TENSIOMETER BASED AUTOMATED IRRIGATION FOR TOMATO UNDER PLASTICULTURE - Management, Performance, and Applications of Micro Irrigation Systems - page 209

FIGURE 2 (A-D) Leaf water potential for five automated, tensiometer-controlled irrigation
regimes: on/off −30/-10, −30/-25, −45/-10, −45/-40 kPa, and −35 or −40 kPa for 'Mt. Fresh'
tomato grown in Lexington, KY in 2009 and 2010. Midday water potential in 2009 (A) and
2010 (B), and predawn leaf water potential in 2009 (C) and 2010 (D); 1 kPa = 1.0 cbar, 1 MPa
= 10.0 bar.
Predawn and midday leaf RWC, were measured. Generally leaf RWC remains
stable during initial increases in Ψ L and then decreases with further increases in Ψ L
[3, 31]. Predawn leaf RWC was signifi cantly higher than midday leaf RWC in 2009
and 2010 (Fig. 3A-D). Predawn and midday leaf RWC was signifi cantly affected by
sampling date in both years, fl uctuating in response to the environment. Typically on
those dates when Ψ L increased, leaf RWC decreased. This was particularly evident
on 28 July and 11 Aug. 2010. In 2010 midday leaf RWC was signifi cantly affected
by treatment (Fig. 3B). In 2010 midday leaf RWC was signifi cantly greater in the
−40 kPa treatment than the other treatments. The season average midday leaf RWC
of the −40 kPa treatment was 89.5%, while the other treatments averaged 87.2% (Fig.
3B). This indicates that the −40 kPa treatment experienced slightly less water stress
during midday sampling in 2010. The −40 kPa treatment irrigated at a much greater
frequency (44 events) than all others in 2010 (Table 1). Leaf RWC, which measures
water in leaves relative to a state of full turgor, may remain stable despite changes in
Ψ L , as plants compensate for changes in soil moisture or the environment [3, 4, 31].
Frequent irrigation events could have allowed for water to be readily available to the
plant during midday stress.