An efficient and economic disposal strategy for effluents from hydroponics culture in Mauritius

1. An efficient and economic disposal strategy for effluents from hydroponics culture in Mauritius By: Prathima SEECHURN Supervisor: Dr B. Lalljee Associate Professor, University of Mauritius

2. STATEMENT OF PROBLEM Intensive Agriculture Open field Hydroponics Culture Heavy use of fertiliser /agrochemicals Only 50 % of fertiliser absorbed by plants – 50% lost Excess leachate dispose in environment Groundwater, surface water, soil contamination

3. STATEMENT OF PROBLEM Local Studies – E.g Nitrate concentration • Values measured from boreholes of Choisy and Poudre D’or between 10-20 mg/L with occasional peaks exceeding 40mg/L at times • At Fond du Sac, Riche Terre and Petite Rivière concentrations measured oscillated between 20 to 40 mg/L A sign of warning

4. Flow of excess solution from greenhouse

5. RATIONALE OF THE STUDY • Today, public is much concerned about protecting our environment for future generation Sustainability • Sustainable production using Good Agricultural Practices (GAP) • Optimise use of fertiliser/water i.e reduce wastage • price of fertiliser escalating and water becoming a scarce resource

6. AIMS & OBJECTIVES To assess the potential risk associated with hydroponics effluents and evaluate the potential of using it as a source of nutrients and water in crop production

7. ACTIVITIES • To carry out survey among hydroponics growers • To assess the amount of liquid effluent discharge from hydroponics system • Characterisation of hydroponics effluents • To assess the performance of crops fertilised with hydroponics effluents - pot trials

8. METHODOLOGY Activity 1: Survey among hydroponics growers • Face to face interview Activity 2: Assessing the amount of liquid effluent discharge from hydroponics system • To record the amount of effluents for the whole crop cycle at different greenhouses for different crops

9. METHODOLOGYActivity 3: Characterisation of Hydroponics Effluents • To conduct a preliminary analysis • Leaching of nutrients at different substrates • Collecting samples at three times interval to evaluate for any variation in concentration • To collect effluents from different greenhouses • Tomato • Sweet Pepper • Cucumber • & others

10. METHODOLOGY Activity 3 (Contd’): Characterisation of Hydroponics Effluents • Plastic tank of 50 litres capacity buried outside the greenhouse to collect the over drain solution. Collection of effluents from greenhouse

11. METHODOLOGY Activity 3 (Contd’): Characterisation of Hydroponics Effluents HYDROPONICS EFFLUENTS ANALYSIS Determination of : • pH • Electrical Conductivity • Nitrate • Phosphate • Macro & micro elements

12. METHODOLOGY Activity 4: Assessing the performance of crops fertilised with hydroponics effluents - pot trials (bean) • EXPERIMENTAL DESIGN Randomised complete Block Design - 6 treatments replicated 4 times • TREATMENTS T1 :No fertiliser and no hydroponics effluents T2 :Hydroponics effluents only T3:25% mineral fertiliser + hydroponics effluents T4: 50% mineral fertiliser +hydroponics effluents T5: 75% mineral fertiliser + hydroponics effluents T6: 100% mineral fertiliser as per recommended rate

13. METHODOLOGY Activity 4 (Contd’): Assessing the performance of crops fertilised with hydroponics effluents - pot trials (bean) • PARAMETERS RECORDED • Plant height • Full weight of pods at maturity per plant • Weight of whole plant • Percentage dry matter

14. Note: Question 1: How do you dispose the Hydroponics Effluents? Question 2: Are you aware of the economic value of the Hydroponics Effluents? Question 3: Do you know that this solution can be used alternatively for crop production? Question 4: Have you ever thought of having your hydroponics culture along with a small plot in field where hydroponics effluents is used as fertiliser? Question 5: Will you be interested in investing in such technology? RESULTSActivity 1: Survey among hydroponics growers

15. RESULTSActivity 2: Assessing the amount of liquid effluent discharge from hydroponics system • Under normal condition, out of an average of 100 ml of nutrient solution provided per plant around 60% of solution is absorbed by the plant and the rest are leached out as hydroponics effluents. • On average, the amount of hydroponics effluents collected per day from a greenhouse is around 1 litre per square metre and has a nitrate concentration of 108 mg/L. • Hence, the amount of nitrogen lost for a greenhouse of 250 m2 is 27 g per day. Work still under progress

16. RESULTSActivity 3: Characterisation of hydroponics effluentsPreliminary Observation Forecast: • Area of 20 hectares under Hydroponics Culture – 22 Kg of nitrogen will be lost to the environment per day % Solution lost from different substrates

17. RESULTSActivity 3 (Contd’): Preliminary Observation Mean Nitrate concentration at different time interval

18. RESULTSActivity 3 (Contd’): Preliminary Observation At 13.30 p.m the plants did not absorb nitrate nutrients. This could be explained by the fact that in afternoon the demand for water is higher than that of fertiliser. As such it can be concluded that hydroponics effluents do contribute partially to environmental pollution.

19. RESULTSActivity 4 : Assessing the performance of crops fertilised with hydroponics effluents - pot trials (bean) • Analysis under process

20. DISCUSSION • Savings on purchase of fertilisers – price of fertiliser escalating year by year (30% increase over the last year) • Environmental cost – lesser contribution to pollution as compared to disposal in drains

21. CONCLUSION • The use of Hydroponics Effluents for crop production can help to make savings on fertiliser and be considered as a practical alternative to prevent further environmental damage. • Further research needs to be undertaken to understand the fate of hydroponics effluents to the soil/water profile

22. RECOMMENDATION • Strategies to minimise possible damage caused by Hydroponics Effluents would be: - sensitization of farmers on the potential risk of disposing Hydroponics Effluents in drain, - Training of farmers - Use of Hydroponics Effluents in an integrated system - Reset fertigation time - Electrical Conductivity Meter to be at disposal of each planter - Review of Chemical Fertiliser Control Act To be worked out

23. Reference • Agricultural Research and Extension Unit (2004). Cultures légumières. In Le Guide Agricole. Published by Agricultural Research and Extension Unit/Food and Agricultural Research Council. • Hochmuth. R. C and M.S Sweat, (1999). – Hydroponics Nutrient Effluent, A recoverable Energy Resource. University of Florida. • Howard M. Resh, Ph.D, (1998). A definitive Guidebook for the Advanced Home Gardener and the Commercial Hydroponics Grower, fifth edition. • Ministry of Environment and National Development Unit, Government of Mauritius. (2005). Threat to freshwater resources. In: Mauritius staking out the Future. • Ministry of Environment and National Development Unit, Government of Mauritius. (1991). State of Environment Report. pp 12, 63, 72 & 91.

24. Acknowledgements • Field workers from AREU Crop Research Station • Hydroponics growers • Technical staff of the University of Mauritius • MRC for funding.

25. To end • If you save This • We can save This