Author(s)

Phillip B. Williams¹, Ahmad Khalilian¹, Michael W. Marshall², Joe Mari Maja², Haibo Liu³, Dara Park³, Ali Mirzakhani Nafchi⁴

¹Department of Agricultural Sciences, Clemson University, Clemson, USA.
²Edisto Research and Education Center, Clemson University, Blackville, USA.
³Department of Plant and Environmental Sciences, Clemson University, Clemson, USA.
⁴Cornell University, Cooperative Extension, Ithaca, USA.

Nutrients are injected through overhead irrigation systems at a uniform rate in a process known as fertigation. The highly variable soils in the Southeastern US pose challenges for effective fertigation. Currently, there is no variable-rate fertigation system available to apply the correct amount of N within a field through an overhead irrigation system. Therefore, the objective of this study was to develop and test a variable-rate N application system that works independently of irrigation water flow for site-specific N application. The variable-rate fertigation system (VRFS) was designed to apply different rates N using a pulse width modulation technique. The VRFS utilized the Clemson Lateral Irrigation Control software which controlled the solenoids in each zone by turning the N supply on and off (pulsing) for each zone. In this study, four tests were conducted to determine the uniformity of the VRFS. In test # 1, the pump output showed a linear slope relationship and was the same for water and N. In test # 2, nozzle flow and uniformity were determined using four different irrigation system travel speeds at N application rates of 31, 59, 88, and 113 kg/ha. There was a strong correlation (R² = 0.9998) between irrigation system speed and N rate. In test # 3, the uniformity across the length of the irrigation system was determined. The nozzles produced an average flow of 31.1, 58.7, 87.6, and 112.7 kg N/ha with an overall average error of 0.1% across all N rates. Results also showed the system was capable of accurately applying N based on prescription maps with an error of less than 1.8%. Test # 4 was conducted to determine the accuracy of the map-based controller system for applying variable rate N. There was a strong correlation between target N and actual N rates (R² = 0.9999). In summary, the VRFS applied the correct amounts of N within each zone by either manually controlling the pulsing mechanism or utilizing a prescription map to apply different rates throughout the field.

Cotton, Nitrogen, Fertigation, Irrigation, Variable Rate, Nutrient Management, Precision Agriculture

Williams, P. , Khalilian, A. , Marshall, M. , Maja, J. , Liu, H. , Park, D. and Nafchi, A. (2018) Development and Testing of a Variable Rate Nitrogen Application System through an Overhead Irrigation System. Journal of Water Resource and Protection, 10, 994-1011. doi: 10.4236/jwarp.2018.1010058.