A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science, School of Environment, Resources and Development

Thesis (M.Sc.) - Asian Institute of Technology, 2006

This study was conducted at the Agricultural Systems Research Farni during October 2005 to March 2006. The objectives of the study arc to determine the potential of duckweed to fix atmospheric N and released to its media and to explore the potential to use such N for crop production using lettuce through hydroponics to reduce fertilizer use. The study had two experiments; the first was the quantification on N contribution by different population of duckweed. This study used five duckweed populations and a control (with no duckweed). There was a highly significant (p=0.05) effect of duckweed populations on anmnionium-N (NH.,}-N) Nitrate-N (N03'-N) concentrations. Duckweed initially increased its population, but degeneration commenced at 21 days in higher populations and lower populations it began later (35 days). The second study had seven flow rates of circulating water from duckweed grown containers. Lettuce was grown using N from duckweed only and a control without duckweed was included. The marketable head yield of lettuce of the control treatment was 1153 kg /4 m unit. The treatment that had a flow rate of 300 1/hr gave a 192 g/4 m unit, which is the highest among the duckweed supported treatments. Based on the N in lettuce, a water surface area of 1.4 m2 was found adequate to satisfy all the N requirement of lettuce in a 4 m unit in 20 days. The N contribution by duckweed towards the yield of lettuce at 200 1/hr rate was 95.95 mg/ hydroponic unit, while 121.87 nig was from 300 I/hr rate within a 20-day period. The projected N levels contributed by duckweed were in the range of 87.5 to 111 kg/ha/yr. This shows remarkable benefits from incorporating duckweed as a biological N fixer to hydroponic production of lettuce