Role of blue green algae biofertilizer in ameliorating
the nitrogen demand and fly-ash stress to the growth and yield
of rice (
Oryza sativa
L.) plants
R.D. Tripathi
*, S. Dwivedi, M.K. Shukla, S. Mishra, S. Srivastava, R. Singh,
U.N. Rai, D.K. Gupta
Ecotoxicology and Bioremediation Group, National Botanical Research Institute, Rana Pratap Marg, Lucknow 226 001, India
Received 16 March 2007; received in revised form 22 June 2007; accepted 15 July 2007 Available online 12 September 2007
Abstract
Rice is a major food crop throughout the world; however, accumulation of toxic metals and metalloids in grains in contaminated environments is a matter of growing concern. Field experiments were conducted to analyze the growth performance, elemental composition (Fe, Si, Zn, Mn, Cu, Ni, Cd and As) and yield of the rice plants (Oryza sativaL. cv. Saryu-52) grown under different doses of fly-ash (FA; applied @ 10 and 100 t ha 1denoted as FA
10and FA100, respectively) mixed with garden soil (GS) in combination with
nitrogen fertilizer (NF; applied @ 90 and 120 kg ha 1denoted as NF90and NF120, respectively) and blue green algae biofertilizer (BGA;
applied @ 12.5 kg ha 1denoted as BGA
12.5). Significant enhancement of growth was observed in the plants growing on amended soils as
compared to GS and best response was obtained in amendment of FA10+ NF90+ BGA12.5. Accumulation of Si, Fe, Zn and Mn was
higher than Cu, Cd, Ni and As. Arsenic accumulation was detected only in FA100and its amendments. Inoculation of BGA12.5caused
slight reduction in Cd, Ni and As content of plants as compared to NF120amendment. The high levels of stress inducible non-protein
thiols (NP-SH) and cysteine in FA100were decreased by application of NF and BGA indicating stress amelioration. Study suggests
inte-grated use of FA, BGA and NF for improved growth, yield and mineral composition of the rice plants besides reducing the high demand of nitrogen fertilizers.
2007 Elsevier Ltd. All rights reserved.
Keywords: BGA biofertilizer; Fly-ash; Rice; Metal accumulation
1. Introduction
Coal based power plants generate a variety of pollutants along with a huge quantity of fly-ash (FA) that is usually dumped in nearby areas. According to some estimates, in areas situated close to National Thermal Power Plant (NTPC), Unchahar, Raebareli (UP), FA is deposited at a rate of about 52 t km 2month 1 while in distant areas
the rate is about 26 t km 2month 1 (Tripathi, 2001).
Fly-ash is often used as soil amender (Sikka and Kansal,
1995; Gupta et al., 2002; Tripathi et al., 2004; Mittra et al., 2005; Jala and Goyal, 2006) due to its beneficial prop-erties. However, its usage in agriculture and agronomy sec-tor is still limited (<10%) due to concerns about the presence of toxic elements viz., Cd, As and Ni (Carlson and Adriano, 1993; Gupta et al., 2002; Jala and Goyal, 2006). Recent investigations suggest that FA can find better application if combined with organic amendments, nitrogen fertilizers (NF) and blue green algae (BGA) biofertilizer (Rautaray et al., 2003; Tripathi et al., 2004; Rai et al., 2004). Rice (Oryza sativaL.) is one of the most important cere-als for more than half of the world’s population and spec-ulated demand for five billion rice consumers by the year 2030 is to be met from available land and water resources
0045-6535/$ - see front matter 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2007.07.038
* Corresponding author. Tel.: +91 0522 2205831 35x222; fax: +91 0522
2205836/39.
E-mail address:tripathi_rd@rediffmail.com(R.D. Tripathi).
www.elsevier.com/locate/chemosphere
(Khush, 2005). Blue green algae (BGA) are the diverse group of photosynthetic prokaryotes growing frequently in rice fields, which are known to fix atmospheric nitrogen and to convert insoluble phosphorus into soluble form (Irisarri et al., 2001). Fly-ash is rich in boron and deficient in nitrogen. Boron has been found to be essential for nitro-gen fixation by heterocystous BGA strains such as Ana-baena (Mateo et al., 1986; Blevins and Lukaszewski, 1998). Therefore, BGA appear to be a likely candidate for improving nitrogen status in FA contaminated paddy fields. Nitrogen and phosphorus are major limiting factors to plant growth and addition of fertilizers has thus become a common practice to maintain the healthy growth and persistence of crops (Saleque et al., 2004; Lin et al., 2006). In this scenario, it seems worthwhile to study the application of BGA biofertilizer and recommended/modi-fied dose of NF for safe utilization of FA in paddy cultiva-tion and to develop an integrated technology for the farmers to cultivate rice crops in FA affected areas. The field experiments were conducted to analyze effect of differ-ent doses of FA with and without BGA biofertilizer and NF on growth, yield, phytotoxic and tolerance responses of rice (Oryza sativaL.) var. Saryu-52. Metal composition (Fe, Si, Zn, Mn, Cu, Ni, Cd and As) of various plant tissues (roots, leaves, seed husk and grain) was also investigated for securing health safety related to rice consumption.
2. Material and methods
2.1. Collection and analysis of GS and FA amended soil
Un-weathered FA was collected randomly from dump-ing sites of National Thermal Power Plant, Unchahar, Raebareli (UP) in large plastic bags and brought to the lab-oratory. Various physico-chemical properties and metal composition of GS and FA amended soil were analyzed. pH and EC were measured by ion meter (Orion, USA). Water holding capacity was measured by hydrometry. The total nitrogen (N) and potash (K) contents were esti-mated followingJackson, (1973), phosphorus (P) by Olsen method (Jackson, 1967) and organic carbon following
Walkely and Black, (1949). For analysis of metals (Pb, Al, Si, Cr, B, Cu, Mn, Zn, Fe, Ni, Cd and As in GS, FA10 and FA100), GS and FA amended soil were oven
dried at 80C for 24 h and then digested in HNO3: HClO4
(3:1, v/v) at 70C. The digested samples were diluted with
milli-Q water. For estimation of As, samples were prepared and analyzed followingBleeker et al. (2003). Metal concen-trations were determined on the Atomic Absorption Spec-trophotometer (AAS) (GBC, AvantaR). The detection of As was performed on Inductively-Coupled Plasma Spec-trometer, Perkin Elmer (ICP Optima 3300 RL, USA).
2.2. Experimental setup and treatments
The field experiment was conducted to investigate the effect of different concentration of FA on paddy crop.
Previously, we have screened three cultivars of rice i.e. Saryu-52, Sabha-5204 and Pant-4 for their tolerance to FA toxic-ity and found Saryu-52 and Sabha-5204 to possess higher tolerance to FA as compared to that of Pant-4 (Dwivedi et al., 2007). Based on the fact that Saryu-52 is being culti-vated in a larger area, this present investigation was carried out employing Saryu-52 cultivar. Rice plants were sown in randomized block design in plots of 2 m2size at field labo-ratory of Environmental Science division, NBRI. A total of twelve amendments of GS and FA (applied @ 10 t ha 1 and 100 t ha 1, separately) were prepared with and without urea (NF; applied @ 120 and 90 kg ha 1, separately) and BGA biofertilizer (applied @ 12.5 kg ha 1) viz., T1 (GS),
T2 (GS + NF120), T3 (GS + BGA12.5), T4 (GS + NF90+
BGA12.5), T5 (FA10), T6 (FA10+ NF120), T7 (FA10+
BGA12.5), T8 (FA10+ NF90+ BGA12.5), T9 (FA100), T10
(FA100+ NF120), T11 (FA100+ BGA12.5), T12 (FA100+
NF90+ BGA12.5). Each treatment was applied to three
dif-ferent plots. Fly-ash was applied to GS before paddy trans-plantation. The N, P and K were supplied in the form of NF, single super phosphate (SSP) and muriate of potash @ 120, 60 and 40 kg ha 1, respectively. NF was applied
@ 120 kg ha 1 when BGA biofertilizer was not applied, while in amendments with BGA biofertilizer, amount of urea was reduced to 90 kg ha 1. Fifty percent of urea was applied at the time of transplantation, 25% at the time of tillering stage and remaining 25% was applied at the time of panicle initiation stage, while phosphorus and potash were applied in full dose at the time of transplanting. Seeds were sown in GS for germination and 25 d old seedlings were transplanted in prepared plots at a spacing of 20·15 cm2 between rows and columns. Ideal conditions
for growth were maintained by providing shallow level of submergence (6 ± 2 cm) throughout the growth period.
2.3. BGA biofertilizer production and application
The BGA strains namelyNostocsp., Anabaena doliolum, Calothrixsp., Westiellopsis sp. andPhormidium papyrace-um were isolated from FA dumping sites near NTPC, Unchahar. After their identification as described previously (Dwivedi et al., 2006), they were grown independently under controlled culture conditions (115lmol m 2s 1 light with 14 h photoperiod at 25 ± 2C). For mass
pro-duction, a mixture of these strains was developed at BGA biofertilizer production center at Bakshi Ka Talab, Luc-know with cooperation of Biotechnology cell, Uttar Pra-desh Council of Science and Technology (UPCST), Lucknow. The dried flakes of BGA biofertilizer were applied under waterlogged condition in GS and FA amended plots after seven days of transplantation.
2.4. Growth and yield of rice crop
were uprooted carefully from soil and different plant parts viz., roots, leaves and panicles were separated. After sepa-rating grains and straw, their weights were measured for each plant. Roots were washed thoroughly to remove soil particles and after blotting, their weight was measured. Leaves were washed with ddw to remove adhering dust particles and were used for analysis of various parameters.
2.5. Photosynthetic pigments, protein, cysteine and non-protein thiols
The level of chlorophylls and carotenoid was estimated by the method of Arnon, (1949) and Duxbury and Yentsch, (1956), respectively. Protein content was esti-mated following the method ofLowry et al. (1951) using serum albumin as the standard protein. Estimation of cys-teine was performed by following the method ofGaitonde, (1967) by reaction with acid ninhydrin reagent. Non-protein thiols (NP-SH) were measured following the method ofEllman, (1959)using GSH as standard.
2.6. Metal analysis in various plant parts
For analysis of metals (Fe, Si, Zn, Mn, Cu, Ni, Cd and As) in plant samples, root, leaves, seed husk and seeds of plants were oven dried at 80C for 24 h and then digested
in HNO3: HClO4(3:1, v/v) at 70C. The digested samples
were diluted with milli-Q water. For estimation of As, sam-ples were prepared and analyzed following Bleeker et al. (2003). Metal concentrations were determined on the Atomic Absorption Spectrophotometer (AAS) (GBC, AvantaR). The detection of As was performed on Induc-tively-Coupled Plasma Spectrometer, Perkin Elmer (ICP Optima 3300 RL, USA).
2.7. Quality control and quality assurance
The standard reference material of metals (E-Merck, Germany) was used for the calibration and quality assur-ance for each analytical batch. Analytical data quality of metals was ensured through repeated analysis (n= 6) of EPA quality control samples (Lot TMA 989) and the results were found to be within ±2.79% of certified values. Recoveries of metals from the plant tissues were found to be more than 98.5% as determined by digesting three sam-ples each from an untreated plant with known amount of metals. The blanks were run in triplicate to check the pre-cision of the method with each set of samples. The detec-tion limit of Cu, Mn, Zn, Fe, Ni, Pb, Cd, Al, Si, B, Cr, and As were 0.001, 0.02, 0.005, 0.02, 0.02, 0.06, 0.013, 0.028, 0.012, 0.001, 0.012 and 0.001 ppm, respectively.
2.8. Statistical analysis
Two-way analysis of variance (ANOVA) was done with all the data to confirm the variability of data and validity of results, and Duncan’s multiple range test (DMRT) was performed to determine the significant difference between treatments (Gomez and Gomez, 1984).
3. Results
3.1. Physico-chemical analysis and metal composition of GS and FA amended soil
The analysis of various physico-chemical properties and metal composition of GS and FA amended soil has been pre-sented inTable 1. pH of GS was slightly acidic, while pH of FA amended soils was in alkaline range. Water holding
Table 1
Physio-chemical properties and metal composition of GS and FA amended soil
S.N. Parameters Garden soil FA (@10 t ha 1) FA (@100 t ha 1)
1 pH 6.81 ± 0.36 7.68 ± 0.31 7.84 ± 0.19
2 Electrical conductivity (ls m 1) 740 ± 27 610 ± 26 490 ± 41
3 Water holding capacity (%) 43.53 ± 4.02 48.32 ± 3.63 73.36 ± 5.11
4 Total nitrogen (%) 1.183 ± 0.33 0.806 ± 0.16 0.676 ± 0.21
5 Total phosphorus (%) 0.028 ± 0.041 0.067 ± 0.004 0.75 ± 0.046
6 Total potassium (%) 0.22 ± 0.006 0.32 ± 0.011 0.98 ± 0.013
7 Organic carbon (%) 1.96 ± 0.061 1.26 ± 0.041 0.97 ± 0.022
8 Metals (lg g 1dw)
Cu 27.40 ± 2.12 36.63 ± 2.13 42.63 ± 1.89
Mn 51.70 ± 3.06 61.08 ± 2.11 67.97 ± 3.06
Zn 22.60 ± 0.91 42.08 ± 3.50 65.88 ± 4.33
Fe 2942.00 ± 210.00 3450.02 ± 76.07 3976 ± 32.13
Ni 11.93 ± 1.07 17.11 ± 2.82 19.67 ± 0.59
Cd 0.45 ± 0.01 1.06 ± 0.25 1.87 ± 0.053
Pb 2.61 ± 0.41 4.16 ± 1.46 5.08 ± 0.13
B <0.004 6.11 ± 2.08 18.06 ± 0.86
Al 455 ± 18 752.60 ± 252.00 1263 ± 8.36
Si 446.00 ± 24.00 808.00 ± 312.00 1734 ± 4.91
As 0.050 ± 0.001 0.091 ± 0.008 0.118 ± 0.003
Cr 6.06 ± 1.01 8.19 ± 1.3 9.23 ± 0.073
capacity, total phosphorus and potassium were higher, while electrical conductivity, total nitrogen and organic car-bon were lower in FA amended soils than GS. Level of all the investigated metals was low in control (GS) plants that increased with increase in dose of FA to GS.
3.2. Metal composition of plants
3.2.1. Essential micronutrients (Fe, Si, Zn, Mn and Cu)
Accumulation of Fe and Si (Figs. 1 and 2) in all plant parts increased gradually in various GS, FA10 and FA100
amendments reaching to the maximum level in FA100+ NF90+ BGA12.5. Level of Zn in all plant parts
(Figs. 1 and 2) showed increase in various GS and FA10
amendments. In FA100, level of Zn decreased significantly
in roots, seed coat and seeds, which was restored to control level or significantly higher than that upon NF plus BGA application. Level of Mn also showed similar trend with increase in various GS amendments upon application of NF plus BGA (Figs. 1 and 2). In FA10 and FA100, Mn
declined significantly lower than control in all plant parts
except at FA10 in leaves, however application of NF plus
BGA effectively restored the Mn level to either control lev-els or significantly higher than that. Level of Cu increased significantly upon application of NF to either of GS, FA10
or FA100; however BGA application reduced this
aug-mented level close to control. In FA100, the Cu level
declined significantly lower than control in all plant parts except root and this reduced Cu content was restored to control level or higher than that upon application of NF plus BGA (Figs. 3 and 4).
3.2.2. Toxic metals/metalloid (Cd, Ni and As)
Accumulation of Ni in various amendments was found to be maximum in leaves followed by roots, seed husk and grains while that of Cd was maximum in roots and minimum in grains. Accumulation of both the metals was higher in FA amendments than in GS amendments. Addi-tion of BGA12.5 to GS, FA10 or FA100 produced slight
decline in content of both Ni and Cd, however it remained higher than control in all plant parts (Figs. 3 and 4). Arsenic was not accumulated in detectable levels in GS
f
and FA10 amendments and very low accumulation of As
was observed only in FA100and its amendments with the
maximum being in FA100+ NF120 for all plant parts viz.,
root (0.09lg g 1dw), leaves (0.05lg g 1dw), seed husk (0.0095lg g 1dw) and seeds (0.0077lg g 1dw). Applica-tion of BGA12.5 further reduced the As accumulation
(Table 2).
3.3. Growth and yield attributing characters
All the growth parameters viz., root biomass, plant height, number of tillers, grain and straw weight, exhibited similar response to various ameliorants. Application of NF and BGA to GS significantly enhanced the growth of the plants. Growth of plants was significantly higher in all FA10 amendments (the maximum in FA10+ NF90+
BGA12.5) than GS amendments. In FA100, growth of plants
was severely affected. This suppressed growth was restored to higher than control levels upon application of NF plus BGA (Fig. 5).
3.4. Photosynthetic pigments and protein
Application of NF and BGA to GS did not result in any significant change in the level of pigments and protein, however their application to FA10 resulted in a higher
increase with the maximum being in FA10+ NF90+
BGA12.5 i.e., total chlorophyll (44%), carotenoid (34%)
and protein (14%). Plants grown in FA100 showed least
level of the pigments and protein with decrease in chloro-phyll a, b,total chlorophyll, carotenoid and protein being 30%, 61%, 48%, 65% and 20%, respectively than that of control. Application of NF plus BGA to FA100 produced
significant increase in pigment and protein level in compar-ison to their levels at FA100, however not significantly
higher than control (Fig. 6).
3.5. Effect on level of cysteine and non-protein thiols
Cysteine and NP-SH (Fig. 6c) showed a similar trend and level of both cysteine and NP-SH increased slightly
a
upon application of NF and BGA to GS. At FA10 and
FA100, their level was significantly higher than control
however this induced level declined gradually upon appli-cation of NF or BGA separately and approached control levels in amendment of NF90 plus BGA12.5(Fig. 6).
4. Discussion
Rice is one of the major food crops throughout the world; however increasing pollution of land by different contaminants including FA is reducing its cultivable area and is also affecting the growth and yield of the plants (Dwivedi et al., 2007). In addition, the threats associated with accumulation of heavy metals in rice grains are of con-cerns to humans (Meharg, 2004; Tripathi et al., 2007). In a previous study, we found that some of the rice cultivars viz., Saryu-52 are more tolerant to FA toxicity and accu-mulate less amount of toxic metals (Dwivedi et al., 2007). Hence this present investigation was conducted to further analyze the effects of FA to this variety and to explore
the possibility to use it in proper combination with NF and BGA biofertilizers, for increasing the growth and pro-ductivity of plants by harnessing its beneficial properties (Carlson and Adriano, 1993; Gupta et al., 2002; Jala and Goyal, 2006). Rice plants showed enhanced growth in var-ious amendments of GS and FA10. A similar trend was
noticed for photosynthetic pigments and protein. This response may be attributed to higher availability of many essential nutrients e.g. Fe, Cu, Mn and Zn in FA than GS, which were accumulated to higher levels in the plants growing in various FA amendments than in control plants. These micronutrients are required for optimum functioning of photosynthesis at various levels and their increased accumulation may positively affect the photosynthetic effi-ciency of plants and in turn the growth (Dwivedi et al., 2007). In addition, there was significant increase in Si accu-mulation by plants in various amendments in comparison to control (GS) plants. Fly-ash appears to serve as the high source of Si, which in turn increases the resistance of rice plants to pathogens and water logging (Lee et al., 2006).
a
Addition of FA at lower doses also improves physical, chemical and biological properties of soil and has been demonstrated to result in enhanced growth of a number of plants (Gupta et al., 2002; Jala and Goyal, 2006). FA amended soils in this study showed higher water holding capacity, phosphorus and potassium contents which would have provided better growth conditions to the plants. Application of BGA biofertilizer improves N status of
paddy soil through fixation of atmospheric nitrogen that was evident in this study as in various amendments, NF requirement is reduced to 90 kg ha 1 from 120 kg ha 1 when BGA12.5 was also applied. Blue green algae have
mucilaginous sheath and can show significant adsorption of the metals like Cd and metalloids like As (Tien, 2002) in addition to their absorption, thus reducing the toxic effects of these metals (Rai et al., 2004). At the same time
b
Fig. 4. Accumulation of Cu, Ni and Cd in seed coat (a) and seeds (b) of rice variety Saryu-52 grown in various amendments of garden soil (GS), fly-ash (FA), chemical fertilizer (NF) and blue green algae biofertilizer (BGA). All values are mean ± SD;n= 9. ANOVA significant atp60.01. Different letters indicate significantly different values for a particular metal (DMRT,p60.05). T1(GS), T2(GS + NF120), T3(GS + BGA12.5), T4(GS + NF90+ BGA12.5), T5 (FA10), T6 (FA10+ NF120), T7 (FA10+ BGA12.5), T8 (FA10+ NF90+ BGA12.5), T9 (FA100), T10 (FA100+ NF120), T11 (FA100+ BGA12.5), T12 (FA100+ NF90+ BGA12.5).
Table 2
Accumulation of As in different plant parts of rice plants grown in different amendments of GS, FA, NF and BGA
Treatment As (lg g 1dw)
Roots Leaves Seed husk Seeds
T9 0.08b± 0.002 0.04b± 0.001 0.009a± 0.0023 0.0073a± 0.001
T10 0.09a± 0.0022 0.05a± 0.0008 0.0095a± 0.0016 0.0077a± 0.002
T11 0.05c± 0.001 0.02c± 0.0009 0.0065a± 0.001 0.006a± 0.001
T12 0.088a± 0.0011 0.02c± 0.001 0.0072a± 0.0011 0.0061a± 0.0015
they increase availability of essential micronutrients like Fe and P. Application of BGA has been demonstrated to increase the productivity of crops like rice (Yanni, 1992), wheat (ABD-All et al., 1994) and leguminous plant, Pros-opis juliflora(Rai et al., 2004). Higher level of proteins in various amendments may be attributed to induction of stress proteins including antioxidant enzymes to cope up with ROS, and metal chelating ligands like metallothione-ins (MTs) as a homeostatic mechanism and detoxification strategy (Dwivedi et al., 2007; Grill et al., 2006). However, at higher doses detrimental effects on plant growth are observed (Gupta et al., 2002) as noticed in the present study where growth at FA100 was hampered. However,
the combined application of NF plus BGA ameliorated the FA toxicity and restored the growth of plants.
Increase in NP-SH content is suggestive of increase in thiols viz., cysteine, glutathione and phytochelatins (PCs). These thiols play a major role in the maintenance of redox status of the cell as well as in the binding of metal ions for their detoxification. Level of cysteine also significantly increased in plants grown in different amendments. This
increase is attributed to an increase in the whole S assimi-lation pathway (Rausch and Wachter, 2005; Herbette et al., 2006). Thiolic compounds show positive correlation with accumulation of metals. The levels of both cysteine and NP-SH was found to be maximum in FA100, which
decreased to approach control levels in FA100+ NF90+
BGA12.5, indicating that stress caused by accumulation of
Cd and As, significant inducers of thiols, in FA100 was
relieved by application of BGA, which was also evident by improved growth of plants.
Increased accumulation of metals like Si, Zn, Mn, Fe, Cu, Ni and Cd is attributed to their higher levels as well as to greater availability in FA amendments as compared to GS. Metals like Fe, Zn, Cu, Mn, Ni and Cd have been shown to be available at higher concentrations in DTPA extracts of FA than in that of GS (Gupta et al., 2007). The increased accumulation of essential ions such as Zn, Mn and Cu by the paddy shoot/grain might be due to increased activity of ionic transporters (Hall and Williams, 2002), in turn due to higher essential ion availability in the FA. Silica has many essential roles in rice plants and high
e
Root biomass Number of Tillers Plant Height
de
Si content is considered necessary for healthy growth of rice plants (Ma et al., 2002). FA is considered to be a rich source of Si and application of FA in Si-deficient soils has been demonstrated to improve the Si content of rice plants as well as their growth (Lee et al., 2006). Iron is a cofactor of various proteins that are involved in redox reactions. High potential of rice plants for Si and Fe accumulation has been previously demonstrated (Dwivedi et al., 2007).
The low content of As in FA and its low availability due to high pH of FA (Huang et al., 2006) probably resulted in its low accumulation by the plants only at high FA doses. Further, the accumulation of As decreased to some extent upon BGA application, which might be attributed to accumulation of As by BGA or due to dilution of metalloid due to increased biomass. Nickel was accumulated in higher amount in leaves indicating its efficient transport
a
Chl a Chl b Total Chl Carotenoid
bc
from root-to-shoot probably via histidine chelation ( Kra¨-mer, 2005). Cadmium showed higher retention in roots, which might be attributed to efficient chelation with ligands like PCs and sequestration in root vacuoles that prevented its higher translocation to leaves. In seeds, the observed maximum level of Cd (0.96lg g 1dw), As (0.0077 lg g 1dw) and Ni (2.42lg g 1dw) was not alarming (Williams et al., 2005; Dwivedi et al., 2007) considering the human consumption of rice grains (Mittra et al., 2005). In conclusion, application of FA at lower dose (10 t ha 1) seems beneficial for growth of paddy plants when combined with proper dose of BGA (12.5 kg ha 1). Further, BGA application reduced the NF requirement by 30 kg ha 1, thus use of BGA might prove an economical strategy in paddy cultivation. Besides enhancing the growth, it also improved composition of essential micronu-trients while the level of toxic metals was maintained under safe limit in FA amendments. It may be worthwhile to cul-tivate Saryu-52 variety of rice in FA contaminated areas with balanced doses of BGA and to optimize low exoge-nous NF input for improved yield and grain fortification with trace elements. However, future research is needed to analyze the growth and yield of rice plants in contami-nated areas under field conditions.
Acknowledgements
Authors are thankful to Dr. Rakesh Tuli, Director, Na-tional Botanical Research Institute, Lucknow for support and encouragements. This work was supported by grant from Uttar Pradesh Council of Science and Technology, Lucknow and from one of Institutional Research Project. Award of RA to SD is gratefully acknowledged. S.M. and S.S. are grateful to Council of Scientific and Industrial Research, New Delhi for the award of Junior Research Fellowships.
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