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Purpose
Manure is a critical resource in livestock production as it contains many essential nutrients required for crop growth. However, as a nutrient source, manure is highly variable, and nutrient composition may fluctuate significantly during emptying of manure storages if not properly agitated. Accounting for this variability requires extensive sampling, which is often cost and time prohibitive for haulers and producers.
The aim of this study is to evaluate a commercially available manure nutrient sensor utilizing near-infrared spectroscopy (NIRS) to provide real-time manure nutrient data. The study investigates the impact of NIRS systems in the field to achieve target nutrient application rates and assess effects on crop nutrient use efficiency (NUE) and yield compared to conventional sampling and fixed-rate application methods.
What Did We Do?
A manure tanker was outfitted with a John Deere HarvestLab 3000 setup for manure nutrient sensing. The setup included the sensor, a Krone flow meter, and a John Deere rate controller (Figure 1). Manure nutrient values from the sensor were recorded in real time. The controller then set specific target rates for a nutrient and the automation system adjusted the tractor speed or manure pump rate to meet the target.
Field trials were conducted in Wisconsin on silt loam soil. Manure was applied to strip plots to meet three specific nitrogen application rates using both the NIRS sensor and conventional sampling and application methods. During application, composite manure samples were collected to assess the sensor’s accuracy. After manure application, the field was planted with corn silage, and following harvest, NUE and yield were evaluated.
What Have We Learned?
In the first year of the study, the NIRS sensor outperformed conventional sampling methods in achieving target nitrogen rates. Across the application plots, the NIRS sensor delivered manure at a nitrogen rate in the range of 20 to 30 lbs N/ac over the target rate, whereas conventional sampling led to overapplication by 40 lbs N/ac to 95 lbs N/ac. During application, the system also tracked other nutrients, such as phosphorus and ammonium, but laboratory analysis indicated that the sensor was less accurate for these nutrients compared to nitrogen. While manure application rates varied, there was little difference in crop yield or NUE between treatments at harvest.
The NIRS sensor shows promise as a tool to revolutionize manure nutrient accounting in cropland. Its ability to track manure variation in real time could significantly improve nutrient management. Figure 2 demonstrates how the system tracked manure nitrogen, phosphorus, and potassium levels over time following a reduction in agitation. This type of tracking may help reduce the need for excessive agitation and enhance manure utilization efficiency.
Future Plans
Researchers plan to continue field trials over multiple years to assess long-term impacts on nutrient use efficiency and soil nutrient management. Additionally, with new calibration updates since the original trial, future studies will evaluate the sensor’s accuracy in measuring phosphorus and its ability to meet phosphorus-based manure application targets while simultaneously tracking nitrogen for improved supplemental nitrogen prescriptions. Overall, the goal of the project is to provide producers and haulers with information on how effective the system is and ways in which it can be used to enhance on-farm efficiency.
Authors
Presenting & corresponding author
Joseph R. Sanford, Assistant Professor, University of Wisconsin -Platteville, sanfordj@uwplatt.edu
Additional authors
Rebecca A. Larson, Professor, Nelson Institute for Environmental Studies, University of Wisconsin-Madison; Tyler Liskow, Engineer, Nelson Institute for Environmental Studies, University of Wisconsin-Madison
Acknowledgements
This material is supported by the Wisconsin Dairy Innovation Hub and the National Institute of Food and Agriculture, U.S. Department of Agriculture, under award number 2022-69008-36506. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or the Wisconsin Dairy Innovation Hub.
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