5
Technologies for Soil Improvement

More than two-thirds of the agricultural land in sub-Saharan Africa (SSA) is considered to be severely degraded, and the situation is equally alarming in South Asia (SA) (FAO, 1994; GEF, 2003). If agricultural production in those regions must double in the next 2 decades, as implied by estimates of the future demand for food, substantial effort must be made to restore and maintain the productivity of their soils. If more food must be produced on the same amount of available land, agriculture must be intensified, and this will require that inputs to the soil be used as efficiently as possible (Henao and Baanante, 2006).

This chapter examines technologies to restore and maintain the physical structure of soils, improve the efficiency of water and nutrient use, and manipulate the rhizosphere—where plant roots interact with microbes—to enhance the soil and plant performance. It presents both some well-known methods for protecting and building soils that have not been widely adopted in SSA and SA but are essential for soil health and some novel, science-based concepts for improving soil that require research and additional exploration.

SOIL DEGRADATION IN SUB-SAHARAN AFRICA AND SOUTH ASIA

The severe problems of soil degradation and desertification in SSA and SA are attributed to the long-term use of extractive farming practices that fail to rebuild the soil with organic material and mineral nutrients that maintain soil productivity and prevent erosion. The negative nutri-



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5 Technologies for Soil Improvement More than two-thirds of the agricultural land in sub-Saharan Africa (SSA) is considered to be severely degraded, and the situation is equally alarming in South Asia (SA) (FAO, 1994; GEF, 2003). If agricultural pro- duction in those regions must double in the next 2 decades, as implied by estimates of the future demand for food, substantial effort must be made to restore and maintain the productivity of their soils. If more food must be produced on the same amount of available land, agriculture must be intensified, and this will require that inputs to the soil be used as efficiently as possible (Henao and Baanante, 2006). This chapter examines technologies to restore and maintain the physi- cal structure of soils, improve the efficiency of water and nutrient use, and manipulate the rhizosphere—where plant roots interact with microbes—to enhance the soil and plant performance. It presents both some well-known methods for protecting and building soils that have not been widely ad- opted in SSA and SA but are essential for soil health and some novel, science-based concepts for improving soil that require research and ad- ditional exploration. SOIL DEGRADATION IN SUB-SAHARAN AFRICA AND SOUTH ASIA The severe problems of soil degradation and desertification in SSA and SA are attributed to the long-term use of extractive farming practices that fail to rebuild the soil with organic material and mineral nutrients that maintain soil productivity and prevent erosion. The negative nutri- 4

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emerging technologies benefit farmers 4 to ent balance in soils of SSA (Henao and Baanante, 2006), underpinned by poverty, affects 95 million hectares of arable land that have reached such a state of degradation that only huge investments in soil restoration can make them productive again (IFDC, 2006). In densely populated SA, soil is often irrigated with polluted or contaminated water because of poor re- source management and competition for the resource. The overpumping of groundwater aquifers also has led to the deposit of salt on the land, which destroys soil productivity. Socioeconomic, political, and cultural factors reinforce conditions that affect soil quality. For example, the main source of fuel for household en- ergy in SA, other than fossil fuel, is wood, crop residues, and cattle manure (Venkataraman et al., 2005). The use of those traditional fuels has set in motion a cycle of natural resource degradation. Rather than being used as soil amendments, crop residues and manure are removed, and this has de- pleted the soil organic carbon (SOC) pool, created a negative nutrient bud- get, increased the susceptibility of soils to erosion, and reduced agronomic productivity. Runoff from soil leads to contamination and eutrophication of water resources, and the incomplete combustion of the biomass leads to emission of soot and noxious gases that have adverse effects on human health (Venkataraman et al., 2005). The degradation of the environment as a whole is a self-reinforcing system (Figure 5-1), and there is an urgent need to identify and foster technologies and management practices that can break the cycle of agrarian stagnation, enhance food security, and improve the environment. RESTORING SOIL QUALITY WITH ESTABLISHED MANAGEMENT PRACTICES Soil provides the physical, chemical (including water), and biological environment for sustaining plant growth. There are strong interdepen- dences among soil characteristics, and maximizing the productivity of the soil requires attention to each of them. Because soils and the climatic and socioeconomic conditions in which they exist differ regionally, approaches to soil management are highly situational. There are many soil types in SSA and SA, from the highly erodible desert Aridisols and the easily compacted Alfisols to the less-permeable Vertisols (clayey soils with low infiltration rate and high susceptibility to erosion), and each has distinct needs and vulnerabilities. Some crops grow better than others in particular soil types, and the nutrient content of soils can vary widely. Nevertheless, successful soil management systems have several common objectives: to increase carbon content, enhance water infiltration, ensure the availability of water at the plant-root zone, reduce erosion, create a positive nutrient budget, and encourage beneficial organisms.

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technologies soil imProvement 4 for FIGURE 5-1 Soil-degradation-induced poverty, starvation, and political, ethnic, 5-1.eps and social unrest are linked. SOURCE: Lal, 2007a. Reprinted with permission. bitmap image Established techniques used in various combinations to accomplish those objectives are summarized in Box 5-1. All the techniques have proven agronomic benefits, but for various reasons they have yet to be widely adopted in SSA and SA. Research has shown that the technologies can in- crease crop productivity and improve soil environments within 2 to 5 years (Lal, 1987, 2006a,b, 2007b, 2008; Kapkiyai et al., 1999; Sanchez, 2002; Wani et al., 2003; Singh et al., 2005; Smaling and Dixon, 2006; Rockstrom et al., 2007). The fundamental effects of the techniques in Box 5-1 are to improve soil structure, provide nutrients essential for plant growth, and maintain water availability in the soil. Improving Soil Structure with Established Practices A major benefit of the management approaches in Box 5-1 is that they can be used to restore and maintain optimal SOC for healthy soil structure and tilth. SOC provides energy for soil microbes and other fauna and flora;

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emerging technologies benefit farmers 4 to BOX 5-1 Established Management Practices to Maintain Soil Productivity To improve soil structure and biological health, reduce erosion, and increase efficiency of water and fertilizer use: • Mulching with natural materials and plastic. • Leaving crop residue. • Application of manure and biosolids. • Incorporation of cover crops in the rotation cycle. • Agroforestry. • Contouring of hedge rows. • Terracing and engineering structures. • Precision farming. • Conservation tillage and nontilling. • Controlled grazing. • Improved pasture species. • Controlled use of irrigation. • Land-use planning and land-tenure reform. To improve soil nutrient budget: • Integrated nutrient management. • Biological nitrogen fixation. • Judicious use of chemical fertilizers. enables the soil to hold water and nutrients; increases fertilizer-use efficiency by decreasing losses through erosion, volatilization, and leaching; and ulti- mately improves crop yield. The critical minimal SOC for the productivity of most soils of SSA and SA is 1.1 percent. Most agricultural soils of SSA and SA are severely depleted and have lost 75 to 85 percent of their original SOC pool. The concentration in degraded and desertified agricultural soils in SSA and SA is often as low as about 0.1 to 0.2 percent. SOC is highly correlated with productivity. Field experiments in SA have shown that the yield of mustard grain increased by 360 kg/ha for each ton of increase in the SOC pool in the surface soil layer (the top 15 cm) (Shankar et al., 2002). In central India, adoption of management practices to increase SOC in Vertisols increased crop yield from 1.0 t/ha per year to 4.7 t/ha per year (Wani et al., 2003).

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technologies soil imProvement 4 for In Kenya, an 18-year study showed that maize and bean yields were in- creased from 1.4 t/ha per year to 6.0 t/ha per year when stover was returned to the soil as mulch, and fertilizer and manure were applied to increase the SOC pool from 23.6 t/ha to 28.7 t/ha in the surface layer (Kapkiyai et al., 1999). One estimate suggests that increasing the SOC pool in the agricul- tural soils of SSA and SA by 1 t/ha per year would increase total annual food grain production in SSA by 4.6 ± 1.6 × 106 t and in SA by 18.6 ± 7.1 × 106 t (Lal, 2006a,b). As noted earlier, management practices that rebuild SOC have not been widely applied throughout SSA and SA. Weak government institutions and extension, inadequate infrastructure, and resource-poor agricultural systems are barriers to the adoption of such practices. However, growing interest in carbon sequestration projects (Box 5-2) might provide an opportunity to improve SOC dramatically while increasing farmers’ income. Improving the Soil Nutrient Budget with Established Practices An important limiting factor in soils of SSA and SA is fertilization. Rice, wheat, and maize—the three major staple food crops—can require as much as about 100-200 kg of nitrogen-based fertilizer per hectare to pro- duce optimal yields under ideal moisture and temperature conditions. SSA and SA farmers typically are unable to afford such high rates of nitrogen fertilizer, and crop yields therefore are chronically low. Extractive farming practices are unsustainable, but adoption of man- agement practices listed in Box 5-1 can help to create a positive nutrient balance in the soil. Integrated nutrient management techniques consist of a combination of organic amendments, such as the use of manure and compost, and the judicious use of inorganic fertilizers (Vanlauwe and Giller, 2006). Those practices have to be implemented alongside those that build soil structure and carbon content (Lal, 1987, 2006a,b, 2007b, 2008; Kapkiyai et al., 1999; Sanchez, 2002; Wani et al., 2003; Singh et al., 2005; Smaling and Dixon, 2006; Rockstrom et al., 2007). As noted earlier, biofertilization accounts for about 65 percent of the nitrogen supply of crops worldwide, primarily via Rhizobiaceae-legume symbiosis (Lugtenberg et al., 2002). Although background concentrations of nitrogen fixation by free-living or endophytic bacteria are probably low (about 5 to 10 kg/ha), the bacteria produce bioavailable nitrogen at the root interface. The standard fertilization method of soil amendments is inefficient: only 40 to 60 percent of the nitrogen applied is taken up by plants, because it is lost through leaching or immobilized by soil microbes. Encouraging the growth of beneficial organisms in legume crop systems reduces the need for fertilizer.

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emerging technologies benefit farmers 0 to BOX 5-2 Carbon Sequestration: A Possible Opportunity for Resource-Limited Farmers Carbon sequestered in soils can be traded as a commodity in accord with the Clean Development Mechanism of the Kyoto Treaty, the BioCarbon Fund of the World Bank, the Chicago Climate Exchange, the European Climate Exchange, and national or domestic industry (Schlamadinger and Marland, 1998; Tucker, 2001; Diakoulaki et al., 2007). Although there are only a few projects to date in SSA and SA, carbon trading has the potential to bring a new income stream to resource-poor farmers (Kandlikar, 1996; Persson et al., 2006). Trading carbon credits implies payments to farmers of SSA and SA for environmental services through international industry and private and public sectors. With the adoption of the soil and crop management practices listed in Box 5-1, atmospheric carbon dioxide can be sequestered in agricultural soils. The rate of increase in soil organic carbon (SOC) after conversion to restor- ative land use follows a sigmoid curve and attains a maximum 5 to 20 years after adoption. Sequestration of carbon in agricultural soils worldwide has the potential to sequester 0.4 to 1.2 billion tons of carbon per year, or about 5 to 15 percent of global fossil fuel emission of carbon (Lal, 2004). Control of desertification and restoration of degraded soils have the potential to sequester an additional 0.9 to 1.9 billion tons per year (Lal, 2001). SOC sequestration in improved agricultural and restored ecosystems in SSA and SA ranges from 100 to 1,000 kg of carbon per hectare per year (Lal, 2000). Higher rates of SOC sequestration are observed in humid climates and in fine-textured soils, and lower rates in dry climates and in coarse-textured soils. Projects to sequester carbon in soils receive qualification to be used by world markets through independent validators. Involvement of diverse stakeholders in trading carbon credits has the potential to promote industry’s interest in this strategy (Johnson and Heinen, 2004) and to encourage development of a relevant climate policy for the region (Fouquet, 2003). Soil-Water Conservation with Established Practices Soil and water are closely linked in agricultural systems. Conserving water in the root zone and enhancing the efficiency of its use require that soil structure and quality be improved (Rockstrom et al., 2007). At the same time, the conservation of soil requires that it be protected from ero- sion by water and wind. The management practices listed in Box 5-1 can address both goals. In arid and semi-arid regions with low vegetation cover and crusted or compacted soils of low infiltration capacity, water runoff is high, especially

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technologies soil imProvement  for in the monsoonal climate of SA, where rainfall is concentrated over short periods of 100 hours or 25 consecutive days (Agarwal, 2000; Biswas, 2001; Swaminathan, 2001). Runoff is a source of contamination and pollution of surface water and groundwater, and the leaching of chemicals from agricul- tural lands, especially in the intensively farmed areas of the Indo-Gangetic (IG) Basin, is a severe problem (Pachauri and Sridharan, 1999). Improving soil structure is the key to improving water infiltration into the soil. The maintenance and enhancement of soil organic matter, the use of biosolids or mulch, and conservation and no-till techniques are important strategies for improving soil structure. Mulching with biomass or plastic is also effective in reducing water losses by evaporation. Agroforestry, which is practiced to some degree in SSA and SA, has been shown to improve soil quality. However, trees growing in farmers’ fields may compete with crops, and there has been little success in adop- tion of such systems (Rhoades, 1997; Buresh and Tian, 1998). Recent research in the Sahel suggests that native shrubs are a previously unrecog- nized alternative that potentially can be used to enhance the fertility and quality of soils without such competition (Kizito et al., 2007). Piliostigma reticulatum and Guiera senegalensis play multiple roles in improving soil quality—such as providing carbon to the soil (Lufafa et al., 2008), increas- ing nutrient availability in soil beneath and near the canopy (Dossa, 2007), and moving subsoil water to the surface (Caldwell et al., 1998; Kizito et al., 2009)—and have been shown experimentally to increase yields in peanut and millet by more than 50 percent (Dossa, 2007). Developing woody spe- cies companion plants has great potential throughout semi-arid SSA and SA to restore degraded landscapes, buffer desert encroachment, and increase crop productivity. However, alternatives for fuel are needed because these shrubs are cut and burned each year, and this constitutes a loss of organic inputs that the impoverished soils need. The efficient use of water will be critical in the future, not only because of its increasing scarcity (as described in Chapter 4) but because of its po- tential to bring salts into the soil that inhibit water uptake by crops and damage the physical structure of the soil. In parts of northwestern India, the problem of soil salinity was once associated mainly with a high ground- water table (waterlogging) that brought salt into the root zone through capillary action. More recently, overexploitation of groundwater has led to a decline in water tables, so farmers are forced to use poor-quality saline groundwater for irrigation that has led to high-sodium conditions that destroy the soil (Datta and De Jong, 2002). An important technology, which is gaining momentum in the IG Basin of SA and elsewhere, is the conversion of flooded rice paddies to aerobic rice. The latter, with specific varieties that can be grown as upland culture similar to wheat or corn, can save the scarce water resources and greatly

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emerging technologies benefit farmers  to improve water-use efficiency. Effective weed control measures are important for successful adoption of aerobic rice, but adoption of this technology would be directly relevant to the entire IG Basin and the 12.5 million hect- ares of area now under rice-wheat culture. Soil conservation and desertification control, which have high priority in SSA and SA, also can be effectively controlled by practices outlined in Box 5-1, including no-till or low-till farming with retention of crop residue mulch and incorporation of cover crops in the rotation cycle. To transition into no-till farming, appropriate seeding equipment and herbicides need to be available and affordable. The effectiveness of no-till farming can be en- hanced by integrating it with agroforestry, establishing contour hedge rows of perennial grasses or shrubs, establishing engineering techniques, and using complex crop rotations. Those measures improve ecosystem services of soil resources and increase crop yields. Vertisols can be effectively managed through adoption of the conservation-effective technology described above. The use of soil condi- tioners, such as mulch and biosolids, will result in improved soil structure and productivity. Zeolites and related materials, described in the next sec- tion, also have specific potential for improving Vertisols. NOVEL TECHNOLOGIES TO IMPROVE SOIL PRODUCTIVITY The practices described in the preceding sections are considered estab- lished because their use has been studied extensively and their contributions to increased crop yields have been documented through research. However, understanding which combinations of practices work best in different envi- ronmental and social circumstances requires additional study and planning. Because that has not been done for most of SSA and SA, it presents an important opportunity and an unmet need for agricultural development. The increasing demand for food and changing land and water condi- tions have prompted scientists to search for new tools to build soil struc- ture, maximize the efficient use of water, and provide essential nitrogen and phosphorus to crops. Advances in plant, microbial, and computational biology; materials science; electronics; and optical sensing may provide new tools to improve soil productivity. Several technologies that are emerging from those fields of science are described below. Remote Sensing of Plant Physiology for Nutrient Management and Soil Quality More effective use of remote sensing technologies could enable farmers to better manage inputs to increase crop yields, decrease input costs, and reduce the potential for adverse environmental effects. If farmers could have access to remotely measured plant health and soil conditions—such

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technologies soil imProvement  for as water content, acidity, aeration, and the availability of nutrients—they could take appropriate steps to address soil quality before adverse effects occur. The low yields of cereal crops in SSA (about 1,000 kg/ha) could po- tentially be quadrupled by using sub-surface drip irrigation (mentioned in Chapter 4) and technology to manage fertilizer and nutrients. Remote sensing technology for nutrient management was initially based on the Normalized Difference Vegetative Index, which predicts plant cover (Stone et al., 1996). It was later used to document extensive variability between plants at distances 30 cm or less in production fields (Raun et al., 1998; 2001). The present technology is based on optical sensors with high spatial resolution that have the ability to predict yield potential midway through the growing season. It permits calculations of fertilizer rates based on projected nitrogen removal, and it permits adjustment of fertilizer rates as a result of conversion of organic to inorganic nitrogen (Johnson and Raun, 2003). Considering the extremely low rates of nitrogen application in SSA, improved nitrogen fertilizer practices, such as fertigation with drip ir- rigation, can enhance nutrient-use efficiency and substantially increase crop yields. Spectral data on plants and soils could be measured remotely and the information sent to farmers on cellular phones or other communication de- vices. Alternatively, a simple low-cost handheld “optical pocket sensor” and institutional support to deliver the data and education about management practices to farmers in SSA and SA could be developed. As discussed in Chapter 2, the use of hyperspectral imaging can coupled with the develop- ment of sentinel species able to emit specific stress signals that are detectable remotely or locally would assist farmers’ management practices. Zeolites and Synthesized Nanomaterials Zeolites, members of a family of crystalline aluminum silicates that consist of a unique tetrahedral frame within which sit large ions or other molecules, have multiple applications in soil and water conservation (To- kano and Bish, 2005). Natural deposits of zeolites occur throughout the world, but they can also be synthesized and tailored for specific uses. The utility of zeolites is derived from their unique flexible internal structures that permit the exchange of ions and reversible dehydration (Watanabe et al., 2004). Because they absorb and slowly release water, zeolites can be used as a soil amendment to improve water retention in sandy and low-clay soils and to improve porosity of impermeable soils. They could be used to conserve water in the root zone in conjunction with traditional techniques, such as mulch farming and application of manure (Bhattacharyya et al., 2006; Pal et al., 2006; Oren and Kaya, 2006). When pretreated with nutrients, zeolites can be used as an agent for the slow release of nitrogen and phosphorus. They can also be used to enhance the availability of micronutrients, such as zinc (Oren and Kaya,

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emerging technologies benefit farmers 4 to 2006). Alternatively, zeolites can be used in soil remediation to absorb metal cations and reduce local concentrations of toxic substances that in- hibit plant growth and nitrogen-fixing soil microbes (Pisarovic et al., 2003). The potential diversity and multiple uses of zeolites make them ripe for further research and development. Changing the structure of the molecular framework, the internal cations, and guest molecules can change the char- acteristics of the zeolite and its effectiveness in a particular application. The dimensionality and size of zeolite pores also define many of its properties. Advances in nanotechnology suggest that it is possible to engineer zeo- lites further or develop similar materials with precisely determined proper- ties. One opportunity is to increase the efficiency of fertilizer by developing slow-release delivery molecules that decrease losses to water and air and increase uptake by plants. A second potential application of nanotechnology is as a soil sur- face conditioner that enhances soil structural stability, reduces erosion, and dissipates heat. In many of the countries in SSA and SA, heat stress on crops intersects with other abiotic and biotic stresses to reduce yield (Senthil-Kumar et al., 2007). High-soil temperatures exacerbate the stress of drought and point to a possible point of intervention (Mittler, 2006). Use of innovative technology for conserving water in the soil is a promising option to address heat and drought (Kijne, 2001). In addition, when dry Vertisols are rapidly exposed to water, they re- lease a large amount of heat at the soil surface, which causes slaking of soil aggregates that reduces the ability of water to percolate downward and re- sults in water runoff. Although no current method addresses this problem, it is conceivable that materials could be developed to interrupt the process by improving the biophysical stability of soil aggregates and dissipating the heat emitted during wetting. A third application of nanomaterials is to improve the quality of irriga- tion water. Zeolites have been used in some parts of the world to remove some contaminants from water, but nanoparticle filters of ceramics, carbon, and zinc oxides that effectively remove contaminants—including viruses, bacteria, lead, arsenic, uranium, and pesticides—are now being produced. Inexpensive applications are needed to remove those contaminants and oth- ers, such as sodium and salts, from irrigation water. Further development of this technology has the potential to reduce a major health burden and improve soils in rural communities in SSA and SA. The application of nanomaterials and zeolites, particularly the synthetic types, on an entire farm is prohibitive for resource-poor farmers of SSA and SA, so finding ways to bring the cost down would be essential. However, at their current price, they would be appropriate for specific niches, such as in screenhouses and greenhouses for production of vegetables or horticultural crops to supply large urban centers.

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technologies soil imProvement  for New Cultivars, Plant Breeding, and Biotechnology The productivity associated with soil, water, and nutrients depends in part on the requirements of the crops they support. The tools of modern plant breeding and biotechnology, described in greater detail in Chapter 3, offer the hope that crops can be developed to better tolerate specific soil- related constraints. Genes that provide some degree of tolerance of cold, drought, salinity, aluminum and manganese toxicity, anaerobiosis, and low nutrient conditions are being widely investigated (Fageria and Balizar, 2005; Chinnusamy et al., 2006; Eicher et al., 2006; Umezawa et al., 2006; Sunkar et al., 2007). Because drought is a prevailing concern, improving the water-use ef- ficiency of crops (biomass produced per unit of water transpired) is of particular interest. Breeding for early flowering and developing crops that can be planted at a higher density to minimize soil-water evaporation are two strategies to cope with water deficits. Sowing such crops as sorghum and millet in clumps can increase water-use efficiency and improve yields (Bandaru et al., 2006). Developing new varieties of aerobic rice to shift the rice-wheat-based cropping systems of the IG Basin away from flooded rice paddies would save massive amounts of groundwater and improve soil, although new ways to control weeds would be needed (Peng et al., 2006). Two additional opportunities at the interface of soil and plants are discussed below. Development of Better Roots Current research suggests that it is possible to optimize root structure for various purposes, including increased carbon sequestration, improved grain yields, and better water and nutrient uptake. High-resolution root expression mapping (Birnbaum et al., 2003, 2005; Brady et al., 2007) and root architecture imaging and analysis have potential to enhance or select for desirable root traits, such as rapid and early shallow root emergence, diffuse and extensive root architecture and root hairs, and long tap roots (Philip Benfey, Duke University, presentation to committee, October 15, 2007). It may be possible to develop improved cultivars with a favorable root:shoot ratio and improved harvest index, which favors both grain and biomass production. Development of Transgenic Nitrogen Fixation in Non-legumes As noted earlier, biofertilization accounts for about 65 percent of the nitrogen supply of crops worldwide, primarily through Rhizobiaceae- legume symbiosis, in which Rhizobium bacteria fix atmospheric nitrogen and deliver it to plants via nodules on roots (Lugtenberg et al., 2002).

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emerging technologies benefit farmers  to BOX 5-5 Major Research and Technology Needs for Manipulating Microbes in the Rhizosphere • icrobial genome sequencing and functional genomics of plant-associated M microbes that are important in the agriculture of sub-Saharan Africa and South Asia. • iscovery of the genes that control microbial-plant signaling, biofilm forma- D tion, interspecies interactions, production of plant-growth-promoting sub- stances, nutrient uptake enhancement, plant protection, and the structures of multi-species microbial communities. • asic multidisciplinary research on microbial ecology of microbial-plant inter- B actions that optimize growth of crops. needed to bring the manipulation of the rhizosphere to reality. Given the diversity and complexity of microbial communities and, until recently, the lack of tools to study them, the task requires a major interdisciplinary initiative. In that regard, it is worth pointing out that there is currently a distinct lack of interaction between microbiologists and plant scientists, and this has held back the field of rhizosphere science. The emphasis of plant sciences has been on breeding and developing plants for optimal yield and resistance to disease, pests, and environmental stresses. There has been little research on developing plants to promote interactions with beneficial microbes or to optimize the crop rhizosphere. To benefit farmers in SSA and SA, research should focus on local crops and local soil communities. Teams of soil and rhizosphere microbial ecologists, geneticists, molecular biolo- gists, plant physiologists, plant breeders, agronomists, and anthropologists need to be assembled in an integrative project to conduct multidisciplinary research on the major crops of the regions. As research proceeds, it will be important to put it into a regional and farm-level crop system context. To emphasize that, we present one example related to manipulation of biocontrol microbes. Larkin (2008) compared various biostimulants and known microbial control agents of potato dis- eases. All had measurable effects on soil microbial properties in the field, but none reduced disease in continuous potato plots; rather, effective con- trols occurred only in particular crop rotations. The results indicate that some rotations are better able to support the added beneficial organisms and amendments that enable more effective biocontrol of disease. Estab- lishment and persistence of microbial inoculants, soil amendments, and engineered rhizospheres probably depend on many soil and climate factors.

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technologies soil imProvement  for That emphasizes the need for early testing of promising biological technolo- gies at the farm or crop system level. In addition to biological interactions and adaptation to local condi- tions, research for SSA and SA needs to take into account regional cultural and socioeconomic considerations. Over the last 50 years, the developing world has been littered with agricultural technologies that might have been agronomically superior under controlled research conditions but were unac- ceptable for subsistence farmers because of the local culture, lack of techni- cal support, or management scales and markets of rural economies. To attain practical outcomes for microbial technology, it seems that the emphasis should be placed on approaches that depend on manipulat- ing native populations. For example, there is a body of research on the feasibility of using organic amendments to create soil conditions and mi- crobial responses to naturally suppress soilborne diseases. Similarly, this is an appropriate technology consideration that makes breeding or insertion of transgenic genes attractive. Such an approach is desirable because at- tributes such as optimized roots for efficient water and nutrient uptake or stimulation of beneficial microbial gene expression would require only the introduction of new cultivars into existing systems with minimal technical support and reduce the need for external input. REFERENCES Abbasi, P. A., J. Al-Dahmani, F. Sahin, H. A. J. Hoitink, and S. A. Miller. 2002. Effect of compost amendments on disease severity and yield in conventional and organic tomato production systems. Plant Dis. 86:156-161. Agarwal, A. 2000. Drought? Try capturing the rain. Briefing paper. New Delhi: Centre for Science and Environment. Available online at http://www.rainwaterharvesting.org/ downloads/drought_english.pdf [accessed July 28, 2008]. Alabouvette, C., C. Olivain, F. L’Haridon, S. Aime, and C. Steinberg. 2007. Using strains of Fusarium oxysporum to control Fusarium wilts: Dream or reality. Pp. 157-178 in Novel Biotechnologies for Biocontrol Agent Enhancement and Management. Proceedings of the NATO Advanced Study Institute on Novel Biotechnologies for Biocontrol Agent Enhancement and Management, September 8-19, 2006, Gualdo Tadino, Italy, M. Vurro and J. Gressel, eds. Netherlands: Springer. Alvarez, M. I., R. J. Sueldo, and C. A. Barassi. 1996. Effect of Azospirillum on coleoptile growth in wheat seedlings under water stress. Cereal Res. Comm. 24:101-107. Amara, M. A. T., and M. S. A. Dahdoh. 1997. Effect of inoculation with plant growth pro- moting rhizobacteria (PGPR) on yield and uptake of nutrients by wheat grown on sandy soil. Egypt. J. Soil Sci. 37:467-484. An, Q. L., X. J. Yang, Y. M. Dong, L. J. Feng, B. J. Kuang, and J. D. Li. 2001. Using confocal laser scanning microscope to visualize the infection of rice roots by GFP-labelled Klebsi- ella oxytoca SA2, an endophytic diazotroph. Acta Bot. Sin. 43:558-564. Asghar, H. H., Z. A. Zahir, M. Arshad, and A. Khaliq. 2002. Relationship between in vitro production of auxins by rhizobacteria and their growth-promoting activities in Brassica juncea L. Biol. Fertil. Soils 35:231-237.

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