Phosphorus adsorption capacity and availability of added phosphorus in soils from aquaculture areas in Thailand
Claude E. Boyd and Pasert Munsiri, Department of Fisheries and Allied Aquacultures, Auburn University, AL 36849 USA
15 June 1996, CRSP Research Report 96-96
Abstract A series of 20 soil samples was 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 1 mo. 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 the phosphorus status of aquaculture ponds. The PAC was highly correlated with clay content of soils (r = 0.957; P < 0.01), and a knowledge of clay content will permit a rough assessment of phosphorus status.
This abstract was excerpted from the original paper, which was published in Journal of the World Aquaculture Society 27(2)1996:160-167.
Effect of stocking ratio on semi-intensive polyculture of Colossoma macropomum and Oreochromis niloticus in Honduras, Central America
David R. Teichert-Coddington, Department of Fisheries and Allied Aquacultures, Alabama Agricultural Experiment Station, 203 Swingle Hall, Auburn University, Auburn, AL 36849
25 November 1996, CRSP Research Report 96-97
Abstract Tilapia and tambaquí (Colossoma macropomum) were co-stocked in earthen ponds at 0, 25, 75, and 100% of each species. Total density was three fish m-2. Fish were offered a 28% protein pellet. Mean treatment production ranged from 2537 to 5265 kg ha-1 after 182 days. Total production increased curvilinearly, and feed conversion ratios decreased curvilinearly as the rate of stocked tilapia increased. Feed conversion ratios ranged from 1.13 to 2.71. Total nitrogen and chlorophyll a decreased linearly as rate of stocked tilapia increased, because of grazing by tilapia on phytoplankton. Mean tilapia and tambaquí harvest weights ranged from 187 to 325 g, and 122-270 g, respectively. Tilapia mean weight decreased curvilinearly, and tambaquí mean weight increased linearly as the rate of stocked tilapia increased. Tambaquí growth appeared to be hindered by cool water temperature for part of the season. Thereafter, growth rate increased as stocking rate of tambaquí increased. The best species mixture for high production was 75% tilapia and 25% tambaquí, but the highest economic return would depend on prices for each species and size combination.
This abstract was excerpted from the original paper, which was published in Aquaculture, 143(1996):291-302.
Prasert Munsiri, Claude E. Boyd, and David R. Teichert-Coddington, Dept of Fisheries & Allied Aquacultures, Auburn University, Auburn, AL 36849
Ben F. Hajek, Agronomy and Soils, Auburn University, Auburn, AL 36849
25 November 1996, CRSP Research Report 96-98
Abstract Analyses of bottom soils from three recently-established (newer) and three older ponds on each of two, semi-intensive shrimp farms near Choluteca, Honduras, revealed that the 0 to 2.5 cm layer had greater concentrations of most variables than deeper layers. Concentrations of total carbon, nitrogen, sulphur, phosphorus, calcium, iron, manganese, and zinc were greater in older than in newer ponds on one or the other of the farms. After 8-11 y of continuous production, total carbon concentrations varied over pond bottoms, and concentrations usually were greater (1.5-2.5%) in inlet sections. Nitrogen concentrations were about 20% those of carbon, and changes in nitrogen concentration closely followed those of carbon. Precipitation of iron pyrite (FeS2) in anaerobic soil layers was the apparent cause of sulphur accumulation in older ponds. Phosphorus accumulated in older ponds on the farm where heavy doses of fertilizer were applied. Soils of both older and newer ponds on both farms had large accumulations of major cations, a large portion of which were water-soluble salts. There was no evidence of development of adverse soil quality in older ponds.
This abstract was excerpted from the original paper, which was published in Aquaculture International, 4(1996):157-168.
John F. Moehl, ALCOM, P.O. Box 3730, Harare, Zimbabwe
Joseph J. Molnar, Department of Ag Econ and Rural Sociology, Auburn University, AL, 38649-5406
21 January 1997, CRSP Research Report 97-99
Abstract Ethnic tension has been an enduring part of Rwanda's history. In pre-colonial times, a patron-client relationship existed between the warrior Tutsi tribe and the peasant Hutus. During both the brief German colonial experience and the longer Belgian presence, domination of the majority Hutus by the Tutsi Mwami (chieftains) was used to maintain European control of the territory.
The civil war that led to the founding of Rwanda in 1962 was a rejection of both Belgian and Tutsi control of the state. During the same period, neighboring Burundi's independence movement led to a Tutsi-dominated government. In the early 1990s, incursions into northern Rwanda by Tutsi exiles based in Uganda began to destabilize the country and ethnic tensions increased. Uganda President Yoweri Kaguta Musaveni is of Tutsi ancestry.
In 1992, Hutus comprised 90% of the population, the Tutsi 9%, and the Twa 1%. Hutu resentment of Tutsi victories and territorial concessions to the rebel forces led to village-level violence by Hutu militia and civilians. More than half a million lives may have been lost. After several military victories and the death of Rwanda's long-standing leader, Juvenal Habyarimana, Tutsi forces gained control of the capital in 1994 and now comprise the main component of the government.
At this writing, unrepatriated Hutus living in camps in Zaire are reorganizing and rearming. Many perpetrators of the ethnic slaughter await trial in Rwandan jails. In addition to the vast number of ordinary citizens who were lost, many moderate and educated individuals from both tribes were systematically sought out and killed. The murdered doctors, educators, and other skilled individuals represent a tragic loss of human capital.
The work reported in this chapter was accomplished in the decade immediately preceding the most recent outbreak of hostilities. It nonetheless represents a set of experiences and approaches that bears on aquaculture development in Subsaharan Africa and other places where a weak or conflict-ridden state precludes the expectation of long-term government support for extension and other producer services for fish culture.
This chapter prologue was excerpted from Aquacultural Development: Social Dimensions of an Emerging Industy, a multi-author book edited by C. Bailey, S. Jentoft, and P. Sinclair, 1996. Westview Press, Boulder, CO, USA and Oxford, United Kingdom, pp. 233-247.
This study was funded primarily by USAID National Fish Culture Project. The PD/A CRSP provided limited support to Dr. Molnar during the writing of the chapter.
Nathaniel Hishamunda, Department of Agricultural Economics and Rural Sociology, Alabama Experiment Station, Auburn University, Auburn, AL 36849-5406
Curtis M. Jolly, Department of Agricultural Economics and Rural Sociology, Alabama Experiment Station, Auburn University, Auburn, AL 36849-5406
Carole R. Engle, Aquaculture/Fisheries Center, University of Arkansas at Pine Bluff, Pine Bluff, AR 71601
18 January 1997, CRSP Research Report 97-100
Abstract Consistent low yields are a major problem of many small-scale fish farmers in developing economies. The problem plagues Rwandan fish farmers and is embedded in production factors that act, directly or indirectly, in combination with management practices to influence yields. Little is known, however about the causes and to what extent each factor contributes to the problem. Ordinary least squares (OLS) technique was applied to data collected through a survey of 267 small-scale Rwandan fish farmers, to determine which production and management factors affect yields in Rwanda. Selected variables such as pond ownership, elevation, pond size, stocking density, quantity of compost applied, length of production cycle, ability to pay labour, off-farm income, owner's age, educational level, and marital status were regressed on Oreochromis nilotica yields. At the 5% level, pond size, stocking density, and length of the production cycle had significant effects on yields. Increased pond sizes and long production cycles impeded fish production in Rwanda. Higher stocking densities resulted in increased fish yields. The model that best describes the O. nilotica production function in Rwanda is linear. Yield-maximizing composting rates are yet to be applied to fish ponds in Rwanda. The study indicates that farmers have gone beyond cost-minimizing pond sizes and production cycles, which are yet to be researched. Under the perfectly competitive fish and input markets and ceteris paribus assumptions, the optimal stocking density was found to be approximately 34,000 fingerlings/ha.
This abstract was excerpted from the original paper, which was published in Journal of Aquaculture in the Tropics, 11(1996):49-57.
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