1. Nutrient fluxes in aquaponics systems Harry Ako and Adam Baker Molecular Biosciences and Bioengineering College of Tropical Agriculture and Human Resources University of Hawaii at Manoa

2. I Definition. Aquaponics, our way of looking at it. Feed fish. Fish metabolites remediated by bacteria. Fish water nourishes plants. And is recycled. Feed Plants take up metabolites to grow Bacteria remediate toxic N species bioremediated water Fish grow and excrete metabolites cleaner water Feed

3. I Definition. Benefits. 2 crops from 1 input no effluent (negligible environmental impact) productivity 6 times higher than soil agriculture very suitable for islands Our experiment just before harvest

4. http://rps.uvi.edu/AES/Aquaculture/basil2002.jpg II History. Prevailing system developed by James Rakocy Research began in the 1970’s Plants (in raceways) added to a fish tank system (under black tent)

5. Complex equipment necessitate high capital expense and constant electricity Operation and maintenance requires a trained staff Attempted and failed in Saipan II History. The system is very complex. clarifier degassing tank sump screen filter tank Air pumps, water pump, and 237 air stones (not shown) Fish tank

6. After we finished our work we discovered a nice quote: “Estimates of nutrient uptake and a deeper understanding of culture water nutrient dynamics are required for design criteria” Rakocy and Hargreaves, 1993 Hypothesis: Plants have nutritional needs that can be discovered. Fish can supply these needs if their husbandry can be matched to the nutritional needs of the plants. What model is the starting point? – The Virgin Island model of the ‘70s? Has problems. Failed once before. – UHM hydroponics systems not only academically successful but also commercially successful? – In some subject matter areas UHM and CTAHR are the places to be in the world as homes for intellectual property.

7. III Determination of lettuce nutrients Nutrients Hydroponics nutrients Remaining after 4 weeks Remaining after 6 weeks Manganese (mg)3072%1% Nitrogen (g)3370%5% Potassium (g)53.774%14% Calcium (g)31.183%51% Magnesium (g)16.191%53% Phosphorus (g)11.290%45% Iron (mg)337123%83% Zinc (mg)77.797%62% Copper (mg)55.561%56% Boron (mg)32286%59% Used hydroponics nutrients (Kratky, a UHM colleague) Used ICP-AES to measure nutrients used up in intermediate (4 weeks) and full cycle (6 weeks) grow out In the early weeks not much used up. First benchmark, 48 heads lettuce. Nutrients used up at full cycle were hypothesized to be required nutrients (remember these words in future slides)

8. III Testing the required nutrients hypothesis. Try lower Ca and Mg from original formula. Nutrients Required nutrients Low Ca & Mg Hydroponics Manganese (mg)305 307 Nitrogen (g)31.6 33.3 Potassium (g)46.0 53.7 Calcium (g)15.2 18.8 Magnesium (g)4.72 6.97 Phosphorus (g)6.12 11.2 Iron (mg)58.1 688 Zinc (mg)29.6 77.7 Copper (mg)24.6 55.5 Boron (mg)133 322 1 st column, required nutrients. 2 nd column, lowered Ca and Mg in hydroponics mix should theoretically meet plant needs No reduction in yield found a a

9. III Testing the required nutrients hypothesis. Try higher nitrogen Nutrients Required nutrients Provided to High N Manganese (mg)305 307 Nitrogen (g)31.6 62.2 Potassium (g)46.0 53.7 Calcium (g)15.2 31.1 Magnesium (g)4.72 16.1 Phosphorus (g)6.12 11.2 Iron (mg)58.1 688 Zinc (mg)29.6 77.7 Copper (mg)24.6 55.5 Boron (mg)133 322 1 st column, required nutrients. High N trial theoretically exceeded plant needs N uptake was greater (not shown) But no benefit in yield, even when grown in better sunlight

10. III Testing the required nutrients hypothesis. Try lowering the K Nutrients Required nutrients Provided to Low K Manganese (mg)305 307 Nitrogen (g)31.6 33.3 Potassium (g)46.0 34.3 Calcium (g)15.2 31.1 Magnesium (g)4.72 16.1 Phosphorus (g)6.12 11.2 Iron (mg)58.1 688 Zinc (mg)29.6 77.7 Copper (mg)24.6 55.5 Boron (mg)133 322 1 st column, required nutrients. Lowered K level trial theoretically inadequate for lettuce plants Lettuce yields significantly reduced a b ControlLow K

11. III Testing the required nutrients hypothesis. Temporal experiment. If use ¼ nutrients, the required nutrient curves predict that they will run out by week 4 Growth stunted at Week 4 Biochemical approach not only valid in terms of nutrient amounts but also valid in terms of time 1/4 th nutrients, Week 4Control, Week 4

12. III Testing the required nutrients hypothesis. Temporal experiment. If use 1/2 nutrients, the required nutrient curves predict that they will run out by week 6. Growth stunted at Week 6 Nutrient amounts defined as “required nutrients” seem accurate Lettuce head weight (g) a b Control ½ nutrients

13. Footnote: Supplemental Fe is required However, Mn supplementation was found to be unnecessary Control, Week 3 Aquaponics (no iron) Week 3 Aquaponics, Week 4 Fe chelate With Mn Lettuce head weight (g)

14. IV Determination of conditions to produce nutritious fish water. The math Nutrients Required nutrients (g; determined previously) Daily requirement from 20 L (mg/L) Manganese0.3050.36 Nitrogen31.637.6 Potassium46.0154.8 Calcium15.218.1 Magnesium10.612.6 Phosphorus6.1177.28 Iron0.0580.49 Zinc0.030.036 Copper0.0250.03 Boron0.1330.015 Required nutrients from previous work Assumed that these will be satisfied by a 20 L daily exchange Second benchmark, 6% daily water exchange a day. We need to do more work with flowing systems. Marissa’s is a start. For a tray of 48 lettuce heads

15. IV Determination of conditions to produce nutritious fish water Nutrients (mg/L) Daily requirement from 20 L (mg/L) Fish water 14 g feed daily Fish water 20 g feed daily Fish water 40 g feed daily Manganese0.3600.0020.001 Nitrogen37.6303447 Potassium54.8101100105 Calcium18.122.546.233.9 Magnesium12.613.518.621.0 Phosphorus7.284.466.3610.7 Iron0.490.0010.0110.038 Zinc0.0360.010.0210.095 Copper0.030.040.020.059 Boron0.0150.050.090.079 Stocked tilapia in 200 L of water. Fed and removed 20 L daily. Daily requirement in first data column When fish biomass was such that they ate 14 or 20 g of feed daily, several nutrients would be deficient When fish biomass was such that they are 40 g of feed daily, all requirements would be met (except iron and Mn). Another consequence is that nitrogen may be used as a proxy for all nutrients

16. IV Determination of conditions to produce nutritious fish water. Tank Daily feed input (g) Tilapia biomass (kg) Nitrate N (mg/L) 1592.544 2542.549 Nitrate N (mg/L) Tank size (L) Daily water exchange (L) Daily feed input (g) Tilapia biomass (kg) 4720020402.3 The above was replicated in 5 week experiments. As before 20 L of water were removed daily from a 200 L tank. The following resulted. Alternate third benchmarks, 44-49 mg nitrate N/L, 40-59 g feed/day, and 2.3-2.5 kg fish. Additional benchmark, have to bring the biofilter up slowly and carefully. Fish rearing the hard part. The previous data suggested that 40 grams of feed per day provided to 2.3 kg of tilapia maintained target nutrient concentrations of 47 mg/L nitrate-N in a 200 L tank with a 20 L of water removed daily. Shown below.

17. V Aquaponics = aquaculture + hydroponics, integration. Verification of predicted lettuce needs If benchmarks can be hit, aquaponics lettuce heads were not significantly different in size to hydroponics lettuce heads.

18. V Aquaponics = aquaculture + hydroponics, integration. Fish growth parameters Tank Fish recovered/ stocked Fish biomass (kg) Feed input (kg) FCR Mean weight (g) StartEndGainedStartEnd T1 51/513.355.842.49 4.84 1.9 66114 T2 48/483.386.322.94 4.72 1.6 71132 During the 10 week aquaponics trial, fish growth was measured (tanks proportionate to 1.5 lettuce trays) Can be used to predict fish yields in aquaponics

19. Tank Fish biomass (%) Lettuce biomass (%) Denitrification or solids (%) T1264034 T2324127 T3224929 Mean274330 Of total nitrogen input into the system as feed, about 27% is captured as fish flesh, about 43% is captured as lettuce biomass, and a small fraction is lost as nitrogen gas or as solids used to fertilize garden plants None released into the environment V Aquaponics = aquaculture + hydroponics, integration. Aquaponics is environmentally friendly Denitrification a problem.

20. Midterm conclusions Our nutrient fluxes are for trays with 48 heads of lettuce. Fish are held in 200 L (50 gallon) tanks at about 12.5 kg/m 3 and are fed 40-60 g of feed a day. This is 5 times less than Rakocy’s. Hence, our system proven with only one moving part, an air pump (which we are trying to get rid of) and is very simple and very inexpensive. Some people are using it with great success.

21. VI Scenarios. Single family size Components One lettuce tray (1.2 X 2.4 m) One fish tank (200 L) One small air pump Shade cloth Specifications Other designs are permissible as long as the basic specifications are followed. In this instance fish are under the plants, water flows constantly, etc. Water transfer, manual Fish biomass, about 2.5 kg Daily feed, 40-59 g Iron chelate, 0.25 g/week 1.4 heads lettuce/day; 1.8 kg tilapia/10 weeks Cost, 250 USD

22. VI Scenarios. Micro-farm size Components 8 linked lettuce trays one 1600 L fish tank one air blower water pump Shade cloth (50%) Specifications stock about 19.2 kg of fish feed 0.32-0.47 kg/day iron chelate 2 g/week annual production, 3300 heads of lettuce and 75 kg tilapia annual income about 8600 USD at Hawaii farmgate prices…ratio of lettuce to fish income cost of construction, 2500 USD

23. VI Scenarios. Small farm, 0.1 hectare Components equivalent of 270 lettuce trays 54,000 L in tanks air blower recirculate water with a water pump Specifications stock about 648 kg of fish daily feed, 11-16 kg annual production, 112,000 heads of lettuce, 2,500 kg tilapia Income 234,000 USD/year Cost, <80,000 USD

24. Summary Fine tuned lettuce nutrient requirements Set fish parameters that provide optimal nutrition to plants Verified results in several aquaponics trials These fluxes eliminated all electrical components but aeration in fish tanks Rational parameters will allow for flexible aquaponics design to accommodate different needs and physical environments weidenbach, koch, May’s, Ho Farms, Dave Campbell The methodology described can easily be applied to grow other crops

25. Thank you This work was funded by the United States Department of Agriculture (USDA) Center for Tropical and Subtropical Aquaculture (CTSA) through Grant No. 2004-38500-14602