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991.
Soil erosion continues to represent a major environmental issue in China. This paper considers some of the practical difficulties of assessing the severity of soil erosion in subtropical southern China, with particular reference to a case study in Fujian Province. The administration of soil and water conservation and procedures for erosion evaluation in an area of southern China are outlined. Although the hierarchy of bodies involved in soil conversation is impressive compared to other countries in subtropical environments, little is known about the dynamics of erosion, its impact on productivity or its contribution to sediment yields. 相似文献
992.
V. H. Dale L. K. Mann R. J. Olson D. W. Johnson K. C. Dearstone 《Landscape Ecology》1990,4(4):211-224
Forest structure and composition influence patterns of insect outbreaks and can be explained on the Walker Branch watershed by past land use (timber harvest and agriculture), soils, aspect, and slope. In particular, pine bark beetles caused large losses of pine on sites that had been used for agriculture, on Fullerton silt loam soils, and on north-to-northeast and east-to-southeast exposures. Hickory bark beetles had a high impact on hickory biomass on Bodine soil areas that were forested in 1935 and sloped greater than 11%. Thus, prior land use can have an indirect effect on future disturbances.Because forest disturbances can affect nutrient distribution, land use can also indirectly affect nutrient availability. For example, locations of hickory bark beetle outbreaks experience a large flux of calcium from dead wood to soil because hickory accumulates large amounts of calcium in woody tissue. The research demonstrates a link between past land use, insect outbreaks, and calcium cycling. 相似文献
993.
Abstract. In the extremely arid island of Fuerteventura (Canary Islands, Spain), a traditional water harvesting practice has evolved in slightly sloping areas, which receive runoff water from time to time. The system is particularly effective in the rehabilitation of saline–sodic soils where the improved fertility allows certain crops to be grown, which would not be possible without water harvesting. The influence of the water harvesting on soil fertility was investigated by comparing the properties of the cultivated soils receiving periodic runoff with those of natural control soils that did not receive runoff. The saline–sodic characteristics of the four uncultivated soils were absent from the four cultivated soils which, on average, contained only one quarter of the exchangeable sodium and more than twice the exchangeable calcium content. The clay and silt content of all four of the cultivated soils had been substantially enhanced relative to the control soils, by sediment contained in the runoff. 相似文献
994.
Soil organic matter quantity and quality in mountain soils of the Alay Range, Kyrgyzia, affected by land use change 总被引:4,自引:0,他引:4
Changes in soil management practices influence the amount, quality and turnover of soil organic matter (SOM). Our objective
was to study the effects of deforestation followed by pasture establishment on SOM quantity, quality and turnover in mountain
soils of the Sui Checti valley in the Alay Range, Kyrgyzia. This objective was approached by analysis of total organic C (TOC),
N, lignin-derived phenols, and neutral sugars in soil samples and primary particle-size soil fractions. Pasture installation
led to a loss of about 30% TOC compared with the native Juniperus turkestanica forests. The pasture soils accumulated about 20% N, due to inputs via animal excrement. A change in land use from forest
to pasture mainly affected the SOM bound to the silt fraction; there was more microbial decomposition in the pasture than
in the forest silt fraction, as indicated by lower yields of lignin and carbohydrates, and also by a more advanced oxidative
lignin side-chain oxidation and higher values of plant : microbial sugar ratios. The ratio of arabinose : xylose was indicative
of the removal of carbohydrates when the original forest was replaced by pasture, and we conclude that this can be used as
an indicator of deforestation. The accumulation of lignin and its low humification within the forest floor could be due to
the extremely cold winter and dry summer climate.
Received: 10 March 1999 相似文献
995.
Wetland rice soils as sources and sinks of methane: a review and prospects for research 总被引:5,自引:0,他引:5
S. Kumaraswamy Arun Kumar Rath B. Ramakrishnan N. Sethunathan 《Biology and Fertility of Soils》2000,31(6):449-461
Rice paddies are an important human-made ecosystem for the global CH4 budget. CH4, which is produced in the predominantly anaerobic bulk soil layers, is oxidized significantly before it reaches the atmosphere.
Roots of rice, in addition to supporting the consumption of CH4, contribute to the total CH4 production in the soil. The various controls of CH4 emission from this ecosystem depend on the structure of plant and microbial communities and their interactions. Availability
of organic substrates, electron acceptors and other soil- and plant-related factors influence the activities of microbial
communities. Agronomic practices including fertilization and application of pesticides have effects on CH4 emission. Recent studies using molecular retrieval approaches with small subunit rRNA-encoding gene (rDNA) sequences and
functional genes, showed the richness of diversity of the microbial community in rice paddy soils, which includes members
of the Archaea and methanotrophs. There is need for further research to know the consequences, at the ecosystem level, of changes in microbial
diversity and microbial communities in paddy soils. This will aid in understanding the mechanisms involved in the mitigating
effects of certain agricultural practices.
Received: 13 July 1999 相似文献
996.
D. Contour-Ansel E. Garnier-Sillam M. Lachaux V. Croci 《Biology and Fertility of Soils》2000,31(6):508-516
The origin, nature and quantity of polysaccharides in the walls of the epigeal mounds of a species of soil-feeding termite,
Cubitermes oculatus, and a fungus-growing termite, Macrotermes subhyalinus, found in Senegal, and of soil not considered to be under the influence of termites, were studied to obtain a clearer picture
of the structural stability of these materials. The compounds were extractedand analysed by high performance liquid chromatography.
We found that the walls of mounds made by soil-feeding species were very rich in sugars soluble in aqueous acid or hot water.
Most of the sugars originated from cellulose and hemicellulose, and only a small proportion from microorganisms. There were
also significant amounts of stachyose in the mound walls and in the reference soil. This sugar was probably formed by the
surrounding vegetation, which was mainly leguminous crops. Comparison of the mineral and organic-mineral particle sizes of
samples confirmed that the walls of soil-feeding termite mounds where there is the greatest redistribution of clay have the
best aggregating capacity. The results therefore show that the polysaccharides in mound walls of soil-feeding termites are
mostly of plant origin. Their influence on the stability of these structure is discussed. The walls of fungus-growing termite
mounds contain little organic matter and hence low levels of polysaccharides, which are mainly of plant origin.
Received: 19 July 1999 相似文献
997.
Progress in studies of nitrate leaching from grassland soils 总被引:2,自引:0,他引:2
S.C. Jarvis 《Soil Use and Management》2000,16(S1):152-156
Abstract. The large input of research effort on aspects of nitrate leaching over the last two decades has produced many innovative scientific and practical results. The MAFF Nitrate Programme has enabled considerable progress to be made in unravelling much of the complexity of the grassland nitrogen (N) cycle, and identifying gaps as essential first stages in providing improved managements for N in grassland systems. From a practical standpoint, there have been key outputs which have allowed the identification of options for policy, and which should allow grassland farmers to increase the efficiency of N use throughout their farming system and thereby improve the sustainability of their enterprises. As well as quantifying N transformations, transfers and losses, other important outcomes have been the development of user-friendly models of N cycling (NCYCLE and variants) and an easy to use field kit to determine mineral N in pasture soils. The use of modelling to produce fertilizer recommendations with a Decision Support System and of new approaches developed within the Programme, in particular system synthesis desk studies, and 'farmlet' investigations to determine the consequences of modifying N flows and losses, have allowed us to produce solutions to satisfy the dual aims of meeting environmental and economic production targets. 相似文献
998.
999.
The distribution of iron monosulifde (quantified as acid volatile sulfur:SAV) was compared with geochemical properties that are known to affect its formation and accumulation in three coastal Holocene acid sulfate soils (ASS) at Tuckean Swamp,Mc Leods Creek and Bungawalbyn Swamp respectively,These properties included pH,reactive iron(FeR),pore-water sulfate(SO4^2-) and organic carbon(OC).Iron monosulfide was concentrated at the oxic/anoxic boundary,the Tuckean Swamp and McLeods Creek sites are Holocene sediments,whereas the Bungawalbyn Swamp is a Holocene peat.The concentration of SAV averaged 0.2 g kg^-1 in a 0.5m thick soil layer at the Tuckean Swamp,but was an order of magnitude lower in the oxic/anoxic transition layers at McLeods Creek and Bungawalbyn Swamp,The SAV mineral greigite(Fe3S4) was identified in the Tuckean Swamp by X-ray diffraction and scanning electron microscopy with quantitative energy dispersive X-ray analysis(SEM-EDX),Very small concentrations of greigite were also observed in the McLeods Creek,based on crystal morphology and elemental composition.The concentration of SAV was a small fraction of the total reduced sulfur,representing at most 3% of the pyrite sulfur,However,the presence of this highly reactive sulfide mineral,distributed within pores where oxygen diffusion is most rapid,has important implications to the potential rate of acid production from these sediments. 相似文献
1000.
Salinity and sodicity are prime threats to land resources resulting in huge economic and associated social consequences in several countries. Nutrient deficiencies reduce crop productivity in salt‐affected regions. Soil fertility has not been sustainably managed in salt‐affected arid regions. Few researchers investigated the crop responses to phosphorus and potassium interactions especially in saline–sodic soils. A research study was carried out to explore the effect of diammonium phosphorus (DAP) and potassium sulphate (K2SO4) on sugar beet (Beta vulgaris L.) grown in a saline–sodic field located in Kohat district of Pakistan. The crop was irrigated with ground water with ECiw value of 2.17–3.0 dS/m. Three levels each of K2O (0, 75 and 150 kg/ha) as K2SO4 and P2O5 (0, 60 and 120 kg/ha) as DAP were applied. The application of P significantly affected fresh beet and shoot yield while K fertilizers had significant effect on fresh beet yield and ratio of beet:shoot, while non‐significant effects on the fresh shoot were observed. The application of K1 and K2 promoted sugar beet shoot yield by 49.2 and 49.2% at P1 and 64.4 and 59.7% at P2, respectively over controls. In comparison with controls, fresh beet yield was increased (%) by 15 and 51, 45 and 84, and 50 and 58 for corresponding K1 and K2 at P0, P1 and P2, respectively. Addition of P1 and P2 increased beet yield by 37 and 47% over control. The shoot [P] (mmol/kg) were achieved as 55.2, 73.6 and 84.3 at P0, P1 and P2, respectively. The shoot [Mg] and [SO4] tended to decrease with increasing P levels, while [SO4] was markedly reduced at P2. The effect of P on leaf [Na] was non‐significant, but increasing levels of K decreased [Na] substantially at P0 and P1, but there was no difference in the effect of K level on [Na] at P2. Consequently, K application reduced leaf Na:K ratios. Fresh shoot yield was weakly associated with leaf [P] (R2 = 0.53). The leaf Na:K ratio showed a negative relationship (R2 = 0.90) with leaf [K]. A strongly positive relationship (R2 = 0.75) was observed between leaf [K] and fresh beet yield. The addition of K2SO4 also enhanced [SO4] and SO4:P ratios in leaf tissues. The ratio of Na:K in the shoot decreased with increasing K application. These results demonstrated that interactions of K and P could mitigate the adverse effects of salinity and sodicity in soils. This would contribute to the efficient management of soil fertility system in arid‐climate agriculture. 相似文献