Changes In Agroecosystems Research Articles

Plant and herbivorous insect diversity loss are greater than null model expectations due to land-use changes in agro-ecosystems

The effect of land-use changes on plant diversity is an important issue, as plant diversity is vital to maintaining of threatened insect diversity in agro-ecosystems. Although many studies have examined patterns of a few threatened species, few studies have examined a large number of threatened species while comparing organisms of different trophic levels. Observed and expected community assembly patterns of common and threatened species should be evaluated along land-use gradients in agro-ecosystems, using species richness and red list indicator (RLI). This study examined local and regional diversity of plants and herbivorous insects among abandoned, traditional, and intensified land-use types in semi-natural grasslands and compared observed and expected values via null model analysis. This study showed that the richness and RLI of plants and herbivorous insects were maintained in the traditional land-use. However threatened plants and herbivorous insects at sites of land abandonment and intensified use were significant lower than null model expectations. Although, plant richness, rather than RLI, was responsible for maintaining richness and the RLIs of herbivorous insects, plant richness did not linearly correlate with plant RLIs. Threatened plants did not depend on plant richness, it will be vital to identify and conserve unique environments for diversity of plants and herbivores. In conclusion, we should reintroduce traditional land-use practices in intensified use and abandoned grasslands. National and local governmental support for the appropriate management of semi-natural grasslands is beneficial for biodiversity conservation at both the local (e.g., present study area) and national (Japanese) levels.

From “Integrated Pest Management” to “Ecologically Based Pest Management”

There have been substantial land cover changes in agroecosystems in the world during the last 50 years, including the intensified use of agrochemicals and expansion of croplands, resulting in rapid loss of biodiversity and reduction of ecosystem services. The effects of these changes, at both field and landscape scales, on biodiversity, species composition, pest population dynamics, community structure, interspecific and intraspecific relationships in agroecosystems have become increasingly important.

Dehydrogenase and mycorrhizal colonization: Tools for monitoring agrosystem soil quality

In order to improve food production while reducing environmental impact, the redesign of agrosystems to incorporate monitoring tools for decision-making is a fundamental requirement. Chemical and physical indicators of medium and long-term soil quality have been developed in order to monitor changes in agroecosystems; however, it is crucial to develop parameters that can predict the short-term trajectory of the system. For this reason, the objective of the present study was to determine whether certain soil biological parameters, such as the activities of microbial enzymes (dehydrogenase (DH), acid phosphatase (ACP), urease (URE) and protease (PRO)) and mycorrhizal colonization, could be useful as indicators of soil biological quality, given their sensitivity to different agricultural management practices. An evaluation was conducted over two years in five different agrosystems of Valle de México in Mexico. The activity of DH presented greater sensitivity to changes in agricultural management produced by types of tillage and input (organic or synthetic) and topological arrangement, compared to that of URE, ACP and PRO, which did not present a clear pattern with respect to the different agrosystems or to sampling date (based on the agricultural practices). Mycorrhizal colonization was sensitive to the type of inputs used, but not to tillage type or crop rotation. It is therefore considered that DH and mycorrhizal colonization could represent useful parameters for measuring soil quality and the environmental impact of the use of agrochemicals in agriculturally managed soils. Based on DH and mycorrhization, the agrosystem with the highest quality soil was the Mesoamerican system known as “Milpa” (typified by minimum tillage, intercropping and organic inputs).

Chemotaxonomy and diagenesis of aliphatic hydrocarbons in rice plants and soils from land reclamation areas in the Zhejiang Province, China

Rice is the most important staple food globally and requires large growth areas kept under flooded paddy conditions, contributing significantly to microbial greenhouse gas emissions. Biogeochemical cycling in such agroecosystems has been investigated intensively but molecular biomarker studies are scarce. We conducted a chemotaxonomic investigation of wax alkanes differentiated for plant tissue (leaf, stem, root) of rice and intercrop plants (maize, sorghum, rape, mustard, bean, cotton) and studied the incorporation of these lipids into soil under paddy compared with upland management forms. Soil chronosequences reflecting paddy and upland agroecosystem changes compared with natural soil substrates over the past two millennia were studied in land reclamation areas of Zhejiang Province, China. Soils evolved on tidal wetland sediments contained predominantly lipids derived from terrigenous supply by the Yangtze River (YR=Chang Jiang) and to a lesser extent from marine sources via the East China Sea (ECS). Agricultural usage converted lipid composition of topsoil within 50yr to reflect the n-alkane patterns of crops with their relative proportion increasing with cultivation time. Alkyl chain length distribution of rice was broad compared with upland plants, due to the water regime changing over the growth period. This separated paddy from upland managed soils on the basis of alkyl lipids, allowing reconstruction of past land use change. Combustion of crop biomass after harvest is common practice and generates alkenes upon incomplete combustion which, due to their high reactivity, are immediately converted to alkanes with lower carbon preference index (CPI) in topsoil. The storage of lipids and organic matter over time is greater in paddy than in upland managed agroecosystems and contributes to CO2 sequestration from the atmosphere.

Accuracy, robustness and behavior of the STICS soil–crop model for plant, water and nitrogen outputs: Evaluation over a wide range of agro-environmental conditions in France

Soil–crop models are increasingly used as predictive tools to assess yield and environmental impacts of agriculture in a growing diversity of contexts. They are however seldom evaluated at a given time over a wide domain of use. We tested here the performances of the STICS model (v8.2.2) with its standard set of parameters over a dataset covering 15 crops and a wide range of agropedoclimatic conditions in France. Model results showed a good overall accuracy, with little bias. Relative RMSE was larger for soil nitrate (49%) than for plant biomass (35%) and nitrogen (33%) and smallest for soil water (10%). Trends induced by contrasted environmental conditions and management practices were well reproduced. Finally, limited dependency of model errors on crops or environments indicated a satisfactory robustness. Such performances make STICS a valuable tool for studying the effects of changes in agro-ecosystems over the domain explored.

Using dynamic diversity to achieve durable disease resistance in agricultural ecosystems

Plant Pathology Group, Institute of Integrative Biology, ETH Zurich, 8092 Zurich, SwitzerlandE-mail: bruce.mcdonald@usys.ethz.chGenetically resistant cultivars form the foundation of disease management for most crops. Populations of resistant cultivars grown at the farm and landscape scales keep many important fungal, bacterial and viral diseases in check, sometimes for many years. But eventually, most resistant cultivars fail and an epidemic ensues, often causing significant losses in crop yield and quality. In this letter, disease resistance is considered as a population phenomenon, exhibited mainly at the scale of fields, farms and landscapes and encompassing millions or billions of plants, rather than at the level of individual plants or specific plant tissues, even though cultivar resistance is often measured based on symptoms of individual plants or tissues. But it should be noted that the failure of resistance at the population or landscape level generally begins with a failure of resistance at the individual level.Disease resistance fails because pathogens evolve. Evolution requires genetic diversity. Genetic diversity is affected by mutation, population size, recombination, gene flow, and selection, the same factors that affect an organism’s population genetics. Thus the keys to developing strategies for breeding durable disease resistance lie in understanding pathogen population genetics. The root of the problem of pathogen evolution is the lack of diversity in agricultural ecosystems (agroecosystems). Since the invention of agroecosystems ~12,000 years ago, crop genetic diversity has declined steadily in agroecosystems globally to facilitate gradual improvements in agricultural production systems, including innovations such as tillage, fertilization, controlled irrigation, and mechanization. The decline in crop genetic diversity at the field scale accelerated rapidly during the last 100 years to increase the efficiency of food production and feed the burgeoning human population. The large-scale mechanization of planting and harvesting operations and the green revolutions that swept through agriculture led to replacement of locally-adapted but genetically diverse land races by genetically uniform but broadly-adapted, high-yielding, dwarf cultivars, further depleting genetic diversity and increasing the environmental homogeneity present in agroecosystems worldwide. The highly mechanized modern industrial agroecosystems now found around the world are extremely productive food factories, but also are highly effective incubators of pathogen evolution (as described in Stukenbrock & McDonald, 2008). As a result of the increased planting density and genetic uniformity of host populations in agroecosystems compared to natural ecosystems, pathogen transmission became easier, enabling an increase in pathogen virulence (Read, 1994). The same factors increased pathogen population sizes, which led to more genetic diversity for selection to act upon by increasing the total number of mutations available at the field scale while simultaneously lowering the effects of genetic drift. Due to these changes in agroecosystems over time, pathogen evolutionary potential likely increased as agricultural pathogens (including fungi, bacteria and viruses) became domesticated and adapted to the agroecosystem environment. Other factors unique to agroecosystems are also likely to contribute to more rapid pathogen evolution. The higher host density found in agroecosystems compared to natural ecosystems allows agricultural pathogens to exist at a higher density. This higher pathogen density increases the likelihood of multi-infections in the same plant by different genotypes of the same pathogen (e.g. Linde et al. 2002; Keller et al. 1997; McDonald et al. 1999). Multi-infections have long been thought to favor the development of higher virulence (defined here as the amount of damage done to the plant, but often referred to as aggressiveness or quantitative virulence in plant pathology) as a side effect of competition among strains for host resources (Van Baalen & Sabelis, 1995). The higher host and pathogen density found in agroecosystems also increases the likelihood of co-infection by different pathogen species, which also is thought to select for higher virulence as a result of competition among pathogen species for the same host resources. In addition, co-infection by different pathogen species increases the likelihood of horizontal transfer of genes among pathogens infecting the same host, as reported recently for several wheat pathogens (e.g. Friesen et al. 2006; Gardiner et al. 2012; McDonald et al. 2013).Modern agroecosystems are very well structured to produce high quality produce that can be eaten directly (e.g. rice or apples) or processed into higher value goods

Soil nematode responses to fertilization with ammonium nitrate after six years of unfertilized apple orchard

A nematode community was used as a bioindicator of changes in agroecosystems caused by fertilization. The effect of applying nitrogen (N) fertilizer on a soil nematode community structure was studied in a soil which had not been fertilized for six years in the Rio Negro Valley, Argentina. Treatments were: i) 100 kg N ha-1 (N100); ii) 200 kg N ha-1 (N200); in each case 50% of the dosage was applied at the time of petal fall and 50% at fruit harvest in 2004/2005, 2005/2006, 2006/2007 growing seasons; and iii) control with no fertilizer (N0). Soil samples were collected in the 0 to 30 cm soil layer in October, November, April and July in each growing season. The number of bacterivores increased in N200 compared to N0. Cephalobidae were present in greater numbers in N200 than in N100 and N0. Predator abundance was lower under N200, after the first N application in each growing season. The ratio of fungivores to bacterivores (F/B) was 0.21, 0.3 and 0.41 in N200, N100 and N0, respectively. N200 resulted in a community with a lower maturity index (MI) than N0. Structure index (SI) was lower in N200 than N100 and N0. The enrichment index (EI) was less sensitive at detecting fertilizer effects. In November and April, soil nitrate concentrations were higher in N200 than in N100 and N0. Soil nitrate concentration was positively correlated with EI and negatively with MI, SI and F/B. N200 affected the trophic structure of the nematode community consistent with a less stable soil system.

Birds as qualitative bioindicators in farmlands

Recent productive changes in agroecosystems have damaged many species of European birds. For this reason it is important to improve an evaluation method of environmental quality in farmlands, such as the one here proposed and not yet effectively tested, aimed also at bird conservation.

Effects of inter-annual landscape change on interactions between cereal aphids and their natural enemies

The agricultural intensification and the subsequent habitat changes in agroecosystem can strongly affect biological control services. We here examine the influence of inter-annual landscape change in wheat field area on interactions of cereal aphids and their natural enemies, as well as the efficacy of biological control using data collected from a 4-year experiment in Northwest China. Two hypotheses were tested. (i) Population densities decline following an inter-annual expansion of wheat crop proportion cover due to dilution and crowding effects. (ii) Species that are specialists or at higher trophic levels are more sensitive to bottom-up disturbance by inter-annual change in percent cover of wheat crop. Results showed the population densities of one cereal aphid (Macrosiphum avenae), one parasitic wasp (Aphidius avenae), two specialist predators (ladybirds: Hippodamia variegata and H. tredecimpunctata) and one hyperparasitic wasp (Pachyneuron aphidis) declined following the expansion of wheat crop areas, supporting the predictions of inter-annual dilution and crowding effects. In contrast, the populations of one cereal aphid (Schizaphis graminum), one parasitic wasp (A. gifuensis), two generalist predators (spiders: Pardosa astrigera; carabid beetles: Chlaenius pallipes), and two hyperparasitic wasps (Asaphes suspensus, and Alloxysta sp.) did not respond to inter-annual landscape change. The two hypotheses were partially supported but with noticeable exceptions, and the bio-control efficiency declined with the increase of the proportion cover of wheat field in agricultural landscape. Overall, different responses of cereal aphids and their natural enemies make it difficult but still possible to optimize inter-annual landscape change for enhancing the parasitism rate and predator-prey ratio.

Modelling an ecosystem: The example of agro-ecosystems

Abstract Methods to predict ecosystem responses to changing environmental conditions, including options for mitigation and management, are vital for scientists and policy makers. We propose that modelling ecosystems by grouping species into trophic-functional types has great utility, because it is potentially generic and applicable to any ecosystem. Here we describe in details a trophic-functional ecosystem model of arable agriculture (the TrophicLINK model), constructed using an individual-based model, and present some supporting sensitivity tests of the model performing according to our expectations for the arable ecosystem. We vary parameters for particular plant and invertebrate trophic-functional types and we show that the model is sensitive to the values chosen. Though this trophic-functional method for modelling ecosystems will be subject to further sensitivity tests and empirical validation, we argue that the modelling structure is fit for investigating the impact of changes in agro-ecosystems.

Inorganic N of Atmospheric Wet Deposition From A Typical Agro-Ecosystem In Southeast China During Rainy Season

Atmospheric N (N) deposition, especially for atmospheric wet deposition has led to changes in agroecosystems from N limited to N saturated. Rained agriculture is weather dependent, and in turn the impact of the vagaries of the rainy rainfall on food production has been of great concern. In this paper, rainy season was determined and characteristics of wet-deposition N, including NH+4-N and NO-3 -N was done by rainfall and N concentration in rainwater at Red Soil Ecological Experiment Station, Chinese Academy of Sciences (116°55́E, 28°12́N), a typical red soil agro-ecosystem, located in Yingtan city, Jiangxi province, Southeastern China during the rainy season in 2003, 2005 and 2008. The deposition fluxes of NH+4-N and NO-3-N in the rainy season was in the range of 4.93-7.75 and 1.19-2.51kg ha-1, respectively. The inorganic N (NH+4-N plus NO-3-N) deposition flux varied from 6.12-10.26kg ha-1, which was equivalent to 14.57-24.43kg ha-1 urea or 34.53-57.90kg ha-1 ammonium bicarbonate applied in the red soil agro-ecosystem. So, the N input of wet deposition during the rainy season could not be neglected in farmland ecosystem. And it is worth considering of reducing N application rate in the red soil farmland.

Coping with Multiple Stresses in Rural South Africa

In this paper, we aim to investigate how local communities cope with and adapt to multiple stresses in rural semiarid South Africa. In semiarid regions water scarcity is one of a number of stresses that shape livelihood vulnerability. With climate change, it is predicted that rainfall in South Africa will become more uncertain and variable in the future, exposing more people to water insecurity. At the same time, the impacts of disease, a lack of institutional capacity, and limited livelihood opportunities can combine to limit adaptive capacity. Therefore, adaptation to changing climate should not be viewed in isolation but instead in the context of social, economic, and political conditions, all of which shape local community vulnerability and people’s ability to cope with and adapt to change. This study uses a qualitativequantitative-qualitative framework, including the use of a stated preference survey, to identify the drivers of agroecosystem change, to understand the capacity of households to cope with droughts, and to determine the ability of local institutions to respond to crises. The analysis suggests that the capacity of the agroecosystem to remain productive during droughts is decreasing, individual/household adaptive capacity remains low, and institutional capacity faces considerable barriers that prevent it from supporting households to adapt to multiple stresses. This research adds weight to the claim that vulnerability reflects multiple forces and processes, and that multiple stresses, that are agroecological, socioeconomic, and institutional in nature, need to be examined to understand vulnerability and to prevent maladaptation.

Effect of mechanical disturbances on nematode communities in arable land

Abstract Nematode communities were used as bioindicators of changes in agroecosystems caused by anthropogenic factors. The aim of this study was to examine the impact of plowing and harrowing on nematode communities structure in comparison to “no tillage” treatments. The effects of mechanical disturbing of nematodes were determined on four soil treatments. Differences in nematode community structure were compared between two tillage regimes: standard tillage and no tillage. Research was conducted in 2000, in Kneževo near Osijek. Plowing had impact on increasing of bacterivorous nematodes and decreasing of fungivorous nematodes. Pratylenchus, Helicotylenchus and Tylenchus were dominant plant-feeding nematodes in no tillage treatments, while in plowing treatments Pratylenchus and Tylenchus were dominant. Abundance of Aphelenchoides decreased significantly after plowing. Tillage affected nematode communities in the soil ecosystem by changing the trophic structure and gave a decreasing, but not statistically significant, trend in MI.

Modelling soil organic carbon stock change for estimating whole-farm greenhouse gas emissions

Modelling soil organic carbon (SOC) stock changes in agroecosystems can be performed with different approaches depending on objectives and available data. Our objective in this paper is to describe a scheme for developing a dynamic SOC algorithm for calculating net greenhouse gas emissions from Canadian farms as a function of management and local conditions. Our approach is flexible and emphasizes ease of use and the integration of available knowledge. Using this approach, we assessed the performance of several SOC models having two or more compartments for some common agroecosystems in Canada. Analysis of long-term data for conventional management practices at different sites (n = 36) in Canada, including recent model applications in the literature on some of those data, indicated that the results obtained with two-compartment models, such as the Introductory Carbon Balance Model (ICBM) and Modified Woodruff Model (MWM), yielded results comparable to those of a multi-compartment model (CENTURY). The analysis also showed that a model such as ICBM need stuning to be applied to management and conditions across Canada. Two-compartment models programmable in a simple spreadsheet format, though they may not supplant more complex models in allapplications, offer advantages of simplicity and transparency in whole-farm analyses of greenhouse gas emissions. Key words: Virtual Farm, soil organic carbon, soil disturbance, C inputs, Introductory Carbon Balance Model (ICBM), CENTURY, Modified Woodruff Model (MWM).

Indicators of soil quality: A South–South development of a methodological guide for linking local and technical knowledge

The increasing attention paid to local soil knowledge results from a greater recognition that farmer knowledge can offer many insights into the sustainable management of tropical soils and that the integration of local and technical knowledge systems helps extension workers and scientists work more closely with farmers. A participatory approach and a methodological guide were developed to identify and classify local indicators of soil quality and relate them to technical soil parameters, and thus develop a common language between farmers, extension workers and scientists. This methodological guide was initially developed and used in Latin America and the Caribbean-LAC (Honduras, Nicaragua, Colombia, Peru, Venezuela, Dominican Republic), and was later improved during adaptation and use in eastern African (Uganda, Tanzania, Kenya, Ethiopia) through a South–South exchange of expertise and experiences. The aim of the methodological guide is to constitute an initial step in the empowerment of local communities to develop a local soil quality monitoring and decision-making system for better management of soil resources. This approach uses consensus building to develop practical solutions to soil management constraints identified, as well as to monitor the impact of management strategies implemented to address these constraints. The particular focus on local and technical indicators of agroecosystem change is useful for providing farmers with early warnings about unobservable changes in soil properties before they lead to more serious and visible forms of soil degradation. The methodological approach presented here constitutes one tool to incorporate local demands and perceptions of soil management constraints as an essential input to relevant research for development activities. The participatory process followed was effective in facilitating farmer consensus; for example, about which soil related constraints were most important and what potential soil management options could be used. Development of local capacities for consensus building constitute a critical step prior to collective action by farming communities resulting in the adoption of integrated soil fertility management strategies at the farm and landscape scale.

Agroecosystem sustainability: a system simulation model approach

The sustainability of agroecosystems depends on the maintenance of the economic, biological and physical components that make up the system. The high level of integration of these components implies that any evaluation of agroecosystem sustainability must consider the dynamics of multiple components. In recent years a number of system simulation models have been developed to examine different aspects of agroecosystem sustainability. This paper presents a brief description of a simulation model developed to evaluate agroecosystem changes using a number of indicators. Agroecosystem sustainability is then evaluated using simulation results for a series of agricultural production systems in Saskatchewan, Canada. The results indicate that the economic and environmental sustainability of the system is dependent on the biophysical constraints which determine the management options that are technically, agronomically and economically viable. The simulations revealed that system sustainability did not uniformly increase or decrease according to the indicators used.

The role of long-term sites in agroecological research: A case study

Gradual, episodic or subtle changes in agroecosystems can be definitively measured only in long-term studies. The objective of this paper is to illustrate the benefits and limitations of long-term agroecological sites using a crop rotation study (Rotation ABC) established at Lethbridge, Alberta in 1910. Long-term agroecological sites, envisioned as part of a continuum of research levels, seek to determine the persistence of cropping systems with respect to their effects on soil resources and the larger environment. Examples of research findings arising from such sites include the documentation of long-term changes in agricultural productivity, measurement of organic matter changes over time, calculation of long-term nutrient budgets, and verification of simulation models. For example, soil organic matter concentrations in Rotation ABC were found to decline abruptly within the first few decades of cultivation and then approach a new steady state. Despite the continual removal of N in harvested grain, soil N concentrations also appear to have stabilized, suggesting an accession of N approximately equivalent to the amount harvested. Common limitations of long-term sites like that at Lethbridge include: rudimentary experimental design, evolving management practices, incidental changes at the sites, and variation in sampling protocols. The successful use of long-term agroecological sites depends on well-defined objectives, simplicity of design, adequate scale, consistent data and sample collection, and collaboration among sites. The primary justification for the establishment and maintenance of long-term agroecological sites may be their future role in answering questions not yet envisioned. Key words: Soil organic matter, long-term studies, crop rotations, sustainability, fertilizer

Implications of potential global warming on agricultural pests in Australia

The potential influence of climate warming on the future status of agricultural pests in Australia is discussed in terms of the possible effects that changes in temperature, rainfall and weather patterns will have on the future distribution, numbers, fluctuations and movements of pest populations. Event-driven outbreaks are distinguished from rate-driven processes in pest populations. The future severity and frequency of pest outbreaks will depend on changes in the frequency of extreme weather events, some of which are related to the El Niiio/Southern Oscillation phenomenon. Three scenarios are presented for geographical changes to ratedriven and to event-driven processes: little change (displacement of agroecosystems and their associated pests to new climatic optima); expansion of tropical pests, contraction of Mediterranean (winter rainfall) pests; increased pest multiplication in geographically fixed agroecosystems such as irrigation schemes and some animal production systems. There is considerable uncertainty about the future severity of outbreaks and chronic infestations because of our current difficulties in forecasting and realistically simulating population changes in agroecosystems. This probably results from the complex feedback mechanisms involving natural enemies and other factors. In Australia the overall expansion of areas affected by tropical pests portends an overall worsening of agricultural pest problems.

Agricultural development, migrant labor and the resurgence of malaria in Swaziland

Much of the research on the recent resurgence of malaria in Third World areas has focused on the problem of vector resistance arising out of the widespread use of pesticides in conjunction with the development of large-scale agricultural projects. Evidence from southern Africa, and particularly from Swaziland, where a resurgence of malaria has occurred in the absence of pesticide-resistent strains of Anopheles mosquitoes, suggests that changes in agroecosystems, labor utilization and settlement patterns, which are also associated with large-scale agricultural development, may play an equally important role in the resurgence of malaria. Renewed efforts to control malaria must, therefore, take account of the social and economic, as well as the biological determinants of this disease.

Agricultural Change as an Incremental Process

Abstract At least two major views of agro-ecosystem change can be recognized–systematic and incremental. Systematic change involves the addition of new fields and associated features that are constructed completely prior to cultivation; incremental change involves gradual transformation of fields and features in conjunction with cultivation. The systematic view has been the more dominant of the two, particularly as applied to interpretations of past agro-ecosystems. Using present-day data on temporales or runoff-dependent fields in eastern Sonora, Mexico, this study describes one case of incremental agro-ecosystem change. Small, individual fields are developed into a more complex system by progressive modification resulting from the cumulative actions of individual farmers. In this case, the resulting constructional form of the agro-ecosystem alone does not allow assessment of the process of its development. Interpretations of past agro-ecosystems should recognize that both change processes are possible.