Human alteration of the global environment has triggered the sixth major extinction event in the history of life and caused widespread changes in the global distribution of organisms. These changes in biodiversity alter ecosystem processes and change the resilience of ecosystems to environmental change. This has profound consequences for services that humans derive from ecosystems. The large ecological and societal consequences of changing biodiversity should be minimized to preserve options for future solutions to global environmental problems.

Consequences of changing biodiversity

Plant litter and the microbial biomass are the major parent materials for soil organic matter (SOM) formation Plant litter is composed of complex mixtures of organic components, mainly polysaccharides and lignin, but also aliphatic biopolymers and tannins The composition and relative abundance of these components vary widely among plant species and tissue type Whereas some components, such as lignin, are exclusively found in plant residues, specific products are formed by microorganisms, eg amino sugars A wide variety of chemical methods is available for characterizing the chemical composition of these materials, especially the chemolytic methods, which determine individual degradation products and solid-state 13C NMR spectroscopy, that gives an overview of the total organic chemical composition of the litter material With the development of these techniques, an increasing number of studies are being carried out to investigate the changes during decay and the formation of humic substances An overview is given on the amount of litter input, the proportion of various plant parts and their distribution (below-ground/above-ground), as well as the relative proportion of the different plant tissues Major emphasis is on the organic chemical composition of the parent material for SOM formation and thus this paper provides information that will help to identify the changes occurring during biodegradation of plant litter in soils

The macromolecular organic composition of plant and microbial residues as inputs to soil organic matter

Objectives Basic Processes The Greenhouse Process Global Trends in Greenhouse Gas Emissions The Role of Agriculture in U.S. Emissions of Three GHGs The SOC Pool in U.S. Soils and SOC Loss from Cultivation Processes in Governing Emissions from the Pedosphere Plant Action Soil Processes Soil Quality Strategies for Mitigating Emissions from Cropland U.S. Cropland Sustainable Management Studies Soil Erosion Management Land Conversion and Restoration Conversion of Marginal Land Restoration of Degraded Soils Biofuels for Offsetting Fossil Fuel Intensification of Prime Agricultural Land Conservation Tillage and Residue Management Irrigation Water Management Improved Cropping Systems The Carbon Sequestration Potential of Arable Land U.S. Cropland's Overall Potential to Mitigate the Greenhouse Effect Techniques for Sequestration Rates of SOC Sequestration Possible Implementation Obstacles Required Action Conclusions - The Win-Win Strategy Agricultural Profits from Environmental Improvements SOC's Monetary Value SOC's Environmental Value Global Potential Appendix 1: Definitions Appendix 2: Researchable Topics

The Potential of U.S. Cropland to Sequester Carbon and Mitigate the Greenhouse Effect

Productivity and management of rice–wheat cropping systems: issues and challenges

▪ Abstract The global soil C reservoir, ∼1500 Gt of C (1 Gt = 1012 kg of C), is dynamic on decadal time scales and is sensitive to climate and human disturbance. At present, as a result of land use, soil C is a source of atmospheric CO2 in the tropics and possibly part of a sink in northern latitudes. Here I review the processes responsible for maintaining the global soil C reservoir and what is known about how it responds to direct and indirect human perturbations. “I am fire and air; my other elements I give to baser life”      —William Shakespeare, Antony and Cleopatra

The Carbon Budget in Soils

The rehabilitation or intensified use of Imperata grasslands will require a much better understanding of their area, distribution, and characteristics We generated estimates of the area of Imperata grasslands in tropical Asia, and suggested a typology of Imperata grasslands that may be useful to define the pathways toward appropriate land use intensification We conclude that the area of Imperata grasslands in Asia is about 35 million ha This about 4% of the total land area The countries with the largest area of Imperata grasslands are Indonesia (85 million ha) and India (80 million ha) Those with the largest proportion of their surface area covered with Imperata are Sri Lanka (23%), the Philippines (17%), and Vietnam (9%) Laos, Thailand, Myanmar, and Bangladesh evidently all have similar proportions of their land area infested with Imperata (about 3 to 4%) Malaysia (< 1%), Cambodia (1%), and the southern part of China (2%) have but a minor proportion of their total land area in Imperata The species was found widely distributed on the full range of soil orders It occupied both fertile (eg some of the Inceptisols and Andisols) and infertile soils (Ultisols and Oxisols) across a wide range of climates and elevations Imperata lands fall into four mapping scale-related categories: Mega-grasslands, itmacro-grasslands, meso-grasslands, and micro-grasslands The mega-grasslands are often referred to as ‘sheet Imperata’ They are the large contiguous areas of Imperata that would appear on small-scale maps of say 1:1,000,000 We propose that this basic typology be supplemented with a number of additional components that have a key influence on intensification pathways: land quality, market access, and the source of power for tillage The typology was applied in a case study of Indonesian villages in the vicinity of Imperata grasslands We propose an international initiative to map and derive a more complete and uniform picture of the area of the Imperata grasslands This should include selected studies to understand conditions at the local level These are critical to build the appreciation of change agents for the indigenous systems of resource exploitation, and how they relate to local needs, values and constraints

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The Imperata grasslands of tropical Asia: area, distribution, and typology

https://www.capri.cgiar.org/files/pdf/capriwp16.pdf

The effects of scales, flows and filters on property rights and collective action in watershed management

Soil carbon dynamics in different cropping systems in principal ecoregions of Asia.

Purely annual crop-based production systems have limited scope to be sustainable under upland conditions prone to infestation by Imperata cylindrica if animal or mechanical tillage is not available. Farmers who must rely on manual cultivation of grassland soils can achieve some success in suppressing Imperata for a number of years using intensive relay and intercropping systems that maintain a dense soil cover throughout the year, especially where leguminous cover crops are included in the crop cycle. However, labour investment increases and returns to labour tend to decrease in successive years as weed pressure intensifies and soil quality declines. Continuous crop production has been sustained in many Imperata-infested areas where farmers have access to animal or tractor draft power. Imperata control is not a major problem in such situations. Draft power drastically reduces the labour requirements in weed control. Sustained crop production is then dependent more solely upon soil fertility management. Mixed farming systems that include cattle may also benefit from manure application to the cropped area, and the use of non-cropped fallow areas for grazing. In extensive systems where Imperata infestation is tolerated, cassava or sugarcane are often the crops with the longest period of viable production as the land degrades. On sloping Imperata lands, conservation farming practices are necessary to sustain annual cropping. Pruned tree hedgerows have often been recommended for these situations. On soils that are not strongly acidic they may consistently improve yields. But labour is the scarcest resource on small farms and tree-pruning is usually too labour-intensive to be practical. Buffer strip systems that provide excellent soil conservation but minimize labour have proven much more popular with farmers. Prominent among these are natural vegetative strips, or strips of introduced fodder grasses. The value of Imperata to restore soil fertility is low, particularly compared with woody secondary growth or Compositae species such as Chromolaena odorata or Tithonia diversifolia. Therefore, fallow-rotation systems where farmers can intervene to shift the fallow vegetation toward such naturally-occurring species, or can manage introduced cover crop species such as Mucuna utilis cv. cochinchinensis, enable substantial gains in yields and sustainability. Tree fallows are used successfully to achieve sustained cropping by some upland communities. A variation of this is rotational hedgerow intercropping, where a period of cropping is followed by one or more years of tree growth to generate nutrient-rich biomass, rehabilitate the soil, and suppress Imperata. These options, which suit farmers in quite resource-poor situations, should receive more attention.

Food-crop-based production systems as sustainable alternatives for Imperata grasslands?

Research and policy on property rights, collective action and watershed management requires good understanding of ecological and socio-political processes at different social-spatial scales. On-farm soil erosion is a plot or farm-level problem that can be mitigated through more secure property rights for individual farmers, while the sedimentation of streams and deterioration of water quality are larger-scale problems that may require more effective collective action and / or more secure property rights at the village or catchment scale. Differences in social-political contexts across nations and regions also shape property rights and collective action institutions. For example, circumstances in the Lake Victoria basin in East Africa require particular attention to collective action and property rights problems in specific “hot spot” areas where insecure tenure leads to overuse or under-investment. Circumstances in the uplands of Southeast Asia require analysis of the opportunities for negotiating more secure rights for farmers in exchange for stronger collective action by farmer groups for maintaining essential watershed functions.

D. P. Garrity

Papers

The Imperata grasslands of tropical Asia: area, distribution, and typology

The effects of scales, flows and filters on property rights and collective action in watershed management

Soil carbon dynamics in different cropping systems in principal ecoregions of Asia.

Food-crop-based production systems as sustainable alternatives for Imperata grasslands?

The effects of scales, flows and filters on property rights and collective action in watershed management: