with large contiguous areas of native vegetation for as wide a group of plant and animal species as possible. Remain­ing areas of native habitat within the agricultural landscape (giving priority to patches that are large, intact and ecologi­cally important) can be conserved while further destruction, fragmentation or degradation prevented.
      Active management of landscapes and land uses will be required to maintain heterogeneity at both patch and land­scape levels, making agricultural systems more compatible with biodiversity conservation. Threats to native habitats and biodiversity can be identified and specific conserva­tion strategies applied for species or communities that are of particular conservation concern. Areas of native habitat in degraded portions of the agricultural landscape can be restored and marginal lands taken out of production and allowed to revert to native vegetation.
For freshwaters, some management options include:
•    Maintain or restore native vegetation buffers;
•   Protect wetlands and maintain critical function zone in natural vegetation;
•   Reestablish hydrological connectivity and natural pat­terns of aquatic ecosystems (including flooding);
•   Protect watersheds with spatial configuration of peren­nial natural, planted vegetation and maintain continu­ous year-round soil cover to enhance rainfall infiltra­tion

Nonnative, exotic species. Species that become invasive are often introduced deliberately, and many of these introduc­tions are related to agriculture, including plants and trees in­troduced for agricultural and forestry purposes and species used for biological control of pests (Wittenberg and Cock, 2001; Matthews and Brandt, 2006). Policy for control of invasive species is essential, but AKST must also develop a better understanding of when and how species become in­vasive and how to best monitor and control them. Improved prediction and early detection of pest invasions, appears to rely heavily on the scale and frequency of introductions (not particular phenotypic characteristics of the invader) (La-vergne and Molofsky, 2007; Novak, 2007). Since the scale of introduction is a critical factor, commercial trade in all living organisms, including seeds, plants, invertebrates and all types of animals has the greatest potential to augment the invasion potential of exotic species. The most promising mechanism for targeting this critical phase in invasion is an increase in the capacity of exporting and importing nations to monitor the content of agricultural goods. This cannot be done effectively by individual countries; collective action is needed, through UN or other international bodies with appropriate global capacity development, e.g., UN Biodi­versity Convention and the Cartagena Protocol.

6.6.2 Address poor land and soil management to deliver sustainable increases in productivity
The approach to addressing increased productivity will be distinctly different for fertile and low fertile lands (Har-temink, 2002).

6.6.2.1 Options for fertile lands
On-farm, low input options. The adoption of zero tillage prevents further water erosion losses, increases water use

efficiency, soil organic carbon sequestration, and maintains good structure in topsoil (Díaz-Zorita et al., 2002; Bolliger et al., 2006; Steinbach and Alvarez, 2006; Lal et al., 2007).
       About 95 million ha are under zero tillage management worldwide (Lal et al., 2007) in countries with industrialized agriculture, but the land area may increase in response to fuel prices and soil degradation. Zero tillage has well known positive effects upon soil properties; one negative effect is increased greenhouse gas emissions  (N2O,  CH4)  due to higher denitrification rates (Baggs et al., 2003; Dalal et al., 2003; Passianoto et al., 2003; Six et al., 2004; Steinbach and Alvarez, 2006; Omonode et al., 2007). Tradeoffs between higher C sequestration and higher GHG emissions will need more assessment (Dalal et al., 2003; Six et al., 2004; Lal et al., 2007). Zero tillage can promote shallow compaction in fine textured topsoils (Taboada et al., 1998; Díaz-Zorita et al., 2002; Sasal et al., 2006) and no-till farming can reduce yield in poorly drained, clayey soils. Soil-specific research is needed to enhance applicability of no-till farming by allevi­ating biophysical, economic, social and cultural constraints (Lal et al., 2007). Excessive soil compaction is of critical concern in in­dustrial agriculture due to the use of heavier agricultural machines. A typical hazard is when high yielding crops (e.g., maize) are harvested during rainy seasons. Compaction re­covery is not easy in zero tilled soils (Taboada et al., 1998; Díaz-Zorita et al., 2002; Sasal et al., 2006), which depend on soil biological mechanisms to reach a loosened condi­tion. The alleviation and control of deep reaching soil com­paction can be attained by adopting management strategies that control field traffic (Spoor et al., 2003; Pagliai et al., 2004; Hamza and Anderson, 2005; Spoor, 2006) and use mechanical (e.g., plowing) or biological (cover crop root channels) compaction recovery technology (Robson et al., 2002; Spoor et al., 2003). A better understanding of biological mechanisms are needed, with particular focus on the role played by plant roots, soil microorganisms and meso- and macrofauna in the recovery of soil structure (Six et al., 2004; Taboada et al., 2004; Hamza and Anderson, 2005). Increased botanical nitrogen-fixation can occur when legumes crops are rotated with cereals (Robson et al., 2002); green manure crops improve the N supply for succeeding crops (Thorup-Kristensen et al., 2003). In farms near ani­mal production facilities (feed lots, poultry, pigs, dairy, etc.), organic animal manures may be a cheap source of essential plant nutrients and organic carbon (Edwards and Somesh-war, 2000; Robson et al., 2002). The use of organic manures can be limited by problems associated with storage, han­dling, and transport (Edwards and Someshwar, 2000). In livestock grazing production systems, grazing intervals can be restricted and seasonal grazing intensity altered to reduce soil physical damage (Taboada et al., 1998; Menneer et al., 2004; Sims et al., 2005).
      Continuous crop removal may eventually deplete native soil supplies of one or more nutrients. Some predict deple­tion of easily accessible P by 2025 at present annual exploi­tation rates of 138 million tonnes (Vance et al., 2003) while others estimate far less. Soil microbiology could potentially improve access to P, for example, through the use of P-sol-ubilizing bacteria (Yadav and Tarafdar, 2001; Taradfar and