Site-years Of Data Research Articles

AmeriFlux BASE data pipeline to support network growth and data sharing

AmeriFlux is a network of research sites that measure carbon, water, and energy fluxes between ecosystems and the atmosphere using the eddy covariance technique to study a variety of Earth science questions. AmeriFlux’s diversity of ecosystems, instruments, and data-processing routines create challenges for data standardization, quality assurance, and sharing across the network. To address these challenges, the AmeriFlux Management Project (AMP) designed and implemented the BASE data-processing pipeline. The pipeline begins with data uploaded by the site teams, followed by the AMP team’s quality assurance and quality control (QA/QC), ingestion of site metadata, and publication of the BASE data product. The semi-automated pipeline enables us to keep pace with the rapid growth of the network. As of 2022, the AmeriFlux BASE data product contains 3,130 site years of data from 444 sites, with standardized units and variable names of more than 60 common variables, representing the largest long-term data repository for flux-met data in the world. The standardized, quality-ensured data product facilitates multisite comparisons, model evaluations, and data syntheses.

A soil-air temperature model to determine the start of season phenology of deciduous forests

Forest ecosystems play a major role in sequestering atmospheric carbon dioxide, which can help offset the detrimental effects of anthropogenic carbon emissions. However, climate change has and will continue to affect the phenology of forest ecosystems’ carbon uptake, changing both the “carbon uptake transition date” - when forests shift from being a net carbon source to sink - and the “green-up date” reflecting the onset of bud burst. Previous studies have shown that a forest's carbon uptake transition date correlates to the date when soil temperature warms enough to surpass mean annual air temperature (soil-air temperature model). However, we still don't know if this simple relationship holds across different sites or over longer time periods. In this study, we explore the relationship between climate and both types of phenological transition dates using over 200 site years of data between 1997 and 2022. Using flux tower data from 18 sites across North America and Europe, we derive three potential carbon uptake transition dates corresponding to the dates when 10%, 25%, and 50% of seasonal net ecosystem exchange (NEE) amplitude is reached. Using PhenoCam data, we then derive three potential green-up dates corresponding to when 10%, 25%, and 50% of total seasonal green chromatic coordinate (GCC) is reached (the greenness model). We evaluate our model estimates using concordance coefficients, a metric of agreement between two measures, to determine which process, carbon uptake or budburst, is best predicted by the soil-air temperature model and to what extent. We find that variation in phenological relationships can be attributed to different regional and bioclimatic groups, highlighting potential biome-specific strengths and limitations of the soil-air temperature model. This model offers a simple approach to better understand phenological transitions and identify potential and limitations for a simple universal SOS prediction approach in deciduous forests.

Modeled Surface‐Atmosphere Fluxes From Paired Sites in the Upper Great Lakes Region Using Neural Networks

AbstractThe eddy covariance (EC) method is one of the most widely used approaches to quantify surface‐atmosphere fluxes. However, scaling up from a single EC tower to the landscape remains an open challenge. To address this, we used 63 site years of data to examine simulated annual and growing season sums of carbon fluxes from three paired land‐cover type sites of corn, restored‐prairie, and switchgrass ecosystems. This was also done across the landscape by modeling fluxes using different land‐cover type input data. An artificial neural network (ANN) approach was used to model net ecosystem exchange (NEE), ecosystem respiration (Reco), and gross primary production (GPP) at one paired site using environmental observations from the second site only. With a mean spatial separation of 11 km between paired sites, we were able to model annual sums of NEE, Reco, and GPP with uncertainties of 20%, 22%, and 8%, respectively, relative to observation sums. When considering the growing season only, model uncertainties were 17%, 22%, and 9%, respectively for the three flux terms. We also show that ANN models can estimate sums of Reco and GPP fluxes without needing the constraint of similar land‐cover‐type, with annual uncertainties of 12% and 10%. These results provide new insights to scaling up observations from one EC site beyond the footprint of the EC tower to multiple land‐cover types across the landscape.

Standardized flux seasonality metrics: a companion dataset for FLUXNET annual product

Abstract. Phenological events are integrative and sensitive indicators of ecosystem processes that respond to climate, water and nutrient availability, disturbance, and environmental change. The seasonality of ecosystem processes, including biogeochemical fluxes, can similarly be decomposed to identify key transition points and phase durations, which can be determined with high accuracy, and are specific to the processes of interest. As the seasonality of different processes differ, it can be argued that the interannual trends and responses to environmental forcings can be better described through the fluxes' own temporal characteristics than through correlation to traditional phenological events like bud break or leaf coloration. Here we present a global dataset of seasonality or phenological metrics calculated for gross primary productivity (GPP), ecosystem respiration (RE), latent heat (LE), and sensible heat (H) calculated for the FLUXNET2015 Dataset of about 200 sites and 1500 site years of data. The database includes metrics (i) on an absolute flux scale for comparisons with flux magnitudes and (ii) on a normalized scale for comparisons of change rates across different fluxes. Flux seasonality was characterized by fitting a single-pass double-logistic model to daily flux integrals, and the derivatives of the fitted time series were used to extract the phenological metrics marking key turning points, season lengths, and rates of change. Seasonal transition points could be determined with a 90 % confidence interval of 6–11 d for GPP, 8–14 d for RE, 10–15 d for LE, and 15–23 d for H. The phenology metrics derived from different partitioning methods diverged, at times significantly. This Flux Seasonality Metrics Database (FSMD) can be accessed at the US Department of Energy's (DOE) Environmental Systems Science Data Infrastructure for a Virtual Ecosystem (ESS-DIVE, https://doi.org/10.15485/1602532; Yang and Noormets, 2020). We hope that it will facilitate new lines of research, including (1) validating and benchmarking ecosystem process models, (2) parameterizing satellite remote sensing phenology and PhenoCam products, (3) optimizing phenological models, and (4) generally expanding the toolset for interpreting ecosystems responses to changing climate.

Annual NO2 as a Predictor of Hourly NO2 Variability: Do Defra UK’s Heuristics Make Sense?

Background: In the UK an hourly objective exists for NO2 concentrations and assessment against this objective is required for various administrative purposes. The vast majority of NO2 measurement in the UK is non-hourly however. Thus, Defra guidance provides a heuristic to estimate hourly objective exceedance likelihood from an annual average. Methods: We examine the performance of this heuristic using a Europe wide dataset containing over 20,000 site-years of data, and perform a sensitivity test to account for data uncertainty. Results: The heuristic misses 64% of sites that break the hourly objective. The heuristic is neither a necessary nor sufficient condition for predicting hourly objective breaches. The sensitivity test reveals that the heuristic is input-fragile. Conclusions: The heuristic performs poorly, is weakly coupled to medical evidence, and work is needed to develop new short term exposure limits for NO2.

Predicting in-season maize (Zea mays L.) yield potential using crop sensors and climatological data

The environment randomly influences nitrogen (N) response, demand, and optimum N rates. Field experiments were conducted at Lake Carl Blackwell (LCB) and Efaw Agronomy Research Station (Efaw) from 2015 to 2018 in Oklahoma, USA. Fourteen site years of data were used from two different trials, namely Regional Corn (Regional) and Optimum N rate (Optimum N). Three algorithms developed by Oklahoma State University (OSU) to predict yield potential were tested on both trials. Furthermore, three new models for predicting potential yield using optical crop sensors and climatological data were developed for maize in rain-fed conditions. The models were trained/built using Regional and were then validated/tested on the Optimum N trial. Out of three models, one model was developed using all of the Regional trial (combined model), and the other two were prepared from each location LCB and Efaw model. Of the three current algorithms; one worked best at predicting final grain yield at LCB location only. The coefficient of determination R2 = 0.15 and 0.16 between actual grain yield and predicted grain yield was observed for Regional and Optimum N rate trials, respectively. The results further indicated that the new models were better at predicting final grain yield except for Efaw model (R2 = 0.04) when tested on optimum N trial. Grain yield prediction for the combined model had an R2 = 0.31. The best yield prediction was obtained at LCB with an R2 = 0.52. Including climatological data significantly improved the ability to predict final grain yield along with using mid-season sensor data.

Corn Response Across Plant Densities and Row Configurations for Different Moisture Environments

Corn (Zea mays L.) production in the Southeast can be negatively impacted by erratic summer rainfall and drought-prone, coarse-textured soils, but irrigation combined with conservation tillage and cover crops may support greater plant densities arranged in different row configurations to improve yield. We examined five site-years of data across two soil types in Alabama to compare corn yields in a conservation system across three plant densities for single- and twin-row configurations in dryland and irrigated moisture regimes. Treatments were arranged with a split plot treatment restriction in a RCB design with three replications. Main plots were irrigation level (no irrigation and irrigation), and subplots were a factorial arrangement of three plant densities (5.9, 7.4, and 8.9 plants m−2) and row configurations (single and twin). A moisture environment (low and moderate) variable, defined by growing season rainfall, was used to average over site-years. In general, irrigation in the moderate-moisture environment improved each measured variable (plant height, stover yield, corn yield, and test weight) and decreased grain N concentration and aflatoxin levels compared to the low-moisture environment with no irrigation. Benefits of increased rainfall and irrigation to reduce soil moisture stress across drought-prone soils were evident. Pooled results across all site-years indicated no yield response as plant density increased, but greater yields were observed with the greatest plant densities in the moderate-moisture environments. No advantage for twin-row corn production was observed across five site-years in Alabama, which indicates either row configuration can be successfully adopted.

Relationship between mean square errors and wheat grain yields in long-term experiments

ABSTRACTWhen yield data from field experiments are combined, the impact of environment on treatment is ignored. The objectives of this work were to determine the frequency for combining year-to-year data. Grain yield mean square errors (MSE) were calculated by-year from two long-term winter wheat experiments (E222 and E502). These trials have been continuously planted to winter wheat (Triticum aestivum L), and both annually receive different nitrogen (N), phosphorus (P) and potassium (K) fertilizer rates. Relationships between average grain yields, coefficients of variation (CV), and MSE were evaluated over 42 and 41 years for E222 and E502, respectively. The F-statistics (large MSE/small MSE, 39 dfn, 39 dfd, alpha = 0.10) computed from 2 and 3 consecutive years were consistently more than the minimum F-value required to combine sites. For 83 site years of data, combining any 2 or 3 consecutive year periods was not advisable. Individual years should be analyzed and reported on independently.

Irrigated and rain-fed maize response to different nitrogen fertilizer application methods

ABSTRACTWith the demand for maize increasing, production has spread into more water limited regions. Couple this with increasing resource costs and environmental concerns and the need for efficient nutrient and water management practices has increased. The objective of this trial was to evaluate the effects of different nitrogen (N) fertilizer application methods and timings on maize grain yield, N use efficiency (NUE), and water use efficiency (WUE) under irrigated and rain-fed conditions. Four site-years of data were collected. Fertilizer treatments consisted of all N applied preplant, split surface applied, and split foliarly applied. Irrigation applied prior to and during reproductive growth increased grain yield, NUE, and WUE compared to rain-fed treatments for all site-years. Split surface applied N fertilizer applications typically increased NUE, but not always grain yield compared to preplant applications. The use of split foliar N fertilizer applications was only beneficial in the site-years when leaf burn was not as severe.

Cover Crop Impact on Weed Dynamics in an Organic Dry Bean System

Weed suppression is one possible benefit of including cover crops in crop rotations. The late spring planting date of dry beans allows for more growth of cover crops in the spring. We assessed the influence of cover crops on weed dynamics in organic dry beans and weed seed persistence. Medium red clover, oilseed radish, and cereal rye were planted the year before dry beans; a no-cover-crop control was also included. After cover-crop incorporation, common lambsquarters, giant foxtail, and velvetleaf seeds were buried in the red clover, cereal rye, and no-cover control treatments and then retrieved 0, 1, 2, 4, 6, and 12 mo after cover-crop incorporation. Dry beans were planted in June and weed emergence and biomass measured. Eleven or more site-years of data were collected for each cover-crop treatment between 2011 and 2013, allowing for structural equation modeling (SEM), in addition to traditional analyses. Cereal rye residue increased giant foxtail and velvetleaf seed persistence by up to 12%; red clover decreased common lambsquarters seed persistence by 22% in 1 of 2 yr relative to the no-cover-crop control. Oilseed radish and incorporated cereal rye rarely reduced weed densities. When red clover biomass exceeded 5 Mg ha−1, soil inorganic N was often higher (5 of 6 site-years), as were weed density and biomass (5 and 4 of 12 main site sample times, respectively). Using SEM, we identified one causal relationship between cover-crop N content and weed biomass at the first flower stage (R1), as mediated through soil N at the time of dry bean planting and at the stage with two fully expanded trifoliates. Increasing cover-crop C : N ratios directly reduced weed biomass at R1, not mediated through changes in soil N. Cover crops that make a significant contribution to soil N may also stimulate weed emergence and growth.

Safety Evaluation of Seven of the Earliest Diverging Diamond Interchanges Installed in the United States

Diverging diamond interchanges (DDIs) are increasingly popular because they provide improved traffic operations and cost savings. On the basis of theory, DDIs should be safer than conventional diamonds, but previous empirical safety studies have been limited. The objectives of this work were, therefore, to conduct a broader safety evaluation of DDIs and to recommend a crash modification factor (CMF) for the conversion of a conventional diamond to a DDI. The team analyzed seven of the earliest DDIs in the United States. Four were in Missouri and other sites were in Kentucky, New York, and Tennessee. The team collected more than 28 site years of crash and other data before intersection conversion and more than 19 site years of data after their conversion. The primary analysis was before and after with comparison sites to account for trends and potential simultaneous event biases. The results showed that crashes were reduced at most of the sites, and the team recommended a CMF of 0.67, meaning that installation of a DDI to replace a diamond should reduce all crashes by 33%. The reduction in injury crashes was even larger, with the team recommending a CMF of 0.59. Other analyses indicated that DDI installation should mean a substantial reduction of angle and turning crashes, with some reduction in rear-end crashes as well, although rear-end crashes will still be the dominant crash types after DDI installation. Clearly, DDIs offer potential safety benefits, and agencies should consider them strongly as replacements for conventional diamonds.

By-Plant Prediction of Corn (Zea mays L.) Grain Yield using Height and Stalk Diameter

Methods for determining midseason nitrogen (N) rates in corn have used the parameter normalized difference vegetation index (NDVI) and, in some cases, plant height. The objective of this study was to analyze the relationship of stalk diameter along with predictors of yield, including NDVI and plant height with grain yield. Five site-years of data were analyzed, where several rows of corn plants were selected, and yield from plants within the row was recorded individually. Measurements of stalk diameter, plant height, and NDVI were taken from growth stages V8–VT. Using a value of stalk diameter × plant height gave the best correlation with grain yield (r2 = 0.34, 0.55, 0.67; V8, V10, V12, growth stages respectively). This work showed that stalk diameter × plant height was positively correlated with by-plant corn grain yields, and this parameter could be used for refining midseason fertilizer N rates for growth stages V8–V12.

Wheat yield and quality as influenced by reduced tillage in organic farming

Organic farmers are interested in soil conservation by reduced tillage, techniques well known in conventional agriculture to protect soil quality and limit labor time and energy costs. However, organic farming and reduced tillage can modify weeds, soil structure, and thus soil nitrogen (N) mineralization which strongly influences wheat yield and quality. The main objectives of this study were to analyze how reduced tillage applied to organic wheat influenced (1) grain yield, protein concentration, and weed infestation; (2) deoxynivalenol (DON) contamination on grain; (3) technological quality parameters such as dry gluten, zeleny index, falling number, and gluten index; (4) protein composition (F1, F2, F3, F4, and F5 fractions, and UPP, gliadin/glutenin ratio); and (5) baking test. For this purpose, we analyzed five site-years of data from winter wheat crops where mouldboard ploughing and reduced tillage were compared in three experimental trials (two in France and one in Switzerland). Main results concern wheat yields: the effect of reduced tillage on wheat yield was influenced by several factors such as weed competition. No significant increase in mycotoxin content (DON) due to reduced tillage was detected. Contamination with DON was always below the European threshold for human consumption. The technological quality parameters were less affected by the tillage treatments than grain yield: protein content, gluten index, zeleny index, and falling number showed on average no significant difference between treatments although the protein composition was slightly different. The main results of this study are that the effect of reduced tillage on grain yield depends very much on soil type, weather conditions, and time after conversion, whereas there is only minor impact on wheat quality. This is in contrast to the hypothesis that reduced tillage under organic farming will cause problems in baking quality.

Biosphere-atmosphere exchange of CO<sub>2</sub> in relation to climate: a cross-biome analysis across multiple time scales

Abstract. The net ecosystem exchange of CO2 (NEE) varies at time scales from seconds to years and longer via the response of its components, gross ecosystem productivity (GEP) and ecosystem respiration (RE), to physical and biological drivers. Quantifying the relationship between flux and climate at multiple time scales is necessary for a comprehensive understanding of the role of climate in the terrestrial carbon cycle. Orthonormal wavelet transformation (OWT) can quantify the strength of the interactions between gappy eddy covariance flux and micrometeorological measurements at multiple frequencies while expressing time series variance in few energetic wavelet coefficients, offering a low-dimensional view of the response of terrestrial carbon flux to climatic variability. The variability of NEE, GEP and RE, and their co-variability with dominant climatic drivers, are explored with nearly one thousand site-years of data from the FLUXNET global dataset consisting of 253 eddy covariance research sites. The NEE and GEP wavelet spectra were similar among plant functional types (PFT) at weekly and shorter time scales, but significant divergence appeared among PFT at the biweekly and longer time scales, at which NEE and GEP were relatively less variable than climate. The RE spectra rarely differed among PFT across time scales as expected. On average, RE spectra had greater low frequency (monthly to interannual) variability than NEE, GEP and climate. CANOAK ecosystem model simulations demonstrate that "multi-annual" spectral peaks in flux may emerge at low (4+ years) time scales. Biological responses to climate and other internal system dynamics, rather than direct ecosystem response to climate, provide the likely explanation for observed multi-annual variability, but data records must be lengthened and measurements of ecosystem state must be made, and made available, to disentangle the mechanisms responsible for low frequency patterns in ecosystem CO2 exchange.

Maximum benefit of a precise nitrogen application system for wheat

Research is ongoing to develop sensor-based systems to determine crop nitrogen needs. To be economic and to achieve wide adoption, a sensor-based site-specific application system must be sufficiently efficient to overcome both the cost disadvantage of dry and liquid sources of nitrogen relative to applications before planting of anhydrous ammonia and possible losses if weather prevents applications during the growing season. The objective of this study is to determine the expected maximum benefit of a precision N application system for winter wheat that senses and applies N to the growing crop in the spring relative to a uniform system that applies N before planting. An estimate of the maximum benefit would be useful to provide researchers with an upper bound on the cost of delivering an economically viable precision technology. Sixty five site-years of data from two dryland winter wheat nitrogen fertility experiments at experimental stations in the Southern Plains of the U.S.A. were used to estimate the expected returns from both a conventional uniform rate anhydrous ammonia (NH3) application system before planting and a precise topdressing system to determine the value of the latter. For prices of $0.55 and $0.33 kg−1 N for urea-ammonium nitrate (UAN) and NH3, respectively, the maximum net value of a system of precise sensor-based nitrogen application for winter wheat was about $22–$31 ha−1 depending upon location and assumptions regarding the existence of a plateau. However, for prices of $1.10 and $0.66 kg−1 N for UAN and NH3, respectively, the value was approximately $33 ha−1. The benefit of precise N application is sensitive to both the absolute and relative prices of UAN and NH3.

No-Tillage Corn Hybrids Response to Starter Fertilizer

Starter fertilizer can help improve early-season corn (Zea mays L.) growth, especially under cool soil conditions, but corn hybrids may differ in their response to starter fertilizer. This study evaluated the response of corn hybrids to complete starter fertilizers applied under no-tillage, dryland conditions. Nine site-years of data were collected from 1993 through 1995 at four geographical locations: Doon (NW1) in extreme NW Iowa, Sutherland (NW2) in central NW Iowa, Lewis (SW), and Crawfordsville (SE). The soil types were as follows: NW1-Moody silty clay loam (fine-silty, mixed, superactive, mesic Udic Haplustolls); SW-Marshall silty clay loam (fine-silty, mixed, superactive, mesic Typic Hapludolls); SE-Nira silty clay loam (fine-silty, mixed, superactive, mesic Oxyaquic Hapludolls); and NW2-Primghar silty clay loam (fine-silty, mixed, superactive, mesic Aquic Hapludolls). Each hybrid was planted with and without starter fertilizer applied 2 in, to the side and 2 in, below the seed at planting. Hybrid-by-starter interactions were not significant for early-season dry matter production, nutrient concentration, or grain yield in any of the site-years, indicating that the hybrids, on average, responded similarly to starter fertilizer. Starter fertilizer increased early-season growth significantly in four of eight site-years and grain yield in seven of nine site-years. Average grain yield increases ranged from 4 bu/acre at the NW2 site in 1993 to 18 bu/acre at the SE site in 1995. Yield increases were not significant either year at the NW1 site. Increases in dry matter yield ranged from 18.7% at the SW site to 97.8% at the SE site in 1994. Starter fertilizer affected tissue K concentration to a much larger degree than it did N and P concentrations especially at the SE site. The results suggest that starter fertilizer will likely benefit no-tillage corn for most hybrids in the northern corn belt even on soils with adequate P and K.

Variability of monthly time fraction of excess of atmospheric propagation parameters

This paper investigates the variability of the monthly time fraction of excess of atmospheric propagation parameters. In the first part of the paper a theoretical investigation is carried out regarding the relationship between the variability of monthly time fraction of excess vis‐a‐vis the variability of the annual‐worst‐month time fraction of excess. It is shown that the tail of the distribution of the annual‐worst‐month time fraction of excess can be derived from the average distribution of the monthly time fraction of excess without requiring detailed knowledge of the seasonal behavior of the propagation. In the second part of the paper the modeling of the average distribution of the monthy time fraction of excess (the parent distribution) is investigated using some 92 site years of data (from slant path attenuation and transhorizon measurements). Three competing models were investigated: the conditional exponential, the conditional lognormal, and the shifted gamma distribution. For the testing of the suitability of the model a novel data pooling method is applied. The tests results show the shifted gamma model as the best model, followed by the conditional exponential model and then the conditional lognormal model.

Are there economic benefits of accessing forage in wolf plants of crested wheatgrass?

Wolf plants are common in many crested wheatgrass [Agropyron desertorum (Fischer ex Link) Schultes] pastures, and they represent an inefficient use of forage. The objective of this study was to determine costs and benefits of improving management to exploit the forage in wolf plants. Predictors of the forage left ungrazed in wolf plants (unused residual forage) and economic costs and benefits of improving management to make this forage available to grazing animals were determined using 40 site-years of data from southern and central Saskatchewan. Economic analyses were completed for management practices including: 1) no control of wolf plants, i.e. status quo grazing management; 2) no improvement in grazing management, but the forage is swathed and baled every 5, 10, or 15 yr; 3) burning at 5, 10, or 15-yr intervals, but grazing management is not changed, and; 4) swathing and baling hay once, followed by intensified grazing management involving cross-fencing of the pasture with a four-strand barbed wire or a single-strand electric fence. Unused residual forage in wolf plants averaged 417 kg ha−1 (SE = 7.5) and was correlated (R2 = 0.75, P ≤ 0.001) with total standing crop of wolf plants. On average about 41% of the total standing crop in wolf plants was unused residual forage. Density of wolf plants and dead standing crop were also significantly correlated (P ≤ 0.001) with unused residual forage in wolf plants; however, R2 values of 0.12 and 0.41 suggest that they are not actually strong predictors. Swathing and baling the crested wheatgrass every 5, 10 or 15 yr is economically feasible when unused residual forage in wolf plants averages about 200, 100 and 50 kg ha−1, respectively, whereas burning at the same intervals is profitable when unused residual forage exceeds about 400, 200 and 100 kg ha−1. Results of this research clearly show that substantial amounts of unused residual forage are present in pastures of crested wheatgrass that are dominated by wolf plants. Wolf plants are indicators of poor grazing management and potential economic loss. Management that encourages more uniform and complete use of this unused residual forage is economically beneficial in most situations. Key words: Agropyron desertorum (Fischer ex Link) Schultes, economic analysis, grazing management, pasture management, range improvements

Protein production and nitrogen utilization by barley cultivars in response to nitrogen fertilizer under varying moisture conditions

In a 3-yr field experiment, six barley cultivars — one conventional height malting type, two semidwarf, two conventional height, and one short feed type — were grown at three sites, with six nitrogen application rates ranging from 0 to 200 kg ha−1, to determine the effects of cultivar and N level on N utilization under varying moisture conditions. Nine site-years of data were divided into three levels, low, moderate, and high, based on estimated moisture supply. As moisture level increased, protein concentration of the barley cultivars decreased, while protein yield and total N uptake increased. Cultivars with higher grain yield tended to be lower in protein concentration, but higher in protein yield, total N uptake and N use efficiency than those with lower grain yields. Differences among the cultivars in protein concentration were greater at low than high moisture levels, while differences due to N application were greater at high than low moisture levels. Within the range of N applied, nitrogen use efficiency decreased at high N levels under low and moderate moisture conditions, but was relatively constant at high moisture levels. Protein concentration response to N applications differed slightly among cultivars at all moisture levels, but cultivar by N level interactions in protein yield response only occurred under high moisture conditions. Cultivars respond similarly to N applications in terms of straw N concentration, total N uptake and N use efficiency. Key words: N, nitrogen, barley (Hordeum vulgare), moisture, protein, N use efficiency

Yield response of semidwarf and conventional height barley cultivars to nitrogen fertilizer under varying moisture conditions

A 3-yr field experiment was conducted to evaluate the response of semi-dwarf and conventional height barley cultivars to N fertility. Six spring barley cultivars (one conventional height malting type, and two semidwarf, two conventional height, and one short feed type) were grown at three sites with nitrogen applications ranging from 0 to 200 kg ha−1. The 9 site-years of data were divided into three classes, low, moderate, and high, based on estimated moisture supply. Under low moisture conditions, grain yield response to applied N was low, but yield increased with applications to 200 kg ha−. Under moderate conditions, grain yield response to applied N was greater, but yield did not increase above 80 kg ha−1 of fertilizer N. No interaction was observed between barley cultivar and grain yield response to nitrogen under low or moderate moisture supply, although yields of Virden were higher than those of the other cultivars at most nitrogen levels. Under high moisture conditions, the feed barley cultivars showed a higher grain yield response to applied N than did the malting barley cultivar, Bonanza. The short-strawed cultivar, Heartland had a greater increase in yield with N application than the other cultivars. With a high moisture supply, yield of Bonanza did not increase with fertilizer N applications above 120 kg ha−1, while yield of the other cultivars was still increasing with application of 200 kg N ha−1. Differences among cultivars in grain response to N applications were largely due to differences in the harvest index. Key words: Nitrogen, barley (Hordeum vulgare), cultivar × N interaction, moisture