Total soil organic matter content is a key attribute of soil quality since it has far-reaching effects on soil physical, chemical, and biological properties. However, changes in contents of organic carbon (C) and total nitrogen (N) occur only slowly and do not provide an adequate indication of important short-term changes in soil organic matter quality that may be occurring. Labile organic matter pools can be considered as fine indicators of soil quality that influence soil function in specific ways and that are much more sensitive to changes in soil management practice. Particulate organic matter consists of partially decomposed plant litter, and it acts as a substrate and center for soil microbial activity, a short-term reservoir of nutrients, a food source for soil fauna and loci for formation of water stable macroaggregates. Dissolved (soluble) organic matter consists of organic compounds present in soil solution. This pool acts as a substrate for microbial activity, a primary source of mineralizable N, sulfur (S), and phosphorus (P), and its leaching greatly influences the nutrient and organic matter content and pH of groundwater. Various extractable organic matter fractions have also been suggested to be important, including hot water-extractable and dilute acid-extractable carbohydrates, which are involved in stabilization of soil aggregates, and permanganate-oxidizable C. Measurement of potentially mineralizable C and N represents a bioassay of labile organic matter using the indigenous microbial community to release labile organic fractions of C and N. Mineralizable N is also an important indicator of the capacity of the soil to supply N for crops. It is concluded that individual labile organic matter fractions are sensitive to changes in soil management and have specific effects on soil function. Together they reflect the diverse but central effects that organic matter has on soil properties and processes. (c) 2005 Elsevier Inc.

Labile Organic Matter Fractions as Central Components of the Quality of Agricultural Soils: An Overview

is seen as a basic premise of soil quality (Larson and Pierce, 1991, 1994). If a soil is not suitable for a specific Soil quality concepts are commonly used to evaluate sustainable use, then it is not appropriate to attempt to assign or land management in agroecosystems. The objectives of this review were to trace the importance of soil organic matter (SOM) in Canadian describe quality for that specific use or function. In many sustainable land management studies and illustrate the role of SOM cases, however, it is not possible to make a perfect match and aggregation in sustaining soil functions. Canadian studies on soil between the soil and its intended use. Under these cirquality were initiated in the early 1980s and showed that loss of SOM cumstances, quality must be built into the system using and soil aggregate stability were standard features of nonsustainable best management scenarios. land use. Subsequent studies have evaluated SOM quality using the Ecosystem concepts such as function, processes, attrifollowing logical sequence: soil purpose and function, processes, prop- butes, and indicators, have proved to be a useful frameerties and indicators, and methodology. Limiting steps in this soil work to describe soil quality (Larson and Pierce, 1991, quality framework are the questions of critical limits and standardiza1994; Doran and Parkin, 1994; Doran et al., 1996; Carter tion for soil properties. At present, critical limits for SOM are selected et al., 1997; Karlen et al., 1997). However, a precise using a commonly accepted reference value or based on empirically derived relations between SOM and a specific soil process or function definition of soil quality proves to be elusive. This is (e.g., soil fertility, productivity, or erodibility). Organic matter frac- probably related to the innate difficulty in defining soil tions (e.g., macro-organic matter, light fraction, microbial biomass, itself and to the multifaceted nature (i.e., scientific, perand mineralizable C) describe the quality of SOM. These fractions sonal, and social) of environmental concerns. Carter and have biological significance for several soil functions and processes MacEwan (1996) suggested that although soil quality and are sensitive indicators of changes in total SOM. Total SOM describes an objective state or condition of the soil, it influences soil compactibility, friability, and soil water-holding capac- also is subjective, i.e., evaluated partly on the basis of ity while aggregated SOM has major implications for the functioning personal and social determinations. The above frameof soil in regulating air and water infiltration, conserving nutrients, work of soil quality has utility when it is directed or and influencing soil permeability and erodibility. Overall, organic focused towards the manipulation, engineering, and/or matter inputs, the dynamics of the sand-sized macro-organic matter, and the soil aggregation process are important factors in maintaining management of the soil resource. Thus, soil quality is a and regulating organic matter functioning in soil. technology, an applied science, directed towards better soil management. The objective of this paper is to review the context

http://envismadrasuniv.org/pdf/Soil%20Quality%20for%20Sustainable%20Land%20Management.pdf

Soil Quality for Sustainable Land Management

Use of indicators and pore volume-function characteristics to quantify soil physical quality

Indicators of good soil physical quality: density and storage parameters

The observed and projected increase in emission of greenhouse gases, with attendant effects on global warming and sea level rise, have raised interests in identifying mitigation options. Terrestrial C sequestration involves capture of atmospheric C through photosynthesis and storage in biota, soil and wetlands. Land use, vegetation and soil management have a strong impact on the biotic processes of C sequestration. Losses of C from the terrestrial ecosystems are exacerbated by deforestation, biomass burning, plowing, resource-based and subsistence agriculture, and practices that mine soil fertility and deplete the soil organic C (SOC) pool. Biomass burning may also produce charcoal, which is an inert carbon with long residence time. Practices that enhance C sequestration include afforestation and reforestation, conservation tillage and mulch farming, integrated nutrient management and adopting systems with high biodiversity. Net C sequestration within an ecosystem can be assessed by taking into account the hidden C costs of fertilizers, pesticides, tillage, irrigation and other input. Restoration of degraded soils and ecosystems has a vast potential of C sequestration. The Kyoto Protocol provides for C sequestration in terrestrial sinks and C trading through Clean Development Mechanisms. Terrestrial C sequestration, besides being a win–win strategy, offers a window of opportunity for the first few decades of the 21st century. It is a natural process of reducing the rates of gaseous emissions while alternatives to fossil fuel take effect.

/pdf/agricultural-activities-and-the-global-carbon-cycle-su6moqia85.pdf

Agricultural activities and the global carbon cycle

Publisher Summary The biological attributes of soil include living organisms and material derived from living organisms. Living organisms (the biotic component of soil) include plants, animals, and microbes, ranging in size and function. After these organisms die, their residues remain in the soil in various stages of decomposition. Both living organisms and their residues interface with the abiotic component of the soil, which is nonliving and chemically derived and includes minerals, clays, water, and chemical ions and compounds. These components are tightly linked, shaping and affecting each other. The biological attributes of soil quality include the many soil components and processes related to organic matter cycling, such as total organic carbon and nitrogen, microbial biomass, mineralizable carbon and nitrogen, light fraction enzyme activities, and soil fauna and flora. Soil organic matter, composed of various fractions, is a key attribute of soil quality. It is the primary source of, and a temporary sink for, plant nutrients. It is important for soil quality, because it helps to maintain soil tilth, aids the infiltration of air and water, promotes water retention, reduces erosion, and controls the efficacy and fate of pesticides.

Chapter 4 Biological attributes of soil quality

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Chapter 4 Biological attributes of soil quality