Research Paper Vegetable production in a

Academia Journal of Agricultural Research 1(12): 236-250, December 2013 http://www.academiapublishing.org/ajar ISSN: 2315-7739 ©2013 Academia Publishing

Research Paper Vegetable production in a recirculating aquaponic system using Nile tilapia (Oreochromis niloticus) with and without freshwater prawn (Macrobrachium rosenbergii) Accepted 5th November, 2013 ABSTRACT

of Agriculture and Life Sciences, 1703 E. Seventh Street University of Arizona, Tucson, AZ 857210436 U.S.A

Two recirculating aquaponics systems were installed in a controlled environment greenhouse to study the growth and yield of lettuce (Lactuca sativa), Chinese cabbage (Brassica rapa pekinensis) and pac choi (Brassica rapa) using Nile tilapia (Oreochromis niloticus) culture with and without freshwater prawn (Macrobrachium rosenbergii). Culture water was lifted by a 40 W submersible pump from a 220 L bio-filtration tank to a 250 L fish tank, and allowed to flow by gravity to a 2.44 × 4.88 m raceway in a closed loop. Water was maintained at 20 cm depth permitting rafts to float. Hydroponically germinated seedlings in rockwool blocks were planted on the rafts at 15 cm spacing 30 days after stocking 22 kg of mixed-sex Nile tilapia in the fish tanks while 295 prawns were added in one of the raceways. Environmental conditions were maintained and water quality parameters were monitored in a compromise between the ideal requirements of fish, prawn and vegetables including the beneficial bacteria throughout the108-day culture period. Two sets of data for the three vegetables and one for tilapia and prawn were gathered after the two 35 day growing seasons of vegetables. Results showed that average dissolved oxygen of 5.6 ppm at 98% saturation and 21°C temperature, and a pH of 7.1‒7.7 were established by the systems that provided a favorable environment for tilapia, prawn and nitrifying bacteria. However, the pH was disadvantageous to vegetables. With a low concentration of total dissolved solids of less than 330 ppm which was far below the requirement, the high pH retarded the normal growth of the vegetables resulting in chlorotic and necrotic leaves. Results also revealed that the vegetables demonstrated significantly better growth in the system with prawns. Among the three vegetables, pac choi had the highest growth, yield, and productivity followed by Chinese cabbage and lettuce. It was determined that integrating prawn culture helped stabilize and diversify the system which aided in improving the harvest. It also confirmed that stocking density and component ratio were critical in designing an aquaponic system.

[email protected] Phone: (520) 621-6574 FAX: (520) 621-8911

Key words: Vegetable production, Nile tilapia (Oreochromis niloticus), Nitrosomonas species

Chito F. Sace1*, Kevin M. Fitzsimmons2 1Institute

for Climate Change and Environmental Management 1Central Luzon State University 3120, Science City of Munoz Nueva Ecija, Philippines [email protected] +63 44 4565843 2College

INTRODUCTION Impacts of climate change in Philippine agriculture The Philippines, due to its geographic location, is believed as one of the most defenceless countries to climate change. Frequent occurrences of extreme climatic events such as unpredictable pattern of abnormally heavy monsoon rains,

destructive floods, sea level rise accompanied by barrage of heat waves and prolonged drought, has made climate change a persistent challenge for many Filipinos. Scientific studies also revealed that the country’s foremost water reservoirs are under threat and could result to severe water shortage (Cayabyab, 2012). With increasing intensity, its impacts

Academia Journal of Agricultural Research; Sace and Fitzsimmons.

greatly affect agriculture that will make food production difficult and food supply unsustainable. This is tantamount to an estimated 5‒7% reduction in the country’s production of major crops (Buendia, 2010). The promise of modern agriculture However, many agro-businessmen in the country never lose hope and still believe that agriculture is the only way to recover the country’s economy and pay its foreign debt (De Leon, 1995). Policy-makers in the country believe that by using climate-smart farming methods the food requirement of the population can be met (Sace et al., 2008). This is in accordance with the optimistic prediction of the United Nations Food and Agriculture Organization (FAO) of an abundant world food supply in the coming years. The prediction is based solely on the availability of today’s technical knowledge that is capable of increasing agricultural productivity (FAO, 2011) even in the face of an everincreasing population, a decreasing land resource, less funding support and unpredictable and catastrophic climate (Dolan, 1991; Zoe, 2011). This technical expertise will prove that scientific knowledge combined with computerized equipment is more critical than hard work and muscle power that traditional agriculture customarily requires (Murphy, 1984). Accordingly, the Department of Agriculture cited that one potential solution to the problem of food shortage due to climate change is ensuring self-sufficiency in food (Cayabyab, 2012). One strategy to bolster agricultural production is to cultivate, process, and distribute food in or around villages, towns and cities (Dumlao, 2012). This practice, called urban agriculture, is a type of small scale farming that could give households, not only in the countryside, but also those in the urban areas, additional income and significant access to affordable food from their own backyard. An alternative to intensive farming, it considers agriculture’s dependence on finite resources such as land and water (Connolly and Trebic, 2010). One way to do this is to promote a production system known as aquaponics. Aquaponics is a type of urban agriculture, a portmanteau of two different cultures: aquaculture or raising fish, and hydroponics or crop production in soilless culture. Aquaponics (pronounced: /ˈækwəˈpɒnɨks/) has the benefits of spending less money on fish and vegetables, and no money on fertilizer. In this system, the nutrient-rich water that results from raising fish provides a source of natural fertilizer for the growing plants. The plants help purify the water as they consume the nutrients where the aquacultural crops live in (Roe and Midmore, 2008). History of aquaponics Historically, the first example of aquaponics was believed by

237

some to be the chinampas of the Aztecs. Many believed that aquaponics has originated in Ancient Egypt in the river Nile and in ancient Babylon’s Hanging Garden. Some also said that it started from Far Eastern countries such as China and Thailand where farm wastes are commonly fed to fish often cultured in flooded rice paddies or for vegetable-fish culture. However, one of the first successful commercial aquaponic systems was established at the University of Virgin Islands where several trials for vegetables production were conducted using tilapia culture (Rakocy, 1989). As far back as 1150-1130 CE, chinampas, often referred to as "floating gardens”, were documented as the signs of sustainable agricultural systems (Pennington, 2011). Used extensively by the American nomadic tribe, the gardens were established when their neighbors treated them roughly and drove them onto the marshy shore of Lake Tenochtitlan of the great central valley of what is now Mexico. The Aztecs, denied of arable land, survived by building rafts of branches and stems called chinampas and piling soil dredged up from the shallow bottom of the lake (Rahman, 1994). The Aztecs abundantly grew vegetables, flowers, and even trees on the rafts, with roots of these plants pushing down towards the source of water. The Aztecs later defeated and conquered by force of arms the peoples who had once oppressed them. The chinampas, which were designed in a risk to stave off hunger, flourished to keep pace with the requirements of the capital city of Central Mexico. They never abandoned the lake, despite their empire grew bigger and became a huge, magnificent city. The world is so different now, and it is confronted with more formidable problems than the Aztecs. Man need to be witty and resilient to survive. Using climate-smart techniques, scientists and policy-makers have to work to chart a course that will ensure food security and create a safe operating space for farmers and food producers. Without exhausting earth’s limited resources, research and development ventures are imperative to hone today‘s production systems for the next generation. Amidst the threats of climate change, technologies like chinampas need to be promoted in order to sustainably produce more food. This study was aimed at evaluating the growth and yield of three leafy vegetables in recirculating aquaponic system using tilapia and freshwater prawn poly-culture in controlled environment. LITERATURE REVIEW A recirculating raft system was constructed for vegetable and prawn production in a raceway using tank culture of tilapia. Computerized controls that automatically govern cooling fans, heater and ceiling fan, optimum environmental parameters like temperature and relative humidity inside the greenhouse were checked if properly functioning. Water quality parameters were manually monitored using handheld meters to attain a compromised ecosystem for vegeta-


bles, prawn, tilapia and beneficial bacteria. To achieve the set objectives, major activities were undertaken in an input-process-output concept as reflected in Figure 1. System design Two recirculating aquaponic systems with a bio-filtration tank (Figure 2a), fish tank (Figure 2b) and a raceway (Figure 2c) interconnected by PVC pipes to contain one body of water were constructed in a controlled environment greenhouse. The systems utilized a 40 W submersible pump to lift the culture water from the 220 L bio-filtration tank to a 250 L fish tank and allowed to flow by gravity to a 4.41 L raceway in a closed loop. The systems were active-type polycultures which maintained a water depth enough to keep Styrofoam rafts to float. The systems were installed in a gable-roofed conventional greenhouse made of double-layered polycarbonate sheets containing air spaces that acted as insulators. With side walls made of bricks, the structure allowed good transmission of light. The greenhouse was equipped with environmental control systems with sensors connected to a computer to record air temperature, relative humidity and photosynthetically active radiation (PAR). Cooling and heating devices included an overhead heater, two cooling fans, and a ceiling fan maintained the pre-set optimum environmental conditions for the normal growth of vegetables, prawn, fish and the beneficial bacteria. The Nitrogen cycle Each structure has three essential elements: fish, bacteria and plants (Malcolm, 2007). As part of a fish’s normal protein digestion, ammonia is given off through their gills and urine of the fish, including any wastes or uneaten food. The wastes break down in the fish tank and quickly build up in the water affecting the growth of fish. Two main types of bacteria carry out the essential work. Nitrosomonas species digest ammonia and convert it into nitrites while the Nitrobacter species then convert the nitrites into nitrates which can now be consumed by plants (Rakocy et al., 2006). The fish and prawns are less vulnerable to high levels of nitrites in the water though most plants cannot absorb nitrites. The water flow back to the fish tank cleaned of excess nutrients and freshly oxygenated as demonstrated in Figure 3. There is nothing artificial or unhealthy with these bacteria for they are completely natural and beneficial (Nelson, 2008). Management practices The systems were filled with tap water (September 11, 2011) and were kept running for one week before stocking the fish. This was to check the systems for leaks and volatilize chlorine

238

Twenty-two kilograms of mixed-sex Nile tilapia (Oreochromis niloticus) with an average weight of 150 g were stocked a week later (September 16, 2011) in each of the fish tanks. The density was based from the result of Licameli et al. (2010) of 5 kg/m3 of tilapia and total volume of culture water in the system. Likewise, 295 heads of juvenile freshwater prawns (Macrobrachium rosenbergii) average weight of 1.66 g and average length of about 4.3 cm were stocked under the rafts in one of the systems. The other system, which was the control, contained no prawn. In a week time, 13 pcs of tilapia weighing approximately 2 kg have died in the system with prawn while 12 pcs of tilapia weighing less than 2 kg in the system without prawn. The mortality was due mainly to handling stress. The same number and weight of fish were added to each tank. For 30 days the systems were kept running to allow the growth of algae and bacteria. F1 seeds of lettuce (Brassica rapa: Black-seeded Simpsom variety), Chinese cabbage (Brassica rapa pekinensis), and pac choi (Brassica rapa) hydroponically germinated in rockwool blocks and enhanced for one week with foliar fertilizer. Seedlings were plugged into the holes of the rafts (October 17, 2011) with 15 cm off-center spacing. These vegetables were replicated five times in order to maximize the floor area of the raceway. With this, each experimental unit had 33 plants or165 plants per treatment to contain 495 plants in the raceway for three treatments. No inorganic fertilizer or chemicals were added to the systems. Tilapia was fed with commercial feeds ad libitum using 12 h belt feeder while prawn relied on the scraps and undigested feed that enters the raceway. Seeds for the second crop of vegetables were propagated a week before harvesting using the same procedure and technique of germination applied in the first crop. A sample of culture water from each raceway was sent to a reputable laboratory for complete water analysis to determine pH, TDS, nitrite, nitrate, potassium, phosphorus, calcium, magnesium, iron and other elements after each harvest. The analysis will be used as supplemental data to compare the two systems. Data gathered The experiment was a comparative study of two systems which aimed to evaluate the productivity of three leafy vegetables in an aquaponic system. The first system has tilapia-prawn culture as the independent variable and the three vegetables as the dependent variables while the second system has tilapia as the independent variable and the vegetables as the dependent variable. It was completed in a 108 day culture period with two 35 day growing seasons of vegetables planted in the system with prawn and in the system without prawn. A set of data were collected every harvest for each system. The average biomass and average dry weight of the vegetables were gathered to evaluate the growth of the vegetables while fresh weight of leaves was used to evaluate the yield. Six plants were taken to represent


239

Figure 1. The conceptual framework.

Figure 2. (a) The bio-filtration tank, (b) fish tank and (c) the raceway.

an experimental unit. Plants were carefully removed from the rafts as roots were entangled with the roots of other plants. Weight was determined using a digital weighing scale. Samples were oven dried for 48 h at 80°C. Data were carefully recorded, and statistically analyzed and interpreted using single-factor Analysis of Variance (ANOVA). Similarly, 10 samples of tilapia and prawn were caught to determine the growth and gain weight of aquacultural crops. Increase in length was determined from head to the end of the tail based from initial and previous measurements while gain in weight of tilapia and prawn was computed by subtracting the initial weight from the final weight. These were done during the

first and second harvest of vegetables. Feed conversion ratio was also computed. Likewise, the total water consumption of the systems was determined by adding the daily evaporation losses since the onset of the experiment with the total volume of water in the system. RESULTS AND DISCUSSION System performance The design of the aquaponic systems followed the “one-pump


240

Figure 3. The Nitrogen cycle.

rule”: the culture water must be recirculated by one pump starting from the lowest point and allowing the system to flow by gravity in a close loop. The rule was given by a wise man and former owner of Seagreenbio in Palms Spring, California, USA, Mr. Dean Farrel, who claimed that systems designed in this way saved energy and aggravation (Rakocy et al., 2006). That is why both systems were operated by one pump submerged in the bio-filtration tank, the lowest point, to raise the culture water to the fish tank, the highest point, and allowed to flow by gravity through the raceway and back to the bio-filtration tank. During the course of time conducting the experiment, it was experienced that system failure is possible if a filter in the stand pipe at the exit of water in the raceway is improperly designed. The filter is necessary to prevent the prawn from escaping and find their way to the bio-filtration tank. The possibility that clogging the filter (Figure 4a) can occur is not far as roots and other debris blocked the filter. In addition, the vortex of water coming out of the raceways can eventually create a sucking pressure on the raft, preventing water to flow. The weight of the vegetables and roots as they hang on the raft adds up to the problem. Hence, a perforated pipe (Figure 4b) was fabricated to allow water to flow freely and efficiently recirculate in the system. Several holes on the pipe allowed the flow without restraint. The temperatures of the culture water dropped below the desired level during the advent of winter. The installation of two 300 W water heaters in the bio-filtration tank in each

Figure 4. (a) Fabricated stand pipe filter made from discarded cup and (b) perforated PVC pipe.

system raised the temperature. In addition, the thermal energy absorbed by the culture water in the fish tank, raceway, and bio-filtration tank during the day with sunlight


241

aided in maintaining the water temperature and balanced the effects of low night time temperature to an average of 21.2°C. The installation of a water heater in the bio-filtration tanks created a factor of safety for the living organism from overheating. An excessively high temperature that would kill the fish is possible scenario when pump failure or power outage if heaters were installed in the fish tank. In the same way, DO levels are normally fluctuated as water flowed along the four observation stations in the systems. DO level in the system with prawn in the fish tanks was normally the lowest at 3.8 ppm. This was because most of the excretion of tilapia was produced in the fish tank. This level increased to 5.9 ppm at the entrance in the raceway and further increased to 6.7 ppm at the exit in the raceway. The highest values of DO happened in the raceway because water was highly aerated. Plant roots also added oxygen as part of respiration. DO slightly decrease to 6.2 ppm in the biofiltration tank. In the system without prawn, the average DO in the fish tank was 4.2 ppm then fluctuated to 5.6, 6.3, and 6.3 in the entrance and exit of the raceway and in the biofiltration, respectively. These values were within the recommended limits (Rakocy et al., 2006). The design of the raceway, being rectangular, has poor flow characteristics. Although easier to construct, the incoming water flowed directly to the drain short-circuiting the tank. Waste and organic matter accumulated in some part of the raceway while other areas remained stagnant with pockets of lower oxygen levels. This was one of the disadvantages of having a rectangular raceway as compared to circular design that could create a current to collect the organic matter to the centre and out to the drain.

Tank-bed ratio

Stocking density

The real-time data of environmental factors that were logged at 5 min interval was extracted from the computer. Air temperature, relative humidity and PAR were processed by taking the average values of the day and the night readings based on Julian day. A compromised environmental condition crucial for production of tilapia, prawn, vegetables, and for optimal activity of nitrifying bacteria in the system (Tyson, 2007), was maintained. Data was then tabulated compared to the compromised environmental conditions and tabulated in Table 1. Air temperature and relative humidity inside the greenhouse were maintained at 22‒30°C and 40‒90%, respectively. pH was maintained at 6.0‒7.5, water temperature at >20.0‒30.0°C, TDS at >300 ppm and dissolved oxygen at >3.0‒8.0 ppm with minimum saturation of 60%. Day and night temperatures were pre-set at 22-30°C with the aide of overhead heater, cooling fans and ceiling fans. However, the two systems were subjected to fluctuations of outside temperature that created variations in the interior environment conditions of the greenhouse by approximately ±2°C during the first cropping season (October 11 to Novem-

According to Rakocy (1989), intensive tank culture can produce a very high yield of tilapia by stocking 50‒100 g tilapia at a rate of 100‒200 fish per m3 of culture water or even as high as 250 fish per m3. At this rate, 5‒20 kg of fish or even as high as 25 kg is possible to be reared in a cubic meter of culture water provided that a higher degree of environmental control over parameters is provided by aeration and frequent or continuous water exchange. This is to renew dissolved oxygen supplies, and remove waste and increase the growth of beneficial bacteria in the system. Using these proven facts to compare the stocking density used in the experiment, stocking as many as 71 fish with an initial average weight of 150 g and final average weight of 309.9 g in a 0.25 m3 tank was far too high a stocking density that corresponded to 42 kg/m3. This condition had resulted in a slower growth rate. With this stocking density, DO was low and fish had less space to swim around and finding food became difficult. This indicated that the volume of the fish tank was inadequately matched with the stocking density. This means that stocking density is one of the fundamental considerations in designing aquaponic system.

The tank bed ratio, also known as component ratio, used in this experiment was based on the conclusion made by Licameli et al. (2010) in a study to evaluate the optimal stocking density of tilapia for lettuce production. A density of 5 kg of fish per m3 of culture water resulted in 22 kg of Nile tilapia for the total volume of water of 4.40 m3 in the system including the bio-filtration tank. This volume was later decreased to 2.85 m3 when the depth of water in the raceway was reduced from 33 to 20 cm without changing the stocking density of fish. This was done to increase the concentration of nutrients produced by the fish in the system as a remedy to nutrient deficiencies manifested in the plants leaves. At this depth, the volume of water in the raceway becomes 2.38 m3. With a fish tank volume of 0.25 m3, the component ratio therefore becomes 1:9.5. In comparison, a fish tank: grow bed ratio of 1:1 as used in early systems or 1:2 that is now common or as high as 1:4 that others growers try to intensify, are acceptable. The ratio 1:9.5 maybe an exaggeration and was far too big for growing vegetables. With this ratio, there was no doubt that plants were chlorotic and necrotic. In addition, the Speraneo system, for example, is designed for a component ratio of 1:2 using pea gravel as growing bed media. This means that a fish tank of 0.25 m3 requires a volume of 0.50 m3 in the raceway. This also proves true that component ratio is another crucial factor in designing aquaponics which therefore can devastate production or can favor greater outputs (Diver, 2006). Environmental monitoring parameters


ber 11, 2011). At these air temperature ranges, relative humidity correspondingly fluctuated from 55‒85%. The second cropping season was slightly colder than the last growing season, with air temperature mildly dropped to 20‒28°C while relative humidity rose from 58‒87%. These fluctuations were the effects of low night temperature during the winter season, though ideally, the relative humidity of the air surrounding plants should be maintained around 70% at night and 85% during the day (Rorabaugh, 2011). On the same hand, PAR also changed from 435‒685 nm during the first cropping season to 410‒645 nm during the second cropping, both within the range of the crop requirement. PAR is normally between 400‒700 nm, but the quantity was gradually reduced after the equinox (September 23, 2011). According to Rorabaugh (2011), crop production in Tucson, Arizona is affected by both day length and angle of the sun as season changes. On June 21 for example, the day length is 14 h and 15 min as compared to December 21 with only about 10 h. The quality and quantity of light directly affected plant growth which gives an indication of the possible amount of photosynthesis and growth being performed by the plant. Increasing energy in the PAR range increases plant photosynthesis (Rorabaugh, 2011).

Water quality monitoring parameters Water quality monitoring parameters like pH, TDS, temperature, dissolved oxygen and saturation were targeted to attain a compromised ecosystem that was desirable for the living organisms in the systems. Values to create a compromised habitat and the levels achieved by the systems were presented in Table 2. A desirable pH ranging from 6.0‒7.5 was anticipated since pH is a major limiting factor in aquaponics, any system that can achieve with optimal pH for the aquacultural crops, the hydroponic crops and the bacteria are usually productive (Tyson, 2007). pH higher than this range will be detrimental to plants (Anderson et al., 1989) although beneficial to tilapia, prawn and the bacteria grow best at this level (Rakocy et al., 2006). Religious monitoring was done daily early in the morning when the sun was not yet set, the best time to collect data since photosynthesis stops at night while respiration continues (Francis-Floyd, 2011). Fish, prawn and bacteria prefer a pH 7.0‒9.0 since and most plants grow within 5.8‒6.8 and must be maintained at the desired level. However, the systems found difficulty in achieving the desired requirements. A hand-held pH-TDS-temperature meter was used to measure the parameters. The system with prawn developed a pH of 6.5‒7.5 during the first cropping season and 7.1‒7.9 during the second cropping while the system without prawn achieved a pH slightly higher than the system with prawn and the desired level during the first cropping ranging from 6.7‒7.7 and 7.3‒8.2 during the second cropping season. A pH higher than 8 can prevent plants to absorbed the nutrients which results to deficiency or toxicity

242

when level is too high or too low (Anderson et al., 1989). A TDS of 525‒1,400 ppm was aimed as ideal although these nutrient levels are difficult to attain in aquaponics. During the two cropping seasons, the system with prawn achieved only a TDS of 246‒393 ppm while 228‒344 ppm for the system without prawn. Lettuce requires a TDS ranging from 560‒840 ppm while the requirements of cabbage and pac choi are 1,750‒2,100 and 1,050‒1400 ppm, respectively, as presented in Table 3. Thus, vegetables showed various deficiencies. Water temperature of the two systems was also affected by the advent of winter. Temperature during the two cropping seasons ranged from 17‒24°C while 19‒24°C for the system without prawn. The lower values of the range were below the optimum desired temperature of 20‒30°C. At these range, the water is warm enough to stimulate good growth rates but at the same time cool enough to carry maximum oxygen content for all species in the system including the bacteria (Carruthers, 2002; Connolly and Trebic, 2011; New, 2002). Laboratory analysis Water samples taken from the center of the each raceway after the first harvest of vegetables and analyzed by a reputed agricultural laboratory for water analyses, substantiated the data collected daily. Results (Table 4) confirmed that the pH in the two raceways was above the recommended levels for vegetables and were appropriate for the aquacultural crops with 7.5 in the system with prawn and 7.8 in the system without prawn. Consequently, TDS in both systems was far below the requirement of the three vegetables with 311 ppm and 292 ppm in the system with and without prawn, respectively. Further, the analyses also revealed that the system with prawn contained higher amount of nitrogen, nitrate nitrogen, sulfates, calcium, magnesium, sodium, chlorides, iron, phosphates, manganese and hardness as compared to system without prawn. No wonder plants in the system with prawn were heavier, greener and taller than those planted in the system without prawn. Although nutrient deficiencies were both seen in plants in both systems, plants in the system without prawn had more obvious signs and appeared more chlorotic and necrotic while lettuce had elongated stalks as depicted in Figure 5. Deficiency symptoms were highly noticeable in Chinese cabbage so that its eating quality was poor.

Growth of vegetables The vegetables were harvested 35 days after seeding (Figure 6). The growth of vegetables was determined using the total biomass and total dry weight of the vegetables. Biomass is the material produced by photosynthesis in which the energy from the sun converts carbon dioxide and water to carbohydrates and oxygen. This includes the roots and the


243

Table 1. Compromised and achieved levels of environmental monitoring parameters of the systems.

Parameter

Compromise level*

Air temperature (°C) Relative humidity (%) PAR (nm)

22-30 40-90 400-700

Level achieved by the system With Prawn Without Prawn 1st crop 2nd crop 1st crop 2nd crop 22-30±2 20-28±2 22-30±2 20-28±2 55-85 58-87 55-85 58-87 435-685 410-645 435-685 410-645

* Values compiled from various literatures.

Table 2. Compromised and achieved levels of water quality monitoring parameters achieved of the system.

Parameter

Compromise level*

pH Total dissolved solid (ppm) Water temperature (°C) Dissolved oxygen (ppm) Saturation (%)

6.0-7.5 >300 >20.0-30.0 >3.0-7.0 >60

Level achieved by the system With Prawn Without Prawn 1st crop 2nd crop 1st crop 2nd crop 6.5-7.5 7.1-7.9 6.7-7.7 7.3-8.2 246-344 240-393 228-328 261-344 18.8-22.9 16.3-23.5 19.2-23.9 18.5-24 3.2-6.9 2.8-7.3 3.2-6.7 3.0-7.2 58-125 51-123 52-123 26-127

*Values compiled from various literatures.

Table 3. pH and TDS requirements of lettuce, Chinese cabbage and pacchoi.

Vegetables Lettuce Chinese cabbage Pac choi

pH 5.5-6.5 6.5-7.0 7.0

leaves of the plants. As tabulated in Table 5 and depicted in Figure 7, the total biomass of lettuce, Chinese cabbage and pac choi grown in the system with prawn was heavier than those grown in the other system during the first harvest having total of 86.6, 179.5 and 185.2 g, respectively. Those that were planted in the system without prawn weighed 86.2, 163.3 and 172.9 g, respectively. A similar pattern happened during the second harvest when lettuce, Chinese cabbage and pac choi that were grown in the system with prawn were heavier than those plants grown in the other system with averages of 84.6, 168.5 and 190.0 g, respectively. Those that were planted in the system with prawn weighed 80.9, 165.7 and 178.3 g, respectively. ANOVA revealed no significant differences among the means of total biomass of lettuce and Chinese cabbage grown in systems with and without prawn during the first and second harvest. However, there were significant differences among the means of the total biomass of pac choi during the first and second harvest. Harvest in the system with prawn was better than the system without prawn during the first and second harvest. The combined effects of low pH, low TDS and low temperature the vegetables with greater effects of

Total dissolved solid (ppm) 560-840 1750-2100 1050-1400

temperature during the height of winter caused the temperature drop. Plant roots function best at temperature range between 18‒22°C. The total dry matter was summarized in Table 6 and shown in Figure 8. The total dry matter of vegetables in the system with prawn during the first harvest was heavier than those in the system without prawn having averages for lettuce, Chinese cabbage and pac choi of 4.9, 7.1 and 7.7 g, respectively, while the total dry matter in the system without prawn were 4.9, 6.5 and 7.2 g, respectively. The same trend occurred during the second harvest, with averages in the system with prawn heavier than the system without prawn. The total dry matter in the system with prawn were 3.8, 6.8 and 7.2 g for lettuce, Chinese cabbage and pac choi, respectively while 3.6, 6.1 and 6.3 g in the system with prawn, respectively. ANOVA on the means of total dry matter of lettuce revealed no significant differences during the first and second harvests. This means that lettuce in both systems contained the same amount of dry matter. Lettuce is less tolerant to high pH in both systems which were higher than the desired value. However, there were significant differences in the means of total dry matter of Chinese cabbage and pac choi


244

Table 4. Laboratory analysis of culture water in systems with and without prawn.

Items Nitrogen Nitrate Nitrogen Sulfates pH Calcium Magnesium Sodium Chlorides Total dissolved solid (ppm) Hardness Total iron Phosphates Phosphorus E.coliform Total coliform Copper Zinc Manganese potassium Comments

Parts per million With Prawn Without Prawn 30.8 24.6 7 5.6 41 36 7.5 7.8 180(10.5 g/gal) 155(9.1 g/gal) 45(2.6 g/gal) 35(2.0 g/gal) 48 46 70 68 311 292 225(13.1 g/gal) 190(11.1 g/gal) 0.5 0.1 25 19.75 8.3 6.58 N/A N/A N/A N/A N/A N/A N/A N/A 0.07 0.038 N/A N/A N/A N/A

USEPA Guidelines NO3= 25 ppm N= 100 ppm 250 ppm 6.5-8.6 secondary std

ppm 250 ppm 500 ppm secondary std 0.3 ppm secondary std 0.400 ppm secondary std