Date of Award


Document Type


Degree Name

Master of Science (MS)

Legacy Department

Plant and Environmental Science

Committee Member

Dr. Ahmad Khalilian, Co-Advisor

Committee Member

Dr. Young J. Han, Co-Advisor

Committee Member

Dr. Joe Mari Maja


The first objective of this project was to develop, refine, and employ sensor-based algorithms to determine the mid-season nitrogen requirements for the production of irrigated corn in Coastal Plain soils. The second objective of this project was to develop an “on-the-go” variable rate nitrogen application system. One (1) production field at Clemson’s Edisto Research and Education Center in Blackville, SC was used in the development and refinement of the sensor-based algorithm. This field was equipped with overhead irrigation, and was used in both the 2015 and 2016 growing seasons. The crop was not under scheduled irrigation, the overhead (lateral) irrigation system was only utilized to provide deficit irrigation for corn. The field was divided into two separated zones based on soil electrical-conductivity (EC) data. The algorithm was developed using varied prescription rate nitrogen plots. These plots received nine different rates of nitrogen fertilizer (0, 20, 40, 80, 120, 160, 200, 240, and 260 lbs. N/ac). Nitrogen treatments were replicated 5 times in plots of each zone using a Randomized Complete Block design. To apply nitrogen to the research plots during both growing seasons, a previously constructed custom built applicator utilizing a hydraulic pump in combination with an in-cab control system was used. Optical sensor readings were collected from the test plots between the V6 to V8 growth stages to determine the corn plants Normalized Difference Vegetation Index (NDVI). The sensor readings were used to develop the algorithm to be used in the estimation of side-dress nitrogen application in corn. There was a good correlation between combined sensor readings collected during 2015 and 2016 growing seasons (V6 to V8 stage) and actual corn yields (R2>0.68). In Season Estimated Yield (INSEY) was used along with the actual yield to produce a yield potential (YP0) for each growing season for deficit irrigated corn crop. During the 2015 growing season the algorithm for estimating the amount of mid-season side-dress nitrogen application was developed. Data collected from the 2016 growing season was then used to further refine this algorithm. The algorithm developed during 2015 and 2016 growing seasons was used during the 2016 to estimate the amount of mid-season side-dress nitrogen required for corn in two different management zones of a 5-acre production field. The algorithm recommended reduced rates of nitrogen, 21% and 34% in zone 1 and 2, respectively, compared to the normal grower practice (200 lbs. N/acre) with no reduction in corn yields. Three different methods of nitrogen application were tested, one during each of the growing seasons of 2007-2009. During the 2007 production year a typical pull behind nitrogen side-dress applicator with a ground driven piston pump was used. This applicator was the most crude and inaccurate method of fertilizer application used during the study. During the 2008 production year a custom built applicator was used. The applicator operated using a hydraulic pump in combination with an in-cab control system. The rates The accuracy of the optical sensor (GreenSeeker®) was tested to determine if the time of day, temperature, or solar radiation affect its performances. The results of this test showed that the sensor is affected by the time of day that the readings are taken, but during the time frame of three hours after sunrise and one hour before sunset the readings were not affected. The second objective of this study was specifically to develop an "on-the-go" variable rate nitrogen application system. Current nitrogen application systems are designed to apply a relatively uniform amount of nitrogen to agricultural fields. There are several commercially available variable rate nitrogen application systems, such as John Blue pumps equipped with Rawson controller (Porter, 20010) or John Blue’s Direct Drive Hydraulic Piston Pump (CDS-John Blue Company, Huntsville, AL). However, with these systems only limited rage of flow rates can be achieved by changing the drive shaft speed. This limited flow range is not sufficient for applying variable-rate crop inputs (such as nitrogen) in the Southeastern USA, with tremendous amount of variations in field conditions and soil types. There is a need for a controller which can adjust the pump stroke on-the-go, for real-time, variable-rate application of crop inputs. As a result of this study a control system was developed 'The Clemson electro-mechanical controller for adjusting pump stroke on-the-go' to replace the current manual stroke adjustment system on positive displacement piston pumps. This affordable system could be retrofitted on any existing piston pump (such as John Blue), which makes it possible to change the flow rate of the pump automatically from zero to a pumps full capacity. The resulting system has the ability to be controlled either manually by an electronic dial (rotary potentiometer) from tractor's cab or by a map-based control program.