The influence of time,soil characteristics,and land‐use history on soil phosphorus legacies: a global meta‐analysis

Agriculturally driven changes in soil phosphorus (P) are known to have persistent effects on local ecosystem structure and function, but regional patterns of soil P recovery following cessation of agriculture are less well understood. We synthesized data from 94 published studies to assess evidence of these land‐use legacies throughout the world by comparing soil labile and total P content in abandoned agricultural areas to that of reference ecosystems or sites remaining in agriculture. Our meta‐analysis shows that soil P content was typically elevated after abandonment compared to reference levels, but reduced compared to soils that remained under agriculture. There were more pronounced differences in the legacies of past agriculture on soil P across regions than between the types of land use practiced prior to abandonment (cropland, pasture, or forage grassland). However, consistent patterns of soil P enrichment or depletion according to soil order and types of post‐agricultural vegetation suggest that these factors may mediate agricultural legacies on soil P. We also used mixed effects models to examine the role of multiple variables on soil P recovery following agriculture. Time since cessation of agriculture was highly influential on soil P legacies, with clear reductions in the degree of labile and total P enrichment relative to reference ecosystems over time. Soil characteristics (clay content and pH) were strongly related to changes in labile P compared to reference sites, but these were relatively unimportant for total P. The duration of past agricultural use and climate were weakly related to changes in total P only. Our finding of reductions in the degree of soil P alteration over time relative to reference conditions reveals the potential to mitigate these land‐use legacies in some soils. Better ability to predict dynamics of soil nutrient recovery after termination of agricultural use is essential to ecosystem management following land‐use change.     

Risk Attitudes of Organic and Conventional Hazelnut Producers in Turkey

Understanding farmers’ attitudes and responses to agricultural risks is important for designing financial support services and effective extension activities. Risk attitudes of farmers are also one of the critical barriers for conversion to organic agriculture. Few studies have been conducted to explore and compare risk perceptions between organic and conventional farmers. The purposes of this research were to elicit and compare the risk attitudes of organic and conventional Turkish hazelnut producers and to determine the barriers additional to their risk attitudes toward conversion to organic agriculture in the Terme district of Samsun, Turkey. The Equally Likely Certainty Equivalent (ELCE) model was used to elicit responses from producers. The data used in this study were collected by using a structured questionnaire administered to both 64 randomly selected conventional hazelnut producers and all organic hazelnut producers (39) in the research area. Research results revealed that organic hazelnut producers were less risk averse than conventional producers. It was also found that the variables of education level of operators, farm income, total assets, time allocated outside the farm, farm land area, size of hazelnut orchard, number of hazelnut plots, and total information score were other barriers for conversion to organic hazelnut production, in addition to the producers’ risk attitudes. Providing better extension services and farmers’ training activities relating to organic agriculture and land consolidation, focusing on raising the educational level of producers, facilitating producers with greater access to credit to increase farm land and to enhance farm assets are factors that may accelerate the process of conversion to organic hazelnut production.     

Waterfowl Nesting in Fall-Seeded and Spring-Seeded Cropland in Saskatchewan

Abstract: Waterfowl nesting in annual croplands has remained a little-known aspect of waterfowl nesting ecology because of the inability of many studies to systematically search this habitat through the nesting season. Where searches have been conducted, they are generally restricted to the period prior to seeding, and many nests found are destroyed by the seeding operation. Consequently, fall-seeded crops have been promoted as an alternative cropping practice that could increase nest survival of waterfowl nesting in croplands. During 1996–1999, we conducted 3–4 complete nest searches on 4,274 ha of cropland, including spring-seeded wheat and barley, winter wheat, and fall rye in southern Saskatchewan, Canada. Using suites of predictive models, we tested hypotheses regarding relative nest abundance and nest survival among crop types and tested the influence of several landscape-scale covariates on these metrics. Apparent nest densities were higher in fall-seeded crops (winter wheat: 0.39 nests/ha, fall rye: 0.25 nests/ha) than in spring-seeded crops (0.03 nests/ha), and nest density in spring-seeded croplands increased with percent cropland and percent wetland habitat in the surrounding landscape. Nest survival was higher in winter wheat (38%) than in either fall rye (18%) or spring-seeded crops (12%), and nest survival in spring-seeded crops increased with relative nest initiation date. Nest survival was unaffected by surrounding landscape characteristics but tended to be higher in years of average wetness. Based on our findings, winter wheat and fall rye have the potential to provide productive nesting habitat for ≥7 species of upland nesting ducks and fall-seeded crops are a conservation tool well suited to highly cropped landscapes.     

Reduced susceptibility to DDT in field populations of Anopheles quadriannulatus and Anopheles arabiensis in Malawi: evidence for larval selection

Abstract.  Bioassays for insecticide resistance in adult mosquitoes were conducted on samples of Anopheles gambiae Giles s.l . (Diptera: Culicidae) species collected as larvae from breeding sites in the lower Shire Valley, Malawi. The results indicate full susceptibility to permethrin, deltamethrin and malathion, but reduced susceptibility to DDT in one sample from Thom (LT₅₀ of 8.39 min for females and 25.09 min for males). Polymerase chain reaction-based species identification of the mosquitoes assayed revealed a mixture of Anopheles arabiensis Patton and Anopheles quadriannulatus (Theobold). The LT₅₀ did not differ significantly between species. Genotyping of the L1014F and L1014S kdr alleles showed all mosquito specimens to be homozygous wild type; thus the reduced susceptibility detected is not attributable to target site insensitivity and instead is likely to be metabolic in nature. Anopheles quadriannulatus is characteristically zoophagic and exophilic. Indeed, of 82 Anopheles collected through knockdown collections within dwellings, only one was An. quadriannulatus and the rest were An. arabiensis . They are unlikely, therefore, to have been exposed to selection pressure arising from insecticide-treated net usage or to DDT indoor residual spraying. Therefore, it is suggested that this example of reduced susceptibility to DDT in An. quadriannulatus reflects selection in the larval stages.     

Piaroa Manioc Varietals: Hyperdiversity or Social Currency?

The maintenance of exceptionally high numbers of folk varieties by the Piaroa people of the Venezuelan Amazon is considered. We cataloged 113 manioc folk varieties, their nomenclature, use and relevant characters, revealing significant insights into the role of manioc in Piaroa social life. Through a qualitative investigation of the cultivation, processing and symbolic significance of manioc (Manihot esculenta) in two Piaroa regions over a period of 18 years, we have found that such agrobiodiversity can only be fully explained by a combination of multiple factors, including pragmatic and ecological considerations, the subtle and complex diversity of Piaroa manioc preparations and a variety of sociocultural factors, such as manioc’s role as a mediator of social relationships and as a marker of cultural and social heritage.

Ethnobotanical Knowledge and Crop Diversity in Swidden Fields: A Study in a Native Amazonian Society

Crop diversity protects food consumption in poor households within developing nations. Here we estimate the association between crop diversity on swidden fields and ethnobotanical knowledge. We conducted research among 215 male household heads from a native Amazonian society. Using multivariate regressions, we found higher crop diversity among households that depend on agricultural production for household consumption. We also found a statistically significant and positive, but low, association between the ethnobotanical knowledge of the male household head and crop diversity. Doubling the stock of ethnobotanical knowledge of the male household head is associated with a 9% increase in the number of crops sown by a household. The association remained after we controlled for the household level of market exposure, but vanished after we controlled for the social capital of the male household head. Future research should compare the association between ethnobotanical knowledge and crop diversity across different agricultural systems (i.e., home gardens, fallow fields).     

Home Garden Production and Energetic Sustainability in Calakmul,Campeche, Mexico

Energy flows were studied for the 2002–2003 agricultural cycle in four households for which agriculture is part of a diversified survival strategy and four that practice agriculture as a business. Home garden inputs and outputs were measured monthly. Quantified inputs were: household labour, household agro-system production, and purchased external renewable and non-renewable energy. Outputs measured were: sales, family and animal foods. While both strategies had similar indicators in biomass and energy production, vegetable richness, and soil quality, household garden function and sustainability differed between subsistence and commercial householders. Subsistence gardens complemented family diet and contributed to household system resiliency. They relied heavily on renewable energy sources from within their agro-system. Gardens in commercial households reduced fruit tree area and increased animal husbandry for the market. They depended more on purchased non-renewable energy sources and were less sustainable and much less energy efficient than traditional gardens.

谈中国植物科学基础研究与农业发展

该文讨论了加强植物科学基础研究的必要性及其对我国农业发展的重要影响。为了更好地为中国的农业发展服务,进一步加强植物科学基础研究非常重要。为了促进植物科学的发展,我国既要积极参与国际竞争,又要重视知识创新、技术发展以及技术平台建设等多个方面,还要重视传统学科如植物分类学等的发展。过去10年间,我们见证了中国科学家在植物科学领域取得的重要成就,随着越来越多的高水平人才回国,建议国家增加投入支持我国的植物科学基础研究。     

Community analysis of arbuscular mycorrhizal fungi and bacteria in the maize mycorrhizosphere in a long-term fertilization trial

In this study, we investigated the impact of organic and mineral fertilizers on the community composition of arbuscular mycorrhizal (AM) fungi and bacteria in the mycorrhizosphere of maize in a field experiment established in 1956, in south-east Sweden. Roots and root-associated soil aggregates were sampled four times during the growing season in 2005, in control plots and in plots amended with calcium nitrate, ammonium sulphate, green manure, farmyard manure or sewage sludge. Fungi in roots were identified by cloning and sequencing, and bacteria in soil aggregates were analysed by terminal-restriction fragment length polymorphism, cloning and sequencing. The community composition of AM fungi and bacteria was significantly influenced by the different fertilizers. Changes in microbial community composition were mainly correlated with changes in pH induced by the fertilization regime. However, other factors, including phosphate and soil carbon content, also contributed significantly to these changes. Changes in bacterial community composition and a reduction in bacterial taxon richness throughout the growing season were also manifest. The results of this study highlight the importance and significant effects of the long-term application of different fertilizers on edaphic factors and specific groups of fungi and bacteria playing a key role in arable soils.     

Interactions between land use,habitat use,and population increase in greater snow geese: what are the consequences for natural wetlands?

The North American greater snow goose population has increased dramatically during the last 40 years. We evaluated whether refuge creation, changes in land use on the wintering and staging grounds, and climate warming have contributed to this expansion by affecting the distribution, habitat use, body condition, and migration phenology of birds. We also reviewed the effects of the increasing population on marshes on the wintering grounds, along the migratory routes and on the tundra in summer. Refuges established before 1970 may have contributed to the initial demographic increase. The most important change, however, was the switch from a diet entirely based on marsh plants in spring and winter (rhizomes of Scirpus/Spartina) to one dominated by crops (corn/young grass shoots) during the 1970s and 1980s. Geese now winter further north along the US Atlantic coast, leading to reduced hunting mortality. Their migratory routes now include portions of southwestern Québec where corn production has increased exponentially. Since the mid‐1960s, average temperatures have increased by 1–2.4°C throughout the geographic range of geese, which may have contributed to the northward shift in wintering range and an earlier migration in spring. Access to spilled corn in spring improved fat reserves upon departure for the Arctic and may have contributed to a high fecundity. The population increase has led to intense grazing of natural wetlands used by geese although these habitats are still largely undamaged. The foraging in fields allowed the population to exceed limits imposed by natural marshes in winter and spring, but also prevented permanent damage because of their overgrazing.