Resources In Agroecosystems Research Articles

Important agricultural and cotton pests detected in the diet of two threatened insectivorous bats in a cotton agroecosystem: insights from a molecular study

Australian insectivorous bats are known to occupy and use resources in agroecosystems, yet little is known about their diets. We analysed a scat sample each from two individual bats, both threatened species (Chalinolobus picatus and Vespadelus baverstocki), in a major dryland cotton production zone. Both bats consumed economically important agricultural and cotton pests such as Helicoverpa sp. (bollworm). Our results suggest that these two bat species share around half of the insect prey resources available whilst consuming a wide range of prey items. This snapshot of dietary data provides further evidence that insectivorous bats consume a wide range of insect prey, including pests in cropping areas.

Organic substitutions aggravated microbial nitrogen limitation and decreased nitrogen-cycling gene abundances in a three-year greenhouse vegetable field

Partially substituting chemical fertilizer with organic fertilizer has substantially changed the stoichiometric imbalances of carbon (C), nitrogen (N) and phosphorus (P) between microbial communities and their available resources in agroecosystems. However, how organic substitution alters microbial nutrient limitation and then affects soil N cycle in intensive greenhouse vegetable ecosystem, remain unknown. Thus, we performed a three-year greenhouse vegetable field experiment in China with different fertilization strategies: no N fertilization, chemical N fertilization, and substituting 20% (1M4N) or 50% (1M1N) of chemical N with organic fertilizer (organic substitutions). Our results demonstrated that the microbial communities presented N limitation, accompanying with a strong N:P but a weak C:N (or P) microbial homeostasis in response to high N:P imbalance among all treatments. Organic substitutions at 1M1N and 1M4N significantly aggravated microbial N limitation and decreased the gene abundances of nitrification and denitrification by 4.7%–27.3% than that of chemical N fertilization. Microbial N limitation was strongly influenced by N:P stoichiometric imbalance illustrated from regression analysis. The N-cycling gene abundances were not only dependent on the inorganic N pool and soil physicochemical properties (i.e. pH and electrical conductivity), but also affected by microbial nutrient limitation inferred from random forest analysis. Furthermore, the 1M1N treatment performed better than the 1M4N in terms of improved crop yield and less microbial N limitation. Overall, these results highlight the importance of ecological stoichiometry in regulating soil N cycle under different fertilization strategies for intensive greenhouse vegetable ecosystem.

Seasonality of floral resources in relation to bee activity in agroecosystems.

The contribution of wild insects to crop pollination is becoming increasingly important as global demand for crops dependent on animal pollination increases. If wild insect populations are to persist in agricultural landscapes, there must be sufficient resources over time and space. The temporal, within‐season component of floral resource availability has rarely been investigated, despite growing recognition of its likely importance for pollinator populations. Here, we examined the visitation rates of common bee genera and the spatiotemporal availability of floral resources in agroecosystems over one season to determine whether local wild bee activity was limited by landscape floral resource abundance, and if so, whether it was limited by the present or past abundance of landscape floral resources. Visitation rates and landscape floral resources were measured in 27 agricultural sites in Ontario and Québec, Canada, across four time periods and three spatial scales. Floral resources were determined based on species‐specific floral volume measurements, which we found to be highly correlated with published measurements of nectar sugar mass and pollen volume. Total floral volume at varying spatial scales predicted visits for commonly observed bee genera. We found Lasioglossum and Halictus visits were highest in landscapes that provided either a stable or increasing amount of floral resources over the season. Andrena visits were highest in landscapes with high floral resources at the start of the season, and Bombus visits appeared to be positively related to greater cumulative seasonal abundance of floral resources. These findings together suggest the importance of early‐season floral resources to bees. Megachile visits were negatively associated with the present abundance of floral resources, perhaps reflecting pollinator movement or dilution. Our research provides insight into how seasonal fluctuations in floral resources affect bee activity and how life history traits of bee genera influence their responses to food availability within agroecosystems.

Soil Mulching as an Important Element in the Strategy of Using Natural Water Resources in Agroecosystems of the Steppe Crimea

Using the earlier developed MULCH model of heat-and-water exchange in the “soil–mulch cover–vegetation cover–land-surface atmosphere layer” system, we showed that the zero (minimum) tillage technology in combination with mulching the soil surface with plant residues is the most promising method for increasing the water availability and yield of wheat in steppe regions of the Crimea. It was found that the optimal thickness of the mulching layer on rainfed fields under wheat is ~4–5 cm. It was shown that minimum tillage in combination with mulching the soil surface with a 5-cm-thick layer of plant residues increases the water availability of wheat plants (which is determined by the ratio between the actual and potential transpiration of plants) on rainfed fields in the steppe regions of Crimea by 13% on the average. The yield of wheat increases compared to the conventional tillage practice (with consideration for the increase of humus content in the soil under long-term (about 8–10 years) mulching of soil surface) by 12% (~5.3 dt/ha) on the average. The obtained results can be used in the development of methods for using natural water resources in agroecosystems of the steppe Crimea.

Sphaerophoria rueppelli adults change their foraging behavior after mating but maintain the same preferences to flower traits

Hoverflies can play an important role in aphid biological control. Adult hoverflies depend on pollen and nectar to survive. Therefore the placement of flower resources in agroecosystems is a common method to enhance the populations of these insects. When foraging, hoverflies rely on visual cues to select flowers. We studied the preference of Sphaerophoria rueppelli (Wiedemann) (Diptera: Syrphidae) adults for several flower traits and examined whether mating influenced foraging behavior. We observed that these insects were greatly attracted to bouquets of 12 flat circle-shaped flowers (half white and half yellow). Furthermore, yellow flowers elicited landing more than other colors, regardless of the type of bouquet. With respect to the effect of mating on posterior foraging behavior, virgin individuals showed more movement than gravid ones. Our results shed light on the behavior of adult hoverflies and can be used to improve habitat management practices that seek to promote biological control.

Qualidade do solo em sistemas de integração lavoura-pecuária no Bioma Pampa

The increasing level of soil degradation has promoted the adoption of agricultural management that combines agricultural production to soil conservation. In this context, Integrated Crop-Livestock Systems have been successfully adopted, because they occupy the available resources in agroecosystems, concomitant to the improvement of soil quality. This study aimed to evaluate the soil quality in family farmers under integrated crop-livestock systems in the South Region of Rio Grande do Sul state, defining physical, chemical and biological indicators to detect the effect of the different management practices adopted in different use systems: native grazed field, ryegrass pasture and corn. Soil samples were collected in the layers from 0-0.05, 0.05-0.10 and 0.10-0.20 m to quantify the bulk density, total porosity, diameter weighted average, total organic carbon, total nitrogen, carbon of the coarse fraction, carbon associated with minerals, carbon of the free light fraction, carbon of the free occlude fraction, carbon of the heavy fraction, microbial biomass carbon and basal soil respiration. The factorial analysis applied to the 12 soil quality indicators, showed that the “Organic Matter Factor” was the one that most contributed to the total variation of the data in the three layers evaluated, being the most sensitive to detect the effects of the different management practices used. The indicators that compose the “Organic Matter Factor” are more associated to the native grazed field system, those that compose the “Aggregation Factor”, “Compression Factor” and “Microbial Carbon Factor” are more associated to the ryegrass pasture system. The indicators basal soil respiration, carbon of the free light fraction and total porosity are more related to the corn system. And finally, the bulk density is related to the three use systems evaluated.

Selective effects of floral food sources and honey on life‐history traits of a pest–parasitoid system

AbstractMany parasitoids and their herbivorous hosts forage on the same floral resources in agroecosystems. Floral resources that benefit natural enemies without supporting pests can improve the efficacy of biological control agents. Here, we report the results of a study on selective effects of floral and non‐floral food sources on the life‐history traits of the parasitoid Diadegma insulare (Cresson) (Hymenoptera: Ichneumonidae) and its host Plutella xylostella (L.) (Lepidoptera: Plutellidae). Under standard laboratory conditions, insects were exposed to four flowering plant species, 10% honey solution, and water. All food sources increased the longevity of the herbivore and its parasitoid by as much as four‐ to nine‐fold, respectively, compared to the water control diet. Diadegma insulare survived the longest on Thlaspi arvense L. (Brassicaceae) and P. xylostella on Sinapis arvensis L. (Brassicaceae). However, none of the food sources tested was beneficial to the parasitoid alone, though Lobularia maritima L. (Brassicaceae) was found to selectively favor the longevity of D. insulare. Diadegma insulare adults were heavier when fed on S. arvensis, whereas feeding on the honey solution led to higher body weights of P. xylostella. In conclusion, we demonstrated that floral and non‐floral food sources varied in their suitability and acted differently on life‐history traits of a host–parasitoid system. The selective characteristics of nectar‐producing plants and their influence on the herbivore‐natural enemy combination can, therefore, be employed to increase their impact in integrated P. xylostella management.

Effects of species and soil‐nitrogen availability on root system architecture traits – study on a set of weed and crop species

AbstractBetter managing crop : weed competition in cropping systems while reducing both nitrogen and herbicide inputs is a real challenge that requires a better understanding of crop and weed root architecture in relation to soil‐nitrogen availability. An original approach was used which considered the parameters of a simulation model of root architecture as traits to analyse (a) the interspecific diversity of root system architecture, and (b) its response to soil‐nitrogen availability. Two greenhouse experiments were conducted using three crop and nine weed species grown at two contrasted concentrations of soil‐nitrogen availability. Plant traits were measured to characterise both overall plant growth and root architecture, with a focus on primary root emergence, root elongation and branching. The studied root traits varied among species (from a twofold to a fourfold factor, depending on the trait), validating their use as indicators to analyse the interspecific variability of root architecture. The largest interspecies differences were for two traits: ‘maximal apical root diameter’ and ‘interbranch distance’ (distance between two successive laterals on the same root). Conversely, most of the studied root traits varied little with soil‐nitrogen availability (from no variation to a 1.1‐fold factor, depending on the trait) even though soil‐nitrogen availability varied with a 17‐fold factor and impacted the overall shoot and root biomass. So, the root traits used in this article are stable whatever soil‐nitrogen availability. As they reflect processes underlying root system architecture, this low effect of nitrogen suggests that the rules governing root architecture are little affected by plant nitrogen status and soil‐nitrogen availability. We propose that the determinants of differences in root system architecture between soils with contrasted nitrogen availability mainly originate from differences in the amount of carbon allocated to and within the root system. Characterising each plant species by a combination of root traits gave insights regarding the potential species competitive ability for soil resources in agroecosystems.

Incorporation of root C and fertilizer N into the food web of an arable field: Variations with functional group and energy channel

Agroecosystems occupy large areas of the land surface and arable soil food webs are of significant importance for global cycling of carbon (C) and nitrogen (N). In a field experiment we labeled maize plants (Zea mays L.) in 13CO2 atmosphere and by K15NO3 fertilization. During 25days, the incorporation of 13C and 15N was traced in plant compartments, soil and soil arthropods, as well as 13C in microbial phospholipid fatty acids (PLFAs) and nematodes. Highlighting the importance of root-derived resources in agroecosystems, 13C was incorporated into all food web compartments, including microorganisms (PLFAs), nematodes and arthropods. The amount of incorporated 13C (as compared to unlabeled samples) markedly decreased along the food chain with ∆13C decreasing from 500‰ in plant roots and 900‰ in microbial PLFAs, to less than 40‰ in nematodes and arthropods. Incorporation of 13C into fungal PLFAs considerably exceeded that into bacterial PLFAs, highlighting the importance of soil fungi as compared to bacteria in C cycling. Fertilizer-derived 15N uniformly increased with time in plant compartments and soil arthropods, indicating that N is distributed homogeneously in the soil food web. High channeling of both root-derived 13C and fertilizer-derived 15N to higher trophic levels by fungi, and intensive feeding on fungi by soil animals highlight the central role of saprotrophic fungi in C and nutrient fluxes in soil food webs of arable ecosystems.

Utilisation of plant functional diversity in wildflower strips for the delivery of multiple agroecosystem services

AbstractIncreased plant diversity in cropping systems can play an important role in agriculture by enhancing arthropod‐mediated ecosystem services, including biological control and pollination. However, there is limited research investigating the concurrent influence of plant functional diversity within cultivated systems on different arthropod functional groups, the provision of multiple ecosystem services, and crop yield. During a field experiment, repeated over 2 years, we measured the effect of increasing plant functional diversity on community structure of arthropod visitors, the abundance of multiple pests and induced crop damage, and fruit production in two varieties of tomato. Plant resources (floral and extra‐floral nectar and pollen) were included within experimental plots in four levels, with each level increasing the plant functional group richness, based on floral morphology and availability of resources, in a replacement series. The presence of sown flower mixtures in experimental plots was associated with increased abundance and diversity of natural enemy functional groups and an enhanced abundance of bees (Hymenoptera:Apiformes). However, we only detected relatively small variability in arthropod visitors among types of mixtures, and increased abundance of natural enemies did not translate into stronger pest suppression or reduced crop damage. Lepidoptera pest damage was significantly higher in plots adjacent to wildflower strips, an ecosystem disservice, but a significantly higher crop productivity was recorded from these plots. Our results provide evidence that inclusion of non‐crop plant resources in agroecosystems can improve the conservation of beneficial arthropods and may lead to increased crop productivity.

Dynamics of hill agriculture in emergent rural economy of Kangra district, Himachal Pradesh

The existence of human beings depends on the mountains and ecosystem services. Farming systems are facing immense difficulties owing to severe water shortage, changing climate patterns, dying traditional knowledge and increasing animal menace. Mountain ecosystem is adversely affected by the pressing population and resultant poverty. Natural resources are under huge pressure with diminishing land and water resources. The present paper examines the agriculture based livelihood security in changing socio-economic environments in district Kangra, Himachal Pradesh. Resource mapping, indexing, scoring and ranking of agro-ecosystem along with human and social capital have been used. In Kangra, about 45% of the work force is dependent on agriculture and the agricultural labourer accounted for 8% of the total work force. There is sluggish growth of employment opportunities in other sectors primarily in secondary and tertiary sectors to absorb surplus labour force from agricultural sector. The district has the largest number of cultivators i.e. 0.3 million out of 2 million cultivators in the state. The diminishing importance of the agro-ecosystem resources and their role as source of income are not sufficient in the present context of livelihood opportunities. The traditional sources of services have been decreasing in importance because of other sources of diversified income along with tourism in the hill region of Kangra. About 60 per cent of the households depend on the livestock for their additional income as well as other nonfarm sources. Integrated farming system improves the livelihood situation and brings financial stability and security.

Ecohydrological modeling in agroecosystems: Examples and challenges

AbstractHuman societies are increasingly altering the water and biogeochemical cycles to both improve ecosystem productivity and reduce risks associated with the unpredictable variability of climatic drivers. These alterations, however, often cause large negative environmental consequences, raising the question as to how societies can ensure a sustainable use of natural resources for the future. Here we discuss how ecohydrological modeling may address these broad questions with special attention to agroecosystems. The challenges related to modeling the two‐way interaction between society and environment are illustrated by means of a dynamical model in which soil and water quality supports the growth of human society but is also degraded by excessive pressure, leading to critical transitions and sustained societal growth‐collapse cycles. We then focus on the coupled dynamics of soil water and solutes (nutrients or contaminants), emphasizing the modeling challenges, presented by the strong nonlinearities in the soil and plant system and the unpredictable hydroclimatic forcing, that need to be overcome to quantitatively analyze problems of soil water sustainability in both natural and agricultural ecosystems. We discuss applications of this framework to problems of irrigation, soil salinization, and fertilization and emphasize how optimal solutions for large‐scale, long‐term planning of soil and water resources in agroecosystems under uncertainty could be provided by methods from stochastic control, informed by physically and mathematically sound descriptions of ecohydrological and biogeochemical interactions.

Keystone resources available to wild pollinators in a winter‐flowering tree crop plantation

Abstract Homogeneous tree crop plantations can adversely impact wild pollinator communities by limiting the temporal continuity of food and the availability of nesting sites. Identifying how structural differences between plantations and natural vegetation influence pollinator communities is necessary for ecological management of agroecosystems. Communities of potential wild pollinators (native bees, wasps, flies) were compared between monoculture almond plantations and native vegetation in a semi‐arid region of southern Australia, before, during and after the late winter almond flowering period. Abundance and richness of each insect group were related to site heterogeneity and keystone structural resources at each site, focusing on food and nesting resources. Relationships with site heterogeneity varied between taxa and across months. Native bee abundance and richness were strongly associated with specific keystone resources, despite showing no association with site heterogeneity. The present study highlights the value of focusing on biologically meaningful resources when investigating relationships between insects and habitat, rather than on generalized heterogeneity metrics. The results suggest that maintaining keystone resources in agroecosystems can support the conservation of insects and ecosystem services, especially in areas where homogeneous agricultural systems overlap dynamic natural ecosystems.

Ecohydrology of agroecosystems: quantitative approaches towards sustainable irrigation.

Irrigation represents one of the main strategies to enhance and stabilize agricultural productivity, by mitigating the effects of rainfall vagaries. In the face of the projected growth in population and in biofuel demands, as well as shifts in climate and dietary habits, a more sustainable management of water resources in agroecosystems is needed. The field of ecohydrology, traditionally focusing on natural ecosystems, has the potential to offer the necessary quantitative tools to assess and compare agricultural enterprises across climates, soil types, crops, and irrigation strategies, accounting for the unpredictability of the hydro-climatic forcing. Here, agricultural sustainability and productivity are assessed with reference to water productivity (defined as the ratio between yield and total supplied water), yields, water requirements, and their variability-a crucial element for food security and resource allocation planning. These synthetic indicators are quantified by means of a probabilistic description of the soil water balance and crop development. The model results allow the interpretation of patterns of water productivity observed in Zea mays (maize) and Triticum aestivum (wheat), grown under a variety of soils, climates, and irrigation strategies. Employing the same modeling framework, the impact of rainfall pattern and irrigation strategy on yield and water requirements is further explored. The obtained standard deviations of yield and water requirements suggest the existence of a nonlinear tradeoff between yield stabilization and variability of water requirements, which in turn is strongly impacted by irrigation strategy. Moreover, intermediate rainfall amounts are associated to the highest variability in yields and irrigation requirements, although allowing the maximum water productivity. The existence of these tradeoffs between productivity, reliability, and sustainability poses a problem for water management, in particular in mesic climates.

Floral Resources Effect on the Longevity of the Aphid Parasitoid Aphidius erviHaliday ( Hymenoptera : Braconidae ) and its Hyperparasitoid Alloxysta VictrixWestwood ( Hymenoptera : Charipidae )

Changing biodiversity can impact higher trophic levels, which may in turn influence food-web structure and ecosystem functioning. In this study, some floral resources were evaluated in the laboratory to assess their effect on the longevity of the fourth-trophic-level parasitoid Alloxysta victrix Westwood (Hymenoptera: Charipidae), which parasitises aphid parasitoids. When the hyperparasitoid was exposed to flowering buckwheat (Fagopyrum esculentum Moench cv. Katowase) or coriander (Coriandrum sativum L. cv. Slowbolt), it survived ten times longer than it did when fed on water only and five times longer with phacelia (Phacelia tanacetifolia Bentham cv. Balo) or sweet alyssum (Lobularia maritima L. cv. Carpet of Snow). Aphidius ervi Haliday (Hymenoptera: Braconidae) exposed to buckwheat survived, on average, between four to five times as long as those in the control (water) and those in phacelia, alyssum and coriander treatments survived three to four times as long as those in the control. These results indicate that floral resources deployed in conservation biocontrol should also be screened for their effects on the fourth trophic level. Modelling or field-cage experiments could be useful in elucidating the possible population and community consequences of deploying floral resources in agro-ecosystems to enhance biological control effectiveness.

Effect of seven species of the family Asteraceae on longevity and nutrient levels of Episyrphus balteatus

Adult hoverflies feed on pollen, nectar and honeydews. Thus, the implementation of floristically diverse resources in agroecosystems can enhance biological control of pests by increasing populations of these natural enemies. The objective of this work was to study the effect of seven species of Asteraceae (Andryala integrifolia L., Anthemis arvensis L., Calendula arvensis L., Carduus tenuiflorus Curtis, Chamaemelum nobile (L.) All., Coleostephus myconis (L.) Rchb.f. and Crepis vesicaria L.) on adult longevity and nutrient levels of Episyrphus balteatus (De Geer) (Diptera: Syrphidae). Crepis vesicaria and C. nobile gave the highest mean longevities while, for the other plant species, longevities were not significantly different from those in the water only treatment. In addition, all species tested resulted in significantly lower longevities than the positive control (glucose). In terms of nutrient levels, C. nobile generated high levels of total sugars and C. vesicaria high levels of lipids which suggests the consumption of flower resources. However, the majority of the plants tested would not allow hoverflies to complete their life cycle. Thus, further experimentation needs to be done before considering these plants for implementation in agroecosystems.

EVALUATING POTASSIUM-USE-EFFICIENT COTTON GENOTYPES USING DIFFERENT RANKING METHODS

Identification of cotton (Gossypium hirsutum L.) genotypes efficient in potassium (K) uptake and utilization, under K-deficient conditions represents a cost-effective and environmentally friendly approach for low-K-input agriculture. It would reduce the costly input of K-fertilizers and manage K resources in agro-ecosystems. We ranked 25 cotton genotypes for their K use efficiency under deficient and adequate K regimes in hydroponics, using two different methods. K deficiency generally reduced cotton growth; however, K-efficient genotypes accumulated more biomass due to higher K uptake. Genotype NIBGE-2 exhibited excellent adaptation potential in terms of high shoot dry weight under both K regimes and ranked as the only most desirable, “efficient-responsive” genotype. Genotype CIM-506 produced low shoot dry weight under low K condition and ranked as “non-efficient.” Genotype Desi okra produced low shoot dry weight at adequate K level and ranked as “non-responsive.” Genotype ranking using two different methods ensured the validity of results.

Soil Science and the Carbon Civilization

Soil science must play a crucial role in meeting present and emerging societal needs of the 21st century and beyond for a population expected to stabilize around 10 billion and having increased aspirations for a healthy diet and a rise in the standards of living. In addition to advancing food security by eliminating hunger and malnutrition, soil resources must be managed regarding numerous other global needs through interdisciplinary collaborations. Some of which are to mitigate global warming; to improve quantity and quality of freshwater resources; to enhance biodiversity; to minimize desertification; serve as a repository of waste; an archive of human and planetary history; meet growing energy demands; develop strategies of sustainable management of urban ecosystems; alleviate poverty of agricultural communities as an engine of economic development; and fulfill aspirations of rapidly urbanizing and industrializing societies. In addition to food and ecosystem services, bio‐industries (e.g., plastics, solvents, paints, adhesives, pharmaceuticals and chemicals) through plant‐based compounds (carbohydrates, proteins, and oils) and energy plantations (bioethanol and biodiesel) can revolutionize agriculture. These diverse and complex demands on soil resources necessitate a shift in strategic thinking and conceptualizing sustainable management of soil resources in agroecosystems to provide all ecosystem services while also meeting the needs for food, feed, fiber, and fuel by developing multifunctional production systems. There is a strong need to broaden the scope of soil science to effectively address ever changing societal needs. To do this, soil scientists must rally with allied sciences including hydrology, climatology, geology, ecology, biology, physical sciences (chemistry, physics), and engineering. Use of nanotechnology, biotechnology, and information technology can play an important role in addressing emerging global issues. Pursuit of sustainability, being a moral/ethical and political challenge, must be addressed in cooperation with economists and political scientists. Soil scientists must work in cooperation with industrial ecologists and urban planners toward sustainable development and management of soils in urban and industrial ecosystems. More than half of the world's population (3.3 billion) live in towns and cities, and the number of urban dwellers is expected to increase to 5 billion by 2030. Thus, the study of urban soils for industrial use, human habitation, recreation, infrastructure forestry, and urban agriculture is a high priority. Soil scientists must nurture symbiotic/synergistic relations with numerous stake holders including land managers, energy companies and carbon traders, urban planners, waste disposal organizations, and conservators of natural resources. Trading of C credits in a trillion‐dollar market by 2020 must be made accessible to land managers, especially the resource‐poor farmers in developing countries. Soil science curricula, at undergraduate and graduate levels, must be revisited to provide the needed background in all basic and applied sciences with focus on globalization. We must raise the profile of soil science profession and position students in the competitive world of ever flattening Earth.

Wheat genotypes differ in potassium efficiency under glasshouse and field conditions

A novel approach to the sustainable management of potassium (K) resources in agro-ecosystems is through better exploitation of genetic differences in the K efficiency of crop plants. Potassium efficiency is a measure of genotypic tolerance to soils with low potassium availability and can be quantified as the K efficiency ratio (the ratio of growth at deficient and adequate K supply). This study investigated the magnitude of variation in K efficiency among wheat (Triticum aestivum L.) genotypes grown in a glasshouse and in the field. Genotypes differed significantly in response to low soil K availability in terms of shoot biomass during the vegetative growth phase and grain yield at maturity under glasshouse (144 genotypes) and field (89 genotypes) conditions. K-efficient and K-inefficient genotypes were identified. The main factor determining K efficiency for grain yield was the capacity of genotypes to maintain a high harvest index (grain yield/total shoot weight) at deficient K supply. Genotypes that had reduced harvest index under deficient K supply were K-inefficient. Capacity to tolerate low concentrations of K in shoot tissue where K supply was deficient was also important in determining K efficiency for grain yield. Potassium-efficient genotypes have the potential to enhance the productivity and sustainability of cereal cropping systems.

Fungal infection and soybean competition induce plastic responses in velvetleaf (Abutilon theophrasti) growth and reproductive output

The historic maternal environment; the identity of competing, neighboring plants; and biotic stresses, such as fungal disease and herbivory, interact to influence the competitive ability, reproductive output, and plasticity of weed populations. A weed capable of altering its phenotype in response to environmental factors is better able to compete for resources in agroecosystems, thereby reducing crop yields and contributing more seeds to the seed bank. Velvetleaf is a highly competitive annual weed in many North American cropping systems, exhibiting a high degree of phenotypic plasticity in response to biotic and abiotic factors. We examined the effects of seed size (small and large), competitive environment (with and without soybean), and stress level (none = no treatment, moderate = pathogen inoculation, high = pathogen plus herbicide) on velvetleaf allometry and reproductive output during three field seasons. Only under the high-stress treatment was velvetleaf biomass, height, and reproductive output compromised (> 15% each), and these traits were further reduced with soybean competition. Soybean competition alone reduced velvetleaf biomass (> 50%), height (25%), and seed output (50%), but effects of competition varied with stress level. Velvetleaf plants that originated from large seeds (≥ 10 mg) generally outperformed plants originating from small seeds (< 10 mg) except under the high-stress treatment. These findings suggest that velvetleaf life-history traits and reproductive output in the current generation are a function of both present and historic factors. Management strategies for this species should involve tactics that not only reduce its competitive ability (e.g., biomass, height) but also decrease its seed production via synergistic stressors such as increased crop competitiveness, reduced-rate herbicide applications, and pathogen infection.