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The scale dependency of spatial crop species diversity and its relation to temporal diversity
Get PDFIncreasing crop species diversity can enhance agricultural sustainability, but the scale dependency of the processes that shape diversity and of the effects of diversity on agroecosystems is insufficiently understood. We used 30 m spatial resolution crop classification data for the conterminous United States to analyze spatial and temporal crop species diversity and their relationship. We found that the US average temporal (crop rotation) diversity is 2.1 effective number of species and that a crop’s average temporal diversity is lowest for common crops. Spatial diversity monotonically increases with the size of the unit of observation, and it is most strongly associated with temporal diversity when measured for areas of 100 to 400 ha, which is the typical US farm size. The association between diversity in space and time weakens as data are aggregated over larger areas because of the increasing diversity among farms, but at intermediate aggregation levels (counties) it is possible to estimate temporal diversity and farm-scale spatial diversity from aggregated spatial crop diversity data if the effect of beta diversity is considered. For larger areas, the diversity among farms is usually much greater than the diversity within them, and this needs to be considered when analyzing large-area crop diversity data. US agriculture is dominated by a few major annual crops (maize, soybean, wheat) that are mostly grown on fields with a very low temporal diversity. To increase crop species diversity, currently minor crops would have to increase in area at the expense of these major crops.EEA BalcarceFil: Aramburu Merlos, Fernando. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Balcarce; Argentina.Fil: Aramburu Merlos, Fernando. University of California Davis. Department of Environmental Science and Policy; Estados Unidos.Fil: Hijmans, Robert. University of California Davis. Department of Environmental Science and Policy; Estados Unidos
Potential, attainable, and current levels of global crop diversity
Get PDFHigh levels of crop species diversity are considered beneficial. However, increasing diversity might be difficult because of environmental constraints and the reliance on a few major crops for most food supply. Here we introduce a theoretical framework of hierarchical levels of crop diversity, in which the environmental requirements of crops limit potential diversity, and the demand for agricultural products further constrain attainable crop diversity. We estimated global potential, attainable, and current crop diversity for grid cells of 86 km2 . To do so, we first estimated cropland suitability values for each of 171 crops, with spatial distribution models to get estimations of relative suitability and with a crop model to estimate absolute suitability. We then used a crop allocation algorithm to distribute the required crop area to suitable cropland. We show that the attainable crop diversity is lower in temperate and continental areas than in tropical and coastal regions. The diversity gap (the difference between attainable and current crop diversity) is particularly large in most of the Americas and relatively small in parts of Europe and East Asia. By filling these diversity gaps, crop diversity could double on 84% of the world’s agricultural land without changing the aggregate amount of global food produced. It follows that while there are important regional differences in attainable diversity, specialization of farms and regions is the main reason for low levels of local crop diversity across the globe, rather than our high reliance on a few crops.EEA BalcarceFil: Aramburu Merlos, Fernando. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Balcarce; Argentina.Fil: Aramburu Merlos, Fernando. University of California Davis. Department of Environmental Science and Policy; Estados Unidos.Fil: Hijmans, Robert J. University of California Davis. Department of Environmental Science and Policy; Estados Unidos
Adopting yield-improving practices to meet maize demand in Sub-Saharan Africa without cropland expansion
No full textMaize demand in Sub-Saharan Africa is expected to increase 2.3 times during the next 30 years driven by demographic and dietary changes. Over the past two decades, the area cropped with maize has expanded by 17 million hectares in the region, with limited yield increase. Following this trend could potentially result in further maize cropland expansion and the need for imports to satisfy domestic demand. Here, we use data collected from 14,773 smallholder fields in the region to identify agronomic practices that can improve farm yield gains. We find that agronomic practices related to cultivar selection, and nutrient, pest, and crop management can double on-farm yields and provide an additional 82 million tons of maize within current cropped area. Research and development investments should be oriented towards agricultural practices with proven capacity to raise maize yields in the region.EEA BalcarceFil: Aramburu Merlos, Fernando. University of Nebraska-Lincoln. Department of Agronomy and Horticulture; Estados UnidosFil: Aramburu Merlos, Fernando. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Balcarce. Instituto de Innovación para la Producción Agropecuaria y el Desarrollo Sostenible; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Innovación para la Producción Agropecuaria y el Desarrollo Sostenible; ArgentinaFil: Tenorio, Fátima. University of Nebraska-Lincoln. Department of Agronomy and Horticulture; Estados UnidosFil: Mashingaidze, Nester. One Acre Fund; KeniaFil: Sananka, Alex. One Acre Fund; KeniaFil: Aston, Stephen. One Acre Fund; KeniaFil: Ojeda, Jonathan. Regrow Ag; AustraliaFil: Grassini, Patricio. University of Nebraska-Lincoln. Department of Agronomy and Horticulture; Estados Unido
Estimating lime requirements for tropical soils: Model comparison and development
Get PDFAcid tropical soils may become more productive when treated with agricultural lime, but optimal lime rates have yet to be determined in many tropical regions. In these regions, lime rates can be estimated with lime requirement models based on widely available soil data. We reviewed seven of these models and introduced a new model (LiTAS). We evaluated the models’ ability to predict the amount of lime needed to reach a target change in soil chemical properties with data from four soil incubation studies covering 31 soil types. Two foundational models, one targeting acidity saturation and the other targeting base saturation, were more accurate than the five models that were derived from them, while the LiTAS model was the most accurate. The models were used to estimate lime requirements for 303 African soil samples. We found large differences in the estimated lime rates depending on the target soil chemical property of the model. Therefore, an important first step in formulating liming recommendations is to clearly identify the soil property of interest and the target value that needs to be reached. While the LiTAS model can be useful for strategic research, more information on acidity-related problems other than aluminum toxicity is needed to comprehensively assess the benefits of liming.EEA BalcarceFil: Aramburu Merlos, Fernando. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Balcarce; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto de Innovación para la Producción Agropecuaria y el Desarrollo Sostenible; Argentina.Fil: Aramburu Merlos, Fernando. University of California Davis. Department of Environmental Science and Policy; Estados Unidos.Fil: Vasco Silva, João. International Maize and Wheat Improvement Center; Zimbabue.Fil: Baudron, Frédéric. International Maize and Wheat Improvement Center; Zimbabue.Fil: Hijmans, Robert J. University of California Davis. Department of Environmental Science and Policy; Estados Unidos
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Pattern and process in crop species diversity and lime requirements models
Get PDFTesis para obtener el grado de Doctor of Philosophy in Horticulture and Agronomy, de la University of California Davis, 2022Changes in crop species diversity can affect agroecosystem function. However, most crop diversity studies insufficiently account for the influence of scale on spatial crop diversity, and its relation to temporal diversity has not been explored. Moreover, crop diversity might be limited by environmental constraints and market demand for specific crops, which needs to be considered when assessing opportunities for diversification. This dissertation developed and applied new approaches to gaining a quantitative understanding of diversity patterns and processes, allowing for improved comparison between regions and countries. It includes an analysis of the scale dependency of crop species diversity and its relation with temporal diversity using high-resolution crop-specific land-cover data for the conterminous US. It also shows the magnitude of environmental and demand-side constraints to crop diversity globally. For that purpose, a theoretical framework of hierarchical levels of crop species diversity is presented, in which potential, attainable, and current diversity levels are compared to compute diversity gaps. We found that spatial diversity monotonically increases with the size of the observational unit, and the strongest association between spatial and temporal diversity is observed when measured in areas comparable to farm sizes. In larger areas, the association weakens because of the increasing diversity among farms. At the national level, the diversity among farms is usually higher than the diversity within them, which needs to be considered when inferring diversity effects with national-level data. v Environmental limits to crop diversity are higher in temperate and continental areas than in tropical and coastal regions. Crop diversity is also constrained by a high demand for a few crop species, which results in an attainable diversity that is much lower than the potential. Nevertheless, there are large gaps between current and attainable diversity levels in most croplands. These gaps are particularly large in the Americas, where croplands are dominated by a few major annual crops (maize, soybean, wheat) mostly grown on fields with a very low temporal diversity. In contrast, diversity gaps are relatively small in Europe and East Asia. Changes in food demand favoring minor crops could positively impact spatial and temporal crop species diversity by increasing the attainable diversity. But given current consumption patterns, the most effective strategy to increase crop diversity in areas with high diversity gaps might be to expand the area of a major crop adapted to that specific environment, but that is not widely planted. Securing adequate soil fertility is also critical for diversification, especially in the tropics, where low soil pH is one of the main limiting factors of potential crop diversity, and soil acidity remains a key management challenge for smallholder farmers. Liming can boost the productivity of acid soils, but the lime rate required to achieve this is unknown for many tropical regions where food production increases are urgently needed. Therefore, lime requirement models based on readily available soil data could be very useful in these places. However, the great variety of lime requirement models available in the literature introduces much uncertainty. We evaluated current lime requirement models for acid tropical soils and introduced a new model based on acidity saturation using data from four soil incubation studies and 31 soil types. Foundational models based on acidity or base saturation are reasonably accurate (r ≥ 0.9), but later attempts to vi improve these models were unsuccessful. The new model, in contrast, has more precision than all earlier models across a wide range of acid tropical soils from different regions. Moreover, lime requirement estimates largely depend on the target soil chemical property of the model. For instance, many more African soils would require liming based on base saturation models than acidity saturation models, regardless of the accuracy. The new acidity saturation model can effectively estimate the lime rate required to address aluminum toxicity. This model could be incorporated into more comprehensive models once lime rates needed for other acidity problems are well established.EEA BalcarceFil: Aramburu Merlos, Fernando. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Balcarce; Argentina
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