Lotus-Fish Culture in Ponds: Recycling of Pond Mud Nutrients
(Originally titled Taro-Fish Culture in Ponds:
Recycling of Pond Mud Nutrients)
New Aquaculture Systems/New Species Research 1 (9NS1)/Experiment
Note: The following work plan replaces that in the Ninth Work Planin full.
Experimental Location and Design Modification
Due to the unavailability of facilities in Nepal, the study was conducted at the Asian Institute of Technology. Additionally, lotus is more appropriate than taro to be cultured in fish ponds in terms of nutrient removal and economic return.
Regular fertilization in fish ponds accumulates nutrients in pond mud. One hectare of old pond mud was reported to have the equivalent of 1.85 tons of urea and 2.30 tons of TSP (Shrestha and Lin, 1996) or 2.8 tons of urea and 3.0 tons of TSP (Yang and Hu, 1989). Pond muds are a major sink for phosphorus, and adsorption capacity is related to mineral composition and clay content of pond muds (Shrestha and Lin, 1996). Release of adsorbed-P to the water column is minimal, and phytoplankton are not as effective to utilize adsorbed-P as rooted crops. Roots extended in interstitial water of soil provide a better opportunity to extract P from soil (Denny, 1972; Boyd, 1982; Smart and Barko, 1985) and hence, pond muds have been widely used to fertilize land crops (Muller, 1978; Little and Muir, 1987; Christensen, 1989; Shrestha and Lin, 1996). However, removing pond mud is labor intensive and its practicability is questionable (Edwards et al., 1986). Alternatively, lotus-fish culture may be considered to utilize reserve nutrient in muds. Lotus (Nelumbo nucifera) is an aquatic emergent plant that is seen to grow as tall as one meter. Lotus is an important and popular cash crop in many Asian countries. It is commonly planted in fields or ponds with nutrient-rich muds, with a growing season of 100 to 150 days. It can extract nutrients from pond sediments efficiently. The co-culture and rotated culture of lotus and fish have been practiced in China for many years. Water levels of ponds can be increased as lotus grows. Fish can be stocked when water levels reach 30 cm and harvested 4 to 5 months after lotus is planted. Additionally, lotus shoots will provide a substrate for the growth of epiphytic algae, which is consumed by tilapia (Bowen, 1982; Lowe-McConnell, 1982; Shrestha and Knud-Hansen, 1994).
Results of the experiment will provide information on lotus-fish culture and recycling of pond mud nutrients, which are otherwise wasted. It will generate information on bottom mud characteristics altered by rooted plants. It may benefit small-scale farmers of Asian countries for resource utilization where lotus is commonly grown as a cash crop.
Location:Asian Institute of Technology.
Pond Facility:9 ponds of 200 m2 size.
Culture Period:5 months.
Test Species:Nile tilapia (Oreochromis niloticus); lotus (Nelumbo nucifera).
Stocking Density:Tilapia 2/m2; lotus plant spacing 2 x 1 m.
Nutrient Input:Weekly fertilization by urea and TSP @ 4 kg N and 1 kg P ha-1 d-1. No fertilization for the lotus-only treatment.
Water Management:After lotus planting, water level will be increased as the height of lotus plant increases. Once the water level reaches 30 cm, tilapia will be stocked. Water level will be increased with growth of lotus up to 1 m depth.
Sampling Plan:Biweekly and monthly diel water quality following standard CRSP protocol. Initial and final pond mud sampling for organic C, total N, available N, total P, available P, soil pH.
Partial budgets will be estimated for cost of inputs and value of fish and lotus. Fish growth and survival will only be assessed at the end of the experiment due to sampling difficulties. Fish and lotus will be harvested by draining. Nutrient budgets will be estimated for all ponds.
Experimental Design, Hypotheses, and Statistical Methods:Experiment will have 3 treatments in triplicates: a) lotus-fish culture, b) only fish, and c) only lotus. The null hypotheses are that there will be no differences in mud nutrient contents, soil characteristics, fish growth, and nutrient recovery between pairs of treatments. Significant differences will be tested using ANOVA.
Lotus is a popular cash crop in many Asia countries. Nile tilapia is commonly cultured in the region. Small-scale farmers are resource limited and lotus-fish culture may utilize waste nutrient resources otherwise.
February to August 2000
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