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Displacement ratio is an important factor in the calculation of carbon payback time

That is to say, 1 additional MJ of corn ethanol is assumed to take the place of 1 MJ of gasoline. For example, suppose gasoline production is 500 MJ this year and is predicted to reach 600 MJ next year to keep up with rising demand under business-as-usual , and then comes 100 MJ of corn ethanol in the second year. If gasoline production remains 500 MJ in the second year, with the other 100 MJ of demand met by corn ethanol, this is considered a perfect 1:1 displacement ratio. Due to the complexity of economic systems and human behaviour, however, it is more likely less than one unit of gasoline will be displaced by corn ethanol . The introduction of corn ethanol into the market will put downward pressure on gasoline prices, leading to a higher demand for the fuel. To continue with our example, because of the higher demand, suppose 550 MJ of gasoline and 100 MJ of corn ethanol are produced and consumed in the second year, all else being equal. Thus the net result is that 50 MJ of gasoline is displaced by 100 MJ of corn ethanol .A 10% decrease from the perfect displacement ratio would increase the CPT by 63% for unproductive land yield to 27% for highly productive land . If only 0.6 MJ of gasoline is displaced, most of the marginal land would fail to provide any carbon benefits within the 100-year time horizon studied. If only 0.5 MJ of gasoline is displaced, even the most productive land would fail to yield any carbon benefits within the time horizon studied. These results suggest that whether corn ethanol provides carbon benefits depends importantly on the extent to which gasoline can be displaced by additional corn ethanol production. In future research,blueberry in pot effort may be directed to estimate a more realistic displacement ratio that takes into account such market mechanisms as supply-demand price changes than the perfect ratio assumed in this and previous CPT studies. Models such as the partial equilibrium analyses can be used to derive such market-mediated displacement ratios .

Concern has been raised over the eco-toxicity impact of emerging pesticides and the lack of characterization models to evaluate them. This is a general question of data gap. In fact, in addition to emerging pesticides, there are also pesticides whose usage data are withheld by the USDA . However, the ecotoxicity impact of these ‘undocumented’ pesticides is likely small as a large majority of the pesticides applied to the crops studied are covered by both usage and characterization data. Specifically, such data are available for 50 to 90 different types of pesticides; they generally account for 90% to 95% of the total amount of all pesticides applied; and they include the key pesticides that contribute the largest toxicity impacts identified by recent research . It is worth noting that in terms of the number of pesticides covered, our analyses in chapters 2 and 4 are by far the most comprehensive in comparison to similar studies, which evaluated at most a dozen of pesticides . Nevertheless, our analyses may benefit from evaluating the possible ecotoxicity impact of the “uncovered” pesticides. For emerging pesticides, their characterization factors may be derived from models such as the USEtox based on their physicochemical properties and ecotoxicity effect data if available. For pesticides without usage data, their total usage is in fact aggregated in the total amount of pesticides applied and can be derived by subtracting the pesticides with usage data. Next, sensitivity analysis can be carried out to compute the possible range of their total ecotoxicity impact by assuming different amounts for individual pesticides subject to the total usage derived. Following the approach developed in previous studies , we assumed a generic factor for the fraction of pesticides in aquatic systems through leaching and runoff. However, this factor is likely to vary by pesticide – due to differences in their intrinsic physio-chemical properties – and by location – due to differences in local topographic, climatic, and soil conditions. To better estimate pesticide emissions after application, future studies may conduct field experiments – at least for the key pesticides identified – or rely on more sophisticated models than used in this dissertation, such as the PestLCI, that take into consideration pesticides’ properties, environmental factors, and application methods . Soil microbial communities are shaped by diverse, interacting forces.

In agroecosystems, management practices such as crop rotation, fertilization, and tillage alter soil physicochemical parameters, influencing the diversity and composition of bulk soil bacterial and fungal communities. Plant roots create additional complexity, establishing resource-rich hotspots with distinct properties from the bulk soil and selectively recruiting microbial communities in the rhizosphere. Root uptake of ions and water coupled with exudation of carbon-rich compounds results in a rhizosphere soil compartment where microbial cycling of nitrogen, phosphorous, and other nutrients is rapid, dynamic, and competitive in comparison to the bulk soil. Although impacts of agricultural management and the rhizosphere environment on microbiomes and their ecological outcomes have frequently been analyzed separately, understanding interactions has important implications for assembly, ecology, and functioning of rhizosphere microbial communities which are critical to plant health and productivity. Agricultural management establishes soil physicochemical properties that influence microbial community composition, structure, and nutrient-cycling functions. Organic fertilizer increases bulk soil microbial diversity and heterogeneity, and organically managed systems differ from conventional systems in bacterial and fungal community composition. Co-occurrence network analysis has shown that these taxonomic shifts can shape patterns of ecological interactions regulating structure, function, and potential resilience of soil microbial communities. In fact, nutrient management strategies are strong drivers of co-occurrence network structural properties, although outcomes across regions and agroecosystems are inconsistent and also a function of other environmental and management factors. Plant roots are similarly powerful drivers of microbial community assembly, creating rhizosphere communities that are taxonomically and functionally distinct from bulk soil. The strength of plant selection, or rhizosphere effect, is evident in observations of core microbiomes across different field environments. As for management, plant effects on microbial communities also extend beyond taxonomy to network structure. Rhizosphere networks have frequently been found to be smaller, less densely connected, and less complex than bulk soil networks, although counterexamples exist.

Whether plasticity in rhizosphere recruitment can occur across management gradients and how such plasticity could impact plant adaptation to varying resource availabilities in agroecosystems remains unclear. The potential for adaptive plant-microbe feed backs is especially relevant for acquisition of nitrogen , an essential nutrient whose availability in agroecosystems is controlled by interactions between fertility management practices and microbial metabolic processes. Microbial communities supply plant-available N through biological N fixation and mineralization of organic forms, and limit N losses by immobilizing it in soil organic matter. Conventional and organic agroecosystems establish unique contexts in which these transformations occur, shaping microbial communities through system-specific differences in soil N availability and dominant N forms as well as quantity and quality of soil organic matter. Organic fertility inputs such as compost and cover crop residues alter the abundance, diversity,plastic planters wholesale and activity of various nitrogen-cycling microorganisms, while synthetic fertilizers mainly increase the abundance of Acidobacteria and can decrease the abundance of ammonia-oxidizing archaea. Synthetic fertilizers may affect microbial community structure via changes in pH, increasing the abundance of acid-tolerant taxa indirectly through soil acidification, or may alter the relative abundance of specific taxa even when pH is relatively constant. Changes in microbial community structure and activity in bulk soil affect not just the rates but also the outcomes of agriculturally and environmentally relevant Ncycling processes such as denitrification. Roots are also key regulators of N transformations, leading to higher rates of N cycling that are more closely coupled to plant demand in the rhizosphere than in bulk soil compartments. The maize rhizosphere harbors a distinct denitrifier community and is enriched in functional genes related to nitrogen fixation , ammonification , nitrification , and denitrification relative to soil beyond the influence of roots. Understanding regulation of tight coupling of rhizosphere N cycling processes to plant demand could provide new avenues for more efficient and sustainable N management, particularly in an era of global change. However, it is necessary to go beyond exploration of individual effects of plant selection and agricultural management on rhizosphere microbial communities and consider how these factors interact. This knowledge can contribute to managing rhizosphere interactions that promote both plant productivity and agroecosystem sustainability. While management-induced shifts in bulk soil microbiomes affect environmental outcomes, plant-regulated rhizosphere communities are more directly relevant to yield outcomes. Improved understanding of how plant selection changes across management systems is thus an essential component of sustainable intensification strategies that decouple agroecosystem productivity from environmental footprints, particularly in organic systems where yields are formed through transformation of natural resources rather than transformation of external synthetic inputs.

When management and plant rhizosphere effects shape rhizosphere microbial communities, a number of scenarios are possible: one could be greater than the other , their effects could be additive , or they could interact . Typically, these effects are considered additive , where management shapes bulk soil communities and plant effects act consistently, such that rhizosphere communities are distinct from bulk soil and differ from one another to the same degree as their respective bulk soil communities. However, variation in rhizosphere microbiomes and co-occurrence networks between management systems and the unique responses of bulk soil and rhizosphere bacteria to cropping systems point toward M × R interactions shaping microbial community composition. Nonetheless, the functional significance of these interactive effects on critical functions such as N cycling is complex and remains difficult to predict. For example, biological N fixation is driven in large part by plant demand, but high inputs of synthetic fertilizer reduce rates of biological N fixation, diminishing the role of soil microbial communities in supplying plant nutrients and increasing the potential for reactive N losses. Understanding how the M × R interaction affects ecological functions is thus a knowledge gap of critical agricultural and environmental relevance. Adaptive plant-microbe feed backs in the rhizosphere have been described for natural ecosystems, but whether this can occur in intensively managed agricultural systems where resources are more abundant is less clear. We asked whether adaptation to contrasting management systems shifts the magnitude or direction of the rhizosphere effect on rhizosphere community composition and/or N-cycling functions across systems. For instance, can the same genotype selectively enrich adaptive functions that increase N mineralization from cover crops and compost when planted in an organic system and also reduce denitrification loss pathways from inorganic fertilizer when planted in a conventional system? We hypothesized that an M × R interaction would result in differences in the magnitude or direction of the rhizosphere effect on microbial community structure and functions and that differences between rhizosphere communities, cooccurrence network structure, or N-cycling processes would reflect adaptive management-system-specific shifts. To test these hypotheses, we investigated microbial community composition and co-occurrence patterns in bulk and rhizosphere samples from a single maize genotype grown in a long-term conventional-organic field trial. We further quantified the abundance of six microbial N-cycling genes as case study for M × R impacts on rhizosphere processes of agricultural relevance. Our approach integrated ordination, differential abundance and indicator species analyses, construction of co-occurrence networks, and quantitative PCR of N-cycling genes to gain a deeper understanding of the factors that shape rhizosphere community and ecological interactions.A greater number of ASVs showed a significant response to plant selection in conventional than organic soil . Five bacterial and five fungal ASVs were differentially abundant between the conventional bulk and rhizosphere soils , as compared to one bacterial and two fungal ASVs in the organic bulk and rhizosphere soils . The number of differentially abundant taxa between the rhizosphere communities of the two systems was at least as great as the number responding to within-system rhizosphere effects . More fungal than bacterial ASVs were differentially abundant between these rhizosphere communities: 24 fungal ASVs but only six bacterial ASVs were significantly different in abundance between CR and OR, indicating strong M × R interactions.

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A different kind of adaptation among edge growers is to change the commodities grown

Anticipating either that they will have the chance to sell their land for development or that surrounding urbanization will restrict their farming activities, farmers in such situations avoid continuing investment in their enterprises with capital improvements, new technologies, and management time and energy. This uncertainty about the future may in fact serve as a self-fulfilling prophesy, pushing landowners to seek development deals and thus accelerating the rate of farmland conversions in high growth areas. In the interim, much farmland may be idled or underutilized, production shifted from more to less intensively cultivated crops, and individual farm parcels bypassed or surrounded by development. For California farmland owners, the annexation plans of nearby cities are a key sign as to whether or not agriculture is likely to survive in particular areas . Research in other states suggests that urban-related uncertainties often lead to inefficient land use .Not all agricultural landowners in edge locations give up on the future, accepting what others regard as the inevitable demise of productive farming in their areas. There are sufficient stories of individual farmers continuing to invest in and aggressively manage their edge properties to suggest that continued farming in the shadow of urbanization is an important pattern for California agriculture. One reason is that not all edges experience ongoing development pressures. Even in high growth regions, California cities do not grow out in all directions at the same time; rates of expansion also are often gradual, allowing years of stability to some edges. Some landowners thus are unrealistic in anticipating that the path of urban expansion in their area will give them the near-future opportunity to sell their land for development.

In a guide to the easement option for California agricultural landowners,growing raspberries in pots the authors estimate that more than three-quarters of Central Valley farmland “cannot realistically be expected to develop to urban uses within the next 40 years” . Yet even in stable edge areas where agricultural operations are likely to continue indefinitely, the very proximity to residential and other urban land uses usually requires some degree of adjustment on the part of farmers. Operating in the shadow of urbanization demands more in farm management skills and the use of technology, according to some accounts. These abilities and the willingness to adapt and continue to farm in urban-influenced areas are not equally distributed among farmers in such locations. Age and family circumstances play a role.A study of dairy farms in a Hudson Valley area of New York experiencing growth pressures, finds that younger operators with fewer family problems were more likely to stay in business at that location and adapt their operations to the urban environment . Adaptations include various kinds of changes in production practices to minimize negative impacts on urban neighbors and to secure crops and equipment from vandals and trespassers. Integrated Pest Management techniques for reducing or controlling the use of pesticides and other chemicals are widely used by California farmers, drawing from a large body of university and private sector research. IPM covers both biological and engineering innovations, including investment in new spray equipment . Other changes include muffling pump motors, measures to reduce dust, and avoiding late-night and early morning operations that are noisy. Because of these and other adaptations, production costs for edge farming are usually higher than in other locations, whether because of equipment investment or the inefficiencies created by operational changes.One example of urban-influenced adaptation is provided by the experience of Southern California’s poultry farmers during the 1980s.

They invested in new types of buildings to remove laying hens from the floor and thus isolate waste material, changed procedures for drying and disposing of waste, landscaped the areas around poultry housing, and improved fencing and installed alarm systems to reduce vandalism and theft . Some poultry farms in the region chose instead to sell their land for development and relocate in more remote locations, investing some of their proceeds in new facilities—the ultimate strategy by farm operators impacted by urban growth. Generally this means shifting to higher value commodities, or to those that are less vulnerable to urban impacts. Commodities that produce more income per acre, such as tree, ornamental, and vineyard crops, also typically involve more intensive and expensive cultivation practices. But the motivation for shifting in this direction is the already higher costs of farming in urban-influenced areas, including the land costs for farms that acquire more land to expand their operations . Such adaptations allow some productive and profitable agricultural operations to continue in locations highly impacted by urban growth. This is suggested by changes in farm operations in several of California’s largest metropolitan counties recorded in the half century between 1950-2001, a period of considerable population growth and farmland conversion. Table 3 shows the changes during this period in population, agricultural market value, and top four farm commodities for five of the state’s eight counties with more than 1 million residents . Located in coastal areas, they include the four most populous counties of California. All five counties recorded a substantive shift in dominant commodities over the half century, with nursery products or flowers taking over the top spot. Citrus, poultry, dairy products, and field crops—ranking commodities in 1950—were largely eliminated from the top four spots by 2001.The significance of the shift to nursery plants is that they are often grown in greenhouses, enclosed environments that limit impacts on urban neighbors and are relatively secure from vandalism and other encroachments. Nursery products also have a ready market in nearby urban areas. Table 3 also reveals the continued importance of agricultural to local economies in four of these metropolitan counties.

With the exception of Alameda, all had farm market values of at least $250 million in 2001. Even Los Angeles County made this list in 2001, due to $152 million in nursery sales, although the agricultural significance of this most populous California County dropped greatly from the late 1940s when it was the state’s top producer in market terms. In 2001 Los Angeles ranked 27th in farm value among California’s 58 counties. San Diego County stands out as the only county in this sample with an increase in farm market value during 1950-2001 that exceeded the rise in California’s consumer price index during this half-century. In 2001 San Diego ranked eighth in the state with a market value of $1.3 billion, fueled by more than $700 million in nursery and flower production and $138 million in avocados.In pointing to the survivability of farming in metropolitan areas, however, these numbers are more suggestive than conclusive. The “metropolitan” designation is only a rough and imprecise indication of the extent to which local agriculture is influenced by urbanization. The counties in this small sample in fact contain vast rural areas, leaving open the possibility that many of the most productive farms are not close to urban development. Also not examined in this analysis is the extent to which commodity shifts are the result of other factors, including market forces and water supply.Research in several eastern states supports the survivability thesis for urban influenced farming. The common generalization from several studies is that urban proximity can provide profit-making opportunities as well as problems for farmers, considering the potential for direct marketing, other forms of access to urban consumers, and off-farm income for operators. . But only certain kinds of intensely-cultivated farms,plastic plant pot including vegetable producers, seem to benefit from such locations . A USDA review of the available information on farms in metropolitan areas characterizes them as smaller, producing more per acre, more diverse, and more focused on high-value production than farms in non-metropolitan areas .Land use policies and regulations can be seen as largely proactive efforts to direct the location and form of new urban development in ways that would minimize impacts on agricultural activities. This is the general intent of policies that call for keeping development away from agricultural areas, in particular restricting residential growth in the countryside and directing it instead to existing cities, either as infill development or as incremental additions to municipal areas as cities gradually annex adjacent territory. Some conversion of farmland is inevitable in this process where cities are surrounded by agricultural uses, as throughout the Central Valley. But the assumption is that this is preferable to allowing building in unincorporated areas, because city development occurs at relatively high densities that convert less farmland in relation to population housed, it is less costly in public infrastructure terms, and it is more likely to produce solid and less exposed edges with farming. Also cities that are surrounded by agricultural land of varying quality and productivity have the option of directing their expansion away from the best farmland. City-oriented growth strategies are supported by the LAFCO process and county city agreements on the location of future urban development.

LAFCOs are California’s boundary control agencies at the county level, semi-independent boards that have the power to review, deny, or change city plans to annex territory and to designate their future growth areas . LAFCO actions, guided by orderly growth and farmland projection objectives, are a major restraint on extensive sprawl. Some counties and cities in agricultural areas have negotiated agreements that divert urban development from unincorporated areas to city areas, usually in return for financial considerations that allow the county to share in municipal growth revenues . The two land use policies that most specifically address edge issues are agricultural buffers and mitigations imposed on new development for the loss of farmland or to limit negative impacts on farming. The two are closely related, since buffers are a type of mitigation frequently recommended by the environmental reviews conducted by county and city governments of proposed urban projects. Buffers essentially create a separation between agricultural and urban uses, using barriers or distance to minimize negative impacts on both sides of an edge boundary, especially the effects of chemical drift from farming activity. Agricultural buffers come in different forms—natural barriers created by landscape features such as waterways, roads, landscaping, walls, residential setbacks, open space greenbelts, and combinations of various types. Key issues in their design and creation are their permanence, maintenance, and which landowners—developer/homeowner or farmer—provide the land or barrier. Although the general plans of many California counties and cities call for use of buffers to protect farmland, the implementation of the technique and application to specific urban projects is quite spotty, as Mary Handel noted in a 1994 M.S. thesis in Community Development at UC Davis. Especially controversial are the desired widths for setbacks and greenbelts, with farm chemical applicators and other agricultural experts calling for the biggest possible separations while urban developers and city governments argue for smaller widths because of land cost considerations. In Handel’s study of buffer use in 16 counties and 6 cities, designated widths range between 50-800 feet. She also finds great variations among farmers and urban neighbors in the perceived effectiveness of different forms of buffers to limit specific negative impacts. For example, farmers generally judge setbacks or open space buffers as ineffective in dealing with trespass, vandalism, litter, theft, and dogs while urban residents see them as generally effective in reducing chemical drift, odor, and dust from farm operations . More recently, the Great Valley Center published a short guide on agricultural buffers for urban planners .As contrasted with the land-use control approach of trying to head off edge problems by influencing the location and design of urban development, other strategies seek to deal more directly with farm-urban neighbor tensions, often after they have emerged. Government policies and programs in this category include right-to-farm ordinances, California’s extensive regulation of pesticides and other agricultural chemicals, and restrictions on farm animal facilities driven by clean water policies. When first adopted by California local governments in the late 1980s after enabling state legislation, right-to-farm ordinances were seen as a promising tool for protecting routine farm operations from nuisance law suits and complaints by urban neighbors. The central feature of most such local laws is a disclosure requirement—notifying home buyers of parcels adjacent to farms of the possibly negative effects of agricultural operations. In this way, the assumption goes, new residents especially would learn about the realities of modern farming and would be less inclined to complain or even go to court over sprays, dust, odors, noise and other results of nearby agriculture.