Experiments were conducted to select suitable plant-based bioadsorbents for the reduction of the electrical conductivity (EC) of bore well water (EC 2.20 dS m−1). Twenty-seven bioadsorbents were tested against salt reduction. Amla leaves, amla stem, prosopis leaves, calotropis flower and neem bark were efficient in reducing the EC from 1.89 to 1.77, 1.73, 1.69, 1.68 and 1.63 dS m−1 respectively. Among all, neem bark powder at 0.05% concentration was superior in reducing the salt content of bore well water (0.39 dS m−1 in 168 hours saturation time). The neem bark powder at 0.05% concentration was successfully used in an azolla multiplication tank and achieved salt reduction from 2.13 to 1.83 dS m−1. Azolla grew well in water with EC 1.83 dS m−1 having failed to grow in water having EC above 2.0 dS m−1.

INTRODUCTION

The world's water resource is drying out fast due to rapid industrialization, over-exploitation, increased population, climate change and failure of the monsoon. The people of Tamil Nadu started using well water for drinking and irrigation purposes, when the river water was not sufficient to meet their demands. People started digging bore wells during the late 1990s as the well water dried out due to decrease in the ground water table. In Tamil Nadu, particularly the Vellore region, the ground water table is declining rapidly due to low rainfall and non-adoption of a water harvesting system. The crucial role of ground water, the only available natural resource for drinking and irrigation purposes for millions of rural and urban families, cannot be overstated. Ground water is generally less susceptible to contamination and pollution when compared with surface water bodies. Variations of water quality in an area are a function of physical and chemical parameters that are generally influenced by geological formations and anthropogenic activities. The preliminary study conducted at our laboratory confirmed that the ground water of the Vellore region contains high electrical conductivity (EC) (1.83 to 7.52 dS m−1) and alkaline pH (7.70 to 9.12).

Although many technologies are available for purifying water, biotechniques have attracted attention due to their effectiveness and environmentally benign nature. In biotechniques, agro-wastes may be the potential sources for producing bioadsorbents, which can be used for improving the quality of water. Additionally, they are cheap, readily available and simple to use (Shailey et al. 2014). Different bioadsorbents have been developed from agro-wastes and used for the removal of heavy metals (Ashraf et al. 2011). Some of these include rice straw, seaweed, wood and bark, tea wastes, maize cob, jatropha oil cake, sugarcane bagasse, tamarind hull, sawdust, rice husk and sunflower stem (Malik et al. 2005; Memon et al. 2005; Hasany & Ahmad 2006). Previous studies conducted by many scientists across the world have confirmed that some of the plants, like gooseberry and amla, were efficient in reducing the salt load of irrigation water. Salinity removal efficiencies by Phyllanthus emblica and Cynodan dactylon were found to be 55% and 44% respectively for a dosage of 1 g and at a time period of 240 minutes (Varalakshmi et al. 2014). Removal of salts and minerals from water is expensive. Plenty of plant resources and weeds are available in and around us. One among them may have salt removal potential. Even a fractional reduction in the EC of water by a natural bioadsorbent will be a breakthrough in an area like Vellore where ground water availability is limited with high salt load. Natural plants contain cellulose, hemicelluloses, lignin and protein (Bassyouni et al. 2012). These constituents are able to absorb a wide range of solutes, especially divalent metal cations (Aksu 2002). Polyphenolic compounds such as tannin and lignin which are found in natural plants are considered to be the active sites to attract heavy metal cations and salts (Dakiky et al. 2002; Chantawong et al. 2003; Wang & Lin 2010). The differences in conductivity before and after treatment may be small, but are relevant because the conductivities are on the edge of poor and acceptable irrigation water. The present study was undertaken to explore suitable low-cost, plant-based bioadsorbents for effective reduction of EC in bore well water and to use this treated water for growing azolla, which can be used as animal and poultry feed in an area like Vellore where the water is not suitable for growing crops.

METHODS

Twenty-seven plant-based bioadsorbents, usually thrown away as wastes and available in plenty, namely coconut (Cocos nucifera) buttons, coconut rachillae, amla (Phyllanthus emblica) stem, amla leaves, silk cotton tree (Ceiba pentandra) bark, tamarind tree (Tamarindus indica) stem, tamarind tree leaves, puncture vine (Tribulus terrestris) seeds, Sudan grass, prosopis (Prosopis juliflora) stem, prosopis leaves, acid lime stem, acid lime (Citrus limonella) leaves, Tahiti lime (Citrus latifolia) stem, Tahiti lime leaves, abutilon (Abutilon indicum) leaves, Bermuda grass (Cynodon dactylon), nut grass (Cyperus rotundus), banana (Musa paradisiaca) stem, wild indigo (Tephrosia purpurea), neem tree (Azadirachta indica) stem, neem tree bark, neem leaves, wild basil (Ocimum americanum) leaves, tulsi (Ocimum sanctum) leaves, calotropis (Calotropis gigantea) leaves, and calotropis flower were taken (150 g each) separately in 27 plastic containers of 5-litre capacity with 3 litres of bore well water (EC 2.20 dS m−1). The bioadsorbents were made into small pieces of 1 to 2 cm size. The bioadsorbents were collected from the farmland of the Agricultural Research Station, Virinjipuram, Vellore, Tamil Nadu, India. All the containers with test water (3 litres) and bioadsorbents (150 g each) were placed under shade and a control was maintained (test water alone) for comparison. The experiment was laid out in a completely randomized design (CRD) with 27 treatments and three replications. The EC of the water was tested once in every 6 hours to know the salt reduction potential of each bioadsorbent.

Statistical analysis

The experimental data were subjected to statistical scrutiny as per methods suggested by Gomez & Gomez (1984) and statistical analysis of mean data was done as per the procedure of analysis of variance and significance of a CRD and was tested by ‘F’ test. Standard error of means (SEd+) and critical differences were worked out at probability level p ≤ 0.05 using ANOVA (analysis of variance) for CRD and were worked out for mean values of EC alone. This was executed with the software AGRES by Tamil Nadu Agricultural University. The values followed by at least one common character are not statistically different at 0.05 probability level.

Adsorption study with efficient bioadsorbents

Another experiment was conducted with amla leaves, amla stem, prosopis leaves, neem bark and dry calotropis flower as they were found efficient in reducing the EC of bore well water based on the statistical analysis of the first experiment. These bioadsorbents were taken (30 g each, i.e. 1% concentration) in five plastic containers of 5-litre volume with 3 litres of bore well water (pH 8.46, EC 1.89 dS m−1). Changes in pH and EC were recorded at different hour intervals up to 96 hours. In another study, these bioadsorbents were used in powder form and tested against salt reduction at 0.05% concentration. The bore well water used in this study was collected from the bore well at a depth of 400 ft at the Agricultural Research Station, Virinjipuram, Vellore, Tamil Nadu, India.

Adsorption study with best bioadsorbents

In the previous experiment, neem tree bark powder (NBP) and prosopis leaf powder (PLP) exhibited good salt reduction potential at 1% and 0.05% concentrations. NBP and PLP were taken in a one-bucket treatment model at different concentration. The one-bucket treatment model is a plastic bucket (25-litre capacity) provided with a tap on the side wall of the bucket just 2 cm above the bottom of the bucket. In this treatment system, NBP and PLP were added in 20 litres of water at 0.05%, 1.0% and 10% concentrations separately. Changes in the EC of the water were tested up to 168 hours. The PLP reduced the salt load of the bore well water but caused a foul odour on the third day of treatment. Neem bark produced no odour even after 7 days and performed better salt reduction. Hence NBP was used for further study.

Optimizing the dosage of NBP

To optimize the dose of NBP, the experiment was conducted with different concentrations of NBP (0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 1.0%). The salt reduction potential of NBP was good at 0.05% concentration. Further, a confirmation study was conducted in a one-bucket treatment system. In this study, 20 litres of water was taken in the one-bucket treatment model in which NBP was added at 0.05% concentration (10 g in 20 litres of water). The changes in the EC were recorded up to 168 hours. The scanning electron microscopy (SEM) image and SEM EDAX profiles of the NBP used in this study are given in Figures 1 and 2.
Figure 1

SEM images of neem bark powder at different magnifications.

Figure 1

SEM images of neem bark powder at different magnifications.

Figure 2

SEM EDAX profile of neem bark powder.

Figure 2

SEM EDAX profile of neem bark powder.

NBP on salt reduction and azolla growth

The growth of the aquatic fern, Azolla microphylla, was studied with different water levels of 10, 15, 20, 30, 60, 90, and 120 cm in an azolla multiplication tank. At first, the water level was maintained at 120 cm height from the bottom of the tank and the growth of azolla was studied for about 5 weeks. Then the water level was maintained at 90 cm after discarding the used water. The growth of azolla in salt water (EC 2.12 dS m−1) was studied by changing the water levels to 60, 30, 20, 15, and 10 cm. After standardizing the water level, the growth of azolla was studied by treating the salt water with NBP at 0.05% concentration. Later, two pits were dug with dimensions of 8′ × 4′ × 2′ (length × breadth × height, LBH) and artificial tanks were formed using silpaulin sheet (12′ length and 6′ breadth). Soil layers of about 10 cm were formed by using clay and red soil mix at 1:1 ratio. Then, in each pit 500 litres of bore well water (EC 2.12 dS m−1) was taken separately and maintained a water level at 15 cm height from the soil layer. The soil was made free of stones, iron, glass pieces and other foreign bodies. The soil and water in the azolla multiplication tanks were stirred manually for about half an hour and left for another 1 hour without any disturbance. Then the water foam and floating bodies were removed from the tank by using a wire mesh. After that 5 kg of cow dung slurry was added in both the tanks. One of the tanks was added with 10 g NBP (0.05% concentration) and the other tank was left without NBP for comparison. The NBP was prepared from the dry neem bark obtained from the well matured neem tree (trunk diameter above 90 cm). The neem barks were shade-dried and made into powder form. After the application of NBP, both the tanks were left undisturbed for 24 hours. Then 5 kg of fresh azolla (Azolla microphylla) was added in the tanks and the growth of azolla was recorded for about 42 days. The changes in EC of both treated water and untreated water were also recorded.

The growth of azolla under different growing environments was also studied using three types of multiplication tanks, namely a tank made of cement, a tank made of silpaulin sheet and a tank made of native clay soil with the dimensions of 8′ × 4′ × 2′ LBH. In all the three tanks, the water level was maintained at 15 cm height. First the growth of azolla was studied using red soil (10 cm height) as the base layer in all the three tanks. Then the soil layer was changed to red soil and clay soil mix (10 cm height). In the third study, NBP was added at 0.05% concentration and the basal layer was clay and red soil mix. The growth of azolla was observed for about 42 days after releasing 500 g fresh azolla in each tank.

RESULTS AND DISCUSSION

The water used in this study was slightly alkaline in nature (pH 8.52) with an EC value of 2.20 dS m−1. In the first 24 hours, the bioadsorbents, namely coconut rachillae, amla stem, amla leaves, silk cotton bark, acid lime stem, acid lime leaves, Tahiti lime leaves, neem bark, wild basil, tulsi, and calotropis flower, increased the pH of the water whereas the other bioadsorbents used in the study decreased the pH of the water. But this trend was not continued in the 48th hour of incubation. In the 48th hour of incubation, coconut rachillae, amla leaves, prosopis leaves, and Cyperus increased the pH of the water whereas the other bioadsorbents reduced the pH. In the 64th hour of incubation, silk cotton bark, prosopis leaves and lime leaves increased the pH whereas the other bioadsorbents decreased the pH (Table 1). Changes in the pH of water under a biological filter system are mainly because of the possible adsorption of free anions and cations (Quek et al. 1998). With respect to changes in the EC of the bore well water, prosopis leaves, amla stem, and amla leaves showed a sign of slight reduction in the EC during the first 24 hours of incubation and exhibited variations afterwards. Neem bark and calotropis flower showed a steady decrease in the EC of the water. The other bioadsorbents showed an increasing trend of EC (Table 1). An earlier study confirmed that the EC of water was drastically reduced in a bioadsorbent treatment system (Selvarathi & Murugalakshmi Kumari 2013).

Table 1

Influence of raw bioadsorbents on changes in the pH and EC of irrigation water

TreatmentsChanges in pH
Changes in EC (dS m−1)
InitialAfter 64 hoursInitialAfter 64 hours
T1 - Coconut buttons 8.52 8.46 2.20 5.16g 
T2 - Coconut rachillae 8.52 8.98 2.20 3.37e 
T3 - Amla stem 8.52 7.97 2.20 1.96b 
T4 - Amla leaves 8.52 8.04 2.20 1.99b 
T5 - Silk cotton bark 8.52 8.87 2.20 2.56c 
T6 - Tamarind stem 8.52 8.23 2.20 2.21b 
T7 - Tamarind leaves 8.52 7.94 2.20 2.12b 
T8 - Puncture vine 8.52 7.96 2.20 3.87f 
T9 - Sudan grass 8.52 8.32 2.20 2.35c 
T10 - Prosopis stem 8.52 8.00 2.20 2.94d 
T11 - Prosopis leaves 8.52 8.59 2.20 2.73d 
T12 - Acid lime stem 8.52 8.45 2.20 2.36c 
T13 - Acid lime leaves 8.52 8.56 2.20 2.55cd 
T14 - Tahiti lime stem 8.52 8.35 2.20 2.55cd 
T15 - Tahiti lime leaves 8.52 8.44 2.20 2.41c 
T16 - Abutilon leaves 8.52 8.33 2.20 2.65d 
T17 - Bermuda grass 8.52 8.35 2.20 2.76d 
T18 - Nut grass 8.52 8.40 2.20 2.89d 
T19 - Banana stem 8.52 8.22 2.20 2.04b 
T20 - Wild indigo 8.52 7.73 2.20 2.06b 
T21 - Neem stem 8.52 8.09 2.20 2.10b 
T22 - Neem bark 8.52 8.12 2.20 1.68a 
T23 - Neem leaves 8.52 7.97 2.20 2.61d 
T24 - Wild basil 8.52 8.28 2.20 2.02b 
T25 - Tulsi 8.52 8.21 2.20 1.96b 
T26 - Calotropis leaves 8.52 8.17 2.20 2.00b 
T27 - Calotropis flower 8.52 8.48 2.20 1.75a 
T28 - Control 8.52 8.49 2.20 2.20 
TreatmentsChanges in pH
Changes in EC (dS m−1)
InitialAfter 64 hoursInitialAfter 64 hours
T1 - Coconut buttons 8.52 8.46 2.20 5.16g 
T2 - Coconut rachillae 8.52 8.98 2.20 3.37e 
T3 - Amla stem 8.52 7.97 2.20 1.96b 
T4 - Amla leaves 8.52 8.04 2.20 1.99b 
T5 - Silk cotton bark 8.52 8.87 2.20 2.56c 
T6 - Tamarind stem 8.52 8.23 2.20 2.21b 
T7 - Tamarind leaves 8.52 7.94 2.20 2.12b 
T8 - Puncture vine 8.52 7.96 2.20 3.87f 
T9 - Sudan grass 8.52 8.32 2.20 2.35c 
T10 - Prosopis stem 8.52 8.00 2.20 2.94d 
T11 - Prosopis leaves 8.52 8.59 2.20 2.73d 
T12 - Acid lime stem 8.52 8.45 2.20 2.36c 
T13 - Acid lime leaves 8.52 8.56 2.20 2.55cd 
T14 - Tahiti lime stem 8.52 8.35 2.20 2.55cd 
T15 - Tahiti lime leaves 8.52 8.44 2.20 2.41c 
T16 - Abutilon leaves 8.52 8.33 2.20 2.65d 
T17 - Bermuda grass 8.52 8.35 2.20 2.76d 
T18 - Nut grass 8.52 8.40 2.20 2.89d 
T19 - Banana stem 8.52 8.22 2.20 2.04b 
T20 - Wild indigo 8.52 7.73 2.20 2.06b 
T21 - Neem stem 8.52 8.09 2.20 2.10b 
T22 - Neem bark 8.52 8.12 2.20 1.68a 
T23 - Neem leaves 8.52 7.97 2.20 2.61d 
T24 - Wild basil 8.52 8.28 2.20 2.02b 
T25 - Tulsi 8.52 8.21 2.20 1.96b 
T26 - Calotropis leaves 8.52 8.17 2.20 2.00b 
T27 - Calotropis flower 8.52 8.48 2.20 1.75a 
T28 - Control 8.52 8.49 2.20 2.20 

The values followed by at least one common character are not statistically different at 0.05 probability level. Each value in the table is an average of three replications.

In the second incubation study, five efficient bioadsorbents, namely amla leaves, amla stem, prosopis leaves, neem bark and calotropis flower, were tested against salt reduction potential. The 96 hours of the incubation study showed that adding amla leaves, amla stem and calotropis flower to the water increased the pH whereas the prosopis leaves and neem bark reduced the pH. Among the five bioadsorbents used in this study, the neem bark was superior in reducing the EC from 1.89 to 1.63 dS m−1, followed by calotropis flower (1.89 to 1.68 dS m−1), prosopis leaves (1.89 to 1.69 dS m−1), amla stem (1.89 to 1.73 dS m−1) and amla leaves (1.89 to 1.77 dS m−1). When these bioadsorbents were used in powder form, they showed a better performance in reducing the EC than when they were used in non-powder form. With respect to concentration, the bioadsorbents at 0.05% concentration showed more salt reduction when compared with their concentration level at 1%. For example, when amla leaf powder was used at 1% concentration it reduced the EC of the water from 1.89 to 1.69 dS m−1 whereas at 0.05% concentration the reduction was from 1.89 to 1.64 dS m−1. Other adsorbents also showed a similar trend of reduction in EC (Table 2). This study confirmed that the performance of bioadsorbents is good when they are used in powder form and at 0.05% concentration. The NBP at 0.05% concentration achieved maximum EC reduction (0.39 dS m−1) in 96 hours (Table 3). The presence of phenolic compounds in NBP might be the reason for its greater efficiency in reducing the EC of the water.

Table 2

Influence of natural bioadsorbents (1% concentration) on changes in the pH and EC of irrigation water

TreatmentsChanges in pH
Changes in EC (dS m−1)
Initial24 hours48 hours96 hoursInitial24 hours48 hours96 hours
T1 - Amla leaves 8.46 8.62 8.63 8.65 1.89 1.81 1.79 1.77 
T2 - Amla stem 8.46 8.53 8.55 8.59 1.89 1.79 1.77 1.73 
T3 - Prosopis leaves 8.46 8.40 8.38 8.37 1.89 1.77 1.74 1.69 
T4 - Neem bark 8.46 8.51 8.46 8.45 1.89 1.70 1.69 1.63 
T5 - Calotropis flower 8.46 8.54 8.55 8.50 1.89 1.73 1.74 1.68 
T6 - Control 8.46 8.45 8.45 8.45 1.89 1.88 1.88 1.87 
TreatmentsChanges in pH
Changes in EC (dS m−1)
Initial24 hours48 hours96 hoursInitial24 hours48 hours96 hours
T1 - Amla leaves 8.46 8.62 8.63 8.65 1.89 1.81 1.79 1.77 
T2 - Amla stem 8.46 8.53 8.55 8.59 1.89 1.79 1.77 1.73 
T3 - Prosopis leaves 8.46 8.40 8.38 8.37 1.89 1.77 1.74 1.69 
T4 - Neem bark 8.46 8.51 8.46 8.45 1.89 1.70 1.69 1.63 
T5 - Calotropis flower 8.46 8.54 8.55 8.50 1.89 1.73 1.74 1.68 
T6 - Control 8.46 8.45 8.45 8.45 1.89 1.88 1.88 1.87 
Table 3

Influence of natural bioadsorbents (powder form) on changes in the EC of irrigation water

TreatmentsChanges in EC (dS m−1) @ 1.0% Concentration
Changes in EC (dS m−1) @ 0.05% Concentration
Initial24 hours48 hours96 hoursInitial24 hours48 hours96 hours
T1 - Amla leaves 1.89 1.79 1.77 1.69 1.89 1.77 1.77 1.64 
T2 - Amla stem 1.89 1.78 1.75 1.65 1.89 1.75 1.75 1.62 
T3 - Prosopis leaves 1.89 1.81 1.78 1.66 1.89 1.79 1.75 1.62 
T4 - Neem bark 1.89 1.79 1.72 1.57 1.89 1.73 1.69 1.46 
T5 - Calotropis flower 1.89 1.75 1.69 1.61 1.89 1.73 1.65 1.55 
T6 - Control 1.89 1.89 1.87 1.87 1.89 1.89 1.87 1.87 
TreatmentsChanges in EC (dS m−1) @ 1.0% Concentration
Changes in EC (dS m−1) @ 0.05% Concentration
Initial24 hours48 hours96 hoursInitial24 hours48 hours96 hours
T1 - Amla leaves 1.89 1.79 1.77 1.69 1.89 1.77 1.77 1.64 
T2 - Amla stem 1.89 1.78 1.75 1.65 1.89 1.75 1.75 1.62 
T3 - Prosopis leaves 1.89 1.81 1.78 1.66 1.89 1.79 1.75 1.62 
T4 - Neem bark 1.89 1.79 1.72 1.57 1.89 1.73 1.69 1.46 
T5 - Calotropis flower 1.89 1.75 1.69 1.61 1.89 1.73 1.65 1.55 
T6 - Control 1.89 1.89 1.87 1.87 1.89 1.89 1.87 1.87 

In order to upscale the technology a small treatment model was designed using a plastic bucket of 25-litre capacity. The bucket was fitted with a tap at the bottom. Six treatment models (one-bucket treatment system) were taken in which 20 litres of bore well water (EC 1.87 dS m−1) was added. Then the NBP and PLP were added at 0.05%, 1.0% and 10% concentrations. Changes in the EC of the water were recorded up to 168 hours. The NBP and PLP used at 0.05% and 1.0% concentrations showed a salt reduction, whereas when they were used at 10% concentration, they actually increased the EC (Table 4). The reason for the increase in EC at the higher concentration of neem bark powder is unclear. However, it may be due to the presence of elements like Ca, K and Al in the neem bark powder. So the bioadsorbents in the range of 0.05% to 1% concentration would be ideal for salt reduction in irrigation water. To make sure, another experiment was conducted with neem bark powder at different concentration levels of 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5% and 1.0%. It was found that the salt reduction capacity of neem bark powder was decreased (decrease in the EC from 0.27 to 0.07 dS m−1) with the increased concentration of neem bark powder from 0.05% to 1.0% (Table 5). The present study confirmed that neem bark powder at 0.05% concentration played a vital role in reducing the EC of ground water to the level of 0.35 dS m−1 and it varied with the EC of salt water beyond 1.90 dS m−1. The potential of neem bark powder in reducing the EC was decreased when the initial EC of the ground water was above 1.90 dS m−1. Also the salt reduction potential of neem bark powder was decreased with high EC content of ground water.

Table 4

Influence of natural bioadsorbents (powder form) on the changes in the EC of irrigation water under the one-bucket treatment system

Time of observationConcentration of neem bark powder
Concentration of PLP
0.05%1.0%10%0.05%1.0%10%
Initial 1.87 1.87 1.87 1.87 1.87 1.87 
6 hours 1.84 1.86 1.98 1.86 1.89 1.93 
12 hours 1.81 1.84 1.96 1.86 1.87 1.91 
24 hours 1.80 1.83 1.95 1.84 1.88 1.91 
48 hours 1.75 1.82 1.89 1.81 1.87 1.91 
96 hours 1.71 1.80 1.87 1.75 1.82 1.88 
168 hours 1.52 1.77 1.87 1.65 1.79 1.92 
Time of observationConcentration of neem bark powder
Concentration of PLP
0.05%1.0%10%0.05%1.0%10%
Initial 1.87 1.87 1.87 1.87 1.87 1.87 
6 hours 1.84 1.86 1.98 1.86 1.89 1.93 
12 hours 1.81 1.84 1.96 1.86 1.87 1.91 
24 hours 1.80 1.83 1.95 1.84 1.88 1.91 
48 hours 1.75 1.82 1.89 1.81 1.87 1.91 
96 hours 1.71 1.80 1.87 1.75 1.82 1.88 
168 hours 1.52 1.77 1.87 1.65 1.79 1.92 
Table 5

Influence of neem bark powder at different concentrations on the reduction of the EC of irrigation water

TreatmentsChanges in EC (dS m−1)
Initial24 hours48 hours72 hours168 hours
T1 - Neem bark powder (0.05%) 1.93 1.85 1.82 1.80 1.66 
T2 - Neem bark powder (0.1%) 1.93 1.85 1.83 1.79 1.71 
T3 - Neem bark powder (0.2%) 1.93 1.86 1.85 1.83 1.79 
T4 - Neem bark powder (0.3%) 1.93 1.87 1.84 1.85 1.80 
T5 - Neem bark powder (0.4%) 1.93 1.86 1.83 1.83 1.81 
T6 - Neem bark powder (0.5%) 1.93 1.86 1.84 1.83 1.83 
T7 - Neem bark powder (1.0%) 1.93 1.87 1.86 1.87 1.86 
T8 - Neem bark powder (control) 1.93 1.93 1.91 1.92 1.92 
TreatmentsChanges in EC (dS m−1)
Initial24 hours48 hours72 hours168 hours
T1 - Neem bark powder (0.05%) 1.93 1.85 1.82 1.80 1.66 
T2 - Neem bark powder (0.1%) 1.93 1.85 1.83 1.79 1.71 
T3 - Neem bark powder (0.2%) 1.93 1.86 1.85 1.83 1.79 
T4 - Neem bark powder (0.3%) 1.93 1.87 1.84 1.85 1.80 
T5 - Neem bark powder (0.4%) 1.93 1.86 1.83 1.83 1.81 
T6 - Neem bark powder (0.5%) 1.93 1.86 1.84 1.83 1.83 
T7 - Neem bark powder (1.0%) 1.93 1.87 1.86 1.87 1.86 
T8 - Neem bark powder (control) 1.93 1.93 1.91 1.92 1.92 

In order to utilize the salt reduction potential of NBP at the field level, a growth study with aquatic fern (Azolla microphylla) was conducted. The EC of the ground water used in this study was 2.13 dS m−1. The preliminary study confirmed that the growth of azolla was affected when the EC of the water was beyond 2.00 dS m−1. So water with EC above 2.00 dS m−1 was taken for this study by keeping in view the reduction of the EC below 2.00 by the neem bark powder in the azolla multiplication tank to boost the growth. In the study on the growth of azolla at different water levels, the azolla grew well at the 15 cm water level and failed to multiply at increased water levels of 30 cm, 60 cm, 90 cm and 120 cm (Table 6). The influence of neem bark powder on the reduction of the EC of the water used in the azolla multiplication tank was studied by maintaining the water level at 15 cm in the silpaulin-sheet-based tanks. The EC of azolla tank water treated with neem bark powder was reduced from 2.13 to 1.83 dS m−1 in 7 days and continued to be maintained in the range between 1.79 and 1.84 dS m−1 (Table 7). The EC of untreated water in the other azolla tank ranged from 2.10 to 2.15 dS m−1. The reduction in EC of the water supported the growth of azolla, which failed to grow earlier in the untreated water. The neem bark powder reduced the EC of the water and also maintained the azolla tank free from pests and disease. About 35 kg of azolla was harvested from the azolla multiplication tank (8′ × 3′× 2′ LBD) treated with neem bark powder in 42 days whereas in the untreated tank the growth of azolla stopped on day 14. In another study the growth of azolla was compared by changing the growing environment and soil medium with water treated and untreated with neem bark powder. The growth of azolla was good under water treated with neem bark powder at 0.05% concentration along with red soil and clay soil as the soil medium (Table 8). With regard to the growing environment, it grew well in the natural tank followed by the silpaulin tank and cement tank (Table 8). The growth of azolla was very good in the water treated with neem bark powder along with clay soil and red soil as the soil medium. A maximum yield of 47 kg of azolla was recorded in the cement tank, 89 kg in the silpaulin tank and 91 kg in the natural tank.

Table 6

Influence of water level (EC 2.12 dSm−1) on the growth of azolla

TreatmentsQuantity of azolla (cumulative yield in kg)
Day 1Day 7Day 14Day 21Day 28Day 35
T1 - water level (10 cm) 2.00 2.50 3.00 3.20 3.90 3.70 
T2 - water level (15 cm) 2.00 2.80 3.20 3.50 4.10 4.20 
T3 - water level (20 cm) 2.00 1.90 1.80 1.90 2.30 
T4 - water level (30 cm) 2.00 1.50 1.50 
T5 - water level (60 cm) 2.00 2.00 1.40 1.40 
T6 - water level (90 cm) 2.00 1.30 1.30 0.40 
T7 - water level (120 cm) 2.00 2.00 1.40 0.30 
TreatmentsQuantity of azolla (cumulative yield in kg)
Day 1Day 7Day 14Day 21Day 28Day 35
T1 - water level (10 cm) 2.00 2.50 3.00 3.20 3.90 3.70 
T2 - water level (15 cm) 2.00 2.80 3.20 3.50 4.10 4.20 
T3 - water level (20 cm) 2.00 1.90 1.80 1.90 2.30 
T4 - water level (30 cm) 2.00 1.50 1.50 
T5 - water level (60 cm) 2.00 2.00 1.40 1.40 
T6 - water level (90 cm) 2.00 1.30 1.30 0.40 
T7 - water level (120 cm) 2.00 2.00 1.40 0.30 
Table 7

Influence of neem bark powder (0.05%) on the reduction of EC and the growth of azolla

Time of observationUntreated
Treated
Changes in EC (dS m−1)Quantity of azolla (cumulative yield in kg)Changes in EC (dS m−1)Quantity of azolla (cumulative yield in kg)
Day 1 2.13 5.0 2.13 5.0 
Day 7 2.10 2.6 1.83 12.0 
Day 14 2.16 1.0 1.84 18.0 
Day 21 2.17 1.82 21.0 
Day 28 2.15 1.82 24.5 
Day 35 2.13 1.79 31.0 
Day 42 2.15 1.80 35.0 
Time of observationUntreated
Treated
Changes in EC (dS m−1)Quantity of azolla (cumulative yield in kg)Changes in EC (dS m−1)Quantity of azolla (cumulative yield in kg)
Day 1 2.13 5.0 2.13 5.0 
Day 7 2.10 2.6 1.83 12.0 
Day 14 2.16 1.0 1.84 18.0 
Day 21 2.17 1.82 21.0 
Day 28 2.15 1.82 24.5 
Day 35 2.13 1.79 31.0 
Day 42 2.15 1.80 35.0 

Untreated: water level 15 cm, SSP 50 g, clay + red soil 10 cm, cow dung slurry 5 kg.

Treated: water level 15 cm, SSP 50 g, clay + red soil 10 cm, cow dung slurry 5 kg, neem bark powder (0.05%).

Table 8

Influence of neem bark powder on the yield of azolla (g) grown in different tanks with salt water (EC 2.13 dS m−1)

Time of observationRed soil
Red soil + Clay
Red soil + Clay + Neem bark powder (0.05%)
Cement tankSilpaulin tankNatural tankCement tankSilpaulin tankNatural tankCement tankSilpaulin tankNatural tank
Day 1 500 500 500 500 500 500 500 500 500 
Day 7 320 1,200 1,450 600 1,400 1,500 850 1,900 2,100 
Day 14 20 650 675 420 3,100 3,100 1,650 4,100 4,200 
Day 21 120 150 180 4,600 4,700 2,700 6,300 6,300 
Day 28 4,800 4,900 3,800 7,500 7,600 
Day 35 4,000 4,100 4,200 8,100 8,000 
Day 42 3,300 3,400 4,700 8,900 9,100 
Time of observationRed soil
Red soil + Clay
Red soil + Clay + Neem bark powder (0.05%)
Cement tankSilpaulin tankNatural tankCement tankSilpaulin tankNatural tankCement tankSilpaulin tankNatural tank
Day 1 500 500 500 500 500 500 500 500 500 
Day 7 320 1,200 1,450 600 1,400 1,500 850 1,900 2,100 
Day 14 20 650 675 420 3,100 3,100 1,650 4,100 4,200 
Day 21 120 150 180 4,600 4,700 2,700 6,300 6,300 
Day 28 4,800 4,900 3,800 7,500 7,600 
Day 35 4,000 4,100 4,200 8,100 8,000 
Day 42 3,300 3,400 4,700 8,900 9,100 

CONCLUSION

The EC of salt water can be reduced to the level of 0.39 dS m−1 by using neem bark powder at 0.05% concentration. The azolla can be successfully grown in salt water (EC up to 2.20 dS m−1) by treating the water with neem bark powder at 0.05% concentration, 15 cm water level and 10 cm clay + red soil (1:1 ratio) mix.

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