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  • 1
    Electronic Resource
    Electronic Resource
    Modelling soil organic matter changes in ley–arable rotations in sandy soils of Northeast Thailand (1998)
    Oxford, UK : Blackwell Science Ltd
    European journal of soil science 49 (1998), S. 0 
    Details
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The effects of a 3-year ley-arable rotation (2 years under grass, legume or a grass-legume mixture, followed by 1 year under cassava) on the organic C content of upland sandy soils in Northeast Thailand were evaluated using four field trials (Khon Kaen, Chaiyaphum, Mahasarakham and Udon Thani). At all sites under the existing management system of continuous cassava, soil organic C decreased by 9-20% during the 3-year experiment. The carbon model developed at Rothamsted (RCM-26) predicted that soil organic C would decrease consistently under continuous cassava until it reached very small amounts (0.2–0.3%). This was the case for all sites, except Chaiyaphum, where soil organic C had already declined to 0.1%. Evaluatin the rotations using RCM-26 showed that introducing a ley could increase soil organic C, except at Udon Thani where the organic C exceeded 0.47% before the start of the experiment. The data obtained with the rotations showed that RCM-26 could be used to predict the effects of changes in management on organic C content in the upland sandy soils of Norrtheast Thailand over the 3 years. To compensate for an underestimation of the effects of soil moisture deficit on the decomposition rates of organic matter, we propose that because of the prolonged dry season (from December to the following May) soil moisture deficit and the rate-modifying factor for moisture (Am) should be estimated independently of crop cover. Furthermore, to accommodate the very slow decomposition during this time, (Am) should be allowed to decrease to 0.1. Adopting this simple modification provides a more realistic estimate of the organic C inputs needed to simulate the content of soil organic C measured before trials began.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2389.1998.4930463.x
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  • 2
    Electronic Resource
    Electronic Resource
    Seasonal responses in microbial biomass carbon, phosphorus and sulphur in soils under pasture (1997)
    Springer
    Biology and fertility of soils 24 (1997), S. 421-428 
    Details
    ISSN: 1432-0789
    Keywords: Key words Seasonal responses ; Microbial biomass C ; Microbial biomass P ; Microbial biomass S ; Nutrient cycling ; Pasture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The response of the soil microbial biomass to seasonal changes was investigated in the field under pastures. These studies showed that over a 9-month period, microbial biomass carbon, phosphorus and sulphur (biomass C, P, S), and their ratios (C:P, C:S, and P:S) responded differently to changes in soil moisture and to the input of fresh organic materials. From October to December (1993), when plant residues were largely incorporated into the soils, biomass C and S increased by 150–210%. Biomass P did not increase over this time, having decreased by 22–64% over the dry summer (July to September). There was no obvious correlation between biomass C, P, and S and air temperature. The largest amounts of biomass C and P (2100–2300μg and 150–190μgg–1 soil, respectively) were found in those soils receiving farmyard manure (FYM or FYM+NPK) and P fertilizer, whereas the use of ammonium sulphate decreased biomass C and P. The C:P, C:S, and P:S ratios of the biomass varied considerably (9–276:1; 50–149:1; and 0.3–14:1, respectively) with season and fertilizer regime. This reflected the potential for the biomass to release (when ratios were narrow) or to immobilize (wide ratios) P and S at different times of the year. Thus, seasonal responses in biomass C, P, and S are important in controlling the cycling of C, P, and S in pasture and ultimately in regulating plant availability of P and S. The uptake of P in the pasture was well correlated with the sum of P in the biomass and soil available pools. Thus, the simultaneous measurement of microbial biomass P and available P provide useful information on the potential plant availability of P.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003740050267
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  • 3
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    Indicators and thresholds for the evaluation of sustainable land management (1995)
    Canadian Science Publishing
    Details
    Publication Date: 1995-11-01
    Description: Within the context of major land uses such as agriculture, the indicators of sustainability must be framed within the social and economic conditions of the society in question. Whereas an indicator is used to measure changes in key attributes, usually over time, a threshold provides a baseline against which sustainability can be assessed. A direct measure of sustainability using indicators is difficult, and indirect measures or surrogates may be easier to establish. There is some information on threshold values for indicators, particularly for indicators such as soil acidity and nutrient status, and for those relating to root physiology. Because some threshold values are soil specific, it seems likely that range of values will be required for a particular indicator. There have been few case studies involving indicators and thresholds for sustainable land management. Examples of soil and land suitability for the production of Hevea brasiliensis (rubber) in Malaysia and for the management of sloping lands for annual crops in the Philippines are discussed. Biophysical indicators and thresholds for sustainable rubber production appear to be reasonably well-understood, particularly those relating to climate and soil physical factors. For sloping lands in the Philippines, yield data and benefit: cost ratios give a clear picture of trends and sustainability. Key words: Sustainable land management, indicator
    Print ISSN: 0008-4271
    Electronic ISSN: 1918-1841
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Canadian Science Publishing
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  • 4
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    Seasonal responses in microbial biomass carbon, phosphorus and sulphur in soils under pasture (1997)
    Springer
    Details
    Publication Date: 1997-05-05
    Print ISSN: 0178-2762
    Electronic ISSN: 1432-0789
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Springer
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  • 5
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    Modelling soil organic matter changes in ley-arable rotations in sandy soils of Northeast Thailand (1998)
    Wiley
    Details
    Publication Date: 1998-09-01
    Print ISSN: 1351-0754
    Electronic ISSN: 1365-2389
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Published by Wiley
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  • 6
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    Managing soils for long-term productivity (1997)
    The Royal Society
    Details
    Publication Date: 1997-07-29
    Description: Meeting the goal of long–term agricultural productivity requires that soil degradation be halted and reversed. Soil fertility decline is a key factor in soil degradation and is probably the major cause of declining crop yields. There is evidence that the contribution of declining soil fertility to soil degradation has been underestimated. Sensitivity to soil degradation is implicit in the assessment of the sustainability of land management practices, with wide recognition of the fact that soils vary in their ability to resist change and recover subsequent to stress. The concept of resilience in relation to sustainability requires further elaboration and evaluation. In the context of soil degradation, a decline in soil fertility is primarily interpreted as the depletion of organic matter and plant nutrients. Despite a higher turnover rate of organic matter in the tropics there is no intrinsic difference between the organic matter content of soils from tropical and temperate regions. The level of organic matter in a soil is closely related to the above and below ground inputs. In the absence of adequate organic material inputs and where cultivation is continuous, soil organic matter declines progressively. Maintaining the quantity and quality of soil organic matter should be a guiding principle in developing management practices Soil microbial biomass serves as an important reservoir of nitrogen (N), phosphorus (P) and sulphur (S), and regulates the cycling of organic matter and nutrients. Because of its high turnover rate, microbial biomass reacts quickly to changes in management and is a sensitive indicator for monitoring and predicting changes in soil organic matter. Modelling techniques have been reasonably successful in predicting changes in soil organic matter with different organic material inputs, but there is little information from the tropics. Nutrient depletion through harvested crop components and residue removal, and by leaching and soil erosion accentuates the often very low inherent fertility of many soils in the tropics. An integrated approach involving inorganic and organic inputs is required where animal and plant residues are returned, as far as practicable. Chemical fertilizers alone cannot achieve long–term productivity on many soils and organic material inputs are required to maintain soil organic matter levels and crop productivity. A major research effort is required to develop improved strategies for halting and reversing soil degradation if long–term productivity is to be secured.
    Print ISSN: 0962-8436
    Electronic ISSN: 1471-2970
    Topics: Biology
    Published by The Royal Society
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