Preliminary study on broodstock rearing,induced breeding and grow‐out culture of the sea cucumber Holothuria scabra in Sri Lanka

Experiments were conducted to identify suitable methods for broodstock rearing, induced breeding and grow‐out culture of Holothuria scabra in Sri Lanka. Two hundred and seventy‐two brooders (500–600 g) collected from off Mannar were individually packed in oxygen‐filled polythene bags with and without sea water and transported to a sea cucumber hatchery at Kalpitiya. Lagoon pens, sand‐filled fibreglass tanks and bare tanks were used in triplicates to maintain brooders. Spawning was initiated using air dry, water jet and thermal‐stimulation methods. Hatchery produced juveniles with an average weight of 11 ± 5 g were reared (2 individuals m^?2) in lagoon pens, mud ponds and fibreglass tanks in triplicates. The significantly high evisceration rate was observed when brooders were transported without sea water (t‐test, P < 0.05). Brooders maintained in bare tanks showed a significant weight reduction than the brooders in sand‐filled tanks and lagoon pens (anova , P < 0.05, d.f. = 2). Thermal stimulation (ambient temperature ± 3–5°C) was found to be the most successful method of spawning initiation of H. scabra. The mean (±SD) percentage males and females participated for spawning per trial was 9.2 (±10) and 4.6 (±5.6) respectively. On an average, 1.16 millions of eggs (±1.03 SD, n = 5) were obtained per spawning trial. H. scabra juveniles reared in tanks showed significantly lower growth rate than the juveniles in pens and ponds (anova , P < 0.05). Lagoon pens and sand‐filled tanks are suitable to maintain brooders and lagoon pens can be successfully used for mass rearing of juveniles.     

Stability analysis of aggregates in relation to the hydrophobicity of organic manure for Sri Lankan Red Yellow Podzolic soils

Aggregate slaking is linked with rapid pressure buildup within aggregates. Soil water repellency may help hamper the pressure buildup within aggregates by reducing their wetting rates. We examined the effects of animal manure in improving aggregate stability, the hydrophobic effects of green manure, and the possibility of using organic manure mixtures to increase the aggregate stability for Sri Lankan red yellow podzolic soils using model aggregates. Almost all the cow dung (CD) added samples showed extremely low percentages of water stable aggregates (%WSA) demonstrating rapid destruction of aggregates. Although the addition of ≥ 10% goat dung (GD) improved the %WSA, aggregate floating occurred, showing the risk of aggregate floating with runoff water. Addition of 5% GD would be an acceptable solution if the %WSA can be improved. Casuarina equisetifolia L. leaves (CE) was found to be a hydrophobic green manure. Although addition of ≥ 5% CE increased the %WSA up to about 90%, aggregate floating occurred. The possibility of improving %WSA using 1–2% hydrophobic green manure in organic manures mixtures was tested. Samples with 5% GD + 2% CE manure mixture showed the highest and the most stable %WSA without showing aggregate floating. Additions of compost and poultry litter were found not to be effective in improving aggregate stability with or without CE. Strong or higher water repellency was not observed in any of the samples with manure mixtures, showing that the addition of 1–2% hydrophobic CE would not induce detrimental effects of water repellency. There was no clear correlation between %WSA and the hydrophobicity of soils. However, the %WSA can be considered to show a tendency to increase with increasing hydrophobicity, because the %WSA was very high in samples with hydrophobic CE, the %WSA increased when mixed with 1–2% CE, and samples with highest water drop penetration time (WDPT) among all the manure mixtures showed the highest %WSA.     

斯里兰卡的柽麻生长规律及水肥条件对产量的影响

本文是笔者在斯里兰卡连续五次种植柽麻的研究结果。结果表明,柽麻在苗高18厘米时是生长速度的转折点,在此之前是幼苗缓慢生长期,在此之后生长速度增加2—4倍,至初花期生长速度又明显减慢,生长曲线呈S形。因柽麻无论何时播种,从出苗至开花的总天数比较相近,所以缩短幼苗缓慢生长期是获得柽麻高产的关键。采取科学的水肥管理是缩短幼苗缓慢生长期的有效途径。 试验表明,出苗期、生长前期和开花期的适宜土壤含水量分别为不低于田间持水量的60％、40％和50％。在苗期施用磷肥和少量氮肥可促进幼苗生长。因此,只要在出苗后及时地加强水肥管理,就能确保柽麻的高产。     

Water Rights and Multiple Water Uses – Framework and Application to Kirindi Oya Irrigation System Sri Lanka

The growing attention to water rights inrecent years reflects the increasingscarcity and competition for this vitalresource. Because rights are at the heartof any water allocation system, they arealso critical for any reallocation. Notonly efficiency, but also fundamentalissues of equity are at stake. Tounderstand water rights requires goingbeyond formal statutory law (which may ormay not be followed), to look at the manybases for claiming water. Because of thevital nature of this resource, state law,religious law, customary law and localnorms all have something to say in definingwater rights. Delineating water rights isfurther complicated when we take intoconsideration multiple uses (irrigation,domestic, fishing, livestock, industries,etc.) as well as multiple users (differentvillages, groups of farmers in the head andtail, fishermen, cattle owners, etc.) ofthe resource. These overlapping uses bringin different government agencies, as wellas different sets of norms and rulesrelated to water.This paper provides a framework forexamining the statutory and customary waterrights of multiple users of water andapplies it in the Kirindi Oya irrigationsystem in Sri Lanka, based on amultidisciplinary study conducted in1997–1998. It demonstrates that thestakeholders of an irrigation system go farbeyond the owners and cultivators ofirrigated fields. These groups are notonly claimants on the ongoing management ofwater resource systems, but also need to beincluded in any considerations oftransferring water from irrigation to otheruses.     

Introducing monitoring and evaluation into main system management — a low investment approach

The need to develop a framework for performance assessment of irrigation schemes is increasingly dominating discussions in the field of water management. This paper supports the view that the introduction of monitoring and evaluation of water distribution systems as a part of the day to day management activity is a desirable step in the improvement process and can be introduced at little cost.Data already being routinely collected in many schemes provide a valuable insight into scheme operation and can be used to improve planning of operating strategies. One aim of the study being carried out by Hydraulics Research and the Irrigation Department at Hakwatuna Oya in Sri Lanka is to improve the standards of main system management within the constraints of the existing physical infrastructure through the provision of timely performance data. A microcomputer has been installed at the project office to store and analyse rainfall, flow and field wetness data, and to provide performance reports on a regular basis. Early results suggest that the timely processing of an increased level of data collection is effective for both the identification of problems and the quantification of potential for improvement. Particular emphasis is given to providing the necessary software tools and training such that routine monitoring and evaluation becomes an accepted and sustainable proposition.     

The significance of the gastrointestinal parasites of Asian buffalo in Sri Lanka

Buffalo aged 3–15 months on institutional farms and in the villages of an irrigation project were monitored for gastrointestinal nematodes by faecal egg counts over two years. Apart from treatment for Toxocara vitulorum at 10–16 days of age, no anthelmintics were used. Half of the strongylid egg counts were zero and 90% were less than 500 epg of faeces on the institutional farms, and 67% were zero and 97% less than 500 epg in the villages. No problems arose during four years without anthelmintics on the institutional farms and during two years in the villages. Autopsies demonstrated that the eggs which were present were produced by mixed infections of small numbers of Haemonchus spp., Mecistocirrus digitatus, Trichostrongylus spp., Bunostomum phlebotomum and Cooperia spp. High egg counts of Strongyloides papillosus occurred in calves up to six months old, but were not pathogenic.     

Variation in canopy structure, light and soil nutrition across elevation of a Sri Lankan tropical rain forest

Mixed dipterocarp forests are perhaps the single most important rain forest type in the wet tropics. Only a few studies have purposefully examined differences in resource availability across mixed dipterocarp forest landscapes by simply measuring the abiotic variables of light, soil nutrition and soil water availability in relation to forest structure. We sought to directly measure the environment of canopy gaps across elevation and geology—from lowland mixed dipterocarp forest (100 m amsl) to lower montane dipterocarp forest (1200 m amsl) in southwest Sri Lanka. Middle elevation gap sites (300–900 m amsl) were subdivided into valley, mid-slope and ridge topographic positions. Eighteen natural disturbances all of which were canopy openings caused by tree fall, were randomly selected within primary rain forest that ranged across 100–1200 m elevation. Plots were placed in gap centers and in adjacent understories and measurements taken of forest structure (basal area, canopy height, canopy cover index, CCI), shade (light sensors—photosynthetically active radiation [PAR], canopy hemispherical photographs—global site factor [GSF]) and soil nutrition (pH, exchangeable Al, K, Mg and Ca; Total N; and plant available P). Soil moisture was measured at bi-weekly intervals for five years across middle elevation sites only (300–900 m amsl). Stand basal area, mean canopy height, and canopy cover index all declined with increase in elevation. Understory PAR and GSF decreased with increases in canopy height, basal area and CCI. Size of canopy opening decreased with increase in elevation, but PAR and GSF increased. Valley sites had significantly greater levels of mean percent soil water content as compared to mid-slope and ridge sites of middle elevation sites. However, at the onset of the southwest monsoons in May all sites were similar. Differences were most pronounced during the dry season (December–April). No differences in soil moisture content could be found between gap and understory microsites. K and Ca in gap centers and adjacent forest understories increased with increase in elevation and change in associated geology. pH increased and Al decreased with elevation and associated geology but only for forest understory conditions. Results demonstrate strong differentiation in soil and light resources with elevation that appears related to size of tree-fall disturbance, stature of the forest, topographic position and underlying geology and soil-weathering environment. This suggests that forest management and conservation practices need to develop and tailor techniques and treatments (silviculture) to the forest that emulate and/or account for change in elevation, geology and topographic position. Further studies are needed to identify which are the primary underlying mechanisms (e.g. temperature, wind, soil nutrients, soil moisture availability) defining change in forest structure across elevation.