Scholarly article on topic 'A novel organo-mineral fertilizer can mitigate salinity stress effects for tomato production on reclaimed saline soil'

A novel organo-mineral fertilizer can mitigate salinity stress effects for tomato production on reclaimed saline soil Academic research paper on "Biological sciences"

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South African Journal of Botany
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{Antioxidants / Growth / " Organo-mineral fertilizer " / Salinity / Tomato}

Abstract of research paper on Biological sciences, author of scientific article — M.M. Rady

Abstract A novel organo-mineral fertilizer [a 2:10:1 (w/w/w) mixture of calcium sulphate, ground rice bran and humic acid] was used as a soil amendment to study its effect on the growth, fruit yield, leaf nutrient status and antioxidant enzymes activities of tomato (Solanum lycopersicum L.) plants grown in reclaimed saline soil (EC=8.9dSm−1). The organo-mineral fertilizer-treated plants showed increased growth, proline, chlorophyll and nutrient contents. They also revealed increased fruit yield and quality, and increased activity of antioxidant enzymes when compared to the control plants. Therefore, the tested organo-mineral fertilizer may be recommended as a soil amendment for vegetables such as tomato to overcome the adverse effects of salinity stress in newly-reclaimed soils.

Academic research paper on topic "A novel organo-mineral fertilizer can mitigate salinity stress effects for tomato production on reclaimed saline soil"

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South African Journal of Botany 81 (2012) 8 - 14

www.elsevier.com/locate/sajb

A novel organo-mineral fertilizer can mitigate salinity stress effects for tomato production on reclaimed saline soil

M.M. Rady *

Agricultural Botany Department, Faculty of Agriculture, Fayoum University, 63514-Fayoum, Egypt Received 30 September 2011; received in revised form 16 March 2012; accepted 24 March 2012

Abstract

A novel organo-mineral fertilizer [a 2:10:1 (w/w/w) mixture of calcium sulphate, ground rice bran andhumic acid] was used as a soil amendment to study its effect on the growth, fruit yield, leaf nutrient status and antioxidant enzymes activities of tomato (Solanum lycopersicum L.) plants grown in reclaimed saline soil (EC = 8.9 dS m *). The organo-mineral fertilizer-treated plants showed increased growth, proline, chlorophyll and nutrient contents. They also revealed increased fruit yield and quality, and increased activity of antioxidant enzymes when compared to the control plants. Therefore, the tested organo-mineral fertilizer may be recommended as a soil amendment for vegetables such as tomato to overcome the adverse effects of salinity stress in newly-reclaimed soils. © 2012 SAAB. Published by Elsevier B.V. All rights reserved.

Keywords: Antioxidants; Growth; Organo-mineral fertilizer; Salinity; Tomato

1. Introduction

Tomato (Solanum lycopersicum L.) production has a major role in global horticulture, ranking only second in importance to potato in many countries. Tomato is widely cultivated on newly-reclaimed soils in Egypt. However, most of these newly-reclaimed soils are affected by salinity with low fertility and a poor soil structure. Salinity is a major limiting factor in agricultural production and exerts unfavorable influence on various physiological and biochemical processes associated with plant growth and development (Greenway and Munns, 1980; Pitman and Lauchli, 2002). The negative impact of salinity on plant growth and metabolism has been attributed, principally, to enhanced Na+ ion uptake, which causes an excess of Na+ ions in plant tissues (Abbas et al., 1991). One of the primary effects of increasing the salinity of the growth medium is the inhibition of K+, Ca2+ and NO3 ion uptake by plant roots (Maas, 1986). In

* Tel.: +20 2107302668, +20 2119092061; fax: +20 2846343970, +20 2846334964.

E-mail address: mrady2009@yahoo.com.

addition, it is well-established that salinity stress damages plant cells through the production of reactive oxygen species (ROS), including superoxide radicals, hydrogen peroxide, hydroxyl anions, and singlet oxygen (Scandalios, 1997). Soil salinity inhibits the activities of the key enzymes of photosynthesis namely rubisco and PEP carboxylase (Soussi et al., 1998). Moreover, salinity induces the closure of stomata (Bethkey and Drew, 1992) and damages photosynthesis and photosynthetic electron transport chain. All these impaired events finally culminate into a severe loss in the rate of photosynthesis (Sudhir and Murthy, 2004).

Efforts have been made to control salinity by various technological means including soil reclamation, drainage, the use of high leaching fractions, and the application of soil amendments (Abdel-Naby et al., 2001). In recent years, much attention has been paid to the development of sustainable agriculture; hence, several materials have been applied as soil amendments to overcome the adverse effects of soil salinity, to improve the physical and chemical properties of soils, to increase their water retention, and to provide the nutrients required during plant growth.

0254-6299/$ -see front matter © 2012 SAAB. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.sajb.2012.03.013

The application of humic acid as an organic soil amendment, individually or in combination with other materials, resulted in significant increases in plant growth and crop yields in sandy soils by improving the hydrophysical properties and nutrient availability of such soils (Osman and Ewees, 2008). Humic acids enable growing plants to overcome the adverse effects of moderate soil salinity by improving the soil properties such as aggregation, aeration, permeability, water holding capacity, micronutrient uptake and availability, and by the decrease in the uptake of some toxic elements (Tan, 2003).

Calcium is considered as an important factor for the maintenance of cell membrane integrity and the regulation of iontransport. Ca+ is essential for K+ vs Na+ ion selectivity and membrane integrity (Hanson, 1984). Elevated concentrations of Ca2+ in the nutrient solution mitigated the adverse effects of salinity by inhibiting the uptake of Na+ (Greenway and Munns, 1980). In addition, Ca2+ ions reduce ion leakage through membranes (Leopold and Willing, 1984). LaHaye and Epstein (1969) confirmed that Ca2+/Na+ ion interactions took place at the plasmalemma. They suggested that Na+ acted by displacing Ca2+ ions from membranes, leading to increased membrane permeability and higher intracellular Na+ ion concentrations.

Owing to considerable evidence of the adverse effects of soil salinity on plant growth, it was hypothesized that the novel organo-mineral fertilizer used in this study as a soil amendment can overcome the injurious effects of soil salinity (EC = 8.9 dS m-1) on tomato plants. Thus, the primary objective of this work was to examine whether or not the organo-mineral fertilizer could mitigate the effects of soil salinity and regulate tomato plant growth by adjusting the proline content, nutritional status and antioxidant enzymes activities involved in stress tolerance.

2. Materials and methods

2.1. Plant material and growth conditions

The novel organo-mineral fertilizer used in this research was generated by mixing calcium sulphate (CaSO4), ground rice bran (a by-product of rice milling process), and humic acid (Alpha Chemika, Mumbai, India) at a ratio of 2:10:1 (w/w/w). These proportions of the organo-mineralfertilizer used gave the best results among several proportions examined in preliminary studies (data not shown). Therefore, they were selected. Table 1 summarizes the major components of the novel organo-mineral fertilizer used in these experiments. The soil used in this research was obtained from the Experimental Farm (a newly-reclaimed saline soil with EC = 8.9 dS m 1) of the Faculty of Agriculture in South-east Fayoum (29° 17'N; 30° 53'E), Egypt. The main characteristics of the soil according to Wilde et al. (1985) are given in Table 2.

Two greenhouse experiments were initiated on 1 September 2009 and 2010 in which pots were filled with various soil: organo-mineral fertilizer mixtures, with the portion of the organo-mineral fertilizer ranging from 0 (control) to 25 g kg - 1 soil (i.e., 0, 5, 10, 15, 20, or 25 gkg-1 soil). The experiments were arranged in a completely randomized design with these six experimental organo-mineral fertilizer treatments, 20 replications (20 pots) of each. Five-week-old tomato seedlings (cv. Saria), obtained from the Ministry of Agriculture Nurseries, Cairo, Egypt, were transplanted separately in 6 kg of each of the various soil: organo-mineral fertilizer mixtures per pot. All plants were maintained in a greenhouse at 25° ±2 °C under a natural photoperiod. Irrigation was applied twice a week and the pots were irrigated every 2 weeks with a nutrient solution containing 200 mg l-1 nitrogen (N), 100 mgl-1 phosphorus (P), 200 mg l-1 potassium (K), 2.0 mg l-1 iron (Fe), 1.0 mg l-1 manganese (Mn), 0.5 mgl-1 boron (B), 0.1 mgl-1 copper (Cu), 0.1 mg l 1 zinc (Zn), and 0.05 mg l 1 molybdenum (Mo).

2.2. Determination of plant growth and preparation for other estimations

Seven-week-old tomato plants from transplanting were used for the determinations of shoot dry weight (DW) plant 1 and root DW plant 1. The fourth true leaf on each plant was used for determining the activity of antioxidant enzymes, total chlorophyll and free proline contents, as well as leaf N, P, K, Ca and Na contents. In addition, ripe tomato fruit were used to determine fruit quality including vitamin C and total soluble solids (TSS) contents. Four individual plants were randomly selected from each experimental treatment to determine plant growth and other 4 plants for chemical determinations. Shoot and root DWs plant-1 (in g) were estimated after drying the appropriate tissue to constant weight at 70 °C using a forced air-oven for 48 h.

2.3. Determination of pigment and proline contents

Total chlorophyll (in mg g- 1 FW) was estimated adopting the procedure given by Arnon (1949). Leaf discs were homogenized with 80% acetone and centrifuged; the optical density of the acetone extract was measured at 663,645 and 470 nm using a UV-160A UV Visible Recording Spectrometer, Shimadzu, Japan.

Leaf free proline contents (in p,g g-1 DW) were measured using the rapid colourimetric method, as suggested by Bates et al. (1973). Proline was extracted from 0.5 g of each leaf sample by grinding in 10 ml 3% (v/v) sulphosalicylic acid and the mixture was then centrifuged at 10,000 xg for 10 min. Two ml of the supernatant was added to a test-tube, to which 2 ml of a freshly prepared acid-ninhydrin solution was then added. The tubes were incubated in a water-bath at 90 °C for 30 min, and the reaction

Major components of the novel organo-mineral fertilizer * used in these experiments.

Component N P K Ca Fe Mn Zn Humic acid Total fiber Water holding

capacity (gg-')

% (w/w) 2.81 0.71 3.02 7.98 0.31 0.17 0.10 12.49 32.46 7.33

* Organo-mineral fertilizer=2:10:1 (w/w/w) calcium suphate, ground rice bran and humic acid.

Table 2

Some of the physical and chemical characteristics of the reclaimed saline soil used in these experiments.

Composition [% (w/w)] pH EC OCa N P K Ca Fe Mn Zn

Clay Loam Sand (dS m- 1) (g kg-') (g kg-') (mg kg-1) (mgkg-') (mg kg-1) (mgkg-') (mg kg-1) (mgkg-')

11.9 16.6 71.5 7.7 8.9 8.4 0.7 18.6 81.7 85.1 6.4 4.0 2.1

OC, organic content.

was terminated in an ice-bath. The reaction mixture was extracted with 5 ml toluene and vortex mixed for 15 s. The tubes were allowed to stand for > 20 min in the dark at room temperature to separate the toluene and aqueous phases. Each toluene phase was then carefully collected into a clean test-tube and its absorbance was read at 520 nm. The concentration of free proline in each sample was determined using a standard curve prepared using analytical grade proline, and was calculated on % DW basis.

2.4. Determinations ofN, P, K, Ca and Na contents

Leaf nitrogen contents (in mg g 1 DW) were determined according to Hafez and Mikkelsen (1981). An Orange-G dye solution was prepared by dissolving 1.0 g of 96% (w/w) assay-dye in 1.0 l of distilled water with 21.0 g citric acid, which acted as a buffer to maintain the correct pH, and 2.5 ml 10% (v/v) thymol in alcohol as an inhibitor of microbial growth. Ground plant leaf material (0.2 g) was placed in a centrifuge tube and 20 ml of the dye reagent solution was added. The contents of the tube were shaken on auto-shaker at 300 rpm for 15 min. After filtration, the solution was diluted 100-times with distilled water and its absorbance was measured at 482 nm. N contents were calculated using the formulae:

N(%) = 0.39 + 0.954 x Dye absorbed (g/100g), and

Dye absorbed (g/100g)

a-b cfv

-x x 100

where, a was the absorbance of the dye reagent solution at 482 nm without any plant material (blank), b was the absorbance of the dye reagent solution at 482 nm with plant material, c was the concentration of the dye reagent (1.0 g l-1 distilled water), f was the purity factor of the dye reagent (96%), v was the volume of the dye reagent solution used per sample (20 ml), and w was the weight of ground dry material in g (0.2).

The molybdenum-reduced molybdophosphoric blue colour method (Jackson, 1967), in sulphuric acid, was the method used for phosphorus determinations (in mgg-1 DW) in leaf tissue. In addition, diluted sulphomolybdic acid, and 8% (w/v) sodium bisulphite-H2SO4 solution were used as reagents. Leaf potassium ion (K ), calcium ion (Ca2 ) and sodium ion (Na ) contents (in mg g 1 DW) were assessed using a Perkin-Elmer Model 52-A Flame Photometer (Page et al., 1982).

2.5. Determinations of fruit yield, vitamin C and TSS contents

The number of fruit plant 1 and fruit yield plant 1 were recorded, using the remaining 12 pots, at the end ofthe experiment

on 11 November. Ripe fruit were used for determining vitamin C and TSS contents.

The vitamin C contents of fruit (mg 100 g-1 juice) were determined using the 2,6-dichloro-indophenol method (Helrich, 1990). Frozen samples were pulverised in a domestic grinder (Magefesa, Spain) and triplicate 10 g aliquots of each sample were immediately homogenised in 50 ml (w/v) of metapho-sphoric acid/acetic acid solution. The extracts were centrifuged for 15 min at 7000 xg, filtered through six layers of cheese-cloth, and made up to 100 ml (v/v) with metaphosphoric acid/acetic acid solution. Triplicate aliquots of each sample were titrated with 2,6-dichloro-indophenol solution. Ascorbic acid reduced the 2,6-dichloro-indophenol to a colourless solution and a slight excess of unreduced dye, resulting in a characteristic light-pink colour, indicated the end point of the reaction (Helrich, 1990). Total soluble solids (TSS) contents [in % (w/v)] of tomato ripe fruit were measured at 20 °C using an ATC-1E hand-held refractom-eter (Atago, Kyoto, Japan).

2.6. Determination of antioxidant enzymes activities

Peroxidase (POX) and polyphenol oxidase (PPO) activity was assayed in fresh leaf by the method of Kumar and Khan (1982). POX activity was expressed in Unit mg-1 protein. One Unit is defined as the change in the absorbance by 0.1 min-1 mg-1 protein. PPO activity was expressed in Unit mg-1 protein (Unit=Change in 0.1 absorbance min-1 mg-1 protein). Catalase (CAT) activity was measured according to Chandlee and Scandalios (1984). CAT activity was expressed in Unit mg 1 protein (Unit= 1 mM of H2O2 reduction min 1 mg 1 protein).

2.7. Statistical analysis

All data were subjected to ANOVA using SAS software (1996), and means comparisons between the different treatments were performed using the Least Significant Differences (LSD) procedure at the P=0.05 level, as illustrated by Snedecor and Cochran (1980).

3. Results

3.1. Shoot and root dry weights (DWs), free proline and chlorophyll contents

All levels of the organo-mineral fertilizer increased shoot and root DWs in tomato plants (Table 3). An organo-mineral fertilizer level of 25 g kg - 1 soil was more effective and significantly increased shoot and root DWs as compared to the control. The application of the organo-mineral fertilizer also

Table 3

Effect of the novel organo-mineral fertilizer * application rate on shoot dry weight (DW) plant-[means (n=4)±standard deviations] of 7-week-old tomato plants in both 2009 and 2010 seasons.

root DW plant- 1, leaf free proline and chlorophyll contents

Organo-mineral fertilizer level (g kg-1 soil)

Shoot DW plant-1 (g)

Root DW Plant-1 (g)

Proline content (|igg-1 DW)

Chlorophyll content (mgg-1 FW)

2009 season 0 5 10 15 20 25

6.34±0.56f 8.84±0.69e 11.01 ±0.87d 12.95±0.96c 15.87 ± 1.29b 18.59±1.18a

3.05±0.27e 4.38±0.40d 5.64±0.48c 6.15±0.47c 7.78±0.62b 9.04±0.69a

25.12±0.58c 24.98±0.49c 24.84±0.47c 26.87±0.50c 31.80±0.56b 39.99±0.62a

0.70±0.03e 0.85±0.05d 0.90±0.04d 1.14±0.07c 1.31±0.05b 1.52±0.07a

2010 season 0 5 10 15 20 25

7.01 ±0.65e 8.78±0.81e 10.89±0.89d 13.03±1.22c 16.12±1.46b 18.73±1.58a

3.21±0.31e 5.00±0.47d 6.03±0.49c 6.86±0.54c 7.98±0.72b 9.41±0.78a

27.45±0.49c 28.15±0.56c 26.88±0.53c 26.93±0.54c 33.56±0.49b 40.89±0.55a

0.68±0.05e 0.82±0.05d 0.88±0.07d 1.12±0.06c 1.42±0.08b 1.61±0.08a

In a column, treatment means having a common letter(s) are not significantly different at the 5% level.

* Organo-mineral fertilizer=2:10:1 (w/w/w) calcium suphate, ground rice bran and humic acid.

significantly increased leaf free proline and chlorophyll contents, especially at the rate of 25 g kg 1 soil as compared to the control (Table 3). Similar trends were observed in both the 2009 and 2010 seasons.

3.2. Fruit yield and quality

Results of this study showed that all levels of organo-mineral fertilizer significantly increased the average number of fruit plant-1 and fruit yield pot-1. However, the organo-mineral fertilizer rates of 20 or 25 g kg-1 soil were more effective than all others (Table 4). Using the organo-mineral fertilizer as a soil conditioner led to a significant increase in the yield oftomato fruit as compared to the control over both 2009 and 2010 growing seasons. The application of the organo-mineral fertilizer also

significantly increased vitamin C content, especially at the rate of 25gkg-1 soil (Table 4), whereas TSS% content showed no significant differences between any level of the organo-mineral fertilizer and the control. The same trends were seen in both 2009 and 2010 seasons.

3.3. Nutritional status of the tomato plants

The nutrient content, Na content, and Ca:Na ratio of the tomato leaf are presented in Table 5. Statistically significant differences between the organo-mineral fertilizer treatments were noted for N, K and Ca contents, and Ca:Na ratio. The highest N, K and Ca contents, and Ca:Na ratio were obtained from plants amended with 25 g organo-mineral fertilizer kg 1 soil compared to the control plants. Use of the organo-mineral

Table 4

Effect of the novel organo-mineral fertilizer * application rate on fruit number plant- 1, fruit yield plant- 1, vitamin C and total soluble solids (TSS%) contents [means (n =4) ± standard deviations] of 10-week-old tomato plants in both 2009 and 2010 seasons.

Organo-mineral fertilizer level (g kg- 1 soil)

Fruit number plant

Fruit yield plant 1 (kg)

Vitamin C

(mg 100 g-1 juice)

TSS (%)

2009 season 0 5 10 15 20 25

11.25 ±0.94f 13.21 ±0.98e 15.81 ± 1.29d 18.59± 1.25c 21.12±1.64b 24.43 ± 1.78a

0.51 ±0.04e 0.73±0.05e 1.03±0.08d 1.39±0.08c 1.80±0.12b 2.07±0.15a

18.03±0.09e

22.46±0.12d

23.72±0.11 cd

25.26±0.14c

28.45±0.14b

32.66±0.16a

4.14±0.06a 4.16±0.05a 4.19±0.04a 4.16±0.05a 4.14±0.04a 4.22±0.05a

2010 season 0 5 10 15 20 25

10.96±0.89e 12.65±0.93e 15.33±0.99d 19.00± 1.23c 20.95 ± 1.56b 23.90± 1.49a

0.52±0.06f 0.77±0.05e 1.12±0.09d 1.50±0.09c 1.92±0.11b 2.21±0.16a

17.89±0.06e 21.32±0.09d 24.69±0.08c 26.98±016bc 29.94±0.15b 34.78±0.15a

4.26±0.04a 4.22±0.05a 4.28±0.05a 4.32±0.04a 4.29±0.05a 4.36±0.05a

Table 5

Effect of the novel organo-mineral fertilizer application rate on leaf nutrient and Na contents, and Ca:Na ratio [means (n=4) ± standard deviations] in 7-week-old tomato plants in both 2009 and 2010 seasons.

Organo-mineral fertilizer level N

(gkg-1 soil) (mgg-1 DW)

(mgg-1 DW)

(mgg-1 DW)

(mgg-1 DW)

(mgg-1 DW)

Ca:Na ratio

2009 season 0 5 10 15 20 25

10.24±0.56d

10.66±0.54cd

11.15±0.58bc

11.67±0.53ab

11.77±0.60a

12.09±0.58a

0.15±0.01a 0.15±0.01a 0.14±0.01a 0.16±0.02a 0.15±0.01a 0.16±0.01a

11.32±0.66e

12.00±0.59de

12.90±0.62c

13.46±0.57bc

13.93±0.59ab

14.48±0.58a

5.32±0.18d 5.50±0.16d 6.83±0.21c 7.45±0.19b 8.39±0.16a 8.66±0.14a

21.87±0.88a 18.23±0.89b 14.02±0.34c 8.87±0.32d 6.76±0.22e 4.06±0.19f

0.24±0.01e

0.30±0.01de

0.49±0.02d

0.84±0.03c

1.24±0.05b

2.13±0.08a

2010 season 0 5 10 15 20 25

11.14±0.61f

11.68±0.55ef

12.44±0.63d

12.69±0.58 cd

13.08±0.65bc

14.12±0.56a

0.16±0.02a 0.16±0.01a 0.17±0.01a 0.17±0.02a 0.17±0.01a 0.17±0.01a

11.26±0.58f

11.98±0.61ef

13.08±0.59d

13.56±0.57 cd

14.00±0.59bc

14.98±0.55a

6.02±0.14f 6.27±0.12e 6.89±0.15d 7.38±0.15c 8.24±0.14b 9.12±0.15a

22.13 ±0.96a 19.12±0.75b 15.21 ±0.42c 9.14±0.29d 6.33±0.18e 3.94±0.11e

0.27±0.02f

0.33±0.02ef

0.45±0.03de

0.81±0.03c

1.30±0.06b

2.31±0.08a

In a column, treatment means having a common letter(s) are not significantly different at the 5% level.

* Organo-mineral fertilizer=2:10:1 (w/w/w) calcium suphate, ground rice bran and humic acid.

fertilizer had no effects on the contents of P (Table 5). All levels of the organo-mineral fertilizer significantly reduced the Na contents in the tomato leaf when compared to the control (Table 5). This reflected in the increase in the ratio of Ca:Na in the organo-mineral fertilized-plants compared to the control ones. The same trend was observed in results of both 2009 and 2010 seasons.

3.4. Antioxidant enzyme activity

All levels of the organo-mineral fertilizer increased the activity of catalase (CAT) and polyphenol oxidase (PPO) in tomato leaves (Table 6). An organo-mineral fertilizer level of 25 g kg 1 soil significantly increased CAT and PPO activities as compared to the control. In contrast, the activity of peroxidase

(POX) enzyme reduced with the application of all levels of the organo-mineral fertilizer. The same trend was observed over both 2009 and 2010 seasons.

4. Discussion

The organo-mineral fertilizer used in the current study generated positive findings as a result of overcoming the harmful effects of soil salinity by the Ca2+ (Greenway and Munns, 1980) and humic acid (Osman and Ewees, 2008) presented in this organo-mineral fertilizer. The healthy metabolic status of the stressed plants grown in saline soil applied with the organo-mineral fertilizer resulted in the healthy plant growth, in terms of increased shoot and root dry weights (DWs) (Table 3). The mechanisms by which humic acid stimulated plant growth may

Table 6

Effect of the novel organo-mineral fertilizer application rate on the activity of catalase (CAT), polyphenol oxidase (PPO) and peroxidase (POX) in leaves [means (n=4) ± standard deviations] of 7-week-old tomato plants in both 2009 and 2010 seasons.

Organo-mineral fertilizer level CAT PPO POX

(g kg-1 soil) (Unit mg-1 protein) (Unit mg-1 protein) (Unit mg-1 protein)

2009 season

0 4.3±0.03d 2.4±0.02e 2.3±0.03a

5 4.6±0.02c 2.7±0.01d 2.1±0.03b

10 4.6±0.02c 2.9±0.02c 2.1±0.02b

15 4.7±0.03c 2.9±0.02c 2.0±0.03c

20 4.9±0.03b 3.0±0.01b 1.9±0.02d

25 5.2±0.02a 3.2±0.02a 1.7±0.02e

2010 season

0 3.9±0.02e 2.6±0.02d 2.1±0.04a

5 4.3±0.02d 3.0±0.02c 1.8±0.03b

10 4.5±0.03c 3.0±0.03c 1.7±0.03c

15 4.6±0.03c 3.1±0.02c 1.7±0.03c

20 4.8±0.03b 3.3±0.03b 1.5±0.02d

25 5.1±0.03a 3.5±0.02a 1.4±0.02e

be similar to that of other plant growth regulators such as auxins, gibberellins and cytokinins that affect plant metabolism in a positive manner. This may explain the positive results of the organo-mineral fertilizer on proline and chlorophyll contents under saline soil conditions that were then positively reflected in the growth of tomato plants. Humic acid leads to higher rates of uptake of elemental K (Table 5), thus leads to a corresponding increase in chlorophyll fluorescence which can serve as an indicator of the stress induced by alterations in the balance of endogenous hormones (Marschner, 1995). Proline accumulation under stress conditions may either be caused by induction or activation of enzymes of proline biosynthesis or a decreased proline oxidation to glutamate, decreased utilization of proline in protein synthesis, and enhanced protein turnover (Delauney and Verna, 1993). The increased content of proline has been shown to alleviate salinity-induced oxidative stress by scavenging some of harmful reactive oxygen species (ROS). Therefore, being a hydroxyl and singlet oxygen scavenger, proline has efficiently reduced the threat of ROS in the salts-excess tomato leaves under salinity stress (Rady, 2011). However, the interesting thing that emerged in the present study is that the indirect treatment of plants with the organo-mineral fertilizer (as soil amendment) enhanced the level of proline (Table 3) under salt-stress condition. Therefore, maximum values were recorded in the plants grown in the saline soil amended with the highest levels of the organo-mineral fertilizer (20 and 25 g kg- 1 soil). The acceleration of increased pool of proline resulted in an increase in the capacity of tolerance to salinity in the present study.

The increased tolerance to the salt-stress was manifested in terms of improved growth and photosynthetic pigments (total chlorophyll; Table 3) and the subsequent fruit yield (Table 4). The present investigation also shows that salinity stress caused a significant reduction in the chlorophyll concentration (in the control; Table 3). The decrease in chlorophyll content may be attributed to increased activity of chlorophyll-degrading enzyme chlorophyllase, under stress conditions (Reddy and Vora, 1986) and may by the inhibition of their biosynthesis and consequently may disturb the photosynthetic process. While, soil application with the organo-mineral fertilizer enables plants to overcome the adverse effects of salinity stress and consequently the increase in the content of total chlorophyll positively reflecting in the plant growth (Table 3). All levels of the organo-mineral fertilizer significantly increased the fruit yield of tomato plants due to the higher shoot and root DWs (Table 3), nutrient status of plants (Table 5) and activity of antioxidant enzymes (Table 6).

The favourable tomato yield obtained in our experiments may be due to the positive combined effect of calcium, rice bran and humic acid (the components of the novel organo-mineral fertilizer). Calcium has an antagonistic effect to the harmful effects of Na+, whilst rice bran has high percentage of fibers (Table 1) which improves water retention through their high water holding capacity [7.33 (g g-1)], and can bind organic compounds (Schneeman, 1986). Humic acid (a component of the organo-mineral fertilizer) improves chemical properties of the soil by increasing the soil microorganisms which enhance nutrient status of the tomato plants (Table 5). It also promotes

plant growth by its effects on ion transfer at the root level by activating the oxidation-reduction state of the plant growth medium and so increased absorption of nutrients by preventing precipitation in the nutrient solution. Furthermore, it enhances cell permeability, which in turn made for a more rapid entry of nutrients into root cells and so resulted in higher uptake of plant nutrients (Sayed et al., 2007). Jianguo et al. (1998) found that humic acid application improved the nutritional regulation of plants as indicated by changes in various physiological and biochemical indexes. These effects were associated with the function of hydroxyls and carboxyls in these compounds (Osman and Ewees, 2008). Taken together, these amendments enable plants to overcome the adverse effects of soil salinity.

An organo-mineral fertilizer level of 20 or 25 g kg- 1 soil significantly reduced the Na content. This, increased the ratio of Ca:Na, thus generated more antagonistic effects to the harmful effects of Na+ ions. The organo-mineral fertilizer may acts as a reservoir for nutrients, ensuring slow release to the substrate solution or directly to plant roots. It is a relatively abundant mineral resource (Table 1).

According to our results, antioxidant enzymes activities (Table 6) found to be identical with those reported by Lin and Kao (1999) on rice seedling, Sulochana et al. (2002) on groundnut, Ozturk and Demir (2003) on spinach and Jaleel et al. (2008) on Dioscorea rotundata. The decreased POX seems to indicate that this enzyme does not play a crucial role in defense mechanisms against oxidative stress, or that cooperation is activated between different antioxidant enzymes to establish a proper H2O2 balance when POX activity is reduced by salt toxicity (Chaparzadeh et al., 2004). Reduction of catalase (CAT) activity under salt stress may result in H2O2 accumulation and may be associated with its tolerance mechanism through signal transduction (Shim et al., 2003). The organo-mineralfertilizer, in this study, played an important role in increasing the activity of CAT and polyphenol oxidase (PPO) (Table 6) and consequently a weighty role in defense mechanisms against oxidative stress, especially salinity. This may be due to the fact that this novel fertilizer contains calcium, humic acid and rice bran which have many properties for overcoming the salt-stress effects.

5. Conclusion

Our results have shown that reclaimed saline soil (EC = 8.9 dS m - 1) treated with the novel organo-mineral fertilizer [a 2:10:1 (w/w/w) mixture of calcium sulphate, ground rice bran, and humic acid] significantly increased the growth and fruit yield of tomato plants grown in such soil. The organo-mineral fertilizer-treated plants had higher levels of N+, K+, and Ca2+, and lower levels ofNa+ in their leaf tissues. In addition, it enhanced the levels of proline and chlorophyll, and the activities of antioxidant enzymes (CAT and PPO) under salinity stress conditions. The influence of the organo-mineral fertilizer on proline, chlorophyll and antioxidant enzymes activities was more pronounced under stress situation, suggesting that these parameters, at least in part, increased the tolerance of tomato plants to salinity stress, thus protected the photosynthetic machinery and plant growth.

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Edited by AK Cowan