High Rainfall Years Research Articles

Pearl Millet and Cowpea Yields as Influenced by Tillage, Soil Amendment and Cropping System in the Sahel of Burkina Faso

Sole cropped pearl millet and intercropped pearl millet with cowpea are the dominant cropping systems in the Sahelien agroecological zone of Burkina Faso with low and stagnant pearl millet and cowpea yields. Two experiments were conducted in randomized complete block designs with split plot arrangements and three replications. The main plot was tillage method in both experiments and the sub-plot was soil amendment (compost, fertilizer, and crop residues). The objective was to identify the best combination of tillage method, cropping system, and soil amendment to optimize sole and intercropped millet and intercropped cowpea yields. In Exp. 1, sole crop millet grain yield was increased by soil amendment application from 238 kg ha-1 to 450 to 768 kg ha-1, and stover yields from 551 kg ha-1 to 1075 to 1813 kg ha-1. In Exp. 2, zaï tillage increased sole cropped millet grain yield by 348 to 495 kg ha-1, and intercropped millet by 194 to 202 kg ha-1 over use of no till and scarify. Combined zaï with C + F application increased sole cropped millet grain yield from 288 to 777 kg ha-1 and intercropped millet from 114 to 502 kg ha-1 over zaï without soil amendment. Similar trends were observed for millet stover and intercropped cowpea grain and stover yields. Influence of soil amendment application on grain and stover yields was greatest for sole cropped millet with use of zaï in high rainfall years. This first documentation of differential soil amendment response of sole and intercropped pearl millet with zaï, scarify, and no till systems indicates that the greatest pearl millet grain and stover yield is obtained with application of plough or zaï in combination with C + F, F + CR or C + F + CR soil amendment.

Effect of Tillage, Residue and Nitrogen Management on Soil Water Dynamics and Water Productivity of Wheat in an Inceptisol

A field experiment was conducted during rabi season for two consecutive years (2014–15 and 2015–16) on wheat crop in a sandy loam soil (Typic Haplustept) at the research farm of Indian Agricultural Research Institute (IARI), New Delhi with the objective of studying soil water dynamics and water productivity of wheat under different tillage, residue and nitrogen (N) management practices. The treatments comprising of two levels of tillage as main plot i.e. conventional tillage (CT) and no tillage (NT), two levels of residue as subplot i.e. maize residue @ 5 t ha−1 (R+) and without residue (R0)), and three levels of N as sub-sub plot i.e. 60, 120 and 180 kg N ha−1, representing 50% (N60), 100% (N120) and 150% (N180) of the recommended dose of N for wheat, respectively were evaluated in a split-split plot design with three replications. Results showed that there was increase in the profile moisture storage by 7.7 per cent under crop residue mulch. The evaporative flux was lower by 23.9 per cent but deep percolation flux was higher by 8.3 per cent under mulching than without mulch treatment. The water productivity of wheat was not influenced by tillage but increased significantly with the increase in N levels. During high rainfall year, the effect of crop residue mulch on water productivity was not significant but it increased significantly during low rainfall year.

Optimization of sowing date and seeding rate for high winter wheat yield based on pre-winter plant development and soil water usage in the Loess Plateau, China

Sowing date and seeding rate are critical for productivity of winter wheat (Triticum aestivum L.). A three-year field experiment was conducted with three sowing dates (20 September (SD1), 1 October (SD2), and 10 October (SD3)) and three seeding rates (SR67.5, SR90, and SR112.5) to determine suitable sowing date and seeding rate for high wheat yield. A large seasonal variation in accumulated temperature from sowing to winter dormancy was observed among three growing seasons. Suitable sowing dates for strong seedlings before winter varied with the seasons, that was SD2 in 2012–2013, SD3 in 2013–2014, and SD2 as well as SD1 in 2014–2015. Seasonal variation in precipitation during summer fallow also had substantial effects on soil water storage, and consequently influenced grain yield through soil water consumption from winter dormancy to maturity stages. Lower consumption of soil water from winter dormancy to booting stages could make more water available for productive growth from anthesis to maturity stages, leading to higher grain yield. SD2 combined with SR90 had the lowest soil water consumption from winter dormancy to booting stages in 2012–2013 and 2014–2015; while in 2013–2014, it was close to that with SR67.5 or SR112.5. For productive growth from anthesis to maturity stages, SD2 with SR90 had the highest soil water consumption in all three seasons. The highest water consumption in the productive growth period resulted in the best grain yield in both low and high rainfall years. Ear number largely contributed to the seasonal variation in grain yield, while grain number per ear and 1 000-grain weight also contributed to grain yield, especially when soil water storage was high. Our results indicate that sowing date and seeding rate affect grain yield through seedling development before winter and also affect soil water consumption in different growth periods. By selecting the suitable sowing date (1 October) in combination with the proper seeding rate of 90 kg ha–1, the best yield was achieved. Based on these results, we recommend that the current sowing date be delayed from 22 or 23 September to 1 October.

Demography of evergreen and deciduous oaks in a mixed oak savanna: insights from a long‐term experiment

AbstractThe co‐existence of evergreen and deciduous oaks in Mediterranean‐climate savannas has motivated comparative studies on species’ physiological adaptations to light and drought, establishment niche differences in acorn production, dispersal and seedling herbivory, and differential sapling tolerance of ungulate browsing. Understanding how species’ differences collectively affect co‐occurrence or segregation requires long‐term studies that consider multiple life stages. We compare survival, height growth, and modeled population growth rate of the evergreen sclerophyll, Quercus agrifolia, to those of the winter‐deciduous, broadleaved Q. lobata in southern California savanna sites where the species naturally co‐occur. We evaluate species’ performances after 8.7 yr for four cohorts sown as acorns in 1997, 1998, 2000, and 2001 under four different levels of protection from cattle, deer, and rodents. Survival curves for the two species were closely similar, with large differences between cohorts associated with precipitation in the year acorns were sown. Survival and growth rates of Q. agrifolia seedlings and saplings were slightly lower, and were more reduced by ungulates and rodents, than those of Q. lobata. No Q. agrifolia plants (0/1431) exposed to ungulates (cattle and/or deer) and rodents survived to the end of the experiment. Of 1421 Q. lobata acorns planted in these treatments, only 19 plants (1.3%) survived 8.7 yr and none of these plants progressed out of the ungulate browse layer. However, when protected from both ungulates and rodents, survival rates increased significantly for both species, and Q. agrifolia increased height faster than Q. lobata. Simulated population growth rates increased slightly for plants protected from ungulates, and 95% confidence intervals spanned the stable population growth rate of 1. With exclusion of ungulates and rodents, sapling and small tree recruitment rates for both species far exceeded those needed to offset the rate of recent adult mortality, with modeled population growth rates of 1.07–1.11. Our results underscore the essential role of occasional high rainfall years for initial establishment, plus the key role of consumers in limiting early survival and growth of both evergreen and deciduous oaks in mixed oak savannas.

Long-Term Impacts of Exotic Grazer Removal on Native Shrub Recovery, Santa Cruz Island, California

A combination of overgrazing and exotic species introduction has led to the degradation of habitats worldwide. It is often unclear whether removal of exotic ungulates will lead to the natural reestablishment of native plant communities without further management inputs. I describe here my return to sites on Santa Cruz Island, California, 12 years after initial sampling in order to gain a long-term view on native shrub reestablishment into exotic grasslands after exotic grazer removal. Santa Cruz Island was grazed by feral sheep and cattle for over a century; these exotic grazers were removed in the late 1980s and feral pigs were removed in 2005–2006. I resampled 5 sites on south-facing slopes in the Central Valley of the island to quantify native shrub cover, density, and size. Previous data suggested that one species, Eriogonum arborescens, would be able to naturally recruit in exotic grass–dominated areas. Native shrubs have shown a modest increase in cover over time, although more striking was a sharp increase in the amount of dead shrub cover and density. Recruitment events during high rainfall years probably led to the slight increase in Eriogonum cover between sampling periods. Recent drought periods, however, have probably increased mortality and otherwise slowed shrub reestablishment in these arid sites.

Inter-comparison of water balance components of river basins draining into selected delta districts of Eastern India

Quantification of hydrological components in-terms of surface runoff, stream flow and evapotranspiration is important and useful in planning and management of water resources across the river basin, including downstream delta regions. River deltas water availability; management and related disaster risk are largely influenced by the hydrological state of upstream river basins. The paper presents the results of hydrological modelling (SWAT) based long-term water balance components in river basins draining into selected delta Districts of Eastern India. Mahanadi, Brahmani-Baitarani river basins and Hooghly river and adjacent small river basins are considered. The long-term water balance components of Mahanadi and Brahmani-Baitarani river basins are similar and significantly different in Hooghly river and adjacent small river basins. The runoff coefficient is significantly higher in Hooghly river and adjacent small river basins at 0.39 compared to other two river basins (0.247 & 0.256). The evapotranspiration component is relatively low in Hooghly river and adjacent small river basins with smaller range of long-term variation. The time-series model outputs brought out the basin-specific hydrological response variations in low and high rainfall years such as changes in fraction of evapotranspiration and surface runoff. Mahanadi and Brahmani-Baitarani river basins exhibit large inter-annual variation in evapotranspiration, surface runoff fractions. The developed hydrological modelling framework is capable of incorporating future climate data and to predict the basin-scale future water availability, demand, use and to bring out resulting water scenarios that would impact river deltas in-terms of their exposure towards water related adversities, such as drought and flood.

Bayesian Bias Correction of Satellite Rainfall Estimates for Climate Studies

Advances in remote sensing have led to the use of satellite-derived rainfall products to complement the sparse rain gauge data. Although these products are globally and some regional bias corrected, they often show substantial differences relative to ground measurements attributed to local and external factors that require systematic consideration. A decreasing rain gauge network inhibits the continuous validation of these products. Our proposal to deal with this problem was to use a Bayesian approach to merge the existing historical rain gauge information to create consistent satellite rainfall data for long-term applications. Monthly bias correction was applied to Climate Hazards Group Infrared Precipitation with Stations (CHIRPS v2) using a corresponding gridded (0.05°) rain gauge data over East Africa for 33 years (1981–2013). The first 22 years were utilized to derive error fields which were then applied to independent CHIRPS data for 11 years for validation. Assessments of the approach’s influence on the rainfall estimates spatially and temporally were explored. Results showed a significant spatial reduction of the underestimation and overestimation of systematic errors at both monthly and yearly scales. The reduced errors increased with increased rainfall amounts, hence was less so in the relatively drier months. The overall monthly reduction of Root Mean Square Difference (RMSD) was between 4% and 60%, and the Mean Absolute Error (MAE) was between 1% and 63%, while the correlations improved by up to 21%. Yearly, the RMSD was reduced between 17% and 49%, and the MAE between 13% and 48%, while the increase in correlations was between 9% and 17%. Decreased yearly bias correction corresponded with years of high rainfall associated with El Niño. Results for the assessments of the effectiveness of the Bayesian approach showed that it was more effective in reducing systematic errors related to rainfall magnitudes, but its performance decreased in areas of sparse rain gauge network that insufficiently represented rainfall variabilities. This affected areas of deep convection, leading to minimal overestimation reductions associated with the cirrus effect. Conversely, significant corrections were during years of low rainfall from shallow convections. The approach is suitable for long-term applications where consistencies of mean errors can be assumed.

Nestedness patterns reveal impacts of reduced rainfall on seedling establishment in restored jarrah forest

Directional climate change can potentially cause a nested pattern of species occurrences as species move or go extinct. That is, species-poor communities may become a nested subset of species-rich communities. There is a precedent for understanding these patterns in the context of historical climate change but few researchers have studied these patterns in the context of recent changes to climate. Here we show the value of nestedness analyses for understanding plant community responses to reduced annual rainfall using data on seedling establishment in restored jarrah forest between the years of 1992 and 2010. Specifically, we recorded the annual seedling establishment of species assemblages in plots 15 months after restoration. We tested to what extent jarrah-forest assemblages that established in low (<1000 mm) rainfall years were nested within assemblages that established in years of moderate (1000–1200 mm) and high (>1200 mm) rainfall, and whether assemblages established following lower standard restoration practice were nested subsets of those following higher standard practices. We also tested how both types of nestedness patterns varied among trait groups defined by status (i.e., native or non-native), life-form and seed size. We found high support for species and trait assemblages that established in dry years being a nested subset of assemblages that established in years of moderate rainfall, and consistently low support for nestedness of high in low, and moderate in low, rainfall years. Nestedness patterns associated with restoration practice were as we predicted. Recruitment failure in low rainfall years was the most parsimonious explanation for nestedness patterns associated with rainfall (i.e., selective environmental tolerance). Nestedness patterns associated with restoration practice were explained by differential seed dispersal of species via topsoil and their tolerance of inferior restoration practice. Taken together, we demonstrate the application of the nestedness approach for understanding community responses to climate change in a restoration context. Indeed, generalising species responses to climate change by linking these to ecological processes and traits will help to meet the current global demand for forest restoration. Therefore, we anticipate our findings will interest practitioners working to restore the world’s forests under climate change.

Longevity and population age structure of the arroyo southwestern toad (Anaxyrus californicus) with drought implications.

The arroyo southwestern toad is a specialized and federally endangered amphibian endemic to the coastal plains and mountains of central and southern California and northwestern Baja California. It is largely unknown how long these toads live in natural systems, how their population demographics vary across occupied drainages, and how hydrology affects age structure. We used skeletochronology to estimate the ages of adult arroyo toads in seven occupied drainages with varying surface water hydrology in southern California. We processed 179 adult toads with age estimates between 1 and 6 years. Comparisons between skeletochronological ages and known ages of PIT tagged toads showed that skeletochronology likely underestimated toad age by up to 2 years, indicating they may live to 7 or 8 years, but nonetheless major patterns were evident. Arroyo toads showed sexual size dimorphism with adult females reaching a maximum size of 12 mm greater than males. Population age structure varied among the sites. Age structure at sites with seasonally predictable surface water was biased toward younger individuals, which indicated stable recruitment for these populations. Age structures at the ephemeral sites were biased toward older individuals with cohorts roughly corresponding to higher rainfall years. These populations are driven by surface water availability, a stochastic process, and thus more unstable. Based on our estimates of toad ages, climate predictions of extreme and prolonged drought events could mean that the number of consecutive dry years could surpass the maximum life span of toads making them vulnerable to extirpation, especially in ephemeral freshwater systems. Understanding the relationship between population demographics and hydrology is essential for predicting species resilience to projected changes in weather and rainfall patterns. The arroyo toad serves as a model for understanding potential responses to climatic and hydrologic changes in Mediterranean stream systems. We recommend development of adaptive management strategies to address these threats.

Competition reverses the response of shrub seedling mortality and growth along a soil moisture gradient

Abstract Predicting species responses to climate change involves understanding both the direct effects of environmental change, as well as indirect effects mediated by altered interspecific interactions. Indirect effects may be particularly important for understanding native species responses in systems invaded by highly competitive exotic species. For instance, Mediterranean climate regions are predicted to experience more frequent drought, and are increasingly invaded by exotic annual plants. For native shrubs in these regions, seedling establishment is episodic, and associated with high rainfall years. However, exotic annual plants also often increase in abundance with high rainfall, suggesting competition from exotic annual species could alter the relationship between rainfall and shrub seedling establishment. Theories such as the stress gradient hypothesis predict competition intensity should increase with resource supply, but there have been few evaluations of competitive interactions across experimental gradients of soil moisture availability. Here we examined how competition from an exotic annual influenced native shrub establishment, across an experimental soil moisture gradient. Seedlings of two native shrub species (Encelia californica and Eriogonum fasciculatum) were grown with and without an exotic grass competitor (Avena fatua) across eight water availability levels, and monitored for growth and survival. These species are common and abundant in the Mediterranean climate region of coastal Southern California, where climate change projections include long‐term drought for the coming decades. Without competition, shrub seedlings achieved higher growth and survival at high water availability levels. However, when grown in competition with the exotic grass, shrub seedlings had higher growth and/or survival under relatively dry conditions, suggesting competition can modify and even reverse species responses to changing rainfall patterns, compared to predictions made in the absence of competitors. The exotic grass strongly reduced soil nitrate and water availability when it was planted with the native shrub seedlings, and the exotic grass responded with positive but saturating growth with increasing levels of water addition. Synthesis. This experiment demonstrates that competition from invasive species can alter native species responses to climate change; consistent with ecological theories predicting a positive association between the supply of limiting resources and the intensity of competition.

Effects of chaining and burning in Acacia ramulosa shrublands of the Peron Peninsula, Shark Bay, Western Australia

We tested the effect of chained and burnt buffers installed across the Peron Peninsula at Shark Bay, Western Australia, in 1995 on the plant communities. Chaining modified fuel by flattening shrubs to provide a more continuous fuel bed by adding vertically arranged shrub fuel to the in situ sparse ground fuels. Twenty-six, 10 × 10-m permanent plots were established in the treated buffers and adjacent untreated shrubland. Plots were evaluated in 1996, 2001 and 2008. By 1996, fire and chaining had promoted a suite of species that included 29 not observed in adjacent untreated shrubland. High rainfall before the 2001 assessment produced an increase in species richness in both burnt and unburnt treatments. By 2008, 20 of the 29 fire-promoted species were found in the untreated area after rainfall leaving nine species uniquely responsive to the fire and chaining treatment. The Acacia ramulosa W.Fitzg. sandplain communities in our study area appear to be sustained by high rainfall years promoting regeneration of 84% of species with a smaller proportion (16%) regenerated only in burnt areas. The dominance of periodic rainfall in promoting regeneration led to the likely reduced effectiveness of the fire buffers in preventing the spread of fire. There is the potential for extensive fires in this landscape following favourable rainfall.

The impact of inter-annual rainfall variability on African savannas changes with mean rainfall

Savannas are mixed tree-grass ecosystems whose dynamics are predominantly regulated by resource competition and the temporal variability in climatic and environmental factors such as rainfall and fire. Hence, increasing inter-annual rainfall variability due to climate change could have a significant impact on savannas. To investigate this, we used an ecohydrological model of stochastic differential equations and simulated African savanna dynamics along a gradient of mean annual rainfall (520–780 mm/year) for a range of inter-annual rainfall variabilities. Our simulations produced alternative states of grassland and savanna across the mean rainfall gradient. Increasing inter-annual variability had a negative effect on the savanna state under dry conditions (520 mm/year), and a positive effect under moister conditions (580–780 mm/year). The former resulted from the net negative effect of dry and wet extremes on trees. In semi-arid conditions (520 mm/year), dry extremes caused a loss of tree cover, which could not be recovered during wet extremes because of strong resource competition and the increased frequency of fires. At high mean rainfall (780 mm/year), increased variability enhanced savanna resilience. Here, resources were no longer limiting and the slow tree dynamics buffered against variability by maintaining a stable population during ‘dry’ extremes, providing the basis for growth during wet extremes. Simultaneously, high rainfall years had a weak marginal benefit on grass cover due to density-regulation and grazing. Our results suggest that the effects of the slow tree and fast grass dynamics on tree-grass interactions will become a major determinant of the savanna vegetation composition with increasing rainfall variability.

Optimizing nitrogen fertilizer rates and time of application for potatoes under seepage irrigation

Splitting N fertilizer application is recommended to increase crop N use efficiency by reducing risk of leaching. The objective of this study was to optimize the timing and rate of split N fertilizer applications to maximize tuber yield and quality of chipping potatoes grown using seepage irrigation in Florida. A two-year study was conducted on two commercial farms using cultivars Atlantic and FL1867. A factorial of two N rates applied at pre-plant (Npre-pl) 0 or 56kgha−1 30days before planting followed by four N rates applied at plant emergence (Nemerg) 0, 56, 112, or 168kgha−1 were randomized in a complete block design with four replicates. At tuber initiation, all treatments received an additional 56kgha−1 of N. All applications of N were of granular ammonium nitrate banded. Total N applied for the various treatments ranged from 56 to 280kgha−1 of N. Soil N was monitored in the 0–20cm soil depth layer throughout the season. Whole plant biomass peaked at 8.5–8.7Mgha−1 with Nemerg rates between 112–143kgha−1. Plant N uptake range from 66 to 157kgha−1. N uptake use efficiency decreased with increasing N rates. Potato yield ranged from 25 to 42Mg ha−1 in both years. In 2013, application of 56kgha−1 of Npre-pl produced 2.5–5.1Mgha−1 higher yield than treatments receiving 0N. In 2014, there was an interaction between Npre-pl and Nemerg on yield. The higher 56kgha−1 Npre-pl resulted in higher yield only when Nemerg was at or below 56kgha−1. For cv. Atlantic when no Npre-pl was supplied, yield increased linearly in response to Nemerg rates, while with 56kgha−1 of Npre-pl, yield responded quadratically to Nemerg reaching a maximum at 114kgha−1. For cv. FL1867 yield increased quadratically to Nemerg peaking at 138 and 126kgha−1 of when 0 or 56kgha−1 of Npre-pl was applied, respectively. The study shows that while the risk of Npre-pl loss is high, Npre-pl can result in higher yield, especially when subsequent N rates are low. Application of Npre-pl was particularly effective in a dry year. By contrast, when soil mineral N from Npre-pl was largely lost to leaching in a high rainfall year, yield was increased by the Npre-pl application only when subsequent Nemerg rates were less than 112kgha−1. When early-season soil N was low, the Nemerg had a larger impact on tuber yield due to minimum loss to leaching, maximizing yield when Nemerg was 128–168kgha−1. This indicates that applying N fertilizer prior to emergence is necessary to maximize tuber yield.

Evaluation of nitrogen fertilizer additives for enhanced efficiency in corn on Iowa soils

Recent years of high rainfall and prolonged wet soil conditions in Iowa have renewed interest to protect losses of fertilizer nitrogen (N) in corn. This study evaluated effect of N additives and a slow‐release urea product on the soil NO3–N fraction of total inorganic N, mid–vegetative growth N stress, grain yield, and corn nitrogen use efficiency. Earn 1 CEU in Nutrient Management by reading this article and taking the quiz at www.certifiedcropadviser.org/education/classroom/classes/516.

The effect of consumer pressure and abiotic stress on positive plant interactions are mediated by extreme climatic events.

Environmental extremes resulting from a changing climate can have profound implications for plant interactions in desert communities. Positive interactions can buffer plant communities from abiotic stress and consumer pressure caused by climatic extremes, but limited research has explored this empirically. We tested the hypothesis that the mechanism of shrub facilitation on an annual plant community can change with precipitation extremes in deserts. During years of extreme drought and above-average rainfall in a desert, we measured plant interactions and biomass while manipulating a soil moisture gradient and reducing consumer pressure. Shrubs facilitated the annual plant community at all levels of soil moisture through reductions in microclimatic stress in both years and herbivore protection in the wet year only. Shrub facilitation and the high rainfall year contributed to the dominance of a competitive annual species in the plant community. Precipitation patterns in deserts determine the magnitude and type of facilitation mechanisms. Moreover, shrub facilitation mediates the interspecific competition within the associated annual community between years with different rainfall amounts. Examining multiple drivers during extreme climate events is a challenging area of research, but it is a necessary consideration given forecasts predicting that these events will increase in frequency and magnitude.

Strip cropping system as a climate adaptation strategy in semi-arid Alfisols of South Central India

A two year (2013-2015) field experiment was conducted to assess the efficiency of rainfed strip intercropping of sorghum (S) and pigeonpea (PP) under 4:4 replacement series in comparison with 2:1 intercropping under additive series for system productivity, economic efficiency and farm family food security. There were three treatment combinations (S+ PP –relay horsegram (HG), S+ PP -ratoon S and S+ PP -sequence HG) accommodating an opportune crop of relay or sequence HG to be tested against checks of sole crops. S and PP strip system in a high rainfall year (2013)yielded 31% higher grain than 2:1 S and PP intercropping, but such advantages were not observed during a deficit rainfall year (2014). Significant PP yield increase during a high rainfall year in a strip system increased both water productivity (10.1 to 16.5 kg/ha/mm) and net returns (Reupees 57490 to 71680/year). Similarly, during high rainfall year (2013), a superior diverse index (1.63 over 1.19) and production efficiency (19.6 over 13.5 kg/ha/day) was observed.Both relay/sequence cropped HG performed equally well while ratoon S performed poorly. Therefore, for changing climate, 4:4 strip intercropping of S and PP showed higher productivity and economic returns as compared to 2:1 intercropping system. Opportune cropping through relay or sequence HG can be successfully carried out in semi-arid regions during post monsoon season for climate change adaptation.

Modeling the Effects of Biogenic NOX Emissions on the South African Highveld and Waterberg Regions

The Highveld and Waterberg regions in South Africa contain extensive coal fields and therefore have a high concentration of coal-fired power stations. Previous studies assessed the impact of atmospheric deposition of S- and N-containing species from anthropogenic sources in the region but did not include the effect of biogenic emissions. This study models biogenic NOX soil emissions for the regions and includes them in an atmospheric dispersion model to study the effects of biogenic emission on nitrogen deposition rates. Simulated sulfur deposition rates for the Highveld area are also reported on. Anthropogenic and biogenic sulfur and nitrogen emission sources were inventoried for the Highveld and Waterberg regions. Using previous work by Yienger and Levy, biogenic soil NOX emissions were quantified by constructing models for both areas using land use data, rainfall data, and atmospheric ground level temperatures from CALMET data. A CALPUFF dispersion model was used to predict deposition rates for S- and N-containing species with and without biogenic NOx emissions to determine the impact of biogenic emissions for the Highveld. As rainfall is highly variable in the region, meteorological data representative of high, average, and low rainfall years was used to determine the effect of rainfall on deposition rates for the various species. The biogenic NOx made up 3.96, 4.14, and 3.34% of total released NOx for 2001 (average rainfall), 2003 (low rainfall), and 2010 (high rainfall), respectively. Dry nitrogen deposition rates were affected most by the biogenic component, adding from 1.7 to 6.2% at various receptor locations. Wet deposition rates were affected very little (0.13 to 0.75%). Effect on total nitrogen deposition rates ranged from 0.32 to 1.77%. Biogenic emissions for the Waterberg area, being more arid, were calculated to be only 2.3% of total NOx emissions for the area and accordingly have little effect on deposition rates.

Evaluation of Nitrogen Fertilizer Additives for Enhanced Efficiency in Corn on Iowa Soils

Core Ideas Landscape position was selected and N fertilizer treatments were designed to promote significant denitrification and enhanced potential volatilization. No agronomic benefit was found using urea with nitrification and urease inhibitors or urea with a polymer coating. Lack of response to inhibitor products and coated urea were likely due to rainfall timing and amount shortly after application, reduced volatilization due to high soil retention of NH4, and slowed nitrification rates from cool soil temperatures after application. Recent years of high rainfall and prolonged wet soil conditions in Iowa have renewed interest to protect losses of fertilizer nitrogen (N) in corn (Zea mays L.). This study evaluated effect of N additives and a slow‐release urea product on the soil NO3–N fraction of total inorganic N, mid–vegetative growth N stress, grain yield, and corn nitrogen use efficiency (NUE). Field trials were conducted at two Iowa State University Research Farms in 2013 and 2014. Sites were selected for probable response to applied N with different nitrification product treatments and coated urea (fine‐textured soils that were poorly drained with high organic matter) and urease inhibitor products (incorporated vs. unincorporated). Urea and treated urea were applied at 120 lb N/acre and incorporated and left on the surface. Overall, there was no agronomic benefit from using urea with nitrification inhibitors (Instinct and SuperU), urea with urease inhibitors (Agrotain, SuperU, and Factor), or urea with a polymer coating (Environmentally Smart Nitrogen). Lack of response to nitrification and urease products was potentially due to climatic conditions during the study. Significant rainfall shortly after N application moved urea into the soil profile (minimizing NH3 volatilization) and slowed nitrification rates from cool temperatures early in the season.

Increased productivity in wet years drives a decline in ecosystem stability with nitrogen additions in arid grasslands.

Adding nutrients to nutrient-limited ecosystems typically lowers plant diversity and decreases species asynchrony. Both, in turn, decrease the stability of productivity in the response to negative climate fluctuations such as droughts. However, most classic studies examining stability have been done in relatively wet grasslands dominated by perennial grasses. We examined how nutrient additions influence the stability of productivity to rainfall variability in an arid grassland with a mix of perennial and annual species. Of the nutrients, only nitrogen increased productivity, and only in wet years. In addition, only nitrogen decreased the stability of productivity. Thus, nutrient addition makes ecosystem productivity less stable in both wet and arid grasslands. However, the mechanism is very different. In contrast to wet grasslands, adding nitrogen to an arid grassland did not decrease diversity. Rather, stability decreased with nitrogen addition due to an increase in annual species that increased productivity. In other words, in our arid grassland, nitrogen addition decreased ecosystem stability because of increased ecosystem responsiveness to positive climate fluctuations. These climate fluctuations were facilitated by annual species that take advantage of wet years and can escape dry years as seeds. Our data support the conclusion that nutrient additions decrease the stability of productivity in both wet and arid grasslands. Nutrient enrichment increases the sensitivity of productivity to low rainfall years in wet grasslands, whereas nutrient enrichment in arid grasslands increases the sensitivity of productivity to high rainfall years.

Local weather and regional climate influence breeding dynamics of Mountain Bluebirds (Sialia currucoides) and Tree Swallows (Tachycineta bicolor): a 35-year study

Many songbirds are under increasing pressure owing to habitat loss, land-use changes, and rapidly changing climatic conditions. Using citizen science data collected from 1980 to 2014, we asked how local weather and regional climate influenced the breeding dynamics of Mountain Bluebirds (Sialia currucoides (Bechstein, 1798)) and Tree Swallows (Tachycineta bicolor (Vieillot, 1808)). Mountain Bluebird reproduction was strongly associated with local weather: number of nestlings and fledglings both decreased in years of high rainfall. Clutch size and number of fledglings also declined over the study period. Abundance of Mountain Bluebirds was higher in years of lower early-season snowfall and warmer local temperatures, as well as more negative Southern Oscillation Index (SOI) values, indicating a positive influence of El Niño conditions. Tree Swallow reproduction (clutch size, number of nestlings, and number of fledglings) was negatively associated with SOI values, and the number of Tree Swallow nestlings decreased in years of higher rainfall and warmer temperatures. Tree Swallows also showed a marked decline in abundance over the period of the study, consistent with recent range-wide declines. Together, our results demonstrate that local weather and regional climate differentially affect the reproductive dynamics of Mountain Bluebirds and Tree Swallows and highlight the importance of long-term citizen science data sets.