Individual- and scattered-tree influences on ultraviolet irradiance

Many of the potential effects of ultraviolet radiation (UVR)—damage to materials, altered herbivory of insects and activity of microbes, modified growth of vegetation, and adverse or beneficial effects on human health—are modified by the presence of trees that influence UVR exposure to various degrees. Though tree effects on total solar irradiance have been investigated often by measurements and modeling, tree influences on UVR, particularly in the ultraviolet B (UVB, 320–280 nm), differ substantially from tree influences on the rest of the solar spectrum, and thus the ratio of UVB to photosynthetically active radiation (PAR) is altered. Trees greatly reduce both UVB and PAR irradiance in their shade when they obscure both the sun and sky. Beneath dense forest canopies, relative irradiance (I_r=irradiancebeneath trees/above-canopy irradiance) for both UVB and PAR radiation may be 0.01–0.02. In the shade of a single tree, I_r on the horizontal in the PAR and total shortwave (SW) was about 0.1, whereas in the UVB and ultraviolet A (UVA, 320–400 nm), I_r was about 0.4. Conversely, where direct beam radiation came through gaps between crowns in a group of deciduous trees in winter, PAR I_r values averaged 0.95 and UVB I_r averaged only 0.41. In comparisons of minimum values of I_r on horizontal and the south-facing vertical surfaces in tree shade for UVB, UVA, SW, and PAR, where UVB I_r on the horizontal ranged from 0.22 to 0.62, depending on solar zenith angle, UVB I_r on the vertical ranged from 0.05 to 0.27. UVB I_r consistently exceeded UVA I_r on both the horizontal and vertical surfaces. PAR and SW I_r differed little between horizontal and vertical surfaces in tree shade. Modeled average I_r on the horizontal below a regular grid of ellipsoidal tree crowns was given byI_p=1−m−(θ^0.711/5.05)sin(πm), where m is fraction of area covered by tree crowns and θ is solar zenith angle. The tree influences will vary with pollutants in the boundary layer, which affect scattering of UVR.     

The influence of cloudiness on UV global irradiance (295–385 nm)

Two years of continuous measurements of UV (295–385 nm) irradiance recorded at Granada (37.18°N, 3.58°W, 660 m a.m.s.l.), Spain, were combined with concurrent synoptic cloud observations to establish the relative influence of clouds on UV irradiance. A marked influence of cloud cover on UV irradiance is evident, but negligible for fractional cloud coverage below 3 octas. The ratio of UV irradiance to the total solar irradiance increases with cloud cover, especially for cloud cover greater than 4 octas, highlighting the different effects of cloud on total solar irradiance and UV irradiance. In order to determine the effect of cloud on UV irradiance, we considered a cloud modification factor, defined as the ratio between the UV measurements and the corresponding clear sky UV irradiance that would be expected for the same time period and atmospheric conditions. It is shown that the effect of cloud for UV wavelengths is less than that for the whole solar spectrum and less than that for the visible part of the spectrum. On the other hand, the small influence of cloud cover for intermediate cloudiness was accompanied by low variability and variability increases with increasing cloud cover.     

Estimated and measured DNA, plant-chromosphere and erythemal-weighted irradiances at Barrow and South Pole (1979–2000)

In the last two decades as a consequence of ozone depletion there has been an increasing interest in the study of biological effects of ultraviolet radiation (UV). Spectral instruments, which provide detailed information on UV environmental conditions, have been in use systematically only for little more than a decade. These time series are still relatively short and information on spectral historical irradiance levels is not available. Many efforts have been carried out in inferring this information from other available data sets. One of them has been the use of statistical models. Spectral irradiances are available at South Pole (90°00′S 0) and Barrow (71°18′N, 156°47′W) from the NSF UV Radiation Monitoring Program since 1991. In the present paper, daily-integrated biologically weighted irradiances for these sites are inferred back to 1979 using a multi-regressive model, obtaining time series that extend near the beginning of the Antarctic ozone depletion. These datasets are unique since the daily-integrated irradiances were calculated from irradiance measured hourly at the earth’s surface. The biologically weighted irradiances are estimated from irradiance measured with broadband instruments, ozone, and solar zenith angles. From daily-integrated irradiance, monthly means were also calculated. The RMS errors between the estimated and measured daily-integrated irradiances range from 4.69 to 7.49% at South Pole and from 9.57 to 15.20% at Barrow, while the monthly mean errors vary from 2.07 to 3% and 2.95 to 3.91%, respectively. Completing the databases with spectral measurements, the resulting time series extend from 1979 to 2000. Analyzing monthly values an increase relative to 1979–1981 during all years is observed at South Pole. Largest increases are observed for DNA and plant-chromosphere weighted irradiances during October. Although at a lower rate, an increase is also observed at Barrow during the spring. Maximum monthly increase at South Pole during October is near 1200% relative to 1979–1981, while the increase at Barrow is near one tenth of that percentage. Daily-integrated irradiance shows that a slight increase was present during the spring at South Pole for the period 1979–1981 reflecting the beginning of the ozone depletion. Historical maximums of daily-integrated DNA weighted irradiance at South Pole (90°00′S, 0°00′) are about as large as summer maximums at San Diego (32°45′N, 117°11′W).     

Portable monitor for solar radiation that accumulates irradiance histograms for 32 leaf-mounted sensors

A novel and inexpensive instrument to monitor solar radiation interception at up to 32 locations simultaneously is described. It employs small-area, lightweight sensors that are leaf-mountable and have very good spectral and angular responses. A portable computer readily controls fast data acquisition and in-field processing to histograms, which are the most general irradiance measures to relate to nonlinear plant responses such as photosynthesis. Two field tests verified the instrument's reliability and operational convenience, and also directly compared radiation interception at space-fixed locations vs. nearby leaves. A number of new physiological and canopy-model tests that the instrument makes possible are described. The monitor is constructed from standard electronic components and may be readily modified for many expanded capabilities.     

SE—Structures and Environment: Optimal Control Strategies for Carbon Dioxide Enrichment in Greenhouse Tomato Crops—Part 1: Using Pure Carbon Dioxide

Two optimal control strategies for carbon dioxide (CO₂) enrichment in greenhouse tomato crops have been developed. One uses pure CO₂ from a storage tank and the other uses CO₂ contained in the exhaust gases of boilers burning natural gas. The optimal strategies maximize the financial margin between crop value and the combined costs of the CO₂ used for enrichment and the natural gas used for heating. In this paper, the strategy for optimal control using pure CO₂ is presented and compared with strategies used by growers. The optimal strategy for enrichment with exhaust gas derived CO₂ is presented in an accompanying paper. Simulations show that at a cost of £0·09 kg⁻¹ for pure CO₂ and £0·10 m⁻³ for natural gas, the optimal enrichment strategy would increase the annual margin of crop value over CO₂ and heating costs by £4·6 m⁻² (27%) compared to a basic control strategy of enrichment to a concentration of 1000 v.p.m. (parts per million by volume) when ventilators are <5% open, otherwise enrichment to 350 v.p.m. The optimal CO₂ concentration was expressed as an algebraic function of solar radiation, wind speed and ventilator opening angle, and so enabled a quasi-optimal value to be obtained using variables measured by greenhouse environmental controllers. The quasi-optimal equation, with coefficients averaged from simulations over 4 years, gave an increased margin over the basic control strategy of £4·4 m⁻² (26%).     

Sorption Isotherms of Tomato Slices and Onion Shreds

Experiments were conducted to determine the equilibrium moisture content of tomato (cv Roma) slices and white onion shreds at temperatures of 30, 40 and 50°C and relative humidities of 15–85% obtained from an air conditioning unit. The samples were placed on trays and the equilibrium moisture contents were determined once the samples attained the constant mass. The equilibrium moisture content–equilibrium relative humidity data were fitted to the modified Henderson, Chung-Pfost, modified Halsey, modified Oswin, and modified GAB models. The modified Henderson and modified Halsey models fitted well for the tomato slices and onion shreds, respectively, based on the coefficient of regression, mean relative percent error and standard error of moisture. The values of these parameters were, 0·985, 2·58 and 0·52, respectively, for the modified Henderson model for the sliced tomatoes and 0·991, 2·01 and 0·42, respectively, for the modified Halsey model for onion shreds.     

PH—Postharvest Technology: Physical Properties of Okra Seed

The physical properties of okra seed were evaluated as a function of moisture content (m.c.). The average length, breadth and thickness of the seed varied from 5·92 to 7·30, 4·71 to 5·40 and 4·59 to 5·36 mm, respectively, as the moisture content increased from 8·16 to 87·57% d.b. The roundness and sphericity increased from 77·76 to 79·35% and 74·48 to 76·52%, respectively, with increase in moisture content from 8·16 to 19·56% d.b. and then decreased to 72·39 and 70·63%, respectively, with further increase of moisture content. In the moisture range of 8·16–87·57%, the seed volume increased from 0·067 to 0·124 cm³, 1000 seed weight, W₁₀₀₀ from 65·78 to 129·75 g and the angle of repose from 27·60 to 39·47°. The bulk density, true density and porosity decreased from 0·592 to 0·558 g cm⁻³, 1·107 to 0·986 g cm⁻³ and 46·34 to 43·20%, respectively, in the moisture range from 8·16 to 87·57% d.b. The static coefficient of friction increased on four structural surfaces namely, aluminium (0·390–0·484), bakelite (0·345–0·480), galvanised iron (0·368–0·493) and mild steel (0·389–0·480) as the moisture content increased from 8·16 to 87·57% d.b.     

Ecophysiology of the cave isopod Mesoniscus graniger (Frivaldszky, 1865) (Crustacea: Isopoda)

Feeding biology and thermal adaptations of the terrestrial isopod Mesoniscus graniger were studied. M. graniger is a depigmented isopod mainly inhabiting cave systems, although it has also been reported in endogeic (soil) habitats. Physiological adaptations are expected to reflect the unique environmental characteristics of caves, including restricted food sources, and stable microclimate with temperatures not exceeding about 10 °C and high relative humidity. The M. graniger from Domica and Ardovská caves (Slovakian Karst) were investigated. We identified organic deposits with associated microorganisms as sources exploited by M. graniger and assessed how these might supply essential polyunsaturated fatty acids (PUFA) in its nutrition. Algae, fungi and bat guano were found as the most important potential resources of PUFA for isopods. Digestive enzymes amylase, trehalase, saccharase and maltase were confirmed in the whole body homogenates of isopods; neither cellulolytic activity nor activities against xylan, laminaran and lichenan were observed. Amylase, maltase and cellobiase activities were also observed in bacterial strains isolated and cultured from isopod midgut, and may account for the measured whole-animal activities. In an artificial temperature gradient, M. graniger selected temperature 3.5 ± 5.4 °C with lower and upper extremes of –1.5 and 18.5 °C. Respiration, as measured by VO₂, was almost independent of temperature between 5 and 10 °C, then increased between 10 and 30 °C. These ecophysiological measures are consistent with adaptation to a stenothermal environment.     

The topographic thresholds of hillslope incisions in southwestern Rwanda

This article presents new quantitative evidence that land use in Rwanda contributes to the development of hillslope incisions.Two types of hillslope incisions can be distinguished in southern Rwanda. Incisions of the first type drain an area depending on the form and extension on the natural topography and geology. The Runyinya gully (25°) and the Rugabano soil slippage (39°) are two examples. On a logarithmic plot of critical slope inclination at the incision head versus drainage area towards the incision head, both incisions lay sensibly to the right of the Montgomery–Dietrich (M-D) envelope. The latter gives the range of these topographical thresholds for gully and mass-wasting incision in parts of North America. The Runyinya and Rugabano cases obey the linear equation:

S_cr=(±0.6)A^−(±0.6)

where S_cr=critical slope gradient (tangent of slope in °) at the gully head or the scar and A=the area (ha) drained towards the incision head.Hillslope incisions of the second group rely on a run-on area larger than normal because they are localised at the ‘outlet’ of artificially runoff-collecting systems like roads, soil conservational contour trenches, tracks and other linear landscape elements. Such systems often drain a surface much larger in extension than the natural run-on area to the ‘outlet.’ These hillslope incisions, taking into account their artificially big drainage area, concentrate more or less along the line:

S_cr=(±0.3)A^−(±0.6)

This line is about in the center of the Montgomery–Dietrich envelope. If, however, only the natural drainage area of these ‘outlet’ incisions is taken into account, all points fall close to the left border or even to the left of the Montgomery–Dietrich envelope. This indicates a much higher probability for incision in those localities receiving supplementary runoff or interflow from outside the natural drainage area. In the case of a soil slippage at Rwaza Hill, detailed stability calculations show that the slope failure should be due to excessive water infiltration into the bottom of a trench. The digging of the trench provoked an increase in the area drained to the slippage head by a factor of 6.The phenomenon of ‘forward’ erosion is compatible with the existence of threshold combinations of slope and drained area. For slopes steeper than 7–8°, the phase of regressive erosion does often follow the forward incision event with a delay of several years or more.Finally, the scanty data set now available for Rwanda suggests that the drainage area critical to hillslope incision on the red-brown ferrallitic soils in Rwanda might be nearly twice as big as those in North America.     

PH—Postharvest Technology: The Effects of Grain Temperature on Breakage Susceptibility in Maize

To understand the viscoelastic characteristics (i.e. hardness) of the maize (Zea Mays L.) grain in relation to high-temperature drying, a breakage tester (HT-I drop tester) was developed and single-grain breakage at various grain temperatures and times after drying was determined. Both hard and soft maize hybrid varieties had minimal breakage at high grain temperatures (78–110°C), while decreasing grain temperature increased breakage exponentially. After drying at both 60 and 120°C, the percentage breakage measured at ambient temperature increased rapidly during cooling in air at an ambient temperature of 20°C and a relative humidity in the range 65–70%. Breakage reached a maximum after about 10 min from the start of cooling. A Mitscherlich function described the chronological development of percent grain breakage. Analysis of the function parameters for the extent (maximum) and rate of breakage indicated that there was a significant interaction between variety and drying temperature for the development of grain breakage after drying. These results indicated that grain temperature should be considered as a co-factor when assessing grain breakage susceptibility.     

Effect of long-term field exposure of soil to acetylene on nitrification,denitrification, and acetylene consumption

Coated CaC₂ is a newly developed product which can supply nitrification-inhibiting quantities of C₂H₂ (1–10 Pa) to the soil, throughout a cropping season. This method of applying C₂H₂ to the soil maintains C₂H₂ in the soil continuously for several months. It is not know whether these low C₂H₂ concentrations alter soil microbial processes. A field study was initiated to determine the effect of supplying C₂H₂ to a clay soil, using coated CaC₂, on soil respiration, denitrification, nitrification, and C₂H₂ consumption. The C₂H₂ consumption rate increased with length of soil exposure to C₂H₂ (r ²=0.59). The rates of CO₂ production (r ²=0.88) and denitrification (r ²=0.86) were both highly correlated with the C₂H₂ consumption rates. The nitrifier potential decreased to a minimum of 21% of the control after 3 months of C₂H₂ treatment. After this time, nitrifier activity increased to 41% of the control after 11 months of treatment. This increase was due to increased C₂H₂ consumption in the soil. After 3 months of continuous application of C₂H₂ to the soil, the C₂H₂ concentrations were generally below that necessary to inhibit nitrification. No adaptation to the C₂H₂ by nitrifiers was found. Repeating these measurements 1 year later showed that soils previously exposed to C₂H₂ retained their enhanced C₂H₂ oxidation capacity and the capacity to use C₂H₂ to increase denitrification. Nitrification potentials remained about 50% lower in soils exposed to C₂H₂ a year earlier compared to soils not previously exposed to C₂H₂.     

Field Data of Hydrogen Peroxide Concentrations in Urban and Mountain Air in Southwestern Poland

The concentrations of ambient gas-phase hydrogen peroxide were measured during the summer of 1998, 1999 and 2000. The experiments were performed in the city of Wroclaw and in the vicinity of Mount Szrenica, 1362 m a.s.l., Poland. Analysis was carried out by the chemiluminescence method. Typical mean ranges of 30 min H₂O₂ concentrations measured were 1.4–6.0 μg m^-3 at Mount Szrenica, whereas in the urban atmosphere H₂O₂ concentrations were in the range of 2.7–11.7 μg m^-3. In the case of the urban atmosphere, H₂O₂ concentrations were well correlated only with solar radiation and temperature. In the mountain air, H₂O₂ concentrations increased along with the increase of temperature, O₃, CO and the decrease of humidity. The diurnal variation was not only caused by photochemicalprocesses.     

Biodegradation of aged residues of atrazine and alachlor in a mix-load site soil

A selected microbial consortium (SMC) capable of degrading two specific herbicides, alachlor (2-chloro-2′,6′-diethyl-N-[methoxymethyl]-acetanilide; AL) and atrazine (2-chloro-4-ethylamino-6-isopropylamino-S-triazine; AT) was isolated from a pesticide-contaminated mix-load site soil. Evaluation of bioaugmentation as a feasible bioremediation strategy for this mix-load site soil (Site 5A) was initiated in standard laboratory biometer flasks utilizing the isolated SMC. The biometer flasks were monitored for CO₂ evolution and pesticide degradation. The total amount of CO₂ evolved from the treated biometer flasks was significantly different from the control flasks. The rate of CO₂ evolution was 2.6 times faster in the treated soil (0.0123 mM CO₂ d⁻¹ vs. 0.0048 mM CO₂ d⁻¹). The total net CO₂ produced in the treated biometer flasks was 0.9481 mM, representing mineralization of approximately 10% of the AT and AL initially present. Forty-eight percent of AT and 70% of AL was degraded in the inoculated biometer flasks. The first-order rate constants were 0.0064 d⁻¹ and 0.1331 d⁻¹ for AT and AL, respectively. The calculated half-life of AT was 108 d while a 50% decrease in AL occurred by Day 5. In just 2 d, 20% of the AT was degraded while only 10% of the AL disappeared. The initial fast degradation rate of AT was followed by a much slower, more gradual degradation rate period that lasted about 35 d. Alternatively, the rate of AL degradation increased after the second day resulting in 60% of the AL being transformed by the end of the first week. Alachlor degradation appeared to be dependent upon AT degradation especially during the first several days of the incubation period. Complete disappearance of the herbicides over the study time was not achieved.     

Effect of live fences of Gliricidia sepium on CO2 fluxes in tropical livestock systems

Live fences have the potential to improve microclimatic conditions, moderate soil CO₂ fluxes and function as carbon sinks. We quantified variation in soil CO₂ fluxes from livestock silvopastoral systems under the canopies of live fences (LF), formed by Gliricidia sepium trees, or artificial fences (AF). We determined the responses of soil CO₂ fluxes to environmental factors, including diurnal and seasonal variations in temperature and relative humidity in each fencing system. Measurements were made from April to June (dry season) and from July to September (rainy season), 2012. Fluxes were similar between the two livestock systems; LF emitted 1.00 μmol CO₂/m²/s and AF 1.02 μmol CO₂/m²/s. Soil temperatures at 5 cm depth were 3% warmer in AF than in LF, and relative humidity was 16% greater in LF than in AF. Seasonal variation in temperature greatly affected soil CO₂ fluxes, which changed seasonally in parallel with temperature of the topsoil and relative humidity at 1 m height, peaking in late summer. Fluxes in LF and AF were greater in the rainy season (1.1 μmol CO₂/m²/s, for both systems), when soil temperature was cooler and relative humidity was greatest, than during the dry season (0.9 μmol CO₂/m²/s, for both systems). Soil fluxes were larger at night (00:00–06:00 h), when soil temperature was cooler and relative humidity greater, than during the morning (6:00–12:00 h), when soil temperature was warmer and relative humidity was less. The presence of G. sepium trees in LF did not influence soil CO₂ fluxes.     

Interacting effects of temperature, soil moisture and plant biomass production on ecosystem respiration in a northern temperate grassland

Chamber measurements of total ecosystem respiration (TER) in a native Canadian grassland ecosystem were made during two study years with different precipitation. The growing season (April–September) precipitation during 2001 was less than one-half of the 30-year mean (1971–2000), while 2002 received almost double the normal growing season precipitation. As a consequence soil moisture remained higher in 2002 than 2001 during most of the growing season and peak aboveground biomass production (253.9 g m⁻²) in 2002 was 60% higher than in 2001. Maximum respiration rates were approximately 9 μmol m⁻² s⁻¹ in 2002 while only approximately 5 μmol m⁻² s⁻¹ in 2001. Large diurnal variation in TER, which occurred during times of peak biomass and adequate soil moisture, was primarily controlled by changes in temperature. The temperature sensitivity coefficient (Q₁₀) for ecosystem respiration was on average 1.83 ± 0.08, and it declined in association with reductions in soil moisture. Approximately 94% of the seasonal and interannual variation in R₁₀ (standardized rate of respiration at 10 °C) data was explained by the interaction of changes in soil moisture and aboveground biomass, which suggested that plant aboveground biomass was good proxy for accounting for variations in both autotrophic and heterotrophic capacity for respiration. Soil moisture was the dominant environmental factor that controlled seasonal and interannual variation in TER in this grassland, when variation in temperature was held constant. We compared respiration rates measured with chambers and that determined from nighttime eddy covariance (EC) measurements. Respiration rates measured by both techniques showed very similar seasonal patterns of variation in both years. When TER was integrated over the entire growing season period, the chamber method produced slightly higher values than the EC method by approximately 4.5% and 13.6% during 2001 and 2002, respectively, much less than the estimated uncertainty for both measurement techniques. The two methods for calculating respiration had only minor effects on the seasonal-integrated estimates of net ecosystem CO₂ exchange and ecosystem gross photosynthesis.     

黄河流域日潜在蒸散量变化及气象敏感要素分析

潜在蒸散量反映了大气的蒸发能力,准确的估算和科学客观的分析其气象影响要素,是水资源优化配置的重要依据和基础。该文以国家气象局整编的黄河流域109个站点近52a(1961-2012年)逐日气象资料计算潜在蒸散量及其敏感系数,探明黄河流域上游、中游和下游日潜在蒸散量(potential evapotranspiration,ET0)对4种气象要素的敏感性时空变化特征。结果表明:从ET0日值来看,黄河流域上游变化趋势不明显,但其均值高于中游和下游,下游以-0.043 mm/10a的趋势显著(p0.05)递减;在年内变化上,上游、中游和下游太阳辐射和温度及太阳辐射敏感系数均呈单峰型曲线变化,风速敏感系数呈单谷型变化,而相对湿度、风速以及相对湿度和温度的敏感系数波动较大;年际变化上,上游、中游和下游太阳辐射、相对湿度和风速都显著下降,温度显著提升,ET0对太阳辐射量和温度的敏感性减弱,而对相对湿度和风速敏感性增强;相对湿度是上游、中游和下游ET0变化的最敏感的要素,而太阳辐射量是ET0年内和年际变化的主控气象要素;太阳辐射、相对湿度和温度3个气候变量的敏感系数都在研究区西南部形成高值区,表明ET0在黄河流域西南部对气候变化最敏感。该研究对于指导黄河流域不同区域农业种植结构的调整和生态工程科学布局,合理开发调配水土资源,促进农业和生态环境的良性发展,具有重要的科学意义。     

Water use efficiency in a soybean field: influence of plant water stress

Measurements were made in 1980 over a fully-developed soybean (Glycine max (L.) Merrill) canopy at Mead, Nebraska to determine how crop water status influences photosynthesis, evapotranspiration and water use efficiency. Water use efficiency was calculated in terms of the CO₂—water flux ratio (CWFR). Micrometeorological techniques were used to measure the exchange rates of CO₂ and water vapor above the crop canopy. Crop water status was evaluated by reference to volumetric soil moisture (θ_v), stomatal resistance (r_s), and leaf water potential (ψ) measurements.Stomatal resistance (r_s) was independent of ψ when the latter was greater than ?1.1 MPa. r_s increased sharply as ψ dropped below this threshold. Canopy CO₂ exchange (F_c) decreased logarithmically with increasing r_s under strong irradiance. Although F_c was found to be strongly correlated with r_s, the influence of low values of ψ and of high air temperature cannot be discounted since these factors affect the enzymatic reactions associated with photosynthesis. Stomatal closure also reduced evapotranspiration and influenced the partitioning of net radiation.Under strong irradiance the CO₂ water flux ratio (CWFR) decreased with increasing stomatal resistance. This observation is at variance with predictions of certain early ‘resistance’ models, but substantiates predictions of some recent models in which leaf energy balance considerations are incorporated.     

Evaluation of NASA satellite- and assimilation model-derived long-term daily temperature data over the continental US

Agricultural research increasingly is expected to provide precise, quantitative information with an explicit geographic coverage. Limited availability of daily meteorological records often constrains efforts to provide such information through use of simulation models, spatial analysis, and related decision support tools. The Prediction Of Worldwide Energy Resources (NASA/POWER) project at the NASA Langley Research Center provides daily data globally for maximum and minimum temperatures and other weather variables on a 1° latitude–longitude grid. The data are assembled from a range of products derived from satellite imagery, ground observations, windsondes, modeling and data assimilation. Daily temperature data from NASA/POWER for 1983 to 2004 for the continental US were compared with data of 855 individual ground stations from the National Weather Service Cooperative Observer Program (COOP). Additionally, a wheat (Triticum aestivum L.) simulation model was used to compare predicted time to anthesis using the two data sources. Comparisons of daily maximum temperatures (T_max) gave an r²-value of 0.88 (P < 0.001) and root-mean-squared error (RMSE) of 4.1 °C. For minimum temperature (T_min), the r²-value was 0.88 (P < 0.001) and RMSE, 3.7 °C. Mean values of T_max, and T_min from NASA/POWER were, respectively, 2.4 °C cooler and 1.1 °C warmer than the COOP data. Differences in temperature were least during summer months. When data were aggregated over periods of 8 days or more, the RMSE values declined to below 2.7 °C for T_max and T_min. Simulations of time to anthesis with the two data sources were also strongly correlated (r² = 0.92, P < 0.001, RMSE = 14.5 d). Anthesis dates of winter wheat regions showed better agreement than southern, winter-grown spring wheat regions. The differences between the data sources were associated with differences in elevation, which in large part resulted from NASA/POWER data being based on mean elevations over a 1° grid cells vs. COOP data corresponding to the elevation of specific stations. Additional sources of variation might include proximity to coastlines and differences in observation time, although these factors were not quantified. Overall, if mountainous and coastal regions are excluded, the NASA/POWER data appeared promising as a source of continuous daily temperature data for the USA for research and management applications concerned with scales appropriate to the 1° coordinate grid. It further appeared that the POWER data could be improved by adjusting for elevation (lapse rate) effects, reducing seasonal bias, and refining estimation of actual maximum and minimum temperatures in diurnal cycles.