Date of Award

12-2009

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Biosystems Engineering

Advisor

Khalilian, Ahmad

Committee Member

Barnes , Edward M

Committee Member

Farahani , Hamid J

Abstract

Cotton (Gossypium hirsutum L.) is widely grown in the United States with 5.7 million ha grown nationally and 1.2 million ha grown in the humid southeastern states in 2005. From 1969 to 2003, agricultural irrigated farmland acreage and total water applied increased by over 40% and 11% respectively to include a total of 55.3 million acres in 2002. Combined with recent and more frequent drought periods and legal water conflicts between states, there has been an increased interest in more effective southeastern water management, thus making the need to develop improved irrigation scheduling methods and enhanced water use efficiency of cotton cultivars.
Several irrigation scheduling methods (soil moisture monitoring, pan evaporation, and climate based) tested at Clemson and elsewhere have shown that sensor-based irrigation significantly increased cotton yields and provided a monetary savings compared to other methods. There is however limited information on capacitance based soil moisture analysis techniques in the southeastern coastal plain soils and also limited locally developed crop coefficients used in scheduling the ET based treatments.
The first objective of this study was to determine and improve the feasibility of utilizing sensor-based soil water monitoring techniques in Southeastern Coastal Plain soils to more effectively manage irrigation and increase water use efficiency of several cotton cultivars. The second objective was to develop two weighing lysimeters equipped with wireless data acquisition system to determine a crop coefficient for cotton under southeastern humid conditions.
Two multi-sensor capacitance probes, AquaSpyTM and Sentek EnviroSCAN ® , were calibrated in this study. It was found that positive linear calibrations can be used to describe the relationship between the soil volumetric moisture content (VMC) and sensor readings found for both probes and that multi-sensor capacitance probes can be used to accurately measure volumetric soil moisture contents, if installed and calibrated properly. It was determined that a direct installation method should be used rather than a slurry mix method. The slurry method was found to overestimate the VMC in sandy soils.
There were good correlations between In Season Estimated Yield (INSEY) as measured by the plant Normalized Difference Vegetation Index (NDVI) and the VMC of the soil. Results showed that when separated by irrigation regime, the relationship between INSEY and VMC follows good linear correlations. This was due to the health of the plant and its dependency on soil moisture.
There were strong correlations between irrigation depths applied and seed cotton yields. Highest water use efficiency values were 0.55kg seed cotton/m3 water applied in 2008 (0.55kg seed cotton/m3 ET) and 0.788kg/m3 water applied (0.66kg/m3 ET) in 2009.
Two weighing lysimeters were constructed to provide cotton and reference ET measurements. Evaporation pan and weather data from a local station were also used to provide a basis for calculating ET. Because the Penman – Monteith (P – M) method is widely known and trusted, a set of crop coefficients were developed based on P – M and cotton lysimeter data and determined to be 0.91, 1.24, and 0.72 for the initial, mid, and end stages for a Delta Pine 0949 BSRF cultivar.

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