July 24, 2008
Growth and Transpiration of Tomato Seedlings Grown in Hazelnut Husk Compost Under Water-Deficit Stress
By Ozenc, Damla Bender
This study was carried out to determine effects of composted hazelnut husk (CHH) on tomato seedlings grown under water stress conditions. Seven media were prepared using CHH mixed, in different ratios, with native peat and perlite. The following mixtures were used: 100%CHH, 100%peat, 75%CHH+25%peat, 50%CHH+50%peat, 25%CHH+75%peat, 25%CHH+50%peat+25%perlite and 50%CHH+25%peat+25%perlite. The experiment was arranged in a randomized plot design with seven media, three water levels (100%, 50% and 25% of easily available water content) and three replicates under greenhouse conditions. After a growing period (until beginning of flowering) of two months, transpiration rate, total dry matter, root/shoot ratio and plant height were measured. Among these media, 50%CHH+50%peat (M2) and 25%CHH+50%peat+25% perlite (M4) were found more ideal media than the others as physical and chemical properties. Water-deficit stress negatively affected seedling growth and transpiration rate. When water deficiency level increased, transpiration rate is decreased. Therefore, plant growth slowed down and total dry matter content of seedlings and plant height decreased. It was found that 50%CHH+50%peat (M2) and 25%CHH+50%peat+25% perlite (M4) media increased transpiration rate, total dry matter and seedling height. Root /shoot ratio increased under water stress in contrary to the other parameters. Root/shoot ratio raised in 100%peat and 50%CHH+50%peat media (M2). For tomato seedlings growth, 25% and 50% CHH can be used in mixtures with peat as a growing media component under water stress conditions. Besides, further research is recommended on the effects different combinations of CHH media for growth of tomato plant exposed to water stress during different growing period (such as flowering and fruit setting). IntroductionWater stress is one of major environmental constraints in plant growth and development. The main consequence of water stress is decreased growth and development caused by reductions of leaf area, dry matter production, decline in plant water status and transpiration (Gupta et al. 2001; Chaves et al. 2002; Bindi et al. 2005). Transpiration is the key factor to estimate crop water requirement and the rate of transpiration. During water deficiency, stomates close to conserve water and transpiration rate decreases in plant (Delfine et al. 2001; Nagakura et al. 2004; Sinclair et al. 2005; Zang et al. 2005; Xu et al. 2006). Leaf growth will be affected by water stress more than root growth because roots are more able to compensate for water stress (ClifftonBrown and Lewandowski 2000; Liu and Stutzel 2002; Masinde et al. 2005). The effects of water stress vary between plant species (Hasio and Xu 2000; Silvestre and Ferreira 2000) and plants are affected various ways from water stress according to growth periods (Ozenc and Ozkan 2003; Deproost et al. 2004; Font et al. 2005).
Seedling growth control for transplant production in greenhouses can be achieved by regulating the amount of water available to the plants. Therefore, soilless media are widely used, especially in greenhouses. These media show different effects on plant growth depending on its properties (Strojny and Nowak 2004; Raviv et al. 2004; Cardenas-Mendez et al. 2006; Quintero et al. 2006). In previous studies (Cayc> et al. 1998; Arenas and Vavrina 2002; Arbaou et al. 2003; Allaire et al. 2004; Adediran 2005; Dorais et al. 2005; Ashcroft et al. 2006; Dalton et al. 2006), variety of growing media were used for tomato growth. Bender Ozenc (2006) evaluated that effect of composted hazelnut husk on growth of tomato plants. Tomato is highly-sensitive to water stress. Battilani et al. (2000) reported that irrigation scheduling is one of the most relevant conditions in order to obtain good production of processing tomato with high quality level. Water stress decreased fruit yield of tomato. Candido et al. (2000) reported that the highest tomato yield was recorded in the most irrigated treatment. Sirinivasa et al. (2001) studied the effects of plant water stress imposed at vegetative, flowering, and fruiting stages of four tomato cultivars.
Hazelnut is an important crop in Turkey, especially in Black Sea region. Annually, large quantities (about 550, 000 tons) of in- shell hazelnuts are produced in this region. After harvest, dry husk remains, approximately 1/5 ratio from 1kg fresh hazelnut. Although hazelnut husk is used for different purposes, large quantities are wasted. In previous studies, it was suggested that hazelnut husk would be turned into compost and used as organic fertilizers (CaL>flkan et al. 1996; Ozenc and Cal>flkan 2001). In addition, it was shown that both the hazelnut husk and its fractions improved the physical, chemical and biological properties of soil (Ozenc and Cal>flkan 2001; Zeytin and Baran 2003; Ozenc 2005).
The objective of this study was to determine the effect of growing tomato seedlings in hazelnut husk compost under different water stress levels.
Materials and Methods
Composted hazelnut husk (CHH), peat and perlite were used pure as components of different mixtures in this study. Hazelnut husk collected from hazelnut orchards in the Eastern Black Sea Region of Turkey and then composted as described by Cal>flkan et al., (1996) and mixed with different combinations of peat and perlite. Peat was taken from Bolu-Yenica a, located in the Western part of the Black Sea region of Turkey. Perlite had a medium grain size. All materials were sieved through a 4 mm screen before use. Then, CHH was mixed with other materials in order to prepare suitable CHH-based media for growth seedlings. The following mixtures were used (v/v): CHH: 100% CHH, Peat: 100% peat, Ml: 75% CHH + 25% peat, M2: 50% CHH + 50% peat, M3: 25% CHH + 75% peat, M4: 25% CHH + 50% peat + 25% perlite, M5: 50% CHH + 25% peat + 25% perlite.
Some physical and chemical properties of the growing media components, peat, composted hazelnut husk (CHH) and perlite are given in Table 1.
The experiments were carried out in a 250 m^sup 2^ greenhouse. First, tomato seeds were sown in standard potting mix in the growth chamber (May 30 2006) and then the seedlings (after reaching a height of 5cm) were transplanted into pots. A randomized plot design was used for the experiments. The treatments included seven growing media, three water-deficit stress levels with three replicates per treatment. The volume of the pots was 1000cm^sup 3^. Water stress was applied at 100%, 50% and 25% level of easily available water content in the growing media. After interior of pots were covered by polyethylene for preventing water deprivation, prepared media were put in pots. One seedling was planted in each pot (June 20,2006) and a plastic tube was placed in pots. Pots were irrigated in accordance with water-deficit stress levels and total weight of pots was weighted. During the experiment, the plants were irrigated manually with these plastic tubes. Then, upper surface of pots were covered by polyethylene for preventing evaporation from soil. This allowed to measure the transpiration rates from the plants only. Water consumptions of plants were measured using a scale (lysimeter).
Some physical and chemical properties of the growing media components, peat, composted hazelnut husk (CHH) and perlite, on a dry matter basis.
No additional fertilization was used in the experiment. The experiments were continued until the beginning of the flowering. At the end of the experiment, (two months later), all the plants were harvested, and the leaves, shoots, roots were washed and dried at 60[degrees]C, in air-forced oven, for 48 h (Kacar 1984).
Plant and Media Analyses
Total porosity space (TPS), easily available water (EAW), aeration capacity (AC), water buffering capacity (WBC) and bulk density (De Boodt et al. 1973), organic matter (DIN 1978), total nitrogen (Colombo and Giazzi 1982), pH and EC (Gabriels and Verdonck 1992) and cation exchange capacity (CEC) (U. S. Salinity Lab. Staff 1954) were determined. Phosphorus was measured by the molybdate- vanadate calorimetric method as described by Kacar (1972). Potassium was assayed by flame photometry according to Kacar (1972).
Transpiration rate of plants was determined by weighing lysimeter (or a weighing scale). First, the plant height was measured from media surface in each pot. Shoot and root were separated by cutting them off at the base of the root and washed. Fresh weights were determined. Roots and shoots were then dried at 60[degrees]C, in an air-forced oven, for 48 h, and the dry weight was determined. Furthermore, the total dry matter and the root/shoot ratio were calculated according to the root and shoot dry weight.
Statistical analyses were evaluated by ANOVA and differences among the groups were separated by LSD (least significant difference) test at P
Results and Discussions
Properties of the Media
The main physical properties of the growing media are shown in Table 2. The parameters are based on the water retention curve. EAW is defined as the amount of water released between 10 and 50 cm of suction. AC is the difference between porosity and the water at a suction of 10 cm. WBC is the amount of water released between 50 and 100 cm of suction. De Boodt and Verdonck (1972) defined the requirements of an "ideal substrate"; this should exhibit 85% porosity 20-30% AC and EAW, and WBC between 4% and 10%. According to this definition, the substrate that approaches to the definition of "ideal substrate" is M2 and M4, but their %TPS is below the ideal range. While peat medium has ideal total porosity space and easily available water content, the CHH medium has an ideal value of aeration capacity. Ozenc and Cayc> (2005) determined that the most effective materials for total soil porosity were peat and husk compost. Zeytin and Baran (2003) reported that total porosity of soil was increased by addition of CHH, but the incubation period negatively affected total porosity. It is known that the aeration is related to the amount of macro pore. Although CHH has low TPS, it has high AC value. This shows that CHH medium has greater number of larger pores. Thus, CHH additions improved aeration capacity value of mixtures. Ml mixture was found to be the highest, followed by M4. Regarding EAW, the CHH is not an ideal medium. Therefore, the peat additions improved easily available water content of mixtures. M2 has the highest value, followed by M4. The EAW did not show any significant differences among the others. All media have suitable values regarding to WBC. The bulk density is the most important factor in determining the physical and chemical properties of growing media. The low bulk density values have the advantage in portable of media (Munsuz el al. 1982), increasing the number of larger pores. The CHH has low bulk density. Therefore, the CHH additions decreased bulk density of mixtures. M5 has the lowest bulk density, followed by M1. Some researches reported that CHH improved the physical and chemical properties of the soil (Zeytin and Baran 2003; Ozenc 2005; Bender Ozenc 2006). Use of growing media in soilless cultivation was studied by several authors for plant and seedling growth, bedding plant growth, vegetable growth (Baran et al. 2001; Strojny and Nowak 2004; Hernandez-Apaolaza et al. 2005; Benito et al.,2005; Perez-Murcia et al. 2006). TABLE 2.
Some physical properties of growing media
Some chemical properties of growing media
Some chemical properties of the media are given in Table 3. Generally, all media have high values in chemical properties. However, the CHH has the highest level for the properties such as pH, organic matter content, P, K and CEC. Except for M5, the pH values of all mixtures were within the established limits for an ideal substrate (pH = 5.3-6.5) (Abad et al. 2001). Ozenc (2005) reported that when the CHH was mixed with soil, pH of soil increased. Regarding organic matter, P and K contents, CHH has fairly high values, followed by M1. Therefore, these properties of media increased with CHH addition. Cimen et al. (2007) reported that application of the CHH to the soil increased organic matter content and soil pH considerably. Regarding total N, CHH has low value in comparison to peat. But, when CHH was mixed with 75% peat, total N content was fairly increased. The cation exchange capacity of all media was found to be fairly high. Except for CHH, the highest CEC was found in Ml, and the lowest value was found in M5 due to its perlite content. The present study revealed that when CHH is mixed into the peat at a rate of 50% or more of the total volume (Ml and M2), it significantly increased the chemical properties of the media. Cal>flkan and Ozenc (2001) and Ozenc and Cayc> (2005) reported that the hazelnut husk compost can be used in soil improvement.
Table 4 shows the seedling growth and transpiration rate of tomato seedlings grown under water stress. Water stress led to decrease in transpiration rate of seedlings. Transpiration is directly related to whether the stomata are open or closed; furthermore, transpiration is also affected by several factors such as available water content and aeration capacity of soil, humidity. As plants close their stomata under water stress conditions, the transpiration rate is decreased resulting in decreased plant growth and dry matter production. The lowest transpiration rate was found to be in 25% water stress conditions. Nagakura et al (2004) predicted that during soil drying, the transpiration rate is decreased. Similar effects have been reported by Xu et al. (2006), Bindi et al. (2005), Sinclair et al. (2005), Masinde et al. (2006), and Zhang et al (2005).
Under water stress conditions, the CHH medium was negatively affected. This may be its low easily available water content. Thus, the transpiration rates of plants were lower. On the other hand, by mixing CHH with 50% peat, 25% perlite (M4), transpiration rate was increased, and this was followed by M2. These media have adequate available water content (Table 2). Thus, the water moves easily through leaf, stomata/ opening and the transpiration rate increases. Sirinivasa et al. (2001) reported that tolerance to water stress in tomato cultivars was different and the transpiration rate was significant reduced in all cultivars. Ozenc and Ozkan (2003) revealed that the growth of plant was rather susceptible to water stress in seedling stage. Raviv et al. (2004) reported that restricted water uptake results in low leaf water potential, leading to cessation of leaf and shoot expansive growth.
Water stress significantly decreased total dry matter content of the seedlings (Table 4). It is known that soluble nutrient elements are taken by the roots (active absorption) and are moved through xylem. Besides, transpiration affects transport of soluble nutrient elements (passive absorption). Thus, the plant growth is associated with the transpiration rate. When transpiration rate is decreased, dry matter production of plant is also decreased. Liu and Stutzel (2004) reported that drought stress significantly decreased plant total dry mass. Besides, growing media affected dry matter content of seedlings (Table 4). M2 was found to be the most effective medium, and followed by M4. It is consistent a result as seen transpiration rates of these media. These media have suitable as physical properties and chemical properties (Table 2 and Table 3). Allaire et al. (2004) explained that if irrigation was adjusted for the physical properties of substrates, then different recycling organic materials with various particle sizes and shapes can be used for tomato production in greenhouses. On the other hand, Dorais et al. (2005) reported that relationships between water content measurements and physiological parameters varied with the growing media, but no significant differences were observed for the plant development, leaf area, plant dry weight, and yield of tomato plants grown under different growing media. The highest tomato yield was recorded in the most irrigated treatment (Candido et al. 2000).
Root/shoot ratio is one of the growth parameter. Water stress more limited shoot growth than root growth. This means that moving of soluble nutrient elements decreased through shoot. But, there were no statistical differences among the water stress levels. Jin et al. (2000) reported that osmotic-stress has an impact on growth of both the shoot and the roots of tomato; however, growth of the shoot is affected to a greater extent than that of the roots. Xu et al. (2006) explained that water stress significantly improved R/S ratio of seedlings. On the other hand, growing media significantly affected root/shoot ratio of seedlings (Table 4). While seedlings in CHH were the lowest R/S ratio, seedlings in peat were the highest R/ S ratio. It shows that while CHH was increased shoot growth, peat was increased root growth. It is known that organic materials have a positive effect on plant growth. Both peat and composted hazelnut husk are suitable media as physical and chemical properties (Table 2 and Table 3). Bender Ozenc (2006) reported that composted hazelnut husk was increased shoot, root and height of tomato plant as compared with soil. When CHH mixed with peat at rate of 50% (M2), R/ S ratio also increased. Gallardo et al. (2004) reported that water stress decreased stem diameter in greenhouse-grown mature vegetable crops. Warren and Bilderback (2004) predicated that root/top ratio of growing plants in pine bark based container substrates was unaffected by irrigation timing. Lucero et al. (2000) revealed that the effects of shoot + root competition on shoot dry matter growth were substantial and benefited when well-watered or at a moderate soil water deficit, while severely reducing white clover shoot dry matter growth at severe soil water deficit.
Seedling growth and transpiration rate of tomato seedlings grown under water stress
Plant height is another growth parameter. Both water stress and growing media were affected height of seedlings (Table 4). Water stress application decreased plant height. Plant height was the highest in 100% irrigation and decreased depending on the level of water stress. Zhang et al. (2005) reported that dry climate had lower height length, transpiration and total biomass, but higher root/shoot ratio of plants. Similar effects have been reported by Combalicer et al. (2005). Regarding to growing media, the highest plant height was found to be in M2 and M4 media. Similar a result has been found by Bender Ozenc (2006). Adediran (2005) studied a growing media to determine effects of biological waste products in the production of vegetable seedlings. The study showed that the germination of tomato was generally increased with time.
In this study, growth of tomato seedlings in hazelnut husk compost under different water stress levels was investigated. CHH was mixed with peat and perlite in different ratios, and different five media were experimented. Among these media, M2 (50%CHH+ 50%peat) and M4 (25%CHH+50%peat+25% perlite) was found to be more ideal media compared to others in terms of physical and chemical properties. Water stress negatively affected seedling growth and transpiration rate. When water deficiency level increased, the plants closed their stomata; thus, the transpiration rate is decreased. Therefore, the plant growth slowed down and the total dry matter content of seedlings and plant height were decreased. The effects of growing media on seedling growth showed differences depending on their properties. It was found that M2 (50%CHH+50%peat) and M4 (25%CHH+50%peat+25% perlite) media increased transpiration rate, the total dry matter and seedling height. Root /shoot ratio increased under water stress conditions in contrary to the other parameters such as total dry matter, plant height.
Furthermore research is needed to analyze the effect of growing media for plant under water stress conditions, however based on the findings from current study, it can be concluded that 25% and 50% CHH can be used in mixtures with peat as a growing media under water stress conditions. Besides, additional research is needed to determine the effects of different combinations of CHH media on growth of tomato plant exposed to water stress during different growing periods such as flowering and fruit setting.
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