Excessively wet and dry soil conditions can occur during the same year
in the southeastern Coastal Plain of the United States. Water managem
ent systems that provide both subsurface drainage during wet soil cond
itions and irrigation during dry soil conditions are desired. Several
water table management alternatives, possibly with surface irrigation
such as microirrigation, could satisfy these needs. Three water table
management (WTM) systems and microirrigation were evaluated for three
cotton cultivars on a southeastern Coastal Plain soil during 1987-1989
. The WTM systems included controlled drainage-subirrigation (CDSI), c
ontrolled drainage (CD), and subsurface drainage (SSD). All WTM system
s had both surface microirrigation and rainfed treatments. Cotton cult
ivars were Coker 315, DPL 50, and DPL 90. Seasonal rainfall, subirriga
tion, and microirrigation amounts varied considerably during the three
-year period. Water requirements for subirrigation in the CDSI system
were high (1477 to 2841 mm), but neither microirrigation nor subirriga
tion water requirements were closely related to seasonal rainfall amou
nts. Cotton lint yields among WTM systems were significantly different
in two of three years; yields for the CDSI system were lowest (836 an
d 766 kg/ha) and yields for CD and SSD were highest (1022 and 942 kg/h
a, respectively). Wetter-than-optimum soil conditions in all irrigated
treatments, especially in combination with the CDSI system, probably
caused the reduced yield. Microirrigation produced significantly great
er lint yields than the rainfed treatments in the first two years of t
he study (1127 and 1116 kg/ha versus 492 and 801 kg/ha), but not in th
e last year (872 versus 874 kg/ha) when seasonal rainfall was kast of
the three years but was better distributed. There were significant yie
ld differences among cotton cultivars in two years, but no cultivar co
nsistently produced the greatest or least yield. Cotton yield increase
s obtained with these WTM system-microirrigation combinations suggest
the need to control the water table closer to the soil surface in sout
heastern Coastal Plain soils when surface irrigation is not used. The
CDSI could provide a profitable management alternative if a water tabl
e fluctuates near the soil surface much of the time, especially during
the growing season. Where subsurface drainage is needed part of the y
ear, it may be more profitable to use CD or SSD systems with surface i
rrigation, especially when maintaining the water table near the soil s
urface in CDSI systems requires a large water volume. However, the com
bined cost of the subsurface drainage and microirrigation systems woul
d be very high and might not be profitable for crops such as cotton.