PD/A CRSP pond management strategies rely on high nutrient loading rates
to increase pond productivity. However, there is little information on the
effect of semi-intensive pond management strategies on quality of pond
effluents. Discharge of nutrient-rich pond water may result in deteriorated
quality of receiving waters. Development of nutrient budgets would permit
quantification of potential pollution impact of a specific pond management
strategy. The objectives of the Global Experiment for this reporting period
are, therefore, to develop nutrient budgets for nitrogen and phosphorus for
semi-intensively managed freshwater and brackish water production ponds and to
quantify the effect of pond management strategy on water and sediment quality.
Two treatments, each replicated three times will be tested in each environment.
Freshwater treatments for Nile tilapia (Oreochromis niloticus) consist
of chemical fertilization plus commercially formulated fish ration (min. 20%
crude protein) beginning on day 80 (Treatment 1) and chemical fertilization
followed by commercially formulated fish ration (min. 20% crude protein)
beginning on day 80 (Treatment 2). Brackish water treatments for Penaeus
vannamei consist of feeding a commercially formulated shrimp ration
containing 20% crude protein, (Treatment 1) and feeding a commercially
formulated shrimp ration containing 30% crude protein (Treatment 2). The
culture period will be
240 days for tilapia and 120 days for shrimp. Standard PD/A CRSP protocol will
be followed to determine water budget, water quality, and sediment quality
data. The experiment was started at the Honduras and Thailand sites.
Low pond mud pH or pond water alkalinity are indications that lime
should be applied to produce more favorable chemical environments for pond
aquaculture. A number of methods are available for estimating the lime
requirement. A number of workers have suggested the relationship between soil
pH and soil base saturation differs with the amount of clay and organic matter
present, and the mineralogy of the clay fraction. This study was designed to
evaluate the suitability of several lime requirement (LR) estimators for a
variety of soils from global sites. Soil samples were tested for LR and then
added to beakers with 750 ml of soft water and the estimated amount of
limestone. Water alkalinity was then monitored over the following 28 days.
Results suggest different estimators perform better with specific soil types.
Some estimators indicated lime should be added to soils already alkaline, even
though water alkalinity did not increase with added lime. Additional analysis
of these results is underway to identify the most suitable LR estimators for
specific soil types.
Work Plan 7, Africa Study B was designed to evaluate the
suitability of several different lime requirement (LR) estimators for different
soil types by testing them in glass beakers containing soil samples, 750 ml of
soft water and specific lime treatments. The present study was designed to
investigate the use of artificial enclosures (isolation columns) as in-pond
test units and to compare alkalinity response to liming in such enclosures with
results obtained in the laboratory studies. The isolation columns (IC) were
29 cm in diameter, secured to bottomless plastic buckets driven into the pond
soils. Six columns were placed in one pond at a water depth of about
1 m. Three columns were limed according to its estimated LR; three were
controls. Alkalinity response was monitored over the following 28 days. Soil
samples from the same pond were added to
750 ml of similar quality water in glass beakers, along with the appropriate
lime treatment and alkalinity measured over the following 28 days as a
comparison with the IC model. Preliminary analysis of the alkalinity response
patterns for each approach indicate alkalinities for laboratory "microcosms"
and IC were similar after 28 days although the time course of alkalinity
differed. Total alkalinities in unlimed isolation columns remained close to
those in the open pond, while microcosm alkalinities in unlimed treatments
differed from pond patterns, suggesting the columns did not greatly influence
water quality dynamics.
A series of 20 soil samples were collected from aquaculture areas in 14
provinces of Thailand. Samples represented 10 soil suborders, and exhibited
wide variation in physical and chemical properties. Soil samples were treated
with 0, 25, 50, 100, and
200 ppm phosphorus and incubated under water-
saturated conditions for one month. Results show that amounts of added
phosphorus recoverable by water extraction decreased markedly as phosphorus
adsorption capacity (PAC) of samples increased (r=0.88 to 0.96, P<0.01).
This suggests that relative abilities of bottom soils to adsorb and release
phosphorus added to ponds in fertilizers or feeds can be assessed from PAC
data. Because of the importance of phosphorus adsorption by soil in regulating
phosphorus availability to phytoplankton in ponds, the PAC appears to be a more
useful technique than traditional phosphorus extraction methods as an index of
phosphorus status in aquaculture ponds. The PAC was highly correlated with clay
content of soils (r=957: P<0.01), and a knowledge of clay content will
permit a rough assessment of phosphorus status. <P>
As a synopsis of the three main aspects of a larger study conducted
under the aegis of the Pond Dynamics/Aquaculture CRSP, this article summarizes
the main findings of a larger report that establishes how and to what extent
the research is reaching institutions serving farmers in PD/A CRSP countries
and whether they in turn influence the practices of fish farmers. An economic
analysis of experiments featuring various combinations of inputs made in wet
and dry seasons are presented. The primary contours of farmer practices and
perception related to feeding, fertilizing, and marketing tilapia are
summarized. The economic analysis utilizes the survey data and other
information obtained from PD/A CRSP publications, interviews with participating
scientists, and others to examine the economic viability of various
experimental outcomes associated with several years of parallel
experimentation. Economic viability was assessed with primary data obtained
from PD/A CRSP scientists according to their 1983-92 work plan, and nutrient
input regime testing.
Interviews were conducted with tilapia farmers in four PD/A CRSP countries: Rwanda, Honduras, Thailand, and the Philippines. In Rwanda, 21 active Rwandan fish farmers in eight local administrative districts (communes) were interviewed in the Kinyarwanda language during the winter and early spring of 1992. Data were obtained in Spanish from a sample of 51 active Honduran fish farmers in nine of 15 Honduran departments during the fall 1993. Data were obtained from a sample of Philippine fish farmers in four of 15 provinces on the main island of Luzon during winter 1994. The survey was revised and adapted in English; some interviews were conducted in the Tagalog language. Data were obtained in Thai language interviews with 51 active fish farmers in three of 75 Thai provinces during winter 1994.
The institutional connections of the PD/A CRSP were profiled using information obtained in published documents and from interviews and other fieldwork conducted during visits to each country. Based on information obtained from PD/A CRSP scientists, host country counterparts, and other knowledgeables, the institutional context and connections of the research program is portrayed.
Tilapia growers in each of the countries face vastly different institutional systems supporting tilapia production. Where PD/A CRSP activities have the opportunity to influence host country governmental assistance to aquaculture, efforts should emphasize infrastructure and improved functioning of the private sector. Poorly organized fish product markets and input distribution systems often hinder aquaculture development. As markets for tilapia expand, production and support services demand will also expand. Development of private sector marketing services for both production inputs and fish outputs are needed for sustained aquacultural development. Weak connections to the farm level characterize the institutional context in each PD/A CRSP country. Thus, efforts to enhance the transfer and utilization of PD/A CRSP research results will require greater attention to actual and potential pathways of influence and information flow to the farm and village. Better understanding of these relationships will facilitate the conduct of a research program that meets farm-level needs in an environmentally and socially sustainable way.
At the time the Central Data Base was transferred to the University of
Hawaii it was complete through the Fourth Work Plan and nearly complete through
the Fifth Work Plan. Since then data from two experiments in Rwanda and two
experiments in Thailand were added to the Fifth Work Plan data.
The Sixth Work Plan included 19 experiments to be conducted between September 1, 1991 and August 31, 1993. Supplemental Work Plans included nine more experiments to be conducted during that period. All data collected using standard CRSP methods, and which the database could accommodate, were to be reported. (See Sixth Work Plan, page 1). Currently, the CRSP data base includes the following Sixth Work Plan data: two experiments from Honduras, three experiments from the Philippines and five experiments from Thailand. There are no data from Rwanda reported in the data base. In summary, ten experiments from the Sixth Work Plan have been included in the data base.
The Seventh Work Plan experiments covered the period from September 1, 1993 to August 31, 1995. Nine experiments were to be conducted in Honduras; none are reported in the database. Ten studies were to be conducted in Thailand; the results of four of those studies are included in the data base. Two experiments from the Philippines are reported. No data from Egypt are included in the database. Rwanda data are understandably absent. In summary, six experiments from the Seventh Work Plan have been added to the database.