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Ilyas Siddique Caroline Gutjahr Gamini Seneviratne Broder Breckling Sudheera W. Ranwala Ian J. Alexander 《Biology and Fertility of Soils》2007,44(1):163-170
Topsoil properties were determined in forest gardens established about 20 years ago on eroded grassland soils (abandoned tea
lands) in the wet zone of the Sri Lankan highlands. They were compared with adjacent, eroded grasslands (abandoned tea lands)
on strongly weathered soils vs soils at earlier stages of pedogenic development in a two-way analysis of variance. Soil pH
in forest gardens was, on average, 6.1, nearly one unit higher than in the adjacent grasslands. In the garden soils, the cation
exchange capacity (CEC measured at pH 4.8) was nearly double, exchangeable calcium concentrations five times and exchangeable
magnesium three times as high as in the grasslands soils. Total soil N content was found to be nearly 40% higher in the gardens.
Topsoil gravel contents in the gardens were less than half as high as in the grasslands. The increases in exchangeable bases
and N in gardens, relative to grasslands, were attributed to increased nutrient retention and acquisition. Higher retention
was partly due to the higher CECpH4.8, and probably to reduced erosion and increased, continuous fine root density in the garden topsoils. Higher field CEC in
gardens was likely to result from generally higher C contents and from the reversal of acidification, presumably caused by
base accumulation and decomposition processes. Our results suggest that forest garden establishment on degraded grasslands
can lead to accumulation of mobile nutrients in the topsoil, probably due to increased nutrient retention, subsoil uptake
and litter input exceeding nutrient uptake by the standing biomass. 相似文献
3.
Imai K Ishihara R Jayawardane GW Nishimori K Nishimori T 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2002,64(10):953-956
Three different polymerase chain reaction (PCR) protocols were evaluated for their ability to detect bovine herpesvirus 2 (BoHV-2): single-step PCR with 3 reaction stages (denaturation, annealing and extension), 2 reaction stages (denaturation and annealing/extension; shuttle PCR), and semi-nested PCR with 3 reaction stages. All the PCR protocols showed the same sensitivity (detection limit of 0.4 TCID(50)). A non-specific band sometimes appeared in mock cell DNA at annealing temperatures below 64 degrees C. The shuttle PCR was found to be superior to the other protocols under consideration because of the speed of its application. Furthermore, no non-specific band was detected in DNAs of eight other DNA viruses. Thus, the shuttle PCR seems to be an excellent diagnostic tool for BoHV-2 infections. 相似文献
4.
The Regional Forest Agreement process has dominated Australian forest policy for the past decade. The RFA process set in place a mechanism by which benchmark conservation values were established for forest ecosystems, whilst addressing the needs of the timber industry. The outcomes of a number of RFA's have been fraught with controversy. Key stakeholder groups have shown disagreement with processes and outcomes of methods employed by government both in establishing conservation reserves and areas allocated to timber harvesting. This research uses non-linear techniques to examine the dynamical behavior in stakeholder responses and to identify patterns of behavior that may lead to prediction of stakeholder responses. The method developed in this research provides a bridge between social sciences and Chaos theory.1 相似文献
5.
G. Seneviratne L. H. J. Van Holm S. A. Kulasooriya 《Biology and Fertility of Soils》1997,26(2):136-140
During the dry season in the tropics, agriculture which is solely dependent upon rainfall as its source of water is frequently
affected by soil moisture stress, resulting in crop failures. Farmers therefore depend mainly on other sources of limited
water supply during this period, such as ground water. Soil moisture conservation measures, especially surface mulching with
loppings and, occasionally, leaf litter and crop residues, are practised. Our objective was to study the decomposition and
nitrogen (N) release from these plant materials under continuously wet, low moisture regimes, i.e. comparable to those which
prevail in the mulches used in the agriculture. A greenhouse experiment was conducted with fresh, chopped leaves of six leguminous
trees, wild sunflower and rice, which were spread as a mulch on a layer of soil. They were maintained at eight moisture levels
(a total of between zero and 43l water m–2 applied over 8 weeks) by spraying water. Different optimal moisture requirements for the rapid decomposition of these species
were observed. These were presumably determined by different physical and chemical properties of the leaves. The amount of
water received to the mulches and their soluble polyphenolic and carbon (C) concentrations played an important role in determining
the decomposition and the mode of N release under non-limiting conditions of leaf N. Specifically, the C concentration governed
N release, while the effect of polyphenolics was important when their concentration was low, as a result of leaching under
relatively high moisture regimes. Leaves with a high polyphenolic and C content, which were subjected to high leaching losses
of these fractions, underwent a change in their N dynamics from net immobilization to mineralization. This study indicates
that leaves with a fast rate of decomposition should be mixed with other species, leaves which decompose more slowly in order
to increase the conservation of soil moisture and also improve the synchronization between N release from the mulch and its
demand by crops.
Received: 6 January 1997 相似文献
6.
Chakrapani V Angus JC Anderson AB Wolter SD Stoner BR Sumanasekera GU 《Science (New York, N.Y.)》2007,318(5855):1424-1430
Undoped, high-quality diamond is, under almost all circumstances, one of the best insulators known. However, diamond covered with chemically bound hydrogen shows a pronounced conductivity when exposed to air. This conductivity arises from positive-charge carriers (holes) and is confined to a narrow near-surface region. Although several explanations have been proposed, none has received wide acceptance, and the mechanism remains controversial. Here, we report the interactions of hydrogen-terminated, macroscopic diamonds and diamond powders with aqueous solutions of controlled pH and oxygen concentration. We show that electrons transfer between the diamond and an electrochemical reduction/oxidation couple involving oxygen. This charge transfer is responsible for the surface conductivity and also influences contact angles and zeta potentials. The effect is not confined to diamond and may play a previously unrecognized role in other disparate systems. 相似文献
7.
A study of isolates of Pseudomonas solanacearum obtained from several locations in the hill country of Ceylon, which includes two distinct agro-climatic zones, showed that three biotypes, according to Hayward’s classification, occurred in this region. Biotype 2 was obtained from only one host, potato, from cultivations established at elevations of 6,200 ft. and over in virgin lands in the hill country wet zone which is characterized by a cool temperate climate. Biotype 3 was obtained from two plant hosts, tomato and potato, from several locations previously cropped with cultivated species in the warmer dry zone. In what may be considered as a transitional region between the wet and the dry zones, both biotypes 2 and 3 were found, as well as biotype 4, a new record for potato. The nature of their occurrence suggests that biological and environmental factors may play a part in determining the distribution of biotypes.In the absence of any evidence of the introduction of the organism from outside to the virgin soils of the wet-zone cultivations, it is suggested that Pseudomonas solanacearum is endemic in these soils and is a normal component of the soil microflora, existing as a saprophyte or as a non-pathogenic root-inhabiting species, and becoming pathogenic in the presence of susceptible host plants. 相似文献
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G. Seneviratne A.P.D.A. Jayasekara U.P. Abeysekera 《Soil biology & biochemistry》2011,43(5):1059-1062
Nitrogen fixing bacteria play a key role in the growth and persistence of effective microbial communities in the soil by supplying N through biological nitrogen fixation (BNF). In the long run, chemical inputs, particularly N fertilisers are known to adversely affect N2 fixers and hence maintenance of soil fertility and crop productivity. This study examined the effect of developed microbial biofilms with N2 fixers on restoration of soils deteriorated by conventional agricultural practices in tea cultivation. Just reducing recommended chemical fertiliser use by 50% significantly increased soil microbial biomass and BNF, and decreased soil NO3− and pest infestation. The lower chemical fertiliser addition coupled with the biofilm-based biofertilisers known as biofilmed biofertilisers (BFBFs) further increased BNF significantly. The combined application significantly increased soil organic C by ca. 20%, and reduced leaf transpiration by ca. 40%. It also supported plant growth, rhizoremediation and soil moisture conservation in comparison to the 100% chemical fertilisation. Those improved performances were observed to be proportional to the increased density of soil bacteria, and have several agronomic and environmental implications. It is apparent from this study that replenishing the depleted soil microbial communities by applying such biofertilisers is likely to be beneficial in agroecosystems with chemical N fertiliser use, if they are to be sustained for crop production. 相似文献
9.
G. Seneviratne 《Biology and Fertility of Soils》2000,31(1):60-64
Litter of high quality is required for increased soil organic matter turnover and improved crop production in tropical agroecosystems.
Studies on litter quality using plant residues have produced inconsistent results. This study reports on previously published
data on litter quality, in an attempt to define universal chemical determinants controlling N release in tropical agriculture.
N concentrations and polyphenol/N ratios are determinants of the N release of plant residues with limited N concentrations,
i.e. of <2% and <1%, respectively. Lignin levels and lignin/N ratios were not observed to be good predictors of N release.
The C/N ratio was found to be the best determinant of N release for a wide range of residue N concentrations. More specifically,
critical levels of C and plant nutrients which limit the enzyme activities of microbial decomposers were found to be important
for determining nutrient release.
Received: 9 February 1999 相似文献
10.
Tharanga Bandara Indika Herath Prasanna Kumarathilaka Mihiri Seneviratne Gamini Seneviratne Nishanta Rajakaruna Meththika Vithanage Yong Sik Ok 《Journal of Soils and Sediments》2017,17(3):665-673