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The WINDS (Water-Use, Irrigation, Nitrogen, Drainage, and Salinity) model uses the FAO56 dual crop coefficient and a daily time-step soil–water balance to simulate evapotranspiration and water content in the soil profile. This research calibrated the WINDS model for simulation of guayule under full irrigation. Using data from a furrow irrigated two-season guayule experiment in Arizona, this research developed segmented curves for guayule basal crop coefficient, canopy cover, crop height and root growth. The two-season guayule basal crop coefficient (Kcb) curve included first and second season development, midseason, late-season and end-season growth stages. For a fully irrigated guayule crop, the year one midseason Kcb was 1.14. The second year Kcb development phase began after the crop was semi-dormant during the first winter. The second year Kcb value was 1.23. The two-season root growth curve included a growth phase during the first season, no growth during winter, and a second growth phase during the second winter. A table allocated fractions of total transpiration to soil layers as a function of root depth. With the calibrated tables and curves, the WINDS model simulated soil moisture content with a root mean squared error (RMSE) of 1- to 3-% volumetric water content in seven soil layers compared with neutron probe water contents during the two-year growth cycle. Thus, this research developed growth curves and accurately simulated evapotranspiration and water content for a two-season guayule crop. [ABSTRACT FROM AUTHOR]

Guayule (Parthenium argentatum, A. Gray) is a perennial desert shrub with ratoon-cropping potential for multiple harvests of its natural rubber, resin, and bagasse byproducts. However, yield expectations, water use requirements, and irrigation scheduling information for ratooned guayule are extremely limited. The objectives of this study were to evaluate dry biomass (DB), contents of rubber (R) and resin (Re) and yields of rubber (RY) and resin (ReY) responses to irrigation treatments, and develop irrigation management criteria for ratooned guayule. The water productivity (WP) of the yield components were also evaluated. Guayule plants that were direct-seeded in April 2018 were ratooned and regrown starting in April 2020, after an initial 2-year harvest at two locations in Arizona: Maricopa and Eloy on sandy loam and clay soils, respectively. Plots were irrigated with subsurface drip irrigation (SDI) at 50, 75, and 100% replacement of crop evapotranspiration (ETc), respectively, and furrow irrigation at 100% ETc replacement, as determined by soil water balance measurements. The Eloy location did not include the 100% irrigation treatment under SDI due to unsuccessful regrowth for this specific treatment. The irrigation treatments at the locations were replicated three times in a randomized complete block design. After 21–22 months of regrowth, the guayule plants were harvested in plots. The results showed that DB increased with the amount of total water applied (TWA, irrigation plus precipitation), while R and Re were reduced at the highest TWA received at both locations. Ultimately, the SDI treatments with 75% ETc replacement resulted in the best irrigation management in terms of maximizing RY and ReY, and WP for both locations and soil types. Compared to the initial 2-year direct-seeded guayule crop, ratooned guayule required less TWA and attained higher DB, RY, and ReY, as well as higher WP, with average increases of 25% in dry biomass, 33% in rubber yield, and 32% in resin yield. A grower's costs for planting the initial direct-seeded guayule crop would be offset by the additional yield revenue of the ratooned crop, which would have comparatively small startup costs. [ABSTRACT FROM AUTHOR]

Rates and durations of individual phases of wheat (Triticum aestivum L.) apical development are among the most important factors that determine yield components. Because atmospheric [CO.sub.2] has been increasing steadily, it is important to evaluate the effects of elevated [CO.sub.2] on wheat development. This study was conducted to determine rates and durations of leaf, spikelet, and floret primordium initiation in a Free-Air Carbon Dioxide Enrichment (FACE) system. Spring wheat (cv. Yecora Roja) was planted at the University of Arizona Maricopa Agricultural Center. The two [CO.sub.2] concentrations were 550 (elevated) and 370 (ambient) µmol [mol.sup.-1] [CO.sub.2]. Individual plant samples were collected every 3 to 4 d. We dissected the main stem (MS), coleoptile tiller (T0), primary tillers (T1, T2, and T3) and secondary tillers (T00, T01, T02, T10, T11, and T12) and counted primordia. Apex primordium data were fitted to a four-piece linear-spline segmented regression model with the SAS proc NLIN. No influence of elevated [CO.sub.2] (550 µmol [mol.sup.-1]) on leaf primordium initiation of MS was detected. Nevertheless, [CO.sub.2] enrichment significantly increased rates of spikelet primordimn initiation of MS, T1, T2, T10, and T11, and diminished the durations of spikelet development phase of MS, T1, T2, T3, T10, and T11. Within the floret phase, [CO.sub.2] enrichment significantly increased rates of floret primordium initiation of MS, T0, T1, T2, and T3, and diminished the time to the completion of floret primordium initiation of MS, T0, T1, T3, and T11. The information from this study will be utilized to predict wheat apical development and grain production in the elevated atmospheric [CO.sub.2] environments of the future., Wheat apical development consists of three distinct phases: leaf primordium, spikelet primordium, and floret primordium initiation. The transition from initiation of leaf to spikelet, and hence to floret primordia is [...]

Wheat grain weight is a function of rate and duration of grain growth and is affected by photosynthate supply. Drought stress reduces photosynthate production because of stomatal closure. However, this might be partially overcome by an increase in air [CO.sub.2] concentration. This study was conducted to evaluate elevated [CO.sub.2] and drought stress effects on grain-filling rate and duration for spring wheat (Triticum aestivum L.). Spring wheat (cv. Yecora Roja) was grown at two [CO.sub.2] concentrations, 550 (elevated) or 370 (ambient) µmol [mol.sup.-1] and two water treatments in a Free-Air [CO.sub.2] Enrichment (FACE) system at the University of Arizona Maricopa Agricultural Center. Plant samples were collected every 3 to 4 d from 6 d after anthesis until plant maturity. Main stem spikes were separated into upper, middle, and lower sections. Grain weight data for the intact main stem spike, each of its sections, and intact tiller spikes were fitted to a cumulative logistic model. Both elevated [CO.sub.2] and water treatments significantly influenced the grain-filling processes. Under drought stress conditions, elevated [CO.sub.2] increased grain weight in the upper and lower sections of the main stem spike by 10 and 24%, respectively. In well-watered plants, final grain weight in the midsection of the main stem spike was 8% higher than that measured under drought stress conditions. Grain weight increase under elevated [CO.sub.2] was due to a faster rate of grain filling. Effects of elevated [CO.sub.2] on the statistically derived duration of grain filling were inconclusive because of the confounding effect of blower-induced temperature changes on the process. An increase in grain weight of well-watered plants was due to a longer grain-filling period. Later-formed tiller spikes were more responsive to elevated [CO.sub.2] and drought stress than main stem spikes. Information from this study will help us understand the grain growth of wheat and provide information to establish grain growth mechanism., THE CONCENTRATION of atmospheric [CO.sub.2] is predicted to double above pre-industrial levels by the middle of the next century. With the rise in air temperatures, more frequent drought stresses are [...]

Although primordium initiation in wheat (Triticum aestivum L.) has been extensively researched, a complete description of the growth dynamics of the apex at elevated [CO.sub.2] concentrations is lacking. This study determined the rates of main stem and tiller apical elongation and widening in plants grown under two levels of [CO.sub.2] concentration. Spring wheat was grown at the University of Arizona's Maricopa Agricultural Center at elevated (550 µ mol [mol.sup.-1]) or ambient (370 µ mol [mol.sup.-1]) [CO.sub.2] concentrations. Individual plant samples were collected at different developmental stages and dissected. After dissection, the lengths and widths of the apices of the main stem (MS), coleoptile tiller (T0), primary tillers (T1, T2, and T3), and secondary tillers (T00, T01, T02, T10, T11, and T12) were measured with a stage micrometer. Apex dimensions were fitted to an exponential model. Elevated [CO.sub.2] increased the apex lengths of T2 at the double ridge stage, and of T3 and T10 at the double ridge and the terminal spikelet stages, and the apex widths of T2 at double ridge stage, and of T2, T3, T10, and T11 at the flag leaf appearance stage. Combining these results with a parallel study, the longer apices did not have more spikelet primordia, but wider apices had more floret primordia. Elevated [CO.sub.2] changed apex elongation or widening patterns within a plant by enhancing elongation or widening rates of the MS, and laterformed tillers. Earlier-formed tillers were less responsive to elevated [CO.sub.2] levels. This information will be used in modeling wheat apical development and grain production in the elevated atmospheric [CO.sub.2] environments of the future., SPIKELET AND FLORET PRIMORDIA that set potential grain number on a spike reside on the apex dome. The size of the apex dome changes systematically with primordium differentiation and there [...]

Documenting crop senescence rates is often difficult because of the need for frequent sampling during periods of rapid change and the subjective nature of human visual observations. The purpose of this study was to determine the feasibility of using images produced by a digital camera to measure the senescence rate of wheat and to compare the results with changes in greenness determined by two established methods. Measurements were made as part of an experiment to determine the effects of elevated [CO.sub.2] and limited soil nitrogen on spring wheat (Triticum aestivum L.) at the University of Arizona's Maricopa Agricultural Center, near Phoenix, AZ. 'Greenness' measurements were made during senescence of the crop with a color digital camera, a hand-held radiometer, and a SPAD chlorophyll meter. The green to red (G/R) for each pixel in an image was calculated and the average G/R computed for cropped images from a digital camera representing 1 [m.sup.2] for each treatment and sample date. The normalized difference vegetation index (NDVI) was calculated from the red and near-infrared canopy reflectances measured with a hand held radiometer. A SPAD reading was obtained from randomly selected flag leaves. All three methods of measuring plant greenness showed similar temporal trends. The relationships between G/R with NDVI and SPAD were linear over most of the range of G/R. However, NDVI was more sensitive at low values than G/R. G/R was more sensitive above G/R values of 1.2 than SPAD because the upper limits of SPAD measurements were constrained by the amount of chlorophyll in the leaf, while G/R responded to both chlorophyll concentration in the leaves as well as the number of leaves present. Color digital imaging appears useful for quantifying the senescence of crop canopies. The cost of color digital cameras is expected to decrease and the quality and convenience of use to improve., The rate of senescence maturation of during grain crops such as wheat can be affected by fertility levels, water stress, temperature, cultivar, and other factors (Idso et al., 1980; Seligman [...]

Potential impacts of climate change on grain sorghum ( Sorghum bicolor) productivity were investigated using the CERES-sorghum model in the Decision Support System for Agrotechnology Transfer v4.5. The model was first calibrated for a sorghum cultivar grown in a free air CO2 enrichment experiment at the University of Arizona, Maricopa, Arizona, USA in 1998. The model was then validated with an independent dataset collected in 1999. The simulated grain yield, growth, and soil water of sorghum for the both years were in statistical agreement with the corresponding measurements, respectively. Neither simulated nor measured yields responded to elevated CO2, but both were sensitive to water supply. The validated model was then applied to simulate possible effects of climate change on sorghum grain yield and water use efficiency in western North America for the years 2080-2100. The projected CO2 fertilizer effect on grain yield was dominated by the adverse effect of projected temperature increases. Therefore, temperature appears to be a dominant driver of the global climate change influencing future sorghum productivity. These results suggest that an increase in water demand for sorghum production should be anticipated in a future high-CO2 world. [ABSTRACT FROM AUTHOR]

Global warming will likely affect carbon cycles in agricultural soils. Our objective was to deploy infrared (IR) warming to characterize the effect of global warming on soil temperature (Ts), volumetric soil-water content (θs), and intrarow soil CO2 efflux (Φs) of an open-field spring wheat (Triticum aestivum L. cv. Yecora Rojo) crop grown in the semiarid desert Southwest. A temperature free-air controlled enhancement (T-FACE) apparatus using IR heaters maintained canopy air temperature above 3.0-m plots by 1.3 and 2.7°C (0.2 and 0.3°C below the targeted set-points) during the diurnal and nocturnal periods, respectively. A randomized complete block (RCB) design with two IR warming treatments (i.e., Heated; Reference) in three replicates was planted on 10 Mar. and 1 Dec. 2008. Intrarow Ts, θs, and Φs were measured from emergence (bare soil) up until inflorescence emergence (canopy closure). Under ample soil water supply with high θ s, midday Φs was 10% greater in Heated [4.1 μmol (CO2) m-2 s-1] compared with Reference [3.7 μmol (CO2) m-2 s-1]. In contrast, as the soil dried and θ s decreased to a greater degree in Heated compared with Reference, a 10% decrease in Φ s occurred in Heated compared with Reference. Overall, θs had the greatest impact on Φs, whereas it was responsive to Ts only under high θs. Accurate predictions of global climate change effects on Φs in agricultural soils require that interactive effects of Ts and θs be coupled. Infrared warming with T-FACE proved to be an effective experimental methodology to investigate these interactive effects. [ABSTRACT FROM AUTHOR]

Abstract: Atmospheric CO2 concentration (C a) is rising, predicted to cause global warming, and alter precipitation patterns. During 1994, spring barley (Hordeum vulgare L. cv. Alexis) was grown in a strip-split-plot experimental design to determine the effects that the main plot C a treatments [A: Ambient at 370μmol (CO2) mol−1; E: Enriched with free-air CO2 enrichment (FACE) at ∼550μmol (CO2) mol−1] had on several gas exchange properties of fully expanded sunlit primary leaves. The interacting strip-split-plot irrigation treatments were Dry or Wet [50% (D) or 100% (W) replacement of potential evapotranspiration] at ample nitrogen (261kg N ha−1) and phosphorous (29kg P ha−1) fertility. Elevated C a facilitated drought avoidance by reducing stomatal conductance (g s) by 34% that conserved water and enabled stomata to remain open for a longer period into a drought. This resulted in a 28% reduction in drought-induced midafternoon depression in net assimilation rate (A). Elevated C a increased A by 37% under Dry and 23% under Wet. Any reduction in A under Wet conditions occurred because of nonstomatal limitations, whereas under Dry it occurred because of stomatal limitations. Elevated C a increased the diurnal integral of A (A′) that resulted in an increase in the seasonal-long integral of A′ (A″) for barley leaves by 12% (P =0.14) under both Dry and Wet – 650, 730, 905 and 1020±65g (C) m−2 y−1 for AD, ED, AW and EW treatments, respectively. Elevated C a increased season-long average dry weight (DWS; crown, shoots) by 14% (P =0.02), whereas deficit irrigation reduced DWS by 7% (P =0.06), although these values may have been affected by a short but severe pea aphid [Acyrthosiphon pisum (Harris)] infestation. Hence, an elevated-C a-based improvement in gas exchange properties enhanced growth of a barley crop. [Copyright &y& Elsevier]

Gas exchange and water relations were evaluated under full-season in situ infrared (IR) warming for hard red spring wheat ( Triticum aestivum L. cv. Yecora Rojo) grown in an open field in a semiarid desert region of the southwest USA. A temperature free-air controlled enhancement (T-FACE) apparatus utilizing IR heaters maintained canopy air temperature above 3.0 m Heated plots of wheat by 1.3 and 2.7 °C (0.2 and 0.3 °C below the targeted set-points of Reference plots with dummy heaters) during daytime and nighttime, respectively. Control plots had no apparatus. Every 6 weeks during 2007-2009 wheat was sown under the three warming treatments (i.e., Control, Heated, Reference) in three replicates in a 3 × 3 Latin square (LSQ) design on six plantings during 4 months (i.e., January, March, September, December), or in a natural temperature variation treatment (i.e., Control) in three replicates in a randomized complete block (RCB) design on nine plantings during 7 months (i.e., January, February, April, June, July, August, October). Soil temperature ( T) and volumetric soil-water content ( θ) were 1.3 °C warmer and 14% lower in Heated compared with Reference plots, respectively. Other than a 1% shading effect, no artifacts on gas exchange or water relations were associated with the IR warming apparatus. IR warming increased carbon gain characteristic of an increase in metabolic rates to higher temperature that may have been attributed to the well-watered wheat crop and the supplemental irrigation that minimized plant-to-air water vapor pressure differences between IR-warmed and nonwarmed plots. Nevertheless, seasonal oscillations in the IR warming response on carbon gain occurred. IR warming decreased leaf water status and provided thermal protection during freeze events. IR warming is an effective experimental methodology to investigate the impact of global climate change on agronomic cropping and natural ecosystems to a wide range of natural and artificially imposed air temperatures. [ABSTRACT FROM AUTHOR]

As atmospheric carbon dioxide concentrations, [CO2Air], continue their uncontrolled rise, the capacity of soils to accumulate or retain carbon is uncertain. Free-air CO2 enrichment (FACE) experiments have been conducted to better understand the plant, soil and ecosystem response to elevated [CO2], frequently employing commercial CO2 that imparts a distinct isotopic signal to the system for tracing carbon. We conducted a FACE experiment in 1998 and 1999, whereby sorghum (C4 photosynthetic pathway) was grown in four replicates of four treatments using a split-strip plot design: (i) ambient CO2/ample water (365 μmol mol−1, "Control–Wet"), (ii) ambient CO2/water stress ("Control–Dry"), (iii) CO2-enriched (560 μmol mol−1, "FACE–Wet"), and (iv) CO2-enriched/water stressed ("FACE–Dry"). The stable-carbon isotope composition of the added CO2 (in FACE treatments) was close to that of free atmosphere background values, so the subsequent similar 13C-enriched carbon signal photosynthetically fixed by C4 sorghum plants could be used to trace the fate of carbon in both FACE and control treatments. Measurement of soil organic carbon content (SOC (%) = gC/gdry soil × 100%) and δ13C at three depths (0–15, 15–30, and 30–60 cm) were made on soils from the beginning and end of the two experimental growing seasons. A progressive ca. 0.5‰–1.0‰ δ13C increase in the upper soil SOC in all treatments over the course of the experiment indicated common entry of new sorghum carbon into the SOC pools. The 0–15 cm SOC in FACE treatments was 13C-enriched relative to the Control by ca. 1‰, and according to isotopic mass balance, the fraction of the new sorghum-derived SOC in the Control–Wet treatment at the end of the second season was 8.4%, 14.2% in FACE–Wet, 6.5% in Control–Dry, and 14.2% in FACE–Dry. The net SOC enhancement resulting from CO2 enrichment was therefore 5.8% (or 2.9% y−1 of experiment) under ample water and 7.7% (3.8% y−1 of experiment) under limited water, which matches the pattern of greater aboveground biomass increase with elevated [CO2Air] under the Dry treatment, but no parallel isotopic shifts were found in deeper soils. However, these increased fractions of new carbon in SOC at the end of the experiment do not necessarily mean an increase in total SOC content, because gravimetric measurements of SOC did not reveal a significant increase under elevated [CO2Air], at least within the limits of SOC-content error bars. Thus, new carbon gains might be offset by pre-experiment carbon losses. The results demonstrate successful isotopic tracing of carbon from plants to soils in this sorghum FACE experiment showing differences between FACE and Control treatments, which suggest more dynamic cycling of SOC under elevated [CO2Air] than in the Control treatment. [ABSTRACT FROM AUTHOR]

• Understanding how trees are affected by a long-term increase in atmospheric CO2 is crucial to understanding the future impact of global climate change. Measurements of photosynthetic characteristics were made in sour orange trees ( Citrus aurantium) growing under an enhanced CO2 atmosphere and N-replete soil for 14 yr to determine whether photosynthetic down-regulation had occurred. • Photosynthesis, A : Ci gas exchange relationships and Rubisco activity and content were measured throughout the 14th year of the experiment. The CO2-induced enhancement ratio of photosynthesis was calculated and compared with estimates of the enhancement of cumulative wood biomass production. • Content of the large subunit of Rubisco was significantly reduced by CO2 enrichment indicating that down-regulation had occurred. A high correlation between the CO2-induced enhancement of photosynthesis and the enhancement of cumulative wood biomass production suggested that the decline in wood biomass production was closely related to the decline in photosynthesis. • These results indicate that long-term CO2 enrichment can result in photosynthetic down-regulation in leaves of trees, even under nonlimiting N conditions. ♥ New Phytologist (2004) No claim to original US government worksδοι: 10.1011/j.1469-8137.2004.01104.x [ABSTRACT FROM AUTHOR]

Summary • To determine the response of C4 plants to elevated CO2 it is necessary to establish whether young leaves have a fully developed C4 photosynthetic apparatus, and whether photosynthesis in these leaves is responsive to elevated CO2 . • The effect of free-air CO2 enrichment (FACE) on the photosynthetic development of the C4 crop Sorghum bicolor was monitored. Simultaneous measurements of chlorophyll a fluorescence and carbon assimilation were made to determine energy utilization, quantum yields of carbon fixation (φCO2 ) and photosystem II (φPSII), as well as photorespiration. • Assimilation in the second leaf of FACE plants was 37% higher than in control plants and lower apparent rates of photorespiration at growth CO2 concentrations were exhibited. In these leaves, φPSII : φCO2 was high at low atmospheric CO2 concentration (Ca) due to overcycling of the C4 pump and increased leakiness. As Ca increased, φPSII : φCO2 decreased as a greater proportion of energy derived from linear electron transfer was used by the C3 cycle. • The stimulation of C4 photosynthesis at elevated Ca in young leaves was partially due to suppressed photorespiration. Additionally, elevated Ca enhanced energy-use efficiency in young leaves, possibly by decreasing CO2 leakage from bundle sheath cells, and by decreasing overcycling of the C4 pump. [ABSTRACT FROM AUTHOR]

Separating roots from soil is a laborious and costly process, but a commercially available hydropneumatic root elutriator can semi‐automate the job. Hydraulic and pneumatic systems elutriate the roots from the soil, while the electrical system controls the on/off functions of the hydraulic system. The extruded steel frame of the elutriator serves a dual purpose; structural support and transport of water and compressed air. Water is transported in the lower and air in the upper part of the hollow inner cavity of the extruded steel frame. They exit the frame into polyethylene tubes that extend to the base of the elutriator. After prolonged use, however, this design feature can become problematic because flow to the elutriator of either system can be blocked at the nozzle inlets with rust particles that originate from the steel frame's inner walls. The blockage increases sample processing time due to dismantling, clearing, and reassembling, which eventually degrades the elutriator. To resolve these problems a 40‐mesh (420 micron) in‐line stainless steel water filter and a 40‐micron in‐line bronze air filter were installed in the polyethylene tube lines between the extruded steel frame and the base of the elutriator. These filters were found to reduce nozzle blockage, thereby increasing sample processing efficiency by 10% and improving sample quality. [ABSTRACT FROM PUBLISHER]

Determines the growth rate of wheat under two levels of carbon dioxide concentrations. Measurement of wheat crops rate of growth; Results relevant to studies on the impact of atmospheric carbon dioxide on grain production and yields.

To test the predictions that plants will have a larger flavonoid concentration in a future world with a CO2-enriched atmosphere, wheat (Triticum aestivum L. cv. Yecora Rojo) was grown in a field experiment using FACE (free-air CO2 enrichment) technology under two levels of atmospheric CO2 concentration: ambient (370 μmol mol-1) and enriched (550 μmol mol-1), and under two levels of irrigation: well-watered (100% replacement of potential evapotranspiration) and half-watered. We also studied the effects of CO2 on the concentration of total non-structural carbohydrates (TNC) and nitrogen (N), two parameters hypothesized to be linked to flavonoid metabolism. Throughout the growth cycle the concentration of isoorientin, the most abundant flavonoid, decreased by 62% (from an average of 12.5 mg g-1 on day of year (DOY) 41 to an average of 4.8 mg g-1 on DOY 123), whereas the concentration of tricin, another characteristic flavone, increased by two orders of magnitude (from an average of 0.007 mg g-1 of isoorientin equivalents on DOY 41 to an average of 0.6 mg g-1 of isoorientin equivalents on DOY 123). Although flavonoid concentration was dependent on growth stage, the effects of treatments on phenology did not invalidate the comparisons between treatments. CO2-enriched plants had higher flavonoid concentrations (14% more isoorientin, an average of 7.0 mg g-1 for ambient CO2 vs an average of 8.0 mg g-1 for enriched CO2), higher TNC concentrations and lower N concentrations in ukpper canopy leaves throughout the growth cycle. Well-irrigated plants had higher flavonoid concentrations (11% more isoorientin, an average of 7.1 mg g-1 for half watered vs an average of 7.9 mg g-1 for well-watered) throughout the growth cycle, whereas the effect of irrigation treatments on TNC and N was more variable. These results are in accordance with the hypotheses that higher carbon availability promoted by CO2‐enrichment provides carbon that can be invested in carbon‐based secondary compounds such as flavonoids. The rise in atmospheric CO2 may thus indirectly affect wheat‐pest relations, alter the pathogen predisposition and improve the UV‐B protection by changing flavonoid concentrations. [ABSTRACT FROM AUTHOR]

A free-air CO2 enrichment (FACE) experiment was conducted at Maricopa, Arizona, on wheat from December 1992 through May 1993. The FACE apparatus maintained the CO2 concentration, [CO2], at 550 µmol mol-1 across four replicate 25-m-diameter circular plots under natural conditions in an open field. Four matching Control plots at ambient [CO2] (about 370 micro;mol mol-1) were also installed in the field. In addition to the two levels of [CO2], there were ample (Wet) and limiting (Dry) levels of water supplied through a subsurface drip irrigation system in a strip, split-plot design. Measurements were made of net radiation, Rn; soil heat flux, G0; soil temperature; foliage or surface temperature; air dry and wet bulb temperatures; and wind speed. Sensible heat flux, H, was calculated from the wind and temperature measurements. Latent heat flux, γET, and evapotranspiration, ET, were determined as the residual in the energy balance. The FACE treatment reduced daily total Rn by an average 4%. Daily FACE sensible heat flux, H, was higher in the FACE plots. Daily latent heat flux, γET, and evapotranspiration, ET, were consistently lower in the FACE plots than in the Control plots for most of the growing season, about 8% on the average. Net canopy photosynthesis was stimulated by an average 19 and 44% in the Wet and Dry plots, respectively, by elevated [CO2] for most of the growing season. No significant acclimation or down regulation was observed. There was little above-ground growth response to elevated [CO2] early in the season when temperatures were cool. Then, as temperatures warmed into spring, the FACE plants grew about 20% more than the Control plants at ambient [CO2], as shown by above-ground biomass accumulation. Root biomass accumulation was also stimulated about 20%. In May the FACE plants matured and senesced about a week earlier than the Controls in the Wet plots. The FACE plants averaged 0.6°C warmer than the Controls from February through April in the well-watered plots, and we speculate that this temperature rise contributed to the earlier maturity. Because of the acceleration of senescence, there was a shortening of the duration of grain filling, and consequently, there was a narrowing of the final biomass and yield differences. The 20% mid-season growth advantage of FACE shrunk to about an 8% yield advantage in the Wet plots, while the yield differences between FACE and Control remained at about 20% in the Dry plots. [ABSTRACT FROM AUTHOR]

Abstract: Accurate data on crop responses to temperature are essential for predicting the potential impacts of climate extremes. Air temperature can be precisely regulated in controlled environment chambers, but chambers seldom provide realistic radiation, photoperiod, wind and humidity regimes, which raise concerns as to whether responses quantified in such environments accurately reflect field performance. Field experiments employing sowing date (SD) and artificial warming treatments can provide a wide range of temperature regimes under otherwise natural field conditions. We analyzed temperature effects on main stem leaf appearance for the spring wheat (Triticum aestivum L.) cultivar Yecora Rojo using 15 sowing dates at Maricopa, AZ, USA. Six dates included infrared-based temperature free-air controlled enhancement (T-FACE) warming treatments. Mean air temperatures over the 15 periods of measurement varied from 11.6 to 33.2°C. Our objective was to characterize the effect of temperature on leaf number, emphasizing air temperatures above 20°C, a value often cited optimal for wheat development. An underlying concern was how different shapes of temperature responses functions might affect estimates of cardinal temperatures. For comparisons among four segmented linear functions, a quadratic function and two forms of the beta function, the best fit to the data was for a two-segment function with a base temperature (T base) of 1.9°C and an optimum (T optl) of 22.2°C. In attempting to estimate a second, upper temperature for maximum development (T optu), the estimation process failed. This likely reflected the low frequency of data from mean air temperatures over 25°C and possible severe stress responses at extreme low and high temperatures. The results further demonstrated the value of growing crops under a wide range of temperature regimes, which can be attained under field conditions through use of planting date and T-FACE treatments. [Copyright &y& Elsevier]

Abstract: Reliable prediction of the potential impacts of global warming on agriculture requires accurate data on crop responses to elevated temperatures. Controlled environments can precisely regulate temperature but may impose unrealistic radiation, photoperiod and humidity regimes. Infrared warming with automatic control of temperature rise has shown potential for warming field plots above ambient temperatures, while avoiding such biases. In a field experiment conducted at Maricopa, AZ, we assessed the utility of a temperature free-air controlled enhancement (T-FACE) approach by comparing phenology of wheat from a series of six sowing date treatments using T-FACE and an additional nine sowing dates that exposed crops to an exceptionally wide range of air temperatures (<0°C to >40°C). The T-FACE treatments were intended to achieve a warming of +1.5°C during the daytime and +3.0°C at night; the achieved warming averaged +1.3°C during daytime and +2.8°C at night. T-FACE and sowing date treatments had large effects on phenology. A regression-based analysis of simulations with the CSM-CROPSIM-CERES model showed that effects of T-FACE on phenology were similar to what would be expected from equivalent changes in air temperature. However, systematic deviations from the expected 1-to-1 relation suggested that assumed cardinal temperatures for phenology should be revised. Based on the single cultivar and location, it appeared that the base temperature for emergence to anthesis should be reduced from 0°C to −5°C, whereas the base temperature for grain filling should be increased from 0°C to 4°C and the optimal temperature, from 30°C to 34°C. Both T-FACE and extreme sowing date treatments proved valuable for improving understanding of high temperature effects on plant processes, as required for accurate prediction of crop responses to elevated temperatures under climate change. [Copyright &y& Elsevier]

Even brief periods of high temperatures occurring around flowering and during grain filling can severely reduce grain yield in cereals. Recently, ecophysiological and crop models have begun to represent such phenomena. Most models use air temperature ( T air ) in their heat stress responses despite evidence that crop canopy temperature ( T c ) better explains grain yield losses. T c can deviate significantly from T air based on climatic factors and the crop water status. The broad objective of this study was to evaluate whether simulation of T c improves the ability of crop models to simulate heat stress impacts on wheat under irrigated conditions. Nine process-based models, each using one of three broad approaches (empirical, EMP; energy balance assuming neutral atmospheric stability, EBN; and energy balance correcting for the atmospheric stability conditions, EBSC) to simulate T c , simulated grain yield under a range of temperature conditions. The models varied widely in their ability to reproduce the measured T c with the commonly used EBN models performing much worse than either EMP or EBSC. Use of T c to account for heat stress effects did improve simulations compared to using only T air to a relatively minor extent, but the models that additionally use T c on various other processes as well did not have better yield simulations. Models that simulated yield well under heat stress had varying skill in simulating T c . For example, the EBN models had very poor simulations of T c but performed very well in simulating grain yield. These results highlight the need to more systematically understand and model heat stress events in wheat. [ABSTRACT FROM AUTHOR]

Deficit irrigation can maximize the water productivity (WP) of guayule and increase the percent rubber (%R) in shrubs compared to irrigation meeting full crop evapotranspiration (ET c). In this study, we hypothesize that certain deficit irrigation strategies that impose soil water deficits during specific periods of growth or throughout the growing season might produce higher %R and equivalent rubber yield (RY), thereby, increasing WP compared to full irrigation. Herein, growth and yield responses of direct-seeded guayule to different water deficit schemes were evaluated in an experiment on a silty clay loam soil, in a field in central Arizona using furrow irrigation. Two guayule cultivars (AZ2 and AZ6) were grown for 22.5 months (Apr. 2020-Mar. 2022) in a split-plot design, with six irrigation treatments in whole plots and cultivars in split-plots. After homogeneous irrigation for two months, irrigation treatments were begun. A control treatment was irrigated to meet full ET c. The other five treatments were irrigated with less water using various deficit irrigation strategies imposed during the two-year growing period. Measurements included plant height (h), cover fraction (f c), soil water contents, harvest of dry biomass (DB), RY, resin yield (ReY), %R, and percent resin (%Re). Total water applied (TWA) by irrigation and precipitation to treatments varied from 2780 to 1084 mm and DB varied from 20.5 to 9.1 Mg ha−1. The h and f c were significantly greater at higher irrigation levels, while they were also significantly greater in AZ6 than AZ2. The DB, RY, and ReY generally increased linearly with TWA. However, it was found that a treatment applying every other irrigation of the control resulted in statistically equivalent yields to the control, with 36% less irrigation. The %R generally decreased with TWA, while %Re did not change. However, DB, %R, and %Re were significantly greater for AZ2 than AZ6, as were RY, ReY, and WP. Among the deficit treatments evaluated, every other irrigation offers the best strategy to significantly increase guayule WP without causing a yield penalty. • Guayule plant height and cover were significantly higher at higher irrigation rates. • Rubber content decreased with irrigation, while resin content was not affected. • Biomass, rubber and resin contents were significantly higher for AZ2 than AZ6. • Among deficit tactics, every other irrigation was the best-high water productivity. [ABSTRACT FROM AUTHOR]

Guayule (Parthenium argentatum, A. Gray), a perennial desert shrub, produces high-quality natural rubber and is targeted as a domestic natural rubber source in the U.S. While commercialization efforts for guayule are on-going, crop management requires plant growth monitoring, irrigation requirement assessment, and final yield estimation. Such assistance for guayule management could be provided with remote sensing (RS) data. In this study, field and RS data, collected via drones, from a 2-year guayule irrigation experiment conducted at Maricopa, Arizona were evaluated. In-season field measurements included fractional canopy cover (f c), basal (K cb) and single (K c) crop coefficients, and final yields of dry biomass (DB), rubber (RY), and resin (ReY). The objectives of this paper were to compare vegetations indices from MS data (NDVI) and RGB data (triangular greenness index, TGI); and derive linear prediction models for estimating f c , K cb , K c , and yield as functions of the MS and RGB indices. The NDVI and TGI showed similar seasonal trends and were correlated at a coefficient of determination (r2) of 0.52 and a root mean square error (RMSE) of 0.11. The prediction of measured f c as a linear function of NDVI (r2 = 0.90) was better than by TGI (r2 = 0.50). In contrast to TGI, the measured f c was highly correlated with estimated f c based on RGB image evaluation (r2 = 0.96). Linear models of K cb and K c , developed over the two years of guayule growth, had similar r2 values vs NDVI (r2 = 0.46 and 0.41, respectively) and vs TGI (r2 = 0.48 and 0.40, respectively). Final DB, RY, and ReY were predicted by both NDVI (r2 = 0.75, 0.53, and 0.70, respectively) and TGI (r2 = 0.72, 0.48, and 0.65, respectively). The RS-based models enable estimation of irrigation requirements and yields in guayule production fields in the U.S. • Prediction of guayule cover was better by NDVI than an RGB index. • Data extracted from RGB imagery can be used to estimate canopy cover. • Guayule crop coefficients were effectively modeled using NDVI and the RGB index. • Final biomass and rubber yields can be predicted by both NDVI and the RGB index. [ABSTRACT FROM AUTHOR]

Abstract: A major challenge for crop research in the 21st century is how to predict crop performance as a function of genetic architecture. Advances in “next generation” DNA sequencing have greatly improved genotyping efficiency and reduced genotyping costs. Methods for characterizing plant traits (phenotypes), however, have much progressed more slowly over the past 30 years, and constraints in phenotyping capability limit our ability to dissect the genetics of quantitative traits, especially those related to harvestable yield and stress tolerance. As a case in point, mapping populations for major crops may consist of 20 or more families, each represented by as many as 200 lines, necessitating field trials with over 20,000 plots at a single location. Investing in the resources and labor needed to quantify even a few agronomic traits for linkage with genetic markers in such massive populations is currently impractical for most breeding programs. Herein, we define key criteria, experimental approaches, equipment and data analysis tools required for robust, high-throughput field-based phenotyping (FBP). The focus is on simultaneous proximal sensing for spectral reflectance, canopy temperature, and plant architecture where a vehicle carrying replicated sets of sensors records data on multiple plots, with the potential to record data throughout the crop life cycle. The potential to assess traits, such as adaptations to water deficits or acute heat stress, several times during a single diurnal cycle is especially valuable for quantifying stress recovery. Simulation modeling and related tools can help estimate physiological traits such as canopy conductance and rooting capacity. Many of the underlying techniques and requisite instruments are available and in use for precision crop management. Further innovations are required to better integrate the functions of multiple instruments and to ensure efficient, robust analysis of the large volumes of data that are anticipated. A complement to the core proximal sensing is high-throughput phenotyping of specific traits such as nutrient status, seed composition, and other biochemical characteristics, as well as underground root architecture. The ability to “ground truth” results with conventional measurements is also necessary. The development of new sensors and imaging systems undoubtedly will continue to improve our ability to phenotype very large experiments or breeding nurseries, with the core FBP abilities achievable through strong interdisciplinary efforts that assemble and adapt existing technologies in novel ways. [Copyright &y& Elsevier]

Abstract: Ecophysiological models are widely used to forecast potential impacts of climate change on future agricultural productivity and to examine options for adaptation by local stakeholders and policy makers. However, protocols followed in such assessments vary to such an extent that they constrain cross-study syntheses and increase the potential for bias in projected impacts. We reviewed 221 peer-reviewed papers that used crop simulation models to examine diverse aspects of how climate change might affect agricultural systems. Six subject areas were examined: target crops and regions; the crop model(s) used and their characteristics; sources and application of data on [CO2] and climate; impact parameters evaluated; assessment of variability or risk; and adaptation strategies. Wheat, maize, soybean and rice were considered in approximately 170 papers. The USA (55 papers) and Europe (64 papers) were the dominant regions studied. The most frequent approach used to simulate response to CO2 involved adjusting daily radiation use efficiency (RUE) and transpiration, precluding consideration of the interacting effects of CO2, stomatal conductance and canopy temperature, which are expected to exacerbate effects of global warming. The assumed baseline [CO2] typically corresponded to conditions 10–30 years earlier than the date the paper was accepted, exaggerating the relative impacts of increased [CO2]. Due in part to the diverse scenarios for increases in greenhouse gas emissions, assumed future [CO2] also varied greatly, further complicating comparisons among studies. Papers considering adaptation predominantly examined changes in planting dates and cultivars; only 20 papers tested different tillage practices or crop rotations. Risk was quantified in over half the papers, mainly in relation to variability in yield or effects of water deficits, but the limited consideration of other factors affecting risk beside climate change per se suggests that impacts of climate change were overestimated relative to background variability. A coordinated crop, climate and soil data resource would allow researchers to focus on underlying science. More extensive model intercomparison, facilitated by modular software, should strengthen the biological realism of predictions and clarify the limits of our ability to forecast agricultural impacts of climate change on crop production and associated food security as well as to evaluate potential for adaptation. [Copyright &y& Elsevier]

Abstract: Agricultural system simulation models are key tools for assessment of possible impacts of climate change on crop production and environmental quality. In this study, the CERES-Wheat 4.0 module in the RZWQM2 model was calibrated and validated for simulating spring wheat grown under elevated CO2 conditions in the FACE (Free Air CO2 Enrichment) experiments conducted at Maricopa, Arizona, USA from 1992 to 1997. The validated model was then used to simulate the possible impacts of climate change on the crop for a 16-year period centered on 2050 with a projected atmospheric CO2 concentration of 550ppm. Sixteen General Circulation Model (GCM) projections of climate in response to this CO2 concentration were used for this purpose. In the FACE experiment, the crops were grown under ambient (365–370ppm) and elevated (∼550ppm) CO2 concentrations with two irrigation treatments (wet and dry) in 1992–1993 and 1993–1994, and two nitrogen (N) treatments (high and low N) in 1995–1996 and 1996–1997 crop seasons. The model simulated crop growth and grain yield, and soil water responses to CO2 reasonably well, reproducing variations due to the treatments. Under ambient CO2 in 1992–1993 and 1995–1996, biomass was simulated better in the dry and low N treatments with root mean square difference (RMSD) of 181 and 161kgha−1, respectively, compared to the wet and high N treatments with RMSD of 259 and 268kgha−1, respectively. The effects of water and N treatments were higher than those of CO2, and the model reproduced these effects well. Elevated CO2 effects on crop growth were counter-balanced by temperature effects, and projected precipitation had little effect on the simulated crop. The model results provide reasonable confidence for simulations of possible impacts of projected climate change on wheat crop growth in the region, within normal field data uncertainties. [Copyright &y& Elsevier]

Concentrations of three soluble proteins with molecular masses of 33, 31 and 21 kDa were measured weekly for a period of 1 year in leaves of sour orange (Citrus aurantium L.) trees that had been grown for 6 years at atmospheric CO2 concentrations of 400 and 700 ppm. Abundances of the proteins were generally lower in CO2-enriched leaves than in ambient-treatment leaves during the central portion of the year. Over the early and latter parts of the year, however, they typically were much greater in leaves of the CO2-enriched trees. The decrease from their high wintertime levels in the CO2-enriched trees possibly provided a source of nitrogen required for the enhanced new branch growth observed in the spring on the trees growing in CO2-enriched air. The hypothesis that they are vegetative storage proteins (VSPs) is also supported by the N-terminal amino acid sequence obtained for the 21-kDa protein, which has homology with sporamin B, an implicated storage protein in sweet potato tubers. In addition, immunoelectron microscopy demonstrated the presence of these proteins within amorphous material in the vacuoles of mesophyll cells, where VSPs are commonly located. The fact that elevated CO2 had little impact on the amount of leaf rubisco suggests that enhanced branch and fruit growth observed in the CO2-enriched trees was not correlated with an increased rate of breakdown of this major protein, another potential source of the nitrogen. The 33-, 31- and 21-kDa proteins appear to be specific to citrus species, as immunologically related proteins were detected in a variety of orange, grapefruit, lemon, tangelo and kumquat trees, but were not found in a large number of herbaceous plants and unrelated woody species. [Copyright &y& Elsevier]

• Direct-seeded guayule had the highest yield when irrigated with 75–100 % of crop ET. • Sandy loam soil gave 20–30 % higher rubber/resin yield than clay with 25 % more water. • Furrow irrigation is favored for direct-seeded guayule planted in clay soil. • Subsurface drip is preferred for direct-seeded guayule planted in sandy loam soil. Crop establishment costs of guayule (Parthenium argentatum A. Gray), a perennial desert shrub that produces natural rubber, can be significantly reduced using direct seeding rather than the traditional practice of transplanting greenhouse-grown seedlings. However, information regarding the irrigation application, crop evapotranspiration (ET c), and crop coefficients (K c) for managing direct-seeded guayule crops has not been provided. In this study, guayule was direct-seeded in Apr. 2018 in fields at two location in Arizona; Maricopa, on a sandy loam soil and Eloy, on a clay soil, and harvested 23–24 months later in 2020. At each location, five irrigation rates were applied with subsurface drip irrigation (SDI) ranging from 50 to 150 % replacement of ET c (denoted as D50 to D150 treatments), respectively. A 6th treatment using furrow irrigation at 100 % ET c replacement (F100) was included. Treatments were replicated three times. The ET c was estimated for the first 74–84 days of crop establishment and thereafter, actual ET c (ET c act) was determined weekly-biweekly for the D100 and F100 treatments using a soil water balance. The objectives were to evaluate the responses in dry biomass (DB), rubber yield (RY), and resin (ReY) yield to water application rate, develop irrigation management criteria for the two soil types, and determine the ET c and crop coefficients for the 100 % treatments. The total irrigation applied to treatments ranged from 1830−1910 mm to 5090–5470 and averaged 3590 and 3320 mm for the 100 % SDI (D100) and furrow (F100) treatments at Maricopa and Eloy, respectively. The summed estimated ET c plus ET c act for the D100 and F100 treatments were 3663 and 3506 mm at Maricopa, respectively and 3428 and 3320 at Eloy, respectively. Average measured mid-season K c in the 1st year varied from 1.20 to 1.26. Average measured mid-season K c in the 2nd year were higher for D100 (≈1.30) than for F100 (≈1.23). Adjusted to the standard climate proposed in FAO56, mid-season K c are 1.24 for D100 and 1.17 for F100 in the 2nd year. Average DB at Eloy (28.6 Mg ha−1) was not significantly higher than at Maricopa (24.0 Mg ha−1). However, RY and ReY were both significantly higher at Maricopa. At each location, rubber content was significantly higher for the F100 and the two lowest SDI rates than for other treatments. The highest mean RY and ReY were achieved with D100 at Maricopa and D75 at Eloy. These two also had significantly greater water productivity (WP; DB, RY, and ReY per unit of total water applied) than those at higher SDI rates and the F100 treatments. RY and ReY and their WP were generally higher for D100 than F100 in the sandy loam but not in the clay soil. For direct-seeded guayule in clay soils, furrow irrigation should be considered due to the lower rubber content and higher costs associated with SDI. [ABSTRACT FROM AUTHOR]

• A two-year field trial of transgenic guayule was conducted. • Constitutive gene overexpression/downregulation was confirmed at two years of growth. • Photosynthetic rate increased when allene oxide synthase was downregulated. • Plants with lower allene oxide synthase had altered phytohormone levels. • Plants with lower allene oxide synthase had more branches and thicker stembark. Guayule (Parthenium argentatum) is under development in the southwestern United States as a source of domestic natural rubber; increased rubber yield was found for greenhouse-grown guayule with downregulated allene oxide synthase (AOS). The objective of this study was to evaluate natural rubber production in guayule plants with varying levels of AOS gene expression grown in a field environment. Four plant genotypes: wildtype plants, vector controls, and transgenic plants with overexpressed and downregulated allene oxide synthase (total of 960 plants) were grown at the Bridgestone Guayule Research Farm in Eloy, Arizona between May 2016 to May 2018. Plant phenotypes were evaluated at 6-, 12-, 18-, and 24-months. Downregulated allene oxide synthase (AOSi) genotypes showed remarkable phenotypes including higher photosynthetic activity (net assimilation rate), total number of branches per plant, and plant stembark thickness compared with wildtype, vector control, and overexpressed AOS (AOSoe) lines. Moreover, the rubber particles were smaller and had higher activity (radiolabeled isoprenyl pyrophosphate (IPP) incorporation per g of rubber) in the AOSi genotypes than control and AOSoe lines. The downregulation of AOS also led to significant changes in phytohormone levels, which may have influenced the plants' morphology and physiology. However, in contrast to laboratory and greenhouse studies, natural rubber concentration and yield were not higher in AOSi plants. [ABSTRACT FROM AUTHOR]