Methods are focused on the identification of tradeoffs and critical thresholds between the value of economic and eco­logical services in response to different typologies of human intervention.      In the same way, the concept of ecological agriculture needs a better understanding of the relationship among the multiple dimensions of rural development, i.e., agricultural productivity, environmental services, and livelihood. Such questions are still open for further elaboration and pose a challenge to AKST (Buck et al., 2004; Jackson et al., 2007).

6.1.1.2 Land use options for enhancing productivity
Productivity of farming systems can be enhanced by more intensive use of space or time. Intercropping (including re­lay intercropping and agroforestry) is a traditional form of such intensification, widespread in food production in low-income countries, especially in less favored areas. Growing several crops or intercrops in sequence within a year offers the possibility to intensify land use in time. This intensifica­tion was made possible by changes in the crops and varieties grown (day-length-neutral or short-season varieties; variet­ies tolerant to adverse climatic conditions at the beginning or the end of the growing season) or in land management (no-till farming, direct seeding, etc.). On the other hand, farmers quickly change to simpler cropping systems, if eco­nomic prospects are promising (Abdoellah et al., 2006).      The development of new elements (crops or crop vari­eties, pest and land management options), which farmers then integrate according to a multitude of criteria into their farm systems will continue to enhance productivity. Simi­larly, agroforestry initiatives will be most successful, where research concentrates on developing a range of options with farmers (Franzel et al., 2004).      Intercropping has the potential to increase return to land by investing (usually) more labor. The challenge for AKST will be to strike a balance between (1) understanding the interactions in highly complex intercropping and agro­forestry systems (including learning from and with farmers) and (2) developing options that farmers may add to their systems. Adding new elements may offer potential for farm­ers to participate in value chains and enhance income gener­ation while ensuring subsistence. There exists considerable potential for AKST to develop germplasm of agroforestry species with commercial value (Franzel et al., 2004).      AKST has contributed substantially to intensification in time, especially in high potential areas. However, double or triple cropping in rice or rice-wheat production created new challenges on the most fertile soils (Timsina and Con­nor, 2001). In spite of such drawbacks, there is promise for further intensifying land use in time by optimizing rotation management and developing novel varieties that can cope with adverse conditions.

Mixed farming. In many low-income countries, integration of crop and livestock has advanced substantially for the past few decades. In densely populated areas, mixed farming systems have evolved, where virtually all agricultural by­products are transformed by animals (Toumlin and Guèye, 2003). With the demand for livestock products expected to surge in most low-income countries, potential for income generation exists. A major challenge for AKST will be to

understand the tradeoffs between residue use for livestock or soil fertility and to optimize nutrient cycling in mixed systems.

Improve sustainability through multifunctional agriculture and ecosystem services. Ecosystem services are the condi­tions and processes through which natural ecosystems sus­tain and fulfill human life (Daily, 1997) and can be classified in four utilitarian functional groups: (1) provisioning (e.g., food, freshwater), (2) regulating (e.g., climate and disturb regulation), (3) cultural (e.g., recreation, aesthetic) and (4) supporting  (e.g.,  soil  formation, nutrient cycling)   (MA, 2005). Given that many ecosystem services are literally ir­replaceable, estimations of socioeconomic benefits and costs of agriculture should incorporate the value of ecosystem services (Costanza et al., 1997). Because of the rapid expan­sion of agriculture on natural lands (woodlands, grasslands) and the trend to use more external inputs (Hails, 2002; Tilman et al., 2002), the negative impact of agriculture on ecosystem services supply will require increasing attention (Rounsevell et al., 2005).
     The  construction  of multifunctional  agroecosystems can preserve and strengthen a sustainable flow of ecosystem services (Vereijken, 2002). They are best modeled after the structural and functional attributes of natural ecosystems (Costanza et al., 1997). Multifunctional agroecosystems will provide food and fiber, control disturbances (e.g., flood pre­vention), supply freshwater (filtration and storage), protect soil (erosion control), cycle nutrients, treat inorganic and organic wastes, pollinate plants (through insects, birds and bats), control pests and diseases, provide habitat (refugium and nursery), provide aesthetic and recreational opportuni­ties (camping, fishing, etc.) and culture (artistic and spiri­tual). The evaluation of ecosystem services is an evolving discipline that currently has methodological shortcomings. However, methods are improving and site-specific valua­tion will be possible in the coming years. The application of tradeoff analysis to support the design of multifunctional rural landscapes will demand expertise  on multicriteria analysis and participatory approaches.
     Frequently   recommended   measures   (Wayne,   1987; Viglizzo and Roberto, 1998) for addressing multifunctional needs include (1) diversification of farming activities in time and space rotational schemes, (2) the incorporation of agro­forestry options, (3) conservation/rehabilitation of habitat for wildlife, (4) conservation/management of local water resources, (5) the enforcement of natural nutrient flows and cycles (exploiting biological fixation and bio-fertilizers), (6) the incorporation of perennial crop species, (7) the well-bal­anced use of external inputs (fertilizers and pesticides), (8) the application of conservation tillage, (9) biological control of pests and diseases, (10) integrated management of pests, (11) conservation and utilization of wild and underutilized species, (12)  small-scale aquaculture, (13) rainfall water harvesting.

6.1.2 Achieving sustainable pest and disease management
Agricultural pests (insect herbivores, pathogens, and weeds) will continue to reduce productivity, cause post-harvest loss­es and threaten the economic viability of agricultural liveli-