USVI Public Records

Document text

Evaluating Geotextile Technology to Enhance Sustainability of Agricultural Production Systems in the U.S. Virgin Islands By Jason Danaher, UVI-AES Aquaculture Program Technical Bulletin #14 from the University oftheVirgin Islands Agricultural Experiment Station August, 2009 Introduction Cultivating cash crops in a climate like the U.S. Virgin Islands can be challenging even with supplemental irrigation. Integrating recirculating aquaculture systems with the production of other valuable agronomic crops to reuse water and recycle nutrients can provide a viablesolution to sustainable food production in semi-arid regions. Re circulating aquaculture systems discharge nutrient-rich effluent daily that is com posed offeces, algae, and uneaten feed to ensure system sustainability. Experiments at the University of the Virgin Islands (UVI) have demonstrated discharged aquacul ture effluent to be an excellent water and nutrientsource for agronomic crops; thus, effluents should be treated as a resource and not as a disposal problem. One major constraintto the integration of aquaculture and field crops has been clogging ofdrip ir rigation systems due to high levels of total suspended solids (TSS) in the aquaculture effluent. Technology capable of separating the solid fraction from the liquid fraction of aquaculture effluent would improve op tions for integrating aquaculture and field crop production. Geotextile technology now exists that creates a more flexible approach to inte grate aquaculture effluent with agronomic crops, therefore improving on-farm water Figure1. Earthen pad with EPDM liner and gravel for the geotextile bag. and nutrient use. Geotextile technology has been used on dairy, swine, and aqua culture facilities to dewater animal wastes. Ageotextile bag (GTB) is constructed from a high-strength, woven, polypropylene fabric. Small pores in the geotextile retain the majority of organic matter and allow water (i.e. filtrate) to drain out, resulting in effective dewatering and efficient volume reduction of the animal waste. Repeated fillings, resulting in additional filtrate, are possible until the bag reaches its volumet ric capacity. Then, the retained waste mat ter can continue to consolidate by desicca tion through the geotextile fabric.To utilize the solids, the farmer must cut the bag open to extract the solids for land applica tion. A project at UVI evaluated the use of a GTB for the recovery and application of aquaculture effluent for agronomic crops cultivated in the U.S. Virgin Islands. The objectives of this project were: 1) Evaluate a geotextile bag for dewater ing aquaculture effluent and analyzethe nutrient content ofthe filtrate exiting the bag and the manure captured inthe bag. Also, determine ifthe filtrate could pass Figure 2. The geotextile bag resting on the earthen pad. The green, 3-inch PVC hose delivers effluent injected with polymer to the bag. through aT-tape® irrigation system. 2) Evaluate the manure in the geotextile bag as a fertilizer for cucumber production. Objective 1 Materials and Methods Aquaculture effluent was stored in a 40,000 gallon lined pond under anaerobic conditions. Adjacent to the pond a 30 feet x 10 feet earthen pad was constructed with a 2% grade (Figure 1). In addition to the graded pad, a frame was constructed from 3-inch PVC pipe and installed on the pe ripheral edges of the pad to direct water exiting the bag toward a catchment area. Both the frame and the pad were covered with a 45-mil thick Ethylene Propylene Diene Monomer (EPDM) liner and approxi mately 1 inch of gravel was placed over the liner. Then, a GTB with a dimension of 25 feet x 7.5 feet was laid over the gravel (Figure 2). A 3/4-horsepower (hp) vertical lift aerator and horizontal mixer were used to agitate the fish effluent prior to each pumping event (Figure 3).A 1/3-hp pump, pumped effluent at a rate of 10 gallons/ minute to the GTB. Prior to entering the Figure 3. Untreated aquaculture effluent in the anaerobic pond being agitated prior to a pumping event. Table 1. Averages of water quality parameters and nutrient concentrations measured during objective 1 for aquaculture effluent, geotextile bag (GTB) filtrate exiting the bag, and GTB manure inside the bag.The removal efficiency of different parameters as effluent passed through the geotextile bag is also reported (negative numbers represent an increase in nutrient concentration for the filtrate). Aquaculture Effluent (mg/L) GTB Filtrate (mg/L) Percent Removal GTBManure (Ibs/t) Mean ± S.D. Mean ± S.D. pH(-log10[H1) 7.6 ±0.3 7.7 ± 0.4 8.1 Temperature (°C) 24.5 ±0.5 24.5 ± 0.5 Alkalinity 860.0 ± 34.6 801.3 ±90.5 TSS 22,525.0 ±3,892.2 115.0 ±68.7 99 Macronutrients NPK (%) 0.09:0.15:0.03 0.02:0.04:0.03 3.6:6.0:0.2 Total Nitrogen 898.7 ± 27.3 244.5'±59.7 73 8.6 Phosphorus 670.3 ± 550.1 155.7 ±207.5 77 14.4 Potassium 248.4 ±151.1 225.8 ±151.3 9 0.4 Calcium 3,404.5 ± 2,878.4 417.3 ±333.4 88 32.7 Magnesium 127.0 ±62.1 66.3 ±69.4 48 0.6 Micronutrients • Iron 33.3 ±14.1 14.5-±19.9 56 0.5 Copper 8.0 ±7.0 8.3 ±10.5 -4 0.1 Zinc 23.8 ± 22.0 22.3 ±15.9 6 0.3 Boron 5.5 ±3.7 13.5 ±19.1 -73 0.1 Manganese 13.0 ±9.0 5.8 ±10.8 55 0.2 Molybdenum 7.3 ±9.0 13.3 ±20.0 -82 0.0 GTB, a peristaltic pump injected effluent with a polymer, HYPERFLOC® CE 854, at a concentration of 14 mg/L and effluent and polymer mixed by passing through a series of 90-degree PVC elbows (Fig ure 4). Jar tests were performed in the laboratory to determine 14 mg/L of poly mer was necessary for TSS treatment. A polymer is a long-chain carbon molecule with high molecular weight. HYPERFLOC® CE 854 has a cationic charge attracting it to the surface of organic matter and results in coagulation of small particles. Thus, polymer addition helps the GTB to capture the majorityof TSS present in the waste stream. There were three pump- Figure4. Effluent being pumped from the storage pond and injected with polymer prior to entering the geotextile bag. The white box houses the peristal tic pump which injects the polymer. The effluent coagulates as it mixes with the polymer in the series of 90- degree PVC elbows. ing events to fill the GTB: 29 November and 14 December 2007 and 17 January 2008 (Figure 5). On each pumping event a sample of aquaculture effluent was col lected from the storage pond adjacent to the 1/3-hp pump and a sample of filtrate exiting the GTB was collected during filling (Figure 6).A sample of the solids retained inside the GTB was collected on 17 Janu ary prior to the final pumping event and analyzed, moist from the bag, for physical and chemical characteristics. Water qual ity parameters along with physical and chemical characteristics of aquaculture effluent, GTB filtrate, and GTB manure were analyzed at Micro Macro Interna tional (Athens, GA, USA) and results are shown in Table 1. Figure 5. Fillingthe geotextile bag with aquaculture effluent injected with polymer. The slurry entering the bag will dewater as filtrate escapes and evaporation takes place. The bag can be filled multiple times.- Results and Discussion The GTB in combination with the polymer removed 99% of the TSS from the aqua culture effluent (Figure 7). When compar ing nutrient concentrations of aquaculture effluent entering the GTB to filtrate exiting the GTB, the common trend was a de crease in nutrient concentration; however, some nutrient concentrations increased, suggesting the GTB was unable to capture them effectively. Comparison of aqua culture effluent to GTB manure showed macronutrient and micronutrient con centrations were concentrated by factors ranging from 7-40 times and 0-60 times, respectively. Analysis of the GTB manure showed it was composed of 87% moisture content after four weeks of dewatering Figure 6. Collecting filtrate as it slowly exits the bag for water quality and nutrient analysis. (Figure 8). The dry weight of the manure was 59% organic solids.The GTB manure may provide a farmer with an alternative nutrient source for field production of veg etable crops while improving the physical characteristics of soil with the addition of organic matter. The GTB filtrate was also found to pass through a T-tape® irriga tion system withoutclogging emitters over a four-week period. This would allow a farmer to integrate an aquaculture opera tion with agronomic field crops without the clogging problems previously experienced with untreated aquaculture effluent at UVI. The GTB filtrate was low in nutrient con centration and we hypothesize this was a result of storage in an anaerobic environ ment. Under anaerobic conditions nutrient concentrations can decrease over time. Objective 2 Materials and Methods An experiment was conducted to compare GTB manure to a commercial, inorganic fertilizer as a nutrient source for field production of cucumber (Cucu- mis sativus 'Calypso'). A total of six treat ments were used. The four GTB manure treatments were 90, 120, 150, or 180 lbs nitrogen/acre. The inorganic fertilizer used was 13-13-13 Osmocote®. The two inorganic fertilizer treatments used were 90 and 180 lbs nitrogen/acre. A GTB was filled with aquaculture effluent which was analyzed for nutrient content. After sev eral weeks of dewatering, the manure was sampled moist as itwas obtained from the bag (Table 2).Analysis of soil samples was performed on field plots prior to fertilizer application and appropriate amounts of fertilizer, based on nitrogen concentration, were applied to field plots. The experiment was conducted from 14 January to 10 April 2009 at the UVI Ag ricultural ExperimentStation on St. Croix. A Figure 7. Comparison of untreated effluent (left), effluent treated with the polymer prior to entering the geotextile bag (middle), and filtrate exiting the bag virtually free of total suspended solids (right). Randomized Block Design was used with three replicates per treatment. All treat ments were irrigated with rainwater. Plots were established measuring 20 feet long x 8feetwide. On 14JanuaryOsmocote® and GTB manure were applied to their respec tive plots (Figure 9). Fertilizers were roto- tilled about 6 inches deep into the soil and allowed to rest for 2 weeks. One-week-old cucumber seedlings were transplanted on 29 January to the three-row plots with a row spacing of 4 feet and plant spacing within rows of 2 feet. On 2 February straw mulch, composed of dry guinea grass (Panicum maximum L.) was applied at a depth of 2-3 inches over the entire area ofthe plot. Dipel® DF biological insecticide and M-Pede® insecticidal soap were ap plied twice weekly to kill insect pests, and weeds were controlled by hand-weeding when necessary. Cucumbers were har vested starting on 6 March until 10 April for a total of 16 harvests (Figure 10, next page). Plant tissue analysis was performed on the middle rowofeach plot bysampling two or three recently mature leaves per plant at the appearance of first flower. A & L Laboratories (Memphis, TN, USA) per formed the soil and plant tissue analysis. After initial fertilizer application soil sam ples were collected at planting,first flower, and at the end ofthe experiment. One-way analysis of variance (ANOVA) was used to compare total yield, total marketable yield, total number of fruit and marketable fruit, average fruit weight, plant tissue samples, and soil samples between treatments. A marketable fruit was categorized as > 5- inches in length with no insect damage, no canker present, and no excessive yellow ing of the fruit. Results and Discussion Nitrogen and phosphorus concentrations in Figure 8. Cutting open the geotextile bag and removing manure for use as a fertilizer in the cucumber experiment. Table 2. Nutrient analysis of manure removed from the geotextile bag and used as a fertilizer in the cucumber experiment. Test Pounds Per Ton Nitrogen, N 10.6 Phosphorus, P 17.0 P205 Potassium, K 0.96 K20 Sulfur, S 2.40 Magnesium, Mg 0.80 Calcium, Ca 37.0 Sodium, Na <0.50 Iron, Fe 0.54 Aluminum, Al 0.32 Manganese, Mn 0.18 Copper, Cu 0.05 Zinc, Zn 0.29 Result Moisture, % 88.8 Solid, % 11.2 the GTB manure used in objective 2 were similar to concentrations measured in ob jective 1. However, in objective 2 one com posite sample was prepared from multiple samples after the GTB was cut open and more accurately represented manure nu trient concentrations throughout the GTB. No significant differences were found be tween any treatments regarding the total yield and marketable yield (Figure11, next page) of cucumber. Over 97% of the cu cumbers were marketable based on our categorization. There was no significant difference between treatments for total number of fruits and marketable fruits har vested. There was no significant difference in the average fruit weight between treat ments with an overall average weight of 7.5 ounces/fruit. There was no significant difference in plant tissue analysis, and tis sue nutrient levels were in optimal ranges for alltreatments. There were nosignificant Figure 9. Fish manure being broadcasted over research plot prior to being rototilled into the soil. differences insoilanalysis at any sampling ' period. Cucumber growth response, based on number of internodes at first flower, was not significantly affected by either source of fertilizer or different application levels of either fertilizer. Therefore, GTB manure applied at a rate of 90 lbs nitrogen/acre resulted in similar cucumber production as 90 lbs nitrogen/acre of Osmocote® and application rates of > 90 lbs nitrogen/acre did not improve cucumber yield. Physical characteristics of the soil, specifically organic matter, was not improved by the addition of GTB manure. Conclusions • The GTB was highly effective in reduc ing the concentration of TSS in fish efflu ent while providing a filtrate with some dissolved nutrients. • The GTB filtrate was able to pass through standard, commercial irrigation lines with out clogging emitters. • The GTB would allow an integrated farm ing system to utilize aquaculture effluent on agronomic crops during seasonal water shortages or persistent droughts. • There was no difference in cucumber production when comparing the GTB ma nure to a commercially available inorganic fertilizer. Future research should address the economics of integrating fresh aquaculture effluent from the UVI biofloc system with agronomic crop production. Although this project demonstrated the geotextile tech nology is capable of improving on-farm water and nutrient use, a study is needed to determine if there is a cost savings for the farmer through recycling the nutrients with geotextile technology. The UVI Aqua culture Program has a commercial-size biofloc system with an adjacent agronomic field to perform the experiments. Research should also address the effect of crop production to maximize residual nutrient levels in the soil from initial GTB manure application and determine if GTB manure improves physical characteristics of the soil after repeated applications. Figure10. The cucumber research plot was harvested three times each week from 6 March to 10 April. Figure 11. Mean total harvest weight and marketable harvest weight (± standard deviations) of Calypso cucumber as affected by fish manure (FM) or Osmocote® (OZ) treatments. 30 _ 25 a> | 20 tn c 2 15 •*-> 3 10 0) 5 0 L- .op ffi ^ .& ^ ^ ^ ^ Treatment • Total • Marketable 1 # „\# Prepared by Jason Danaher, Aquaculture Research Specialist II. Issued by the University of the Virgin Islands Agricultural Experiment Station, Dr. James Rakocy, Director. This project was funded through the Water Resources Research Institute Program under grant #2007VI90B. University of the Virgin Islands Agricultural Experiment Station RR 2, Box 10,000 Kingshill, VI 00850 Telephone: (340) 692-4020 Fax: (340) 692-4035 http://rps.uvi.edu/AES/aes_home.html UniveoSyVirginIslands www.uvi.edu SPECIALIZING III FUTURES HISTORICALLY AMERICAN UNIQUELY CARIBBEAN GLOBALLY INTERACTIVE