Greenhouse Ambient Temperature and Relative Humidity Values
Crop production is vulnerable to climate variability, and climate change associated with increases in temperature may lead to a considerable decline in crop production (Mall et al, 2017). Temperature, along with photoperiod, is the main driving force for crop development (Shah et al., 2011).
Air humidity is a key component of environmental control in greenhouses (Suzuki et al., 2015). Humidity levels directly control the rate of transpiration water loss and stomatal aperture of plants. Thus, humidity regulates photosynthetic rates, tissue temperatures, plant water potentials, and concentrations of Ca in certain tissues. Humidity also controls water taken in by tissues through condensation and direct vapor uptake (Tibbitts, 1979).
The variation of the daily averages of the temperature and relative humidity values during the growing period of the pepper plant grown in a 20 m long and 6m wide greenhouse with plastic cover, which is open on all sides and closable cover on its sides, is given in Table 2
Table 2 Change in temperature and relative humidity during the experiment
Month
|
Temperature (°C)
|
Humidity (%)
|
|
Lowest
|
Highest
|
Average
|
Lowest
|
Highest
|
Average
|
June
|
16.48
|
32.65
|
24.57
|
45.6
|
92.61
|
68.84
|
July
|
20.98
|
32.22
|
26.61
|
48.66
|
91.57
|
70.11
|
August
|
17.93
|
33.7
|
25.81
|
43.95
|
90.83
|
67.39
|
September
|
17.93
|
32.15
|
25.04
|
51.31
|
96.16
|
73.74
|
October
|
15.5
|
30.98
|
25.26
|
44.05
|
69.71
|
69.71
|
The optimum temperature for pepper cultivation is 21-33 °C. Low and high temperature conditions affect the size of fruit and seed germination ability (Polowick & Sawhney, 1985; Saha, Hossain, Rahman, Kuo, & Abdullah, 2010; Thuy & Kenji, 2015). As can be seen from Figure 4.1, temperatures varied between 15.5-33.7 ° C and in daily averages. It can be said that these temperature levels are in the range required for pepper plant production.
Studies indicated that relative humidity has an effect on plant growth. (Baër & Smeets, 1978) indicated that relative humidity of 95% was the best in pepper plant growth, while (Barker, 1989) found that fruit weight was higher with higher humidity levels.
In Table 2, humidity levels were 44-96% which indicates that some of the times humidity levels were good and sometimes were bad.
Yield
During the study, three different harvests were made. The first harvest was made 40 days after transplanting but due to less effect of irrigation water salinity levels, there was no significant difference in yield. But in the second harvest, the irrigation water salinity levels started to have an effect on yield which caused a difference in the yields of different subjects. Nevertheless, the third harvest has a significant difference in yields of different treatments. According to the data, a clear difference in yields can be seen in the overall yield in the study.
In overall yields of different water salinity levels, a significant difference in yields was observed. The average values of pepper yield obtained from the subjects where different irrigation water salinity levels are applied are given in Table 3
Table 3 Total yield during the Experiment
Yield (g)
|
Average
|
N
|
669.3a
|
T1
|
429.3b
|
T2
|
280.0c
|
T3
|
70.0d
|
According to Table 3 in the overall harvest, various treatments have seen significant changes in productivity. EC levels significantly reduced yield, as the increase in salinity levels decreased yield.
Salinity is known for its effect on yield. (Abrol, Yadav, & Massoud, 1988; Chartzoulakis & Klapaki, 1998) reported a decrease in the yield of pepper with an increase in irrigation water salinity levels. Salinity caused major damage to the yield, where a clear difference in yield was observed. The increase in salinity significantly decreased the yield of plants. T3 (2dS/m) had the least yield with an average yield of 70.0g while Control (N) was the best (669.3g). Statistically, a major difference was spotted within the treatments.
Plant Biomass
(Alam et al, 2015) found that high salinity stress causes a detrimental effect on fresh biomass production of purslane limiting overall growth, plant height, number of leaves, leaf area, and stem diameter.
The average values of pepper plant biomass obtained from the subjects where different irrigation water salinity levels are applied are given in Table 4
Table 4 Plant Biomass of the plant after the harvest
Plant Biomass
|
Means
|
N
|
132.0a
|
T1
|
116.0b
|
T2
|
81.6c
|
T3
|
60.6d
|
Studies confirmed that salinity has a negative impact on plant growth and biomass, different irrigation salinity levels decreased the plant weight and biomass of pepper. (Hussein et al, 2012) studied that salinity has significantly reduced the biomass of pepper plants. In the study, the increase in EC treatment levels significantly decreased the biomass of the plant. T3 (10dS/m) reduced two folds compared to the control treatment. T2 (5dS/m) also showed a major reduction in plant Biomass. Statistically, a significant difference was observed as four groups formed.
Plant Water consumption
Plant water consumption is considered a vital factor for plant growth and yield. Salinity is believed to have a significant on plant water consumption as studied that plant water consumption decreased with the increase of salinity (ÜNLÜKARA et al, 2015a). Different studies reported that the increase in salinity decreased plant water consumption including bell pepper (Kurunc et al, 2011; Ozturk et al, 2004).
The statistical evaluation results of the plant water consumption values obtained from the subjects where different irrigation water salinity levels are applied are given in Table 5
Table 5 Plant Water consumption of the plants during the experiment
ET (L)
|
Means
|
N
|
37.56a
|
T1
|
28.45b
|
T2
|
21.84c
|
T3
|
13.43d
|
Calculating plant water consumption is an important factor for the growth and yield of plants. Studies identified that the use of saline water in irrigation will reduce plant water consumption (Yurtseven, Kesmez, & Ünlükara, 2005).
In the study, treatments showed that increase irrigation water salinity significantly reduced plant water consumption. T3 (10dS/m) showed a very low water consumption rate compared to Control and T1 treatments. T1 (2dS/m) and T2 (5dS/m) also showed a decrease in water consumption compared to the control. Salinity levels T1, T2, and T3 showed a decrease of 25%, 42%, and 65% in water consumption. Statistically, it was divided into four different groups.
Chlorophyll
As photosynthesis is the basic process during which light energy is absorbed and converted into organic matter, the importance of the plant pigment chlorophyll as an intermediary in the transformation of the absorbed solar energy and its activity in the process of photosynthesis and synthesis of organic substances in plants are crucial (Pavlović et al., 2014).
The statistical evaluation results of the plant chlorophyll obtained from the subjects where different irrigation water salinity levels are applied are given in Table 6
Table 6 Chlorophyll Index of the leaves
Chlorophyll
|
Average
|
N
|
25.0a
|
T1
|
20.0b
|
T2
|
14.6c
|
T3
|
8.7d
|
Salinity is well known for its negative effect on chlorophyll (Dhanapackiam & Ilyas, 2010; Djanaguiraman & Ramadass, 2004; Turan et al, 2007). Salinity reduces the chlorophyll pigments of the plants.
According to Table 6, EC treatments have negatively impacted the chlorophyll of pepper plants, as the increase of salinity decreases the chlorophyll of the leaves of the plant. T3 (10dS/m) treatments have the lowest chlorophyll while control treatments have the highest. Statistically, major differences can be observed between treatments.
Ion accumulation in Soil
In general view, irrigation salinity water is known for its effect on soil elements especially on Sodium (Na+), where studies (Mostafazadeh-Fard et al, 2007; Paliwal & Gandhi, 1976) studied that the increase in irrigation water salinity enhances the sodium content in the soil by decreasing the osmotic potential of the soil solution in saline conditions, plant access to water uptake will be reduced. As the soil dries, the concentration of salt in the soil solution will be increased.
The statistical evaluation results of ion concentration in the soil obtained from the subjects where different irrigation water salinity levels are applied are given in Table 7
Table 7 Ion accumulation in Soil
Category
|
Na
|
Ca
|
K
|
N
|
0.5b
|
1.26c
|
0.06a
|
T1
|
0.89ab
|
1.74b
|
0.06a
|
T2
|
1.22a
|
2.24a
|
0.05a
|
T3
|
1.26a
|
2.55a
|
0.06a
|
As indicated in Table 7, The increase of salinity levels increased the ion levels of the soil especially sodium and calcium, while potassium didn’t show a significant difference. Statistically, a significant difference wasn’t observed in sodium levels, but calcium has significant differences as T3 & T2 were the same and control treatments were the lowest. Potassium levels were the same statistically
Soil salinity
At the end of the study, soil samples were taken from each pot and their salinity was determined by making saturation reflection. The results of variance analysis of the salinity values of the soils in the subjects where different irrigation water salinity and water depth are applied are given in Table 8.
Table 8 Soil salinity in the Soil extract after harvesting
Soil ECe
|
Average
|
N
|
1.4a
|
T1
|
4.9b
|
T2
|
7.7c
|
T3
|
9.8d
|
The increase of irrigation water salinity significantly increased the level of salinity in the soil. Statistically, major differences were observed as four different groups were formed.