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Water use and yield of greenhouse grown eggplant under drip irrigation
AgdCVltUK?ll watermanagement
ELSEVIER
Agricultural Water Management 28 ( 1995) 113-120
Water use and yield of greenhouse grown eggplant under drip irrigation IL Chartzoulakis a,*, N. Drosos b ’NAGREF, Subtropical Plants and Olive Trees Institute, 73 IO0 Chania, Crete, Greece ’ Horticultural Research Station, 72 200 lerapetra,
Crete, Greece
Accepted 17 November 1994
Abstract The water consumptive use of eggplant, hyb. Delica, grown in unheated greenhouse was determined using tensiometers. The maximum evapotranspiration (ET,,,), when soil water potential was maintained at values higher than -20 KPa, ranged from 0.5 to 4.5 mm day-‘, with a whole season irrigation requirement corresponding to 380 mm. Water amount equal to 0.85 X ET, had no effect on fruit yield, which was 6.5 kg per plant; water application of 0.65 X ET,,, and 0.40 X ET,,, reduced total yield by 35% and 46%, respectively. Fruit number per plant was significantly reduced at 0.65 XET, and 0.40 X ET,,,, while fruit size was not affected by the amount of water applied. The crop ET, in October (at planting) was 0.2 of A pan evaporation (E,,) located outside the greenhouse. This value remained constant until February and then increased gradually to 0.8 XI&, at the end of the experiment, in May. Salt content was higher at the surface 10 cm soil layer with all amounts of water applied. With 1.OOX ET,,, and 0.85 X ET,,, salts were leached out of root zone, while an additional amount of water was required at 0.65 and 0.40 X ET,,, for salt leaching. Kqvwords:
Evapotranspiration; A pan evaporation; E&/E,,, ratio; Solanum melongema L
1. Introduction
Water is fast becoming an economically scarce resource in many areas of the world, especially in arid and semi-arid regions (Gregory, 1984)) such as the Mediterranean. The need for more-efficient agricultural use of irrigation water arises out of increased competition for water resources and rising environmental anxiety that irrigation practice in some cases, is facilitating a degradation in the quality of those ground and surface waters that receive leachates from the root zone of irrigated fields. With improved water efficiencies water is * Corresponding author. 0378-3774/95/$09.50
0 1995 Elsevier Science B.V. All rights reserved
.SSDIO378-3774(95)01173-O
114
K. Chartzoulakis,
N. Drosos/Agricultural
Water Management 28 (1995) 113-120
saved as less water is needed for the same level of crop production, and wasteful infiltration of applied water beyond the root zone is eliminated. The supply of the required water to the plant is of prime importance for its growth and economic production, especially into greenhouse, where irrigation is the unique source of water for the plant. To obtain the best irrigation regime, the available measurements on water needs of greenhouse crops are based on environmental, physiological and soil parameters. Most physiological indices of plant water stress (leaf water potential, leaf water content, diffusion resistance) involve measurements that are complex, time consuming and difficult to integrate, but are also subject to errors (Meyer et al., 1985). The use of meteorological data (Penman’s, radiation) or canopy temperature measurements, are also complex, very expensive and require highly qualified farmers. Thus, the use of tensiometers, which assures low cost, simple operation and reliable estimation of soil water status, are widely used in greenhouses in Crete. On the island of Crete eggplant occupies about 5% of the area covered by greenhouse grown vegetables. Its cultivation is restricted to southeast coastal areas, where winter temperatures are mild and no heating is required. Water scarcity in these areas, as well as the increasing competition for municipal use, make it necessary to optimize water use by the farmers. Although some papers deals with water requirements of greenhouse-grown eggplant, the results are not applicable to this area of Greece, as they refer to different growing season (Chiaranda and Zerbi, 1986) or to heated greenhouses (Eliades, 1992). The objectives of this study were to determine the water requirements of greenhouse-grown eggplant using tensiometers and to relate them with class A pan evaporation.
2. Materials and methods The experiment was conducted in an unheated greenhouse at the Horticultural Research Station of Ierapetra, southeast Crete, during the 1991-1992 and 1992-1993 growing seasons. The eggplant (Solanum melongema, L.) hybrid Delica, widely grown by farmers, was used. The top 30 cm soil layer was amended and contained 68% sand 20% silt and 12% clay, with a volumetric soil water content of 16% at field capacity and 9% at wilting point, a low salt content (EC, of 1: 1 soil-water extract of 1.2 dS m- ‘) and a pH of 7.5. Irrigation water was of good quality with EC, of 0.6 dS m-‘, containing (meq 1-l) 1.3 Ca’+, 1.l Mg2+, 1.3Na’,O.l K+,O.&?SOi-,3.2HCO;, 1.3Cll andapHof8.1. In both growing seasons eggplant seedlings, raised in peat-filled pots, were transplanted into the greenhouse between 5 and 10 October and the experiment lasted until the end of May. The plants were spaced 50 cm apart in rows which were spaced at 120 cm apart. Each plot consisted of four rows, each of eight plants. The two external rows served as guards, while measurements were taken from four plants from each middle row. A basal fertilizer dressing of 14 g P and 10 g K per plant was mixed with the soil just before planting. In addition plants were uniformly supplied with nutrients ( 1.2 N-O.8 P-2.2 kg per plant) with the irrigation water from the third week after transplanting and every 15 days until the end of the growing season. Cultivation cases (soil fumigation, pruning, pest and disease control) were exactly the same for all treatments.
K. Chartzoulakis, N. Drosos /Agricultural Water Management 28 (1995) 113-120
115
Plants were drip irrigated. The four amounts of irrigation water tested (0.40, 0.65,0.85 and 1 .OOX ET,) were based on maximum evapotranspiration (ET,,,) data obtained with the use of a tensiometer. It was assumed that maximum evapotranspiration (ET,,,) between two successive irrigations was calculated by the formula ET, = Z, - D,, where Z, was the amount of irrigation water needed to keep the soil at field capacity (SWP higher than - 20 KPa), and D, was the amount of water drained at a soil depth of 45 cm. An electrotensiometer was installed in the 1 .OOX ET, treatment at a depth of 25 cm in order to guide irrigation. Irrigation started when soil water potential (SWP) reached - 20 KPa and stopped as soon as applied water reached a depth of 25 cm. Drainage at a depth of 45 cm, after a large number of soil-water content measurements, was considered as negligible. Thus, maximum evapotranspiration was equal to the amount of irrigation water applied to keep SWP higher than -20 KPa, as drainage was zero at a soil depth of 45 cm. Irrigation treatments began after plant establishment ( 15 days after transplanting). Each plant was irrigated by an in-line dripper with a 4 1 h-i discharge rate at 0.14 MPa operational pressure. The frequency of irrigation, determined also by electro-tensiometer, was the same for all treatments, but the corresponding amount of water for the 0.40, 0.65 and 0.85 XET, treatments was applied to plants the next day. Watering frequency was six irrigations in November, five in December and January, four in February, seven in March, 13 in April and 20 in May. The experimental layout was a complete randomized block design with four replications. Evaporation from a USWB Class A pan evaporimeter, located outside the greenhouse, 100 m far away, was recorded daily. In mid April and May, the leaf water potential was estimated using a Scholander et al. ( 1965) pressure chamber (PMS Instruments, USA). Stomata1 conductance ( gs) and photosynthetic rate (P,) were measured using a portable photosynthesis measuring system (Model Li-6200, Li-Cor, USA). The above measurements were made the day before irrigation between 12.00 and 14.00 h. The fourth or fifth fully expanded leaf from the top, of six plants from each treatment, were selected for the measurements. The mature fruits were harvested once or twice a week, and their numbers and weights recorded. In fruit samples soluble solids concentration (SSC) and dry weight (%) were determined. At the end of the experiment the soil salt accumulation (EC,, Cl and Na in 1: 1 soil-water extract) below the dripper was determined.
3. Results and discussion Eggplant yield for different fractions of ET, applied is given in Table 1. The highest yield, about 6.5 kg per plant, was obtained with the treatments 1.OOand 0.85 X ET,,,, irrigated with water equivalent to 380 mm and 325 mm, respectively. Seasonal water application of 0.65 X ET,,, and 0.40 X ET,,,, corresponding to 250 mm and 150 mm, respectively, reduced the yield in both years significantly, because of the formation of fewer fruits. Although the fruit yield of the 1.00 and 0.85 X ET,,, treatments was almost the same, the water use efficiency for harvested yield (kg of fruits per unit of applied water) of treatment 0.85 X ET,,, was higher (3 1.1 instead of 27.2 kg mm- ‘) ; such a difference is significant for a water sort area such as Crete. These suggest that eggplant under our conditions will grow without any significant yield loss with seasonal water application of 325 mm. Eliades (1992) reported
I16
K. Clzartzoulakis, N. Drosos /Agricultural
Table 1 Fruit yield of greenhouse-grown Irrigation treatment
eggplants
Water Management 28 (1995) 113-120
irrigated with different amount of water
Water applied (mm)
Yield
1991-1992
kg per plant
(% ET,,)
1.OOx 0.85 x 0.65 x 0.40 x
1992-1993
ET,,,
3.59
40.5
ET,,,
305
344
ET,, ET,,,
233 143
262 162
Fruits per plant
1991-1992
1992-1993
1991-1992
1992-1993
6.8a” 6.7a 4.5b 3.9b
6.2a 6.0a 4.0b 3.lc
29.6a 30.4a 21.lb 19.2b
24.la 24.2a 17.0b 13.2~
“Different letters within column indicate significant differences
at P < 0.05 (Duncan’s
multiple range test)
280 -s r 260 .-o ; 240 ._ 2 220
200
x
9.0 0 r 2
8.0
i
7.0
r 0
6.0
LSD (5%)
5.0
1
2 7.0 m .I! i 6.0 4 2 ij v)
5.0
4.0
C
100
200 Seaaonal
Fig.
300 irrigation
400 water
500 (mm)
1.Influence of different amounts of applied irrigation water on fruit quality of greenhouse-grown
eggplant.
K. Chartzoulakis, N. Drosos/Agricultural
Water Management 28 (1995) 113-120
117
,_ETa ETm 0.8 1.0 4”“““’
0.6
0.4
/ / /
0
0.2
/
/”
/
0 /
/
_ - 0.2
- 0.4
/ _ 0.6
/
Fig. 2. Relationship between relative yield decrease for greenhouse-grown eggplant
( I-Ya/Ym)
and relative evapotranspiration
(I-ETa/ETm)
that eggplant can grow successfully in a heated greenhouse for a 7 month growing period with as low as 285 mm of water. Some fruit quality characteristics in relation to water applied are presented in Fig. 1. Fruit size was not affected significantly, although there was a trend for smaller fruits with less seasonal water application. However, dry matter and soluble solids concentration (SSC) of the fruit were significantly lower with the treatments 0.85 and 1.00 X ET,. These results show that the water deficit can improve significantly fruit quality (in terms of SSC) of greenhouse-grown eggplant, but this advantage is accompanied with depression of marketable yield. To obtain an evaluation of the sensitivity of eggplant to soil water deficit, yield response factor KY (Doorenbos and Kassam, 1979) was calculated as the regression of relative yield decrease ( 1 - Y,/ Y,,,) on relative evapotranspiration deficit ( 1 - ET,/ET,) , where Y, and Y,,,are the actual and the maximum observed yields, respectively. The K,, value for the total growing period was 0.9 (Fig. 2) ; the eggplant can therefore stand greater drought than can most other vegetables. Behboudian ( 1977) found that eggplant is able to maintain a more favourable water balance by maintaining a higher relative water content for a certain drop of (cllcti,more effective stomata1 control on transpiration, better osmoregulation and a rapid recovery in water status as stress is lifted. Our data on gas exchange parameters are consistent with those findings. Indeed, although leaf water potential decreased to - 1.5 MPa for the plants irrigated with 0.4OXET,, the photosynthetic rate and stomata1 conductance were not affected; both reached the values achieved by plants irrigated with 0.85 and 1.00 X ET,,, (Table 2). Recent work (Srinivasa Rao and Bhatt, 1990) showed that photosynthesis in two eggplant cultivars was reduced under severe water stress ( $,Clleaf 1.7-3.0 MPa) after withholding water for more than 4 days at the fruiting stage. Maintenance of photosynthesis in plants which received less water per irrigation was either due to frequent irrigation (almost every day) so that no severe water stress was developed and/or the physiological responses of the plant to water stress. So that, the reduced yield noted for eggplants irrigated with 0.65
118
K. Chartzoulakis,
Table 2 Midday leaf gas exchange regime
N. Drosos /Agricultural
parameters
Water Management 28 (1995) 113-120
of greenhouse-grown
eggplant
at fruiting stage in relation to soil water
Irrigation treatment
Leaf water potential
Stomata1 conductance
(% ET,)
(MPa)
(cm s-‘)
Photosynthetic rate (I*.molCO,m-zs-‘)
1.OOX ET,, 0.85 X ET,,, 0.65 X ET,,, 0.40 X Et,,
-0.92_+0.12 - 0.97 f 0.09 - 1.45f0.14 - 1.52+0.10
0.70 0.66 0.64 0.61
14.2 -+ 1.2 14.9* 1.5 13.5* 1.3 14.1 * 1.0
Conditions were: 340 mbar, 21% (v/v) are means f SE, n = 6.
f 0.09 * 0.10 + 0.07 f0.12
0,. air temperature
30 * 2°C PPFD 800-1000
pmol m-’ SK’. Values
and 0.40 X ET,,, can be linked to a slower migration of photosynthates towards the sinks, the most important of which is the fruit. The water requirements of the crop, when the soil water potential was kept higher than - 20 KPa, ranged between 0.5 and 4.5 mm day- ‘, corresponding to 0.4-3.2 1 per plant day- ’ (Fig. 3). These values are about 30% lower than those reported by Eliades ( 1992) for hybrid Bonica, determined by a weighting lysimeter. However, as water application of 50% less in that experiment had no effect on fruit yield, it seems that water requirements were overestimated. Two periods can be distinguished from Fig. 3 for the crop demand for irrigation water; a period characterized with low water requirements (October-February) because rates of plant growth and production are low due to low air temperatures (10°C) inside the greenhouse. The second period from March to May is characterized by a fast increase of water requirements, due to the increase in the evaporative demand of the atmosphere and the faster rates of plant growth achieved under the optimum climatic conditions prevailing at that period. The crop ET,,, in October (at planting) was 0.2 of class A pan evaporation (E,,,), located outside the greenhouse. This value remained constant until February and then increased 3.6
5
3.0 . 7% 4 2.5 . 7.. i 2.0. * m ?1 1.6,; i L
1.0
_
0.6
.
I
A
1991-2
A
1992-3
000Ocf
A/ _4
.3
E E zw
-2
_
Nov Oec
Jan
Feb
Mar
Apr
1
May
Months
Fig. 3. Maximum evapotranspiration
(ETm) of eggplants
grown in unheated greenhouse
K. Chartzoulakis,
N. Drosos /Agricultural
Water Management 28 (1995) 113-120
119
1.0
I
.
1991-2
7 f
0.0
w” F 0.4 w 0.2
.
NbvDee 5611Fob
Oh
. Mar
, Apr
. May
Months
Fig. 4. Crop coefficient
curve (k = ETm/Epan)
for eggplant grown in unheated greenhouse
gradually to 0.8 X E,,, at the end of the experiment, in May (Fig. 4). Eliades and Orphanos (1986) compared the ratios of ETP, measured with lysimeters, to Epm or to potential evapotranspiration rates calculated by the Blaney-Griddle or Penman formulae, as modified by Doorenbos and Pruitt (1977). It was found that Epanrecorded outside the greenhouse was a reliable measure of tomato evapotranspiration under cover and the coefficient relating it to ETP increased linearly through the growing season from 0.26 to 1.0. Although no comparisons between ETP methods were made in this experiment, our result on the ET,/ Epanratio is consistent with them. There were no big differences in both ET,,, and the ET,/ Epm ratio between the years; as Epanis an easy measurement to take outside the greenhouse and small deviations ( f 15%) in water application from ET, are not expected to affect yield significantly (Table 1) , the ET,/ Epm ratio can be successfully used to estimate the water demand of greenhouse eggplants. Salt accumulation within plant root-zone in terms of EC, was higher in the surface 10 cm soil layer with all amounts of water tested (Fig. 5). Large differences in salt concentration (EC, Na, Cl) between well-watered ( 1.00 and 0.85 X ET,,,) and less-watered (0.65 and
r
400
2.5
3oo
_ 300
5; * 200
-
1Ocm
w-9
Ucm
\ G
‘b
n 100
L-A
0
100
200 Seasonal
300 irrigation
Fig. 5. Salt distribution
water
400 (mm)
100
do
SRSSOflal
(ECe, Na, Cl) in the soil of greenhouse
Cl Na
200 irrigation
300 water
400 (mm)
in relation to irrigation water applied
120
K. Chartzoulakis,
N. Drosos /Agricultural
Water Management 28 (1995) 113-120
0.40 X ET,,,) treatments were found in the O-25 cm soil layer, where the majority of roots were developed. Salt content below the dripper was lower as the amount of water applied increased; with highest water applied the EC, at the end of the crop was almost the same as it was at planting ( 1.2 dS m- ‘). This means that the salts, mainly coming from fertilizer, were more easily absorbed under optimum soil water conditions while the excess moved laterally out of the root zone and accumulated between the laterals where the wetting fronts merged, as no drainage at a depth of 45 cm was noted. With the least amount of water salt concentration increased by 65%, indicating that the amount of water applied was inadequate to leach the salts vertically down the profile and laterally out of the root zone. As the eggplant is considered a moderately sensitive to salinity crop (Ayers and Westcot, 1985)) the increased salinity in the root-zone may affected its growth and yield. So that, an additional amount of water must be applied in the treatments 0.65 and 0.40 X ET, for salt leaching.
Acknowledgements The authors gratefully acknowledge the technical assistance of E. Kokolakis and G. Papadakis. This work was partially supported by the Mediterranean Integrated Programme of E.U.
References Ayers, R.S. and Westcot, D.W., 1985. Water quality for agriculture Irrigation and Drainage Paper No. 29, FAO, Rome. Behboudian, M.H., 1977. Responses of eggplant to drought. I. Plant water balance. Scientia Hortic., 7: 303-310. Chiaranda, F.Q. and Zerbi, G., 1986. Water requirements of eggplant grown under a greenhouse. Acta Hortic., 191: 149-156. Doorenbos, J. and Pruitt, W.O., 1977. crop water requirements. Irrig. and Dram. Paper, No. 24, FAO, Rome. Doorenbos, J. and Kassam, A.H., 1979. Yield response to water. Irrigation and Drainage Paper No. 33. FAO, Rome. Eliades, G. and Orphanos, P.I., 1986. Irrigation of tomatoes grown in unheated greenhouses. J. Hort. Sci., 61 ( 1): 95-101. Eliades, G., 1992. Irrigation of eggplants grown in heated greenhouses. J. Hort. Sci., 67( 1): 143-147. Gregory, P.G., 1984. Water availability and crop growth in arid regions. Outlook of Agriculture, I3 (4): 208215. Meyer, W.S., Reicosky, D.C. and Schaefer, N.L., 1985. Errors in field measurements of leaf diffusive conductance associated with leaf temperature. Agric. For. Meteorol., 36: 55-64. Scholander, P.F., Hammel, H.T., Bradstreet, E.D. and Hemmingsen, E.A., 1965. Sap pressure in vascular plants. Science, 148: 339-346. Srinivasa Rao, N.K. and Bhatt, R.M., 1990. Response of photosynthesis to water stress in two eggplant (Solanun melongenu L.) cultivars. Photosynthetica, 24 (3): 506513.
ELSEVIER
Agricultural Water Management 28 ( 1995) 113-120
Water use and yield of greenhouse grown eggplant under drip irrigation IL Chartzoulakis a,*, N. Drosos b ’NAGREF, Subtropical Plants and Olive Trees Institute, 73 IO0 Chania, Crete, Greece ’ Horticultural Research Station, 72 200 lerapetra,
Crete, Greece
Accepted 17 November 1994
Abstract The water consumptive use of eggplant, hyb. Delica, grown in unheated greenhouse was determined using tensiometers. The maximum evapotranspiration (ET,,,), when soil water potential was maintained at values higher than -20 KPa, ranged from 0.5 to 4.5 mm day-‘, with a whole season irrigation requirement corresponding to 380 mm. Water amount equal to 0.85 X ET, had no effect on fruit yield, which was 6.5 kg per plant; water application of 0.65 X ET,,, and 0.40 X ET,,, reduced total yield by 35% and 46%, respectively. Fruit number per plant was significantly reduced at 0.65 XET, and 0.40 X ET,,,, while fruit size was not affected by the amount of water applied. The crop ET, in October (at planting) was 0.2 of A pan evaporation (E,,) located outside the greenhouse. This value remained constant until February and then increased gradually to 0.8 XI&, at the end of the experiment, in May. Salt content was higher at the surface 10 cm soil layer with all amounts of water applied. With 1.OOX ET,,, and 0.85 X ET,,, salts were leached out of root zone, while an additional amount of water was required at 0.65 and 0.40 X ET,,, for salt leaching. Kqvwords:
Evapotranspiration; A pan evaporation; E&/E,,, ratio; Solanum melongema L
1. Introduction
Water is fast becoming an economically scarce resource in many areas of the world, especially in arid and semi-arid regions (Gregory, 1984)) such as the Mediterranean. The need for more-efficient agricultural use of irrigation water arises out of increased competition for water resources and rising environmental anxiety that irrigation practice in some cases, is facilitating a degradation in the quality of those ground and surface waters that receive leachates from the root zone of irrigated fields. With improved water efficiencies water is * Corresponding author. 0378-3774/95/$09.50
0 1995 Elsevier Science B.V. All rights reserved
.SSDIO378-3774(95)01173-O
114
K. Chartzoulakis,
N. Drosos/Agricultural
Water Management 28 (1995) 113-120
saved as less water is needed for the same level of crop production, and wasteful infiltration of applied water beyond the root zone is eliminated. The supply of the required water to the plant is of prime importance for its growth and economic production, especially into greenhouse, where irrigation is the unique source of water for the plant. To obtain the best irrigation regime, the available measurements on water needs of greenhouse crops are based on environmental, physiological and soil parameters. Most physiological indices of plant water stress (leaf water potential, leaf water content, diffusion resistance) involve measurements that are complex, time consuming and difficult to integrate, but are also subject to errors (Meyer et al., 1985). The use of meteorological data (Penman’s, radiation) or canopy temperature measurements, are also complex, very expensive and require highly qualified farmers. Thus, the use of tensiometers, which assures low cost, simple operation and reliable estimation of soil water status, are widely used in greenhouses in Crete. On the island of Crete eggplant occupies about 5% of the area covered by greenhouse grown vegetables. Its cultivation is restricted to southeast coastal areas, where winter temperatures are mild and no heating is required. Water scarcity in these areas, as well as the increasing competition for municipal use, make it necessary to optimize water use by the farmers. Although some papers deals with water requirements of greenhouse-grown eggplant, the results are not applicable to this area of Greece, as they refer to different growing season (Chiaranda and Zerbi, 1986) or to heated greenhouses (Eliades, 1992). The objectives of this study were to determine the water requirements of greenhouse-grown eggplant using tensiometers and to relate them with class A pan evaporation.
2. Materials and methods The experiment was conducted in an unheated greenhouse at the Horticultural Research Station of Ierapetra, southeast Crete, during the 1991-1992 and 1992-1993 growing seasons. The eggplant (Solanum melongema, L.) hybrid Delica, widely grown by farmers, was used. The top 30 cm soil layer was amended and contained 68% sand 20% silt and 12% clay, with a volumetric soil water content of 16% at field capacity and 9% at wilting point, a low salt content (EC, of 1: 1 soil-water extract of 1.2 dS m- ‘) and a pH of 7.5. Irrigation water was of good quality with EC, of 0.6 dS m-‘, containing (meq 1-l) 1.3 Ca’+, 1.l Mg2+, 1.3Na’,O.l K+,O.&?SOi-,3.2HCO;, 1.3Cll andapHof8.1. In both growing seasons eggplant seedlings, raised in peat-filled pots, were transplanted into the greenhouse between 5 and 10 October and the experiment lasted until the end of May. The plants were spaced 50 cm apart in rows which were spaced at 120 cm apart. Each plot consisted of four rows, each of eight plants. The two external rows served as guards, while measurements were taken from four plants from each middle row. A basal fertilizer dressing of 14 g P and 10 g K per plant was mixed with the soil just before planting. In addition plants were uniformly supplied with nutrients ( 1.2 N-O.8 P-2.2 kg per plant) with the irrigation water from the third week after transplanting and every 15 days until the end of the growing season. Cultivation cases (soil fumigation, pruning, pest and disease control) were exactly the same for all treatments.
K. Chartzoulakis, N. Drosos /Agricultural Water Management 28 (1995) 113-120
115
Plants were drip irrigated. The four amounts of irrigation water tested (0.40, 0.65,0.85 and 1 .OOX ET,) were based on maximum evapotranspiration (ET,,,) data obtained with the use of a tensiometer. It was assumed that maximum evapotranspiration (ET,,,) between two successive irrigations was calculated by the formula ET, = Z, - D,, where Z, was the amount of irrigation water needed to keep the soil at field capacity (SWP higher than - 20 KPa), and D, was the amount of water drained at a soil depth of 45 cm. An electrotensiometer was installed in the 1 .OOX ET, treatment at a depth of 25 cm in order to guide irrigation. Irrigation started when soil water potential (SWP) reached - 20 KPa and stopped as soon as applied water reached a depth of 25 cm. Drainage at a depth of 45 cm, after a large number of soil-water content measurements, was considered as negligible. Thus, maximum evapotranspiration was equal to the amount of irrigation water applied to keep SWP higher than -20 KPa, as drainage was zero at a soil depth of 45 cm. Irrigation treatments began after plant establishment ( 15 days after transplanting). Each plant was irrigated by an in-line dripper with a 4 1 h-i discharge rate at 0.14 MPa operational pressure. The frequency of irrigation, determined also by electro-tensiometer, was the same for all treatments, but the corresponding amount of water for the 0.40, 0.65 and 0.85 XET, treatments was applied to plants the next day. Watering frequency was six irrigations in November, five in December and January, four in February, seven in March, 13 in April and 20 in May. The experimental layout was a complete randomized block design with four replications. Evaporation from a USWB Class A pan evaporimeter, located outside the greenhouse, 100 m far away, was recorded daily. In mid April and May, the leaf water potential was estimated using a Scholander et al. ( 1965) pressure chamber (PMS Instruments, USA). Stomata1 conductance ( gs) and photosynthetic rate (P,) were measured using a portable photosynthesis measuring system (Model Li-6200, Li-Cor, USA). The above measurements were made the day before irrigation between 12.00 and 14.00 h. The fourth or fifth fully expanded leaf from the top, of six plants from each treatment, were selected for the measurements. The mature fruits were harvested once or twice a week, and their numbers and weights recorded. In fruit samples soluble solids concentration (SSC) and dry weight (%) were determined. At the end of the experiment the soil salt accumulation (EC,, Cl and Na in 1: 1 soil-water extract) below the dripper was determined.
3. Results and discussion Eggplant yield for different fractions of ET, applied is given in Table 1. The highest yield, about 6.5 kg per plant, was obtained with the treatments 1.OOand 0.85 X ET,,,, irrigated with water equivalent to 380 mm and 325 mm, respectively. Seasonal water application of 0.65 X ET,,, and 0.40 X ET,,,, corresponding to 250 mm and 150 mm, respectively, reduced the yield in both years significantly, because of the formation of fewer fruits. Although the fruit yield of the 1.00 and 0.85 X ET,,, treatments was almost the same, the water use efficiency for harvested yield (kg of fruits per unit of applied water) of treatment 0.85 X ET,,, was higher (3 1.1 instead of 27.2 kg mm- ‘) ; such a difference is significant for a water sort area such as Crete. These suggest that eggplant under our conditions will grow without any significant yield loss with seasonal water application of 325 mm. Eliades (1992) reported
I16
K. Clzartzoulakis, N. Drosos /Agricultural
Table 1 Fruit yield of greenhouse-grown Irrigation treatment
eggplants
Water Management 28 (1995) 113-120
irrigated with different amount of water
Water applied (mm)
Yield
1991-1992
kg per plant
(% ET,,)
1.OOx 0.85 x 0.65 x 0.40 x
1992-1993
ET,,,
3.59
40.5
ET,,,
305
344
ET,, ET,,,
233 143
262 162
Fruits per plant
1991-1992
1992-1993
1991-1992
1992-1993
6.8a” 6.7a 4.5b 3.9b
6.2a 6.0a 4.0b 3.lc
29.6a 30.4a 21.lb 19.2b
24.la 24.2a 17.0b 13.2~
“Different letters within column indicate significant differences
at P < 0.05 (Duncan’s
multiple range test)
280 -s r 260 .-o ; 240 ._ 2 220
200
x
9.0 0 r 2
8.0
i
7.0
r 0
6.0
LSD (5%)
5.0
1
2 7.0 m .I! i 6.0 4 2 ij v)
5.0
4.0
C
100
200 Seaaonal
Fig.
300 irrigation
400 water
500 (mm)
1.Influence of different amounts of applied irrigation water on fruit quality of greenhouse-grown
eggplant.
K. Chartzoulakis, N. Drosos/Agricultural
Water Management 28 (1995) 113-120
117
,_ETa ETm 0.8 1.0 4”“““’
0.6
0.4
/ / /
0
0.2
/
/”
/
0 /
/
_ - 0.2
- 0.4
/ _ 0.6
/
Fig. 2. Relationship between relative yield decrease for greenhouse-grown eggplant
( I-Ya/Ym)
and relative evapotranspiration
(I-ETa/ETm)
that eggplant can grow successfully in a heated greenhouse for a 7 month growing period with as low as 285 mm of water. Some fruit quality characteristics in relation to water applied are presented in Fig. 1. Fruit size was not affected significantly, although there was a trend for smaller fruits with less seasonal water application. However, dry matter and soluble solids concentration (SSC) of the fruit were significantly lower with the treatments 0.85 and 1.00 X ET,. These results show that the water deficit can improve significantly fruit quality (in terms of SSC) of greenhouse-grown eggplant, but this advantage is accompanied with depression of marketable yield. To obtain an evaluation of the sensitivity of eggplant to soil water deficit, yield response factor KY (Doorenbos and Kassam, 1979) was calculated as the regression of relative yield decrease ( 1 - Y,/ Y,,,) on relative evapotranspiration deficit ( 1 - ET,/ET,) , where Y, and Y,,,are the actual and the maximum observed yields, respectively. The K,, value for the total growing period was 0.9 (Fig. 2) ; the eggplant can therefore stand greater drought than can most other vegetables. Behboudian ( 1977) found that eggplant is able to maintain a more favourable water balance by maintaining a higher relative water content for a certain drop of (cllcti,more effective stomata1 control on transpiration, better osmoregulation and a rapid recovery in water status as stress is lifted. Our data on gas exchange parameters are consistent with those findings. Indeed, although leaf water potential decreased to - 1.5 MPa for the plants irrigated with 0.4OXET,, the photosynthetic rate and stomata1 conductance were not affected; both reached the values achieved by plants irrigated with 0.85 and 1.00 X ET,,, (Table 2). Recent work (Srinivasa Rao and Bhatt, 1990) showed that photosynthesis in two eggplant cultivars was reduced under severe water stress ( $,Clleaf 1.7-3.0 MPa) after withholding water for more than 4 days at the fruiting stage. Maintenance of photosynthesis in plants which received less water per irrigation was either due to frequent irrigation (almost every day) so that no severe water stress was developed and/or the physiological responses of the plant to water stress. So that, the reduced yield noted for eggplants irrigated with 0.65
118
K. Chartzoulakis,
Table 2 Midday leaf gas exchange regime
N. Drosos /Agricultural
parameters
Water Management 28 (1995) 113-120
of greenhouse-grown
eggplant
at fruiting stage in relation to soil water
Irrigation treatment
Leaf water potential
Stomata1 conductance
(% ET,)
(MPa)
(cm s-‘)
Photosynthetic rate (I*.molCO,m-zs-‘)
1.OOX ET,, 0.85 X ET,,, 0.65 X ET,,, 0.40 X Et,,
-0.92_+0.12 - 0.97 f 0.09 - 1.45f0.14 - 1.52+0.10
0.70 0.66 0.64 0.61
14.2 -+ 1.2 14.9* 1.5 13.5* 1.3 14.1 * 1.0
Conditions were: 340 mbar, 21% (v/v) are means f SE, n = 6.
f 0.09 * 0.10 + 0.07 f0.12
0,. air temperature
30 * 2°C PPFD 800-1000
pmol m-’ SK’. Values
and 0.40 X ET,,, can be linked to a slower migration of photosynthates towards the sinks, the most important of which is the fruit. The water requirements of the crop, when the soil water potential was kept higher than - 20 KPa, ranged between 0.5 and 4.5 mm day- ‘, corresponding to 0.4-3.2 1 per plant day- ’ (Fig. 3). These values are about 30% lower than those reported by Eliades ( 1992) for hybrid Bonica, determined by a weighting lysimeter. However, as water application of 50% less in that experiment had no effect on fruit yield, it seems that water requirements were overestimated. Two periods can be distinguished from Fig. 3 for the crop demand for irrigation water; a period characterized with low water requirements (October-February) because rates of plant growth and production are low due to low air temperatures (10°C) inside the greenhouse. The second period from March to May is characterized by a fast increase of water requirements, due to the increase in the evaporative demand of the atmosphere and the faster rates of plant growth achieved under the optimum climatic conditions prevailing at that period. The crop ET,,, in October (at planting) was 0.2 of class A pan evaporation (E,,,), located outside the greenhouse. This value remained constant until February and then increased 3.6
5
3.0 . 7% 4 2.5 . 7.. i 2.0. * m ?1 1.6,; i L
1.0
_
0.6
.
I
A
1991-2
A
1992-3
000Ocf
A/ _4
.3
E E zw
-2
_
Nov Oec
Jan
Feb
Mar
Apr
1
May
Months
Fig. 3. Maximum evapotranspiration
(ETm) of eggplants
grown in unheated greenhouse
K. Chartzoulakis,
N. Drosos /Agricultural
Water Management 28 (1995) 113-120
119
1.0
I
.
1991-2
7 f
0.0
w” F 0.4 w 0.2
.
NbvDee 5611Fob
Oh
. Mar
, Apr
. May
Months
Fig. 4. Crop coefficient
curve (k = ETm/Epan)
for eggplant grown in unheated greenhouse
gradually to 0.8 X E,,, at the end of the experiment, in May (Fig. 4). Eliades and Orphanos (1986) compared the ratios of ETP, measured with lysimeters, to Epm or to potential evapotranspiration rates calculated by the Blaney-Griddle or Penman formulae, as modified by Doorenbos and Pruitt (1977). It was found that Epanrecorded outside the greenhouse was a reliable measure of tomato evapotranspiration under cover and the coefficient relating it to ETP increased linearly through the growing season from 0.26 to 1.0. Although no comparisons between ETP methods were made in this experiment, our result on the ET,/ Epanratio is consistent with them. There were no big differences in both ET,,, and the ET,/ Epm ratio between the years; as Epanis an easy measurement to take outside the greenhouse and small deviations ( f 15%) in water application from ET, are not expected to affect yield significantly (Table 1) , the ET,/ Epm ratio can be successfully used to estimate the water demand of greenhouse eggplants. Salt accumulation within plant root-zone in terms of EC, was higher in the surface 10 cm soil layer with all amounts of water tested (Fig. 5). Large differences in salt concentration (EC, Na, Cl) between well-watered ( 1.00 and 0.85 X ET,,,) and less-watered (0.65 and
r
400
2.5
3oo
_ 300
5; * 200
-
1Ocm
w-9
Ucm
\ G
‘b
n 100
L-A
0
100
200 Seasonal
300 irrigation
Fig. 5. Salt distribution
water
400 (mm)
100
do
SRSSOflal
(ECe, Na, Cl) in the soil of greenhouse
Cl Na
200 irrigation
300 water
400 (mm)
in relation to irrigation water applied
120
K. Chartzoulakis,
N. Drosos /Agricultural
Water Management 28 (1995) 113-120
0.40 X ET,,,) treatments were found in the O-25 cm soil layer, where the majority of roots were developed. Salt content below the dripper was lower as the amount of water applied increased; with highest water applied the EC, at the end of the crop was almost the same as it was at planting ( 1.2 dS m- ‘). This means that the salts, mainly coming from fertilizer, were more easily absorbed under optimum soil water conditions while the excess moved laterally out of the root zone and accumulated between the laterals where the wetting fronts merged, as no drainage at a depth of 45 cm was noted. With the least amount of water salt concentration increased by 65%, indicating that the amount of water applied was inadequate to leach the salts vertically down the profile and laterally out of the root zone. As the eggplant is considered a moderately sensitive to salinity crop (Ayers and Westcot, 1985)) the increased salinity in the root-zone may affected its growth and yield. So that, an additional amount of water must be applied in the treatments 0.65 and 0.40 X ET, for salt leaching.
Acknowledgements The authors gratefully acknowledge the technical assistance of E. Kokolakis and G. Papadakis. This work was partially supported by the Mediterranean Integrated Programme of E.U.
References Ayers, R.S. and Westcot, D.W., 1985. Water quality for agriculture Irrigation and Drainage Paper No. 29, FAO, Rome. Behboudian, M.H., 1977. Responses of eggplant to drought. I. Plant water balance. Scientia Hortic., 7: 303-310. Chiaranda, F.Q. and Zerbi, G., 1986. Water requirements of eggplant grown under a greenhouse. Acta Hortic., 191: 149-156. Doorenbos, J. and Pruitt, W.O., 1977. crop water requirements. Irrig. and Dram. Paper, No. 24, FAO, Rome. Doorenbos, J. and Kassam, A.H., 1979. Yield response to water. Irrigation and Drainage Paper No. 33. FAO, Rome. Eliades, G. and Orphanos, P.I., 1986. Irrigation of tomatoes grown in unheated greenhouses. J. Hort. Sci., 61 ( 1): 95-101. Eliades, G., 1992. Irrigation of eggplants grown in heated greenhouses. J. Hort. Sci., 67( 1): 143-147. Gregory, P.G., 1984. Water availability and crop growth in arid regions. Outlook of Agriculture, I3 (4): 208215. Meyer, W.S., Reicosky, D.C. and Schaefer, N.L., 1985. Errors in field measurements of leaf diffusive conductance associated with leaf temperature. Agric. For. Meteorol., 36: 55-64. Scholander, P.F., Hammel, H.T., Bradstreet, E.D. and Hemmingsen, E.A., 1965. Sap pressure in vascular plants. Science, 148: 339-346. Srinivasa Rao, N.K. and Bhatt, R.M., 1990. Response of photosynthesis to water stress in two eggplant (Solanun melongenu L.) cultivars. Photosynthetica, 24 (3): 506513.