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Effects of impulse drip irrigation on root response of aerobic rice.

Introduction

'Aerobic rice culture' is an emerging cultivation system aiming to maximize crop water productivity by growing plants in aerobic soil without flooding or puddling (Matsuo and Mochizuki, 2009). Rice plants under aerobic systems undergo several cycles of wetting and drying conditions (Matsuo and Mochizuki, 2009). Rice performance in aerobic culture might be improved through manipulation that promotes lateral root branching and rhizogenesis as well as deep rooting (Kato and Okami, 2011). Wasteful and harmful system of flood irrigated rice cultivation practiced widely in South Asia must be replaced with furrow, drip or sub-irrigation systems (Aujla et al., 2007). Karlberg et al. (2007) reported that two low-cost drip irrigation systems with different emitter discharge rates were used to irrigate tomatoes and concluded that combination of drip systems with plastic mulch increased the yield. Aerobic rice could be successfully cultivated with 600 to 700 mm of total water in summer and entirely on rainfall in wet season (Shailaja, 2007). Aerobic rice varieties will possess large numbers of spikelets and sufficient adaptation to aerobic conditions such that they will consistently achieve yields comparable to the potential yield of flooded rice (Kato et al., 2009). Considering the above, objectives of DS 2011 study were set out to study the performance of aerobic rice, optimize the lateral distance and discharge rate. In SS 2012, the objectives were to compare the performance of sub-surface drip (SDI) and surface drip irrigation methods and discharge rate for better water productivity, root growth and yield response.

Materials and Methods

Field experiment was conducted during Dry Season 2011 (DS 2011) and Summer Season 2012 (SS 2012) in the wetlands of Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu, India situated at 11[degrees] N latitude, 77[degrees] E longitude and at an altitude of 426.72 m above Mean Sea Level. Randomized Block Design was adopted with three replications using ADT (R) 45 as the test variety. Drip irrigation was given through PVC pipe (40 mm OD) by 7.5 HP motor and pressure maintained was 1.2 kg [cm.sup.-2]. From the sub-main, in-line laterals were laid at a spacing of 0.6 m, 0.8 m and 1.0 m with 0.6 or 1.0 lph discharge rate, emitters positioned at a distance of 30 cm. Irrigation was given based on the Open Pan Evaporation (PE) values (125% PE). The physiochemical properties of the soil samples from the experimental site were analyzed and furnished (Table 1).

Weather prevailed during cropping season was observed in Agromet Observatory in Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu, India. The average values for maximum temperature were 30.9 [degrees]C, 34.2 [degrees]C, minimum temperature of 22.7 [degrees]C, 23.3 [degrees]C, sunshine hours of 5.4, 7.3 hrs [day.sup.-1] and total evaporation was 628.3 and 750.4 mm with the total precipitation of 532.7 and 118.6 mm during DS 2011 and SS 2012 respectively.

In Dry Season (2011), there were eleven treatments employing three lateral distances (LD) and two discharge rates of emitters. The treatments were: LD of 0.6 m with the spacing of 20 x 10 cm ([T.sub.1]), LD of 0.6 m, spacing between rows of plants from lateral (20x10x10x20) (instead of three rows of 20 cm each) ([T.sub.2]), LD of 0.8 m, spacing of 20 x10 cm ([T.sub.3]), LD of 0.8 m, spacing between rows of plants from lateral (5x20x30x20x5) (instead of four rows of 20 cm each) ([T.sub.4]), LD of 1.0m, spacing of 20 x 10 cm ([T.sub.5]), LD of 1.0 m, spacing between rows of plants from lateral (7.5x15x15x empty bed (25 cm) x15x15x7.5) (instead of five rows of 20 cm each) ([T.sub.6]), LD of 0.8 m, spacing of 20 x 10 cm + 30% more water ([T.sub.7]), LD of 1.0 m, spacing of 20 x 10 cm + 30% more water ([T.sub.8]), LD of 0.8 m, spacing between rows of plants from lateral (5x20x30x20x5) (instead of four rows of 20 cm each) with 0.6 lph drippers ([T.sub.9]), LD of 1.0 m, spacing between rows of plants from lateral (7.5x15x15x empty bed (25 cm) x15x15x7.5) (instead of five rows of 20 cm each) with 0.6 lph drippers ([T.sub.10]).

In SS 2012, there were ten treatments employing two discharge rates and two irrigation methods (Surface and subsurface laterals). The treatments were LD of 0.8 m, row spacing of 20 cm with dripper flow rate 1.0 lph SDI ([T.sub.1]), LD of 0.8 m, row spacing of 20 cm with dripper flow rate 0.6 lph SDI ([T.sub.2]), LD of 0.8 m, row spacing of (5x20x30x20x5) cm with dripper flow rate 1.0 lph SDI ([T.sub.3]), LD of 0.8 m, row spacing of 20 cm with dripper flow rate 1.0 lph on surface ([T.sub.4]), LD of 0.8 m, row spacing of 20 cm with dripper flow rate 0.6 lph on surface ([T.sub.5]), LD of 0.8 m, row spacing of 20 cm with dripper flow rate 1.0 lph + 30% more water on surface ([T.sub.6]), LD of 0.8 m, row spacing of (5x20x30x20x5) cm with dripper flow rate 1.0 lph + 30% more water on surface ([T.sub.7]), Irrigation according to lysimeter (20% drainage at depth of 60 cm from surface) ([T.sub.8]), LD of 0.8 m, row spacing of 20 cm with dripper flow rate 1.0 lph SDI + 150 kg [K.sub.2]O [ha.sup.-1] ([T.sub.9]) and conventional irrigation at IW/CPE ratio of 1.25 at 30 mm depth of irrigation (conventional irrigation) ([T.sub.10]). Regarding the crop management aspects, recommended cultivation practices were followed. Fertilizer dose of 150:50:50 kg [ha.sup.-1] NPK in the form of water-soluble fertilizers was supplied through fertigation by the ventury flume at a rate of weekly interval splits.

To measure the root growth, roots were removed carefully from the soil without damaging the roots. Randomly selected ten roots were weighed and their length was measured and totaled. Total root length was calculated by total root length (m [hill.sup.-1]) = (Length of sample roots (cm) x Weight of total roots (g)) / Weight of sample roots (g). The volume of the root was measured by volume displacement method (Bridgit and Potty, 2002) and expressed as root volume (cc) [hill.sup.-1]. The Root Mass Density (RMD) was measured and expressed as mg [cm.sup.-3] (Pantuwan et al. 1997). Root biomass values were expressed as g [m.sup.-2]. The yield and its components were recorded at the time of harvest. The number of panicles, number of spikelets, filled grain percentage, 1000 grain weight (Test weight), Harvest Index (HI) were recorded based on the method of Yoshida et al. (1971). Grain yield per hectare was expressed in kg [ha.sup.-1] at 14% moisture content. Water productivity was calculated by the formula of Yang et al. (2005) and expressed as g grain [kg.sup.-1] of water. The recorded data were subjected to statistical analysis in the Randomized Block Design (RBD) using ANOVA Package (AGRES version 7.01) following the method of Gomez and Gomez (1984).

Results and Discussion

The effects of micro irrigation treatment on root parameters of aerobic rice showed significant relation between treatments. Increased root length was recorded in treatment [T.sub.3] (50.7 m [hill.sup.-1]) and lesser in [T.sub.10] (41.8 m [hill.sup.-1]) at DS 2011(Table 2). The root length was increased in 0.8 m lateral distance than 0.6 and 1.0 m lateral distances. In SS 2012, the maximum root length was observed in [T.sub.6] (34.0 m [hill.sup.-1]) and the lowest in [T.sub.10] (28.4 m [hill.sup.-1]). Root length recorded more in surface drippers with 30% excess water treatment ([T.sub.6]) over SDI ([T.sub.1]). Increase in root length under aerobic situation may be an added advantage to combat stress under water limitation. Constitutively, shallow rooting and sensitive responses of rhizogenesis and lateral root branching to unsaturated soils are the main reason for limited adaptability to water-saving aerobic culture (Kato and Okami, 2011) by using the low discharge rate drippers.

The distribution of Root Mass Density (RMD) is an important indicator of the potential of water and nutrient uptake. Higher RMD was observed in [T.sub.3] of DS 2011 (Table 2). Optimum lateral spacing (0.8 m lateral distance) showed better RMD because of better water and nutrient application. Present results was also corroborated with Matsuo and Ozawa (2010) showing variation in availability of nutrients change the RMD in aerobic genotypes. Increased RMD was observed in drip irrigation treatments ([T.sub.6] and [T.sub.1]) in SS 2012. Higher RMD in SDI than surface DI treatment was due to better accessibility of nutrients and water to the roots. Similar result was observed by Zotarelli et al. (2009) in tomato with SDI.

Significantly higher root volume was observed in treatment [T.sub.3] (49.9 cc [hill.sup.-1]) and least by [T.sub.1]1 (26.2 cc [hill.sup.-1]) during DS 2011. In SS 2012, higher root volume in [T.sub.6] (26.6 cc [hill.sup.-1] cc [hill.sup.-1]) and lower in Tw (22.7 cc [hill.sup.-1]). During DS 2011, higher root biomass was noticed in [T.sub.3] (209.2 g [m.sup.-2]) and lesser in [T.sub.10] (124.5 g [m.sup.-2]) (Table 2). By comparing [T.sub.1], [T.sub.3] and [T.sub.5] treatments, increase in lateral distance from 0.6m to 1.0 m, caused reduction in water availability to the root zone. Therefore, root biomass is reduced in aerobic culture primarily on account of fewer adventitious roots (Kato and Okami, 2010). Comparing the discharge rates, 1.0 lph discharge emitter recorded 11.4% increase in root biomass over 0.6 lph emitters. In SS 2012, increased root biomass was observed in treatment [T.sub.6] than conventional aerobic rice ([T.sub.10]). Increase in root biomass under water stress might be an adaptive mechanism for reduction in water uptake as a result of extra root growth. Present study was in accordance with the findings of Kato and Okami (2011) in aerobic rice. Increased number of panicles was observed in treatment [T.sub.3] (681.4 panicles [m.sup.-2]) and lesser in [T.sub.10] (581.9) during DS 2011 (Table 3). In SS 2012, higher in [T.sub.6] (623.0 panicles [m.sup.-2]) and lesser in [T.sub.10] (421.5). In DS 2011, number of spikelets per panicles recorded more in treatment [T.sub.3] (142.6) and very less in [T.sub.10] (95.4) (Table 3). During SS 2012, more number of spikelets was observed in [T.sub.6] (140.0) than other treatments. Increasing the number of spikelets should be a primary target, as this had helped to increase the yield of rice even under water limitation (Peng et al., 2008). The Filled Grain Percentage (FGP) showed significantly superior in treatment [T.sub.3] (89.0%) and least in [T.sub.10] (71.1 %) (Table 3) at DS 2011. In SS 2012, higher filling percentage observed in [T.sub.6] (90.0%) and lesser in [T.sub.10] (81.2 %). The reduction in spikelet production under reduced water supply might be due to the abortion of spikelets in the secondary rachis branch, as documented by Kato et al. (2008) in aerobic rice. In SS 2012, the micro irrigation treatments showed a significant difference for grain test weight. Higher grain test weight was observed in [T.sub.6] (21.73 g) with lower in [T.sub.10] (20.18 g). Reduction in test weight was due to poor translocation of assimilates causing reduction in filling. Present result was in corroborated with Suriyan et al. (2010) in rice.

The Harvest Index (HI) was higher in [T.sub.3] (42.8%) and lesser in [T.sub.9] (38.8%) (Table 3) during DS 2011. Higher HI values leading to increased contribution for yield increment. Water management system could increase growth rate during grain growth and/or enhanced the remobilization of assimilates from vegetative tissues to grains during the grain-filling period usually leading to a higher HI within a crop (Ju et al., 2009). In SS 2012, higher HI was recorded for treatment [T.sub.1] (38.8%) and lower for [T.sub.10] (35.6%). The ability to maintain a higher HI under aerobic conditions has also been reported to be a key factor to higher yields by Lafitte et al. (2002). Significantly higher grain yield was registered in [T.sub.3] treatment (5793 kg [ha.sup.-1]) followed by [T.sub.1] (5554 kg [ha.sup.-1]) with the lower yield as observed in [T.sub.10] (3819 kg [ha.sup.-1]) during DS 2011. Optimal lateral spacing (0.8 m) was reasoned out for such an increase in yield resulting in increased Water Use Efficiency than the wider (1.0 m) or narrower (0.6 m) lateral spacing. The present study is in confirmation with previous work of optimum lateral spacing registering higher maize yield in Turkey (Bozkurt et al., 2006). During SS 2012, higher grain yield was recorded in [T.sub.6] treatment (4249 kg [ha.sup.-1]) and lower yield in [T.sub.10] (3523 kg [ha.sup.-1]). Superior grain yield were obtained in excess water application (30% more water) by surface drip and closely followed subsurface drip than conventional aerobic treatments. Crops were irrigated by subsurface drip irrigation; yields were equal to or greater than those obtained by surface drip. These results corroborated with the findings of Singh et al. (2006). Treatment [T.sub.6] resulting higher yield is supported by increased yield components and better HI. These results were in accordance with the study of Viraktamath (2006). Comparing the discharge variability among two seasons, the 1.0 lph drippers performed better over conventional irrigation treatment as well as 0.6 lph dripper treatments.

The total water applied (TWA) to the crop through the irrigation plus effective rainfall (ER) for the entire growing season was 547 mm in treatment [T.sub.1], [T.sub.2], [T.sub.3], [T.sub.4], [T.sub.5], [T.sub.6], [T.sub.9], [T.sub.10], 631.5 mm for [T.sub.7] [T.sub.8] and 697.9 mm for [T.sub.1]1 treatment (Table 4) during DS 2011. Total water applied to the crop was comparatively lesser in drip irrigation than the conventional irrigation method of aerobic rice in the current study. There was a mean saving of 21.55% of water when applied through the drip system than conventional aerobic cultivation. In SS 2012, total water applied to the crop for the entire growing season was 647 mm for treatments [T.sub.1], [T.sub.2], [T.sub.3], [T.sub.4], [T.sub.5] and [T.sub.9], 692 mm in [T.sub.8] 841 mm in [T.sub.6] [T.sub.7] and 824 mm in case of [T.sub.10]. There was a mean saving of 21.47% of water when applied through the drip system and 15.97% of water when followed by the lysimeter irrigation treatment than the conventional aerobic cultivation. Similar results were obtained in the present study reitareating the results of Bouman et al. (2007). The Water Productivity (WP) is a measure of the productivity of water used by the crop. During DS 2011, higher WP was recorded in [T.sub.3] (1.059 g [kg.sup.-1]) and [T.sub.2] (0.974 g [kg.sup.-1]) (Table 4). The treatment [T.sub.3] recorded a higher value of 1.6 times more water productivity compared to [T.sub.1]1 treatment with 54.4% reduction in water use in the former comparing the conventional irrigation method. In SS 2012, higher water productivity was recorded in [T.sub.1] (0.64 g [kg.sup.-1]) and lower in [T.sub.10] (0.43 g [kg.sup.-1]). The results followed the study of Guang-hui et al. (2008) with 60% lesser water use coupled with 1.6-1.9 times higher total water productivity in the present study.

Conclusion:

From the research findings of DS 2011 revealed that, 0.8 m lateral distance was adjusted as optimum lateral spacing due to better crop performance and yield. Treatment [T.sub.3] (lateral spacing of 0.8 m with 1.0 lph dripper discharge rate) registered superior performance in terms of root parameters, yield and its components along with increased Water Productivity. The research findings of SS 2012 revealed that the subsurface irrigation (SDI) recorded better performance in terms of yield and WP. The treatment [T.sub.6], dripper flow rate 1.0 lph surface drip irrigation under 0.8 m lateral distance along with 30% excess water treatment outperformed all the other treatments in terms of improvement in root traits (higher root length, RMD, root biomass and root volume) yield and its components except WP, but treatment [T.sub.1] (dripper flow rate 1.0 lph Subsurface Drip Irrigation under 0.8 m lateral distance) performed good in terms of root characters, yield and its components along with increased WP values. Comparing the discharge variability effect of two experiments, 1.0 lph dripper outperformed 0.6 lph dripper in terms of root traits, water productivity, yield and its components. So, drip system with lateral spacing of 0.8 m with 1.0 lph drippers with SDI could be recommend for aerobic rice cultivation for the areas with limited water availability.

Acknowledgement

First author is thankful to M/s Netafim Irrigation, Israel for funding to carry out the study. Reference

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(1) T. Parthasarathi, (2) S. Mohandass, (3) S. Senthilvel and (4) Eli Vered

(1&2D) epartment of Crop Physiology, Tamil Nadu Agricultural University, Coimbatore 641003, India.

(3) Department of Soil & Water Conservation Engineering, Tamil Nadu Agricultural University, Coimbatore 4641003, India.

(4) Netafim Irrigation, Israel.

T. Parthasarathi, S. Mohandass, S. Senthilvel and Eli Vered: Effects Of Impulse Drip Irrigation On Root Response Of Aerobic Rice

Corresponding Author: T. Parthasarathi, Department of Crop Physiology, Tamil Nadu Agricultural University, Coimbatore 641003, India.
Table 1: Soil physical and chemical properties of
experimental site

Season    pH    EC                Organic carbon
                (dS [m.sup.-1])   (%)

DS 2011   7.7   0.53              0.64
SS 2012   7.8   0.58              0.61

Season    Available N        Available P (kg   Available K (kg
          (kg [ha.sup.-1])   [ha.sup.-1])      [ha.sup.-1])

DS 2011   284                21                349
SS 2012   301                23                325

Table 2: Effect of various drip irrigation treatments on root
parameters in aerobic rice, DS (2011) and SS (2012)

Treatments    Dry Season 2011

              RL       RMD      RV      RB

[T.sub.1]     50.2     1.48     46.7    199.0
[T.sub.2]     48.3     1.45     45.4    178.4
[T.sub.3]     50.7     1.51     49.9    209.2
[T.sup.4]     46.6     1.42     43.3    173.6
[T.sub.5]     44.6     1.38     42.4    158.0
[T.sub.6]     44.2     1.35     40.7    154.7
[T.sub.7]     48.5     1.47     46.3    184.4
[T.sub.8]     46.2     1.41     41.1    174.8
[T.sub.9]     44.4     1.35     34.5    153.7
[T.sub.10]    41.8     1.24     30.9    124.5
[T.sub.11]    43.1     1.29     26.2    173.9
Mean          46.25    1.394    40.68   171.28
SEd           0.0312   0.0045   2.475   7.181
CD (P<0.05)   0.0651   0.0093   5.163   5.135

Treatments    Summer Season 2012

              RL      RMD      RV      RB

[T.sub.1]     33.1    1.58     25.7    176.9
[T.sub.2]     31.7    1.52     25.5    160.3
[T.sub.3]     31.8    1.56     25.4    168.8
[T.sup.4]     31.4    1.51     25.3    141.0
[T.sub.5]     30.8    1.45     25.2    130.9
[T.sub.6]     34.0    1.64     26.6    179.3
[T.sub.7]     32.4    1.60     25.7    174.8
[T.sub.8]     31.1    1.34     24.6    121.3
[T.sub.9]     30.2    1.41     24.3    114.8
[T.sub.10]    28.4    1.25     22.7    111.1
[T.sub.11]
Mean          31.49   1.486    25.09   147.9
SEd           0.390   0.0331   0.710   1.35
CD (P<0.05)   0.820   0.0696   1.492   2.83

RL--Root Length (m [hill.sup.-1]); RMD--Root Mass Density
(mg [cm.sup.-3]); RV--Root Volume (cc [hill.sup.-1]);
RB--Root Biomass (g [m.sup.-2])

Table 3: Effect of drip irrigation treatments on yield
components in aerobic rice, DS (2011) and SS (2012)

Treatments    Dry Season 2011

              PT       SN       FGP    TW     HI

[T.sub.1]     664.5    142.2    88.1   22.5   41.4
[T.sub.2]     659.4    138.0    84.4   21.9   41.8
[T.sub.3]     681.4    142.6    89.0   23.0   42.8
[T.sub.4]     651.3    135.0    83.9   21.7   42.6
[T.sub.5]     637.6    132.9    83.9   21.2   40.5
[T.sub.6]     627.9    122.7    82.6   21.0   40.0
[T.sub.7]     623.8    133.9    89.4   22.0   42.8
[T.sub.8]     621.4    134.1    87.7   21.8   42.0
[T.sub.9]     616.0    128.4    83.7   21.1   38.8
[T.sub.10]    581.9    95.4     71.1   20.3   39.0
[T.sub.11]    594.3    119.2    78.7   20.5   41.6
Mean          632.73   129.49   83.9   21.6   41.2
SEd           7.285    6.607    1.49   0.99   1.05
CD (P<0.05)   15.196   13.782   3.11   NS     2.20

Treatments    Summer Season 2012

              PT       SN       FGP     TW      HI

[T.sub.1]     574.2    137.7    87.3    21.63   38.8
[T.sub.2]     555.9    135.0    84.1    21.35   38.2
[T.sub.3]     562.0    136.0    86.0    21.16   38.4
[T.sub.4]     513.1    128.9    83.1    20.63   38.0
[T.sub.5]     500.9    123.1    81.9    20.47   37.8
[T.sub.6]     623.0    140.0    90.0    21.73   38.6
[T.sub.7]     597.4    134.0    87.7    21.55   38.4
[T.sub.8]     482.6    122.9    85.4    21.22   38.4
[T.sub.9]     494.8    125.2    83.3    21.03   37.7
[T.sub.10]    421.5    120.6    81.2    20.18   35.6
[T.sub.11]
Mean          532.52   130.35   85.01   21.04   37.99
SEd           1.158    1.739    0.646   0.222   0.496
CD (P<0.05)   2.433    3.652    1.357   0.466   1.041

PT--Productive Tillers (Panicle [m.sup.-2]); SN--Spikelet Number
[panicle.sup.-1]; FGP--Filled Grain Percentage (%); TW--Test
Weight; HI--Harvest Index

Table 4: Effect of drip irrigation treatments on water parameters,
yield and water productivity in aerobic rice, DS (2011) and SS (2012)

Treatments     Dry Season 2011

               IW      ER      TWA     GY (Kg         WP (g
               (mm)    (mm)    (mm)    [ha.sup.-1])   [kg.sup.-1])

[T.sub.1]      444.6   102.4   547.0   5554           1.015
[T.sub.2]      444.6   102.4   547.0   5326           0.974
[T.sub.3]      444.6   102.4   547.0   5793           1.059
[T.sub.4]      444.6   102.4   547.0   5408           0.989
[T.sub.5]      444.6   102.4   547.0   4475           0.818
[T.sub.6]      444.6   102.4   547.0   4255           0.778
[T.sub.7]      555.4   76.1    631.5   4896           0.775
[T.sub.8]      555.4   76.1    631.5   4969           0.787
               444.6   102.4   547.0   4070           0.744
[T.sub.10]     444.6   102.4   547.0   3819           0.698

[T.sub.11]     510.0   187.9   697.9   4612           0.661
Mean           470.7   105.4   576.1   4834           0.845
Sed                                    82.5           0.0254
CD                                     172.2          0.0530
  (P < 0.05)

Treatments     Summer Season 2012

               IW       ER      TWA      GY (Kg         WP (g
               (mm)     (mm)    (mm)     [ha.sup.-1])   [kg.sup.-1])

[T.sub.1]      572.9    74.6    647.5    4152.8         0.64
[T.sub.2]      572.9    74.6    647.5    3897.0         0.60
[T.sub.3]      572.9    74.6    647.5    4039.9         0.62
[T.sub.4]      572.9    74.6    647.5    3848.8         0.59
[T.sub.5]      572.9    74.6    647.5    3691.2         0.57
[T.sub.6]      744.8    97.0    841.8    4249.4         0.50
[T.sub.7]      744.8    97.0    841.8    4171.0         0.50
[T.sub.8]      613.1    79.8    692.9    3880.4         0.56
               572.9    74.6    647.5    3740.6         0.58
[T.sub.10]     750.0    74.6    824.6    3523.1         0.43

[T.sub.11]
Mean           629.01   79.60   708.61   3919.41        0.560
Sed                                      78.027         0.0117
CD                                       163.928        0.0246
  (P < 0.05)

IW--Irrigation water applied; ER--Effective Rainfall;
TWA--Total Water Applied; GY--Grain Yield; WP--Water Productivity
(g grain [kg.sup.-1] of water applied);
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Title Annotation:Original Article
Author:Parthasarathi, T.; Mohandass, S.; Senthilvel, S.; Vered, Eli
Publication:American-Eurasian Journal of Sustainable Agriculture
Article Type:Report
Geographic Code:9INDI
Date:Jul 1, 2013
Words:5113
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