Stephen F. Higgins

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.

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.

Hydrologic Properties of Pervious Concrete

Pervious concrete is concrete made by eliminating most or all of the fine aggregate (sand) in the concrete mix, which allows interconnected void spaces to be formed in the hardened product. These interconnected void spaces allow the concrete to transmit water at relatively high rates. The main objective of this project was to conduct research on the potential application of pervious concrete in agricultural settings, specifically for use in animal feed lots, manure storage pads, animal manure and bedding compost facilities, or floor systems in animal buildings. Laboratory tests were conducted on replicated samples of pervious concrete formed from two rock sources (river gravel and limestone) for coarse aggregates and different size fractions to determine hydrologic relationships. Linear relationships were found between density and porosity, density and permeability, porosity and permeability, and porosity and specific yield. The results suggest that properties such as permeability, porosity, and specific yield are not significantly affected by different aggregate types. However, density and porosity can be effective methods for predicting porosity, specific yield, and permeability. In addition, t-tests were conducted to determine the effect of aggregate types on the solid/liquid separation properties of the pervious concrete after adding composted beef cattle manure and bedding to the surface of the specimens. The amount of composted beef cattle manure and bedding retained within the specimens was significantly less (p = 0.012) when samples constructed of #8 river gravel were used rather than the other aggregates. The #8 river gravel also had significantly less reduction in permeability compared to other aggregates. Although the #8 river gravel had a different effect on the compost retained and the reduction in permeability for the specimens, all four aggregates exhibited a significant reduction in the permeability after the compost was applied.

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.

Corn Stover Availability and Collection Efficiency Using Typical Hay Equipment

Corn stover has been identified as a potential feedstock for the production of fermentable sugars and thermochemical processes. The availability and efficiency of typical hay equipment for collecting corn stover has not been well quantified. Corn stover was collected for two years on a central Kentucky farm near Louisville. Six different harvesting treatments, using traditional hay equipment, were used to harvest corn stover. A rotary mower, rotary scythe (flail-type mower with windrow-forming shields), parallel bar rake, and a round baler were utilized. The average stover moisture content prior to grain harvest was above 40%, and field drying was required before baling. All treatments were analyzed for collection efficiency and corn stover yield. The stover collection yields varied from 1.93 to 5.34 dry t/ha, with collection efficiencies (ratio of stover collected to the total above-ground stover excluding grain) between 32.1% and 94.5%. The most promising collection strategy was disengaging the straw chopper and spreader to produce a windrow behind the combine. This windrow could then be baled in a separate operation that resulted in a collection efficiency of 74.1%.

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.

Relationship of total nitrogen and total phosphorus concentration to solids content in animal waste slurries

Quantifying the nutrient content of liquid swine and dairy manure immediately preceding field application has the potential to reduce environmental impact from over-applying nutrients and better match slurry application rates with the fertility needs of subsequent crops or crop removal rates. This study determined if manure solid content, storage facility, animal growth stage, and season could be used as predictors of the nutrient content of animal manures. Samples were collected from earthen storage basins and deep pits, on one farm, during liquid manure loading into a manure application wagon in 1999, 2000, and 2001. The correlation of nitrogen and phosphorus content with solids content gave good linear fits (R 2 = 0.65 to 0.86) for the earthen storage basins. Data for an earthen storage basin exhibited consistent decrease in solids content by sequential load for a given day. Regression of nitrogen content versus solids content data for manure from deep-pit swine finishing facilities provided an undesirable fit (R2 = 0.19). Regression results support the conclusion that animal growth stage/storage facility affects the base TN concentration (Y-intercept) in the absence of solids. The gestation and finishing TN data suggests TN for an individual manure wagonload could be predicted if the base TN concentration, in the absence of solids, was determined. Total P was found to be highly correlated to TS, but was also affected by animal growth stage/storage facility. Deep pits showed consistent nutrient content across pumping seasons and growth stage with the exception that nitrogen content decreased slightly during fall application.

Comparison of Variable-Rate Granular Application Equipment

The popularity of variable-rate technology (VRT) has grown but limitations and errors of this technology are generally unknown. Therefore, uniform and variable-rate (VR) tests were conducted to characterize distribution patterns at various rates and quantify rate changes for assessing the application accuracy of 3 VRT granular applicators (2 spinner spreaders and 1 pneumatic applicator). The characterized single-pass patterns demonstrated consistent shapes but deviated slightly from the desired patterns for two applicators at all rates. The simulated overlap multiple-pass summary statistics indicated that the three applicators performed satisfactorily with all but one of the CV’s less than 20%. A majority of the CV’s were less than 15%. The average application rates for 2 applicators were less than the desired levels for all tests. The third applicator under-applied at the low rate, over-applied at the high rate, but equaled the desired level at the medium rate. The overlap patterns for the spinner spreaders showed consistent peak levels at the center of the pattern, valleys on either side, and then tails on the ends that exceeded the desired levels. The pneumatic applicator overlap patterns indicated a problem with under-application at its center. The most uniform application occurred at the lower application tests for all applicators. Rate changes were much quicker for the two newer VR control systems. These results showed distribution plots are required along with CV’s to calibrate applicators and correctly assess patterns while new technology has improved response time on VRT equipment.

Nitrogen source and application method impact on corn yield and nutrient uptake

ABSTRACT Farmers are looking for better management practices to utilize animal manure as an alternative to chemical fertilizers. A 2-year field experiment was conducted to study the effects of nitrogen (N) fertilizer source and application methods to Nicholson silt loam soil in central Kentucky, USA for no-till corn (Zea mays) production. The region has a temperate climate with a mean temperature of 14.5°C and rainfall of 1300 mm year−1. Treatments included a control, 179 kg N ha−1 urea ammonium nitrate (UAN) applied as preplant and sidedress, and swine effluent that was applied by three methods: broadcast, injection, and Aerway. Injection method produced the greatest corn grain yield (11.88 Mg ha−1) and biomass yield (18.9 Mg ha−1) in 2007. Results demonstrated that the effluent application methods and the timing of UAN application may not be agronomically important for corn production in this region. Hence, more studies are needed on different soils in this region.