted by randomly placing collection pans across two fields. Murate of potash was then applied using a VR spinner spreader. The “as–applied” spatial data model was used to predict the amount of material each pan should have received. Comparisons were made between the actual and predicted application rates for two fields, with R2 values of 0.45 (field A) and 0.58 (field B) computed. However, R2 values of 0.16 (field A) and 0.21 (field B) were observed when comparing the actual application rates and prescription maps. These low R2 values indicated poor application by the spinner spreader but demonstrated that the “as–applied” model did a better job of representing the distribution of murate of potash when contrasted with the prescription maps. “As–applied” surfaces provide a means for evaluating fixed–rate and VR application of granular products while enhancing researchers’ ability to compare VR management approaches.