Principal Investigator: Adel Shirmohammadi (University of Maryland)
Principal Investigator: Flavio da Silva (The University of Georgia)
Principal Investigator: Daniel L. Thomas (University of Georgia)
Principal Investigator: E. Dale Threadgill (The University of Georgia)
Sponsor: GWRI
Start Date: 1984-09-01; Completion Date: 1985-08-01;
Keywords: Georgia Flatwoods, irrigation, drainage, subirrigation, water table, models, water use, system design, soil hydraulic properties
Description:
This project was conducted on the SEA-MAR farm located in Pierce County, Georgia on Pelham loamy sand soil. The study area included 40 hectares of land under a drainage-subirrigation system of which 38 hectares were in blueberries, 1 hectare in corn and the remaining 1 hectare in soybeans. The system installation included two different drain spacings of 15.3 and 20 m for comparison purposes. Two types of water table management systems were used. They were an open ditch and a closed system network. Seventeen punch-tape water level recorders were used to measure the water level in the soil profile at midfield (on tiles and midway between the tiles), at the open ditch and closed system control structures (one for each), and in an undrained-nonirrigated section of the farm. A punch-tape rainfall recorder was also used to measure rainfall at the site.
Experimental results showed that using inappropriate design criteria or mismanagement can lead to poor performance of the system. Excessive drainage at the early part of the growing season coupled with slow subirrigation phase due to deep drain tiles (tiles were located too deep in less permeable material) resulted in poor performance of the system in the corn field. This led to crop stress. Proper management of the system in the blueberry field resulted in favorable soil water conditions and excellent crop growth.
DRAINMOD, a water management model for shallow water table conditions, was used to simulate the system performance for the conditions of Flatwoods soils. Simulation results indicated that a drain spacing of 18-20 m is appropriate for combined drainage-subirrigation systems for soils similar to those in Pierce County, Georgia. However, more research is required to develop appropriate design guides for other soil types in the Georgia Flatwoods region.
Overall findings showed that a combined drainage-subirrigation system is an appropriate water management scheme to be used in the Flatwoods of south Georgia. A preliminary economic analysis led us to believe that this system, if properly designed, can save up to $144/ha/yr and $129/ha/yr when compared to center pivot/drainage and traveling gun/drainage systems, respectively.
An initial evaluation of the water resources requirement for drainage-subirrigation systems indicated that more water is needed to achieve the same useable application amount than for other systems (center pivot/drainage and traveling gun/drainage). Hopefully, continued research can provide improved management practices and increase the water use efficiency of drainage-subirrigation systems.