Non-irrigated Sites Research Articles

An Observational, Irrigation-Sensitive Agricultural Drought Record from Weather Data

Abstract The historical rise of irrigation has profoundly mitigated the effect of drought on agriculture in many parts of the United States. While irrigation directly alters soil moisture, meteorological drought indices ignore the effects of irrigation, since they are often based on simple water balance models that neglect the irrigation input. Reanalyses also largely neglect irrigation. Other approaches estimate the evaporative fraction (EF), which is correlated with soil moisture under water-limited conditions typical of droughts, with lower values corresponding to drier soils. However, those approaches require satellite observations of land surface temperature, meaning they cannot be used to study droughts prior to the satellite era. Here, we use a recent theory of land–atmosphere coupling—surface flux equilibrium (SFE) theory—to estimate EF from readily available observations of near-surface air temperature and specific humidity with long historical records. In contrast to EF estimated from a reanalysis that largely neglects irrigation, the SFE-predicted EF is greater at irrigated sites than at nonirrigated sites during droughts, and its historical trends are typically consistent with the spatial distribution of irrigation growth. Two sites at which SFE-predicted EF unexpectedly rises in the absence of changes in irrigation can be explained by increased flooding due to human interventions unrelated to irrigation (river engineering and the expansion of fish hatcheries). This work introduces a new method for quantifying agricultural drought prior to the satellite era. It can be used to provide insight into the role of irrigation in mitigating drought in the United States over the twentieth century. Significance Statement Irrigation grew profoundly in the United States over the twentieth century, increasing the resilience of American agriculture to drought. Yet observational records of agricultural drought, and its response to irrigation, are limited to the satellite era. Here, we show that a common measure of agricultural drought (the evaporative fraction, EF) can be estimated using widespread weather data, extending the agricultural drought record decades further back in time. We show that EF estimated using our approach is both sensitive and specific to the occurrence of irrigation, unlike an alternative derived from a reanalysis.

Interplay of legacy irrigation and nitrogen fertilizer inputs to spatial variability of arsenic and uranium within the deep vadose zone

The vadose zone is a reservoir for geogenic and anthropogenic contaminants. Nitrogen and water infiltration can affect biogeochemical processes in this zone, ultimately affecting groundwater quality. In this large-scale field study, we evaluated the input and occurrence of water and nitrogen species in the vadose zone of a public water supply wellhead protection (WHP) area (defined by a 50-year travel time to groundwater for public supply wells) and potential transport of nitrate, ammonium, arsenic, and uranium. Thirty-two deep cores were collected and grouped by irrigation practices: pivot (n = 20), gravity (n = 4) irrigated using groundwater, and non-irrigated (n = 8) sites. Beneath pivot-irrigated sites, sediment nitrate concentrations were significantly (p < 0.05) lower, while ammonium concentrations were significantly (p < 0.05) higher than under gravity sites. The spatial distribution of sediment arsenic and uranium was evaluated against estimated nitrogen and water loading beneath cropland. Irrigation practices were randomly distributed throughout the WHP area and presented a contrasting pattern of sediment arsenic and uranium occurrence. Sediment arsenic correlated with iron (r = 0.32, p < 0.05), uranium negatively correlated to sediment nitrate (r = −0.23, p < 0.05), and ammonium (r = −0.19 p < 0.05). This study reveals that irrigation water and nitrogen influx influence vadose zone geochemistry and mobilization of geogenic contaminants affecting groundwater quality beneath intensive agricultural systems.

Effects of bacterial composition and aquatic habitat metabolites on malaria vector larval availability in irrigated and non-irrigated sites of Homa Bay county, western Kenya.

Gravid Anopheles malaria vectors depend on both chemical and physical (including microbial) cues for selection of preferred habitats for oviposition. This study focused on assessing the effects of bacterial composition and habitat metabolites on malaria vector larval availability in irrigated and non-irrigated potential larval sources. Water samples were collected from larval positive and negative habitats in the irrigated and non- irrigated areas of Homa Bay county. Bacteria cultured from the water samples were subjected to Matrix Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS) for species identification. DNA was extracted from the colonies and polymerase chain reaction (PCR) and sequencing done. Finally, the metabolite composition of larval positive and negative habitats was determined. MALDI-TOF MS results revealed that Bacillus was the only genera identified from larval sources in the non-irrigated zone. In the irrigated area, Shigella was the dominant genera (47%) while Escherichia coli was the abundant species (13/51). Of the sequenced isolates, 65% were Bacillus. Larvicidal isolates Brevibacillus brevis, Bacillus subtilis, and Exiguobacterium profundum were isolated and grouped with Bacillus mojavensis, Bacillus tequilensis, Bacillus stercoris, and Brevibacillus agri. Irrigated areas with larvae had reduced crude fat (0.01%) and protein content (0.13%) in comparison to those without larvae. In irrigated and non- irrigated areas, larval presence was evident in habitats with high total chlorophyll content (1.12 μg/g vs 0.81μg/g and 3.37 μg/g vs 0.82). Aquatic habitats with larvae in both irrigated and non-irrigated areas exhibited higher sugar concentration than habitats without larvae; however, when compared, non-irrigated areas with larvae had higher sugar concentration than similar habitats in irrigated areas. In addition, substantial concentrations of Manganese, Calcium, and Copper were found in aquatic habitats containing larvae in both irrigated and non-irrigated areas. These results allow for prospective examination as potential larvicidal or adulticidal agents and could be considered when designing potential vector control interventions.

Malaria vector bionomics and transmission in irrigated and non-irrigated sites in western Kenya

Irrigation not only helps to improve food security but also creates numerous water bodies for mosquito production. This study assessed the effect of irrigation on malaria vector bionomics and transmission in a semi-arid site with ongoing malaria vector control program. The effectiveness of CDC light traps in the surveillance of malaria vectors was also evaluated relative to the human landing catches (HLCs) method. Adult mosquitoes were sampled in two study sites representing irrigated and non-irrigated agroecosystems in western Kenya using a variety of trapping methods. The mosquito samples were identified to species and assayed for host blood meal source and Plasmodium spp. sporozoite infection using polymerase chain reaction. Anopheles arabiensis was the dominant malaria vector in the two study sites and occurred in significantly higher densities in irrigated study site compared to the non-irrigated study site. The difference in indoor resting density of An. arabiensis during the dry and wet seasons was not significant. Other species, including An. funestus, An. coustani, and An. pharoensis, were collected. The An. funestus indoor resting density was 0.23 in irrigated study site while almost none of this species was collected in the non-irrigated study site. The human blood index (HBI) for An. arabiensis in the irrigated study site was 3.44% and significantly higher than 0.00% for the non-irrigated study site. In the irrigated study site, the HBI of An. arabiensis was 3.90% and 5.20% indoor and outdoor, respectively. The HBI of An. funestus was 49.43% and significantly higher compared to 3.44% for An. arabiensis in the irrigated study site. The annual entomologic inoculation rate for An. arabiensis in the irrigated study site was 0.41 and 0.30 infective bites/person/year indoor and outdoor, respectively, whereas no transmission was observed in the non-irrigated study site. The CDC light trap performed consistently with HLC in terms of vector density. These findings demonstrate that irrigated agriculture may increase the risk of malaria transmission in irrigated areas compared to the non-irrigated areas and highlight the need to complement the existing malaria vector interventions with novel tools targeting the larvae and both indoor and outdoor biting vector populations.Graphical abstract

Soil and Groundwater Investigation for Sustainable Agricultural Development: A Case Study from Brunei Darussalam

Brunei has made significant progress in agricultural development over the past four decades. However, crop production, such as rice, is still insufficient to meet the demands of the growing population, mainly due to the scarcity of water resources, acidic soils, and advancing environmental deterioration. This study conducted soil and groundwater investigations at three selected rice cultivation sites in Brunei Darussalam. The geoelectrical resistivity method using the vertical electrical sounding (VES) technique delineated subsurface stratigraphy with resistivities ranging from 1 to 180 Ωm in the investigated area. A potential aquifer zone was inferred in one of the surveyed areas with resistivities ranging from 10 to 150 Ωm at depths of about 40 to 60 m below ground level. Groundwater levels were also shallower in irrigated sites compared to non-irrigated sites. Groundwater physicochemical properties revealed high alkalinity and mineralisation, as evident from high magnesium, bicarbonate, ammoniacal nitrogen, and iron, as well as pH values in the water samples, believed to be the effects of leaching of salt ions into the shallow aquifer through infiltration recharge. In addition, soil physicochemical properties showed that the soils near a pumping well were more acidic, had lower moisture, and total nutrients, likely due to the effects of groundwater pumping. Our results demonstrate that future irrigation activities need to consider local aquifer characteristics, groundwater flow paths, and nutrient transport to ensure sustainable development in agricultural areas.

Agricultural practices linked to shifts in groundwater microbial structure and denitrifying bacteria

Irrigation enhances the connectivity between the surface and groundwater by facilitating the transport of energy sources and oxygen. When combined with fertilisers, the impact on groundwater microbial communities and their interactions with nitrogen cycling in aquifers is poorly understood. This study examines the impact of different landuses (irrigated and non-irrigated) on groundwater microbial communities. A total of 38 wells accessing shallow aquifers in three sub-catchments of the Murray Darling Basin, Australia, were sampled for water chemistry and microbial community structure using environmental DNA (eDNA) techniques. All sub-catchments showed evidence of intense irrigation and groundwater contamination with total nitrogen, nitrates and phosphorus concentrations often well above background, with total nitrogen concentrations up to 70 mg/L and nitrate concentration up to 18 mg/L. Across sub-catchments there was high microbial diversity, with differences in community structure and function between catchments and landuses. Of the 1100 operational taxonomic units (OTUs) recorded, 47 OTUs were common across catchments with species from Woesearchaeota, Nitrospirales, Nitrosopumilales and Acidobacter taxonomic groups contributing greatly to groundwater microbial communities. Within non-irrigated sites, groundwaters contained similar proportions of nitrifying and denitrifying capable taxa, whereas irrigated sites had significantly higher abundances of microbes with nitrifying rather than denitrifying capabilities. Microbial diversity was lower in irrigated sites in the Macquarie catchment. These results indicate that irrigated landuses impact microbial community structure and diversity within groundwaters and suggest that the ratios of denitrifying to nitrifying capable microbes as well as specific orders (e.g., Nitrososphaerales) may be useful to indicate long-term nitrogen contamination of groundwaters. Such research is important for understanding the biogeochemical processes that are key predictors of redox state and contamination of groundwater by N species and other compounds. This will help to predict human impacts on groundwater microbial structure, diversity, and ecosystem functions, aiding the long-term management groundwater resources.

Effect of Source of Irrigation Water on Soil Chemical Properties in Tamale Metropolis, Ghana

This study analyzed the effect of different water sources of irrigation on the chemical constituents of soils in the Tamale Metropolis of Ghana. Soil samples were taken from depths of 0 – 30 cm and 30 – 60 cm in wastewater, pipe water and non-irrigated (control) sites. Variations in levels of concentration of the various chemical properties, however, occurred among the three different soils. With the exception of % N and Mg, there was no significant difference among all the three soils for all the parameters. The results indicated that N level increased in wastewater irrigated soils as compared to pipe water and non-irrigated soils. P increased with wastewater irrigation but decreased with soil depth. K concentration in wastewater irrigated soils increased in the depth of 0 – 30 cm but decreased in the depth of 30 – 60 cm. Wastewater and pipe water irrigation decreased soil Na and Cl levels compared to the control (non-irrigated soils). Wastewater irrigation increased the level of EC and CEC whilst Cu, Zn and Cd levels increased with soil depth. Cu, Zn and Cd levels of the wastewater, pipe water and non-irrigated soils were higher than the FAO (1985) recommended levels for both depths. It can be concluded that irrigation with wastewater increased soil primary macro nutrients (NPK) whilst micro nutrients such as sodium and chloride decreased with wastewater and pipe water irrigation.

Caractérisation physicochimiques du sol dans les deux cas de conduite : pluvial et irrigué

La nature de sol est influencée par plusieurs facteurs tels que le facteur climatique (érosion, pluviométrie...). Dans ce travail nous avons étudiées les effets d’irrigation sur la composition physicochimique du sol issu de deux sites différents irrigué et non irrigué (El Massreb ou Kasser Ouled Débe et Douiret du gouvernorat de Tataouine). Nous avons procédé à une analyse granulométrique (texture du sol) à l’aide d’un appareil laser. D’autre part, on a déterminé les paramètres physicochimiques du sol (pH, conductivité électrique, calcaire total, calcaire active et matière organique). Nos résultats ont montrés que les sols étudiés appartiennent au même virage granulométrique et que l’irrigation a un effet sur les paramètres physicochimiques tels que le pH el la conductivité électrique.

Perception of Environmental Spillovers Across Scale in Climate Change Adaptation Planning: The Case of Small-Scale Farmers’ Irrigation Strategies, Kenya

The failure to acknowledge and account for environmental externalities or spillovers in climate change adaptation policy, advocacy, and programming spaces exacerbate the risk of ecological degradation, and more so, the degradation of land. The use of unsuitable water sources for irrigation may increase salinisation risks. However, few if any policy assessments and research efforts have been directed at investigating how farmer perceptions mediate spillovers from the ubiquitous irrigation adaptation strategy. In this study, the cognitive failure and/or bias construct is examined and proposed as an analytical lens in research, policy, and learning and the convergence of disaster risk reduction and climate change adaptation discourses. A cross-sectional survey design and multistage stratified sampling were used to collect data from 69 households. To elicit the environmental impacts of irrigation practices, topsoil and subsoils from irrigated and non-irrigated sites were sampled and analysed using AAS (atomic absorption spectrophotometer). A generalised linear logistic weight estimation procedure was used to analyse the perception of risks while an analysis of variance (ANOVA) was used to analyse changes in exchangeable sodium percentage (ESP). The findings from small-scale farmers in Machakos and Kakamega counties, Kenya, suggest multifaceted biases and failures about the existence and importance of externalities in adaptation planning discourses. Among other dimensions, a cognitive failure which encompasses fragmented approaches among institutions for use and management of resources, inadequate policy. and information support, as well as the poor integration of actors in adaptation planning accounts for adaptation failure. The failures in such human–environment system interactions have the potential to exacerbate the existing vulnerability of farmer production systems in the long run. The findings further suggest that in absence of risk message information dissemination, education level, farming experience, and information accumulation, as integral elements to human capital, do not seem to have a significant effect on behaviour concerning the mitigation of environmental spillovers. Implicitly, reversing the inherent adaptation failures calls for system approaches that enhance coordinated adaptation planning, prioritise the proactive mitigation of slow-onset disaster risks, and broadens decision support systems such as risk information dissemination integration, into the existing adaptation policy discourses and practice.

Impact of granular carriers to improve the efficacy of entomopathogenic fungi against wireworms in spring wheat

Wireworms are a major concern for wheat growers and several other crops around the globe. Environmentally friendly management strategies are needed because the present conventional chemical seed treatments can be ineffective and pose environmental risks. While biological control of wireworms in a general sense has not been practical, use of entomopathogenic fungi (EPF) is one environmentally friendly solution for this problem. In 2017, granular formulations of three EPFs, on polenta and millet spent substrate carriers, were applied in furrow at planting, at two rates, against a water control and imidacloprid seed treatment in spring wheat in Montana, USA. The selected EPFs were Beauveria bassiana GHA, Metarhizium robertsii DWR356, M. robertsii DWR2009, applied as granular formulations at 11 kg ha−1 or 22 kg ha−1. In 2017, at Valier, DWR356, DWR2009 on millet carrier at 22.4 kg ha−1 provided greater yield, but all the treatments at lower rate were still cost-effective. In 2018, B. bassiana GHA and M. robertsii DWR2009 were retested along with B. bassiana ERL836 and M. brunneum F52. Millet carrier alone, GHA and ERL836 on millet carrier obtained cost-effective results at irrigated and non-irrigated sites in 2018. However, these were less cost-effective than imidacloprid as a seed treatment. The overall cost–benefit ratio of using EPF granules was higher in both the years compared to control. Millet on which the fungi were grown worked better than the other carriers. Further evaluation of the effect of the carrier while applying EPFs in furrow as granules is required.

A potato model intercomparison across varying climates and productivity levels.

A potato crop multimodel assessment was conducted to quantify variation among models and evaluate responses to climate change. Nine modeling groups simulated agronomic and climatic responses at low-input (Chinoli, Bolivia and Gisozi, Burundi)- and high-input (Jyndevad, Denmark and Washington, United States) management sites. Two calibration stages were explored, partial (P1), where experimental dry matter data were not provided, and full (P2). The median model ensemble response outperformed any single model in terms of replicating observed yield across all locations. Uncertainty in simulated yield decreased from 38% to 20% between P1 and P2. Model uncertainty increased with interannual variability, and predictions for all agronomic variables were significantly different from one model to another (P<0.001). Uncertainty averaged 15% higher for low- vs. high-input sites, with larger differences observed for evapotranspiration (ET), nitrogen uptake, and water use efficiency as compared to dry matter. A minimum of five partial, or three full, calibrated models was required for an ensemble approach to keep variability below that of common field variation. Model variation was not influenced by change in carbon dioxide (C), but increased as much as 41% and 23% for yield and ET, respectively, as temperature (T) or rainfall (W) moved away from historical levels. Increases in T accounted for the highest amount of uncertainty, suggesting that methods and parameters for T sensitivity represent a considerable unknown among models. Using median model ensemble values, yield increased on average 6% per 100-ppm C, declined 4.6% per °C, and declined 2% for every 10% decrease in rainfall (for nonirrigated sites). Differences in predictions due to model representation of light utilization were significant (P<0.01). These are the first reported results quantifying uncertainty for tuber/root crops and suggest modeling assessments of climate change impact on potato may be improved using an ensemble approach.

Natural and anthropogenic controls on the frequency of preferential flow occurrence in a wastewater spray irrigation field

To quantify the frequency of preferential flow (PF) occurrence and its controls, and to examine the interactions of soils and irrigation on water flow dynamics, soil moisture was monitored at six depths every two minutes at four sites in a wastewater spray irrigation field from 2009 to 2011. Two irrigated sites – one cropped and another forested – were compared with two corresponding non-irrigated sites. Activation of preferential flow pathways was determined from the sequences of soil moisture responses at various depths for a total of 633 water input events, including 82 irrigation events. The results showed that the overall averaged frequencies of PF at the non-irrigated sites were 24.9% at the cropped site and 24.7% at the forested site. By contrast, the averaged frequencies at the irrigated sites were 47.1% at the cropped site and 45.0% at the forested site. The temporal stability of PF frequency was evaluated, showing that the overall frequency of PF stabilized after 70 events at non-irrigated sites, while the irrigated sites took as many as 105 events (24 of which were irrigations). Associations between 20 possible controls related to water input, moisture response, and season were quantified using the Student’s t-test between each parameter and PF detection. The most influential factors were water inputs, especially the total input and peak input intensity. Antecedent soil moisture and response slope (maximum 2-min increase in moisture content during the response) were also significant in some but not all cases. Soil horizonation influenced soil water storage and dynamics by restricting flow and causing perched water tables. Irrigated sites experienced saturated conditions for as much as 38% of the monitoring time at some depths, compared to a maximum of 3% at non-irrigated sites. Preferential flow was not only more likely to occur during irrigation events, but also during natural events at the irrigated sites, suggesting that the irrigated soils have physically adapted to accommodate large volumes of water, after decades of spray irrigation. The results of this study have implications for understanding hydrology and contaminant fate in anthropogenically-altered landscapes as well as implementing sustainable management practices.

Impact of long-term wastewater irrigation on the physicochemical properties of humid region soils: “The Living Filter” site case study

Increasing pressure on water resources is a significant challenge for the 21st century. Over the last decade, water reuse has offered a practical approach to wastewater effluent disposal while supporting agricultural production. Irrigation with wastewater can have negative impacts on the soil environment (e.g. increased salinity, reduced hydraulic conductivity) and these are well documented for soils in arid and semi-arid regions; but little research has been conducted for humid regions. Consequently, to understand the impact of wastewater irrigation on humid region soils, a field study was conducted at “The Living Filter” site (central Pennsylvania), where wastewater effluent has been used for irrigation for 50+ years. The study evaluated the differences in physicochemical soil properties throughout the soil profile (to a depth of 120cm) at wastewater irrigated sites and non-irrigated sites at different landscape positions (summits and depressions). Results showed that both the sodium adsorption ratio (irrigated: 4.93±1.22; non-irrigated: 0.88±1.03) and salinity (irrigated: 0.32±0.12dSm−1; non-irrigated: 0.07±0.03dSm−1) of soil extracts were significantly higher in the irrigated soil profiles compared to the non-irrigated soil profiles (but not with regards to landscape position). There was no observable treatment effect on saturated hydraulic conductivity, Ks, (irrigated: 1.96cmh−1; non-irrigated: 2.39cmh−1), but Ks had moderately strong inverse relationships with soil pH (R2=0.70) and percent organic carbon (R2=0.67). Overall, while salts are accumulating in these soils; our data suggest that long-term irrigation with wastewater has not negatively impacted the hydraulic conductivity of this humid region soil. Ongoing monitoring of soil physicochemical properties and wastewater parameters will be needed to maintain the long-term sustainability of the site.

Surface Urban Energy and Water Balance Scheme (SUEWS): Development and evaluation at two UK sites

The Surface Urban Energy and Water Balance Scheme (SUEWS) is evaluated at two locations in the UK: a dense urban site in the centre of London and a residential suburban site in Swindon. Eddy covariance observations of the turbulent fluxes are used to assess model performance over a two-year period (2011−2013). The distinct characteristics of the sites mean their surface energy exchanges differ considerably. The model suggests the largest differences can be attributed to surface cover (notably the proportion of vegetated versus impervious area) and the additional energy supplied by human activities. SUEWS performs better in summer than winter, and better at the suburban site than the dense urban site. One reason for this is the bias towards suburban summer field campaigns in observational data used to parameterise this (and other) model(s). The suitability of model parameters (such as albedo, energy use and water use) for the UK sites is considered and, where appropriate, alternative values are suggested. An alternative parameterisation for the surface conductance is implemented, which permits greater soil moisture deficits before evaporation is restricted at non-irrigated sites. Accounting for seasonal variation in the estimation of storage heat flux is necessary to obtain realistic wintertime fluxes.

Irrigation in the arid regions of Tunisia impacts the abundance and apparent density of sand fly vectors of Leishmania infantum

The distribution expansion of important human visceral leishmaniasis (HVL) and sporadic cutaneous leishmaniasis (SCL) vector species, Phlebotomus perfiliewi and P. perniciosus, throughout central Tunisia is a major public health concern. This study was designed to investigate if the expansion of irrigation influences the abundance of sand fly species potentially involved in the transmission of HVL and SCL located in arid bioclimatic regions. Geographic and remote sensing approaches were used to predict the density of visceral leishmaniasis vectors in Tunisia. Entomological investigations were performed in the governorate of Sidi Bouzid, located in the arid bioclimatic region of Tunisia. In 2012, sand flies were collected by CDC light traps located at nine irrigated and nine non-irrigated sites to determine species abundance. Eight species in two genera were collected. Among sand flies of the subgenus Larroussius, P. perfiliewi was the only species collected significantly more in irrigated areas. Trap data were then used to develop Poisson regression models to map the apparent density of important sand fly species as a function of different environmental covariates including climate and vegetation density. The density of P. perfiliewi is predicted to be moderately high in the arid regions. These results highlight that the abundance of P. perfiliewi is associated with the development of irrigated areas and suggests that the expansion of this species will continue to more arid areas of the country as irrigation sites continue to be developed in the region. The continued increase in irrigated areas in the Middle East and North Africa region deserves attention, as it is associated with the spread of L. infantum vector P. perfiliewi. Integrated vector management strategies targeting irrigation structures to reduce sand fly vector populations should be evaluated in light of these findings.

Insect Damage, Aflatoxin Content, and Yield of Bt Corn in Alabama.

Isoline pairs of hybrid corn, similar except for presence or absence of a Bt trait, were planted at eight sites across Alabama over three years. This study evaluated insect damage, yield, and aflatoxin levels as affected by the Bt traits, YieldGard Corn Borer (expressing Cry1Ab), Herculex I (expressing Cry1F), Genuity VT Triple PRO (expressing Cry1A.105 and Cry2Ab2), Agrisure Viptera 3111 (expressing Vip3Aa20 and Cry1Ab), and Genuity SmartStax (expressing Cry1A.105, Cry2Ab2, and Cry1F). When examined over all sites and years, hybrids with any of the included Bt traits had lower insect damage and higher yields. However, insect damage was not consistently correlated to yield. Bt traits expressing multiple proteins provided greater protection from corn earworm feeding than did traits for single proteins. Yields and aflatoxin levels were highly variable among sites although irrigated sites had higher yields than nonirrigated sites. Aflatoxins commonly accumulate in corn in the southeastern United States because of prevailing high temperatures and frequent dry conditions. Aflatoxin levels were not consistently associated with any factors that were evaluated, including Bt traits.

The effect of texture and irrigation on the soil moisture vertical-temporal variability in an urban artificial landscape: a case study of Olympic Forest Park in Beijing

Soil moisture variability in natural landscapes has been widely studied; however, less attention has been paid to its variability in the urban landscapes with respect to the possible influence of texture stratification and irrigation management. Therefore, a case study was carried out in the Beijing Olympic Forest Park to continuously monitor the soil in three typical profiles from 26 April to 11 November 2010. The texture stratification significantly affected the vertical distribution of moisture in the non-irrigated profile where moisture was mostly below field capacity. In the profile where irrigation was sufficient to maintain moisture above field capacity, gravity flow led to increased moisture with depth and thus eliminated the influence of texture. In the non-irrigated sites, the upper layer (above 80 cm) exhibited long-term moisture persistence with the time scale approximating the average rainfall interval. However, a coarse-textured layer weakened the influence of rainfall, and a fine-textured layer weakened the influence of evapotranspiration, both of which resulted in random noise-like moisture series in the deeper layers. At the irrigated site, frequent irrigation neutralized the influence of evapotranspiration in the upper layer (above 60 cm) and overshadowed the influence of rainfall in the deeper layer. As a result, the moisture level in the upper layer also behaved as a random noise-like series; whereas due to deep transpiration, the moisture of the deep layer had a persistence time-scale longer than a month, consistent with characteristic time-scales found for deep transpiration.

Factors influencing urban tree planting program growth and survival in Florida, United States

High levels of mortality after installation can limit the long-term benefits associated with urban tree planting initiatives. Past planting projects funded by the Florida Forest Service were revisited two to five years after installation to document tree survival and growth and assess program success. Additionally, various site (e.g., soil compaction, installed irrigation) and tree-related (e.g., species, nursery production method, initial size at planting) factors were noted to assess their impact on tree growth. Results show that the overall establishment rate for the 26 sites (n=2354 trees) was high, with 93.6% of trees alive at the time of final inspection. On-site irrigation played a significant role in tree survival and growth, especially for Magnolia grandiflora (97.7% survival on irrigated sites; 73.8% survival on non-irrigated sites). Findings from this work validate the effectiveness of current program policies which include maintenance of tree quality within the first year after planting, and offer further insights regarding the impacts of season of planting and initial size of nursery stock on plant growth and development.

Irrigation as an important factor in species distribution models

Species distribution models (SDMs) that employ climatic variables are widely used to predict potential distribution of invasive species. However, climatic variables derived from climate datasets do not account for anthropogenic influences on microclimate. Irrigation is a major anthropogenic activity that influences microclimate conditions and alters the distribution of species in anthropogenic landuses. SDM-based studies appear to ignore the effects of irrigation on microclimatic conditions. This study incorporated irrigation as a correction to precipitation data, to improve the predictive capacity of SDM. As a case study, we examined a SDM of Wasmannia auropunctata, an invasive species that originates in South and Central America, which has invaded tropical and subtropical regions around the world. The potential distribution of W. auropunctata was predicted using Maxent. The model was built based on climatic variables and species records from non-irrigated sites in the native range and then projected on a global scale. Invasive species records were used to evaluate the performance of the model. Precipitation-related variables were modified to approximate actual water input in irrigated areas. Precipitation correction relied on an estimate of irrigation inputs. The model with irrigation correction performed better than the corresponding model without correction, on a global scale and when it was examined in five different geographical regions of the model. These results demonstrate the importance of irrigation correction for assessing the distribution of W. auropunctata in various geographical regions. Accounting for irrigation is expected to improve SDMs for a variety of species.

Irrigation agriculture affects organic matter decomposition in semi-arid terrestrial and aquatic ecosystems

Many dryland areas are being converted into intensively managed irrigation crops, what can disrupt the hydrological regime, degrade soil and water quality, enhance siltation, erosion and bank instability, and affect biological communities. Still, the impacts of irrigation schemes on the functioning of terrestrial and aquatic ecosystems are poorly understood. Here we assess the effects of irrigation agriculture on breakdown of coarse organic matter in soil and water. We measured breakdown rates of alder and holm oak leaves, and of poplar sticks in terrestrial and aquatic sites following a gradient of increasing irrigation agriculture in a semi-arid Mediterranean basin transformed into irrigation agriculture in 50% of its surface. Spatial patterns of stick breakdown paralleled those of leaf breakdown. In soil, stick breakdown rates were extremely low in non-irrigated sites (0.0001–0.0003day−1), and increased with the intensity of agriculture (0.0018–0.0044day−1). In water, stick breakdown rates ranged from 0.0005 to 0.001day−1, and increased with the area of the basin subject to irrigation agriculture. Results showed that irrigation agriculture affects functioning of both terrestrial and aquatic ecosystems, accelerating decomposition of organic matter, especially in soil. These changes can have important consequences for global carbon budgets.