Radiation Use Efficiency Values Research Articles

Fluctuations in Radiation Use Efficiency Throughout the Growth Cycle in Diploid Potato Crop

The capture of incoming solar radiation under unlimited light, water, and nutrient conditions by plant canopies and converting it into biomass has been described as radiation use efficiency (RUE). RUE has been computed as a function of biomass accumulation and intercepted photosynthetically active radiation without considering the loss of photoassimilates due to respiratory processes. This study evaluated the RUE in diploid potato crop (Solanum phureja Juz. et Buk.) across six experiments in Colombia. Total biomass was measured during the crop season from the early vegetative stage through maturity. However, this proposal involves not only the total biomass accumulated concerning the amount of photosynthetically active radiation intercepted but also took into account the losses by respiration, following Thornley respiration approach. This research demonstrates that the RUE is not a constant value as the respiration process leads to RUE values being variable in a non-linear way over time. The daily RUE simulation, conducted through an interpolation process, revealed significant variation from emergence to the end of the cycle. This indicates an error in assuming a constant RUE throughout the entire growth period, particularly in assessing its physiological impact across the entire growth and development crop cycle.

Eastern Gamagrass Model Simulation Parameters for Diverse Ecotypes: Leaf Area Index, Light Extinction Coefficient, and Radiation Use Efficiency

Eastern gamagrass (Tripsacum dactyloides) is highly palatable, ideal for grazing and hay production in the United States. It is deep rooted and resilient, tolerant of flooding and drought. Objectives of this study were to develop plant parameters for different ecotypes of this grass. Data collected in field plots of diverse ecotypes included biomass, leaf area index (LAI), light extinction coefficient (k), and radiation use efficiency (RUE). Average LAI was 1.06 and average k was −1.05. The power response of k to LAI offers a new approach to simulating light interception at very low LAI values and throughout the range of LAI values of these ecotypes and similar grass species. The RUE values, which ranged from 1.16 to 4.31 g/MJ, highlight the immense diversity of eastern gamagrass. The high RUE values for the most productive ecotypes emphasizes the importance of this grass species for hay and grazing. While not as large as switchgrass (Panicum virgatum) values, it is still a prominent forage species that even is comparable to maize (Zea mays L.) in productivity when expressed as radiation use efficiency. These results are an important step in developing relationships and parameters to simulate the different ecotypes of this grass with process-based models.

Using crop intercepted solar radiation and vegetation index to estimate dry matter yield of Choy Sum.

An accurate assessment of vegetable yield is essential for agricultural production and management. One approach to estimate yield with remote sensing is via vegetation indices, which are selected in a statistical and empirical approach, rather than a mechanistic way. This study aimed to estimate the dry matter of Choy Sum by both a causality-guided intercepted radiation-based model and a spectral reflectance-based model and compare their performance. Moreover, the effect of nitrogen (N) rates on the radiation use efficiency (RUE) of Choy Sum was also evaluated. A 2-year field experiment was conducted with different N rate treatments (0 kg/ha, 25 kg/ha, 50 kg/ha, 100 kg/ha, 150 kg/ha, and 200 kg/ha). At different growth stages, canopy spectra, photosynthetic active radiation, and canopy coverage were measured by RapidScan CS-45, light quantum sensor, and camera, respectively. The results reveal that exponential models best match the connection between dry matter and vegetation indices, with coefficients of determination (R2) all below 0.80 for normalized difference red edge (NDRE), normalized difference vegetation index (NDVI), red edge ratio vegetation index (RERVI), and ratio vegetation index (RVI). In contrast, accumulated intercepted photosynthetic active radiation (Aipar) showed a significant linear correlation with the dry matter of Choy Sum, with root mean square error (RMSE) of 9.4 and R2 values of 0.82, implying that the Aipar-based estimation model performed better than that of spectral-based ones. Moreover, the RUE of Choy Sum was significantly affected by the N rate, with 100 kg N/ha, 150 kg N/ha, and 200 kg N/ha having the highest RUE values. The study demonstrated the potential of Aipar-based models for precisely estimating the dry matter yield of vegetable crops and understanding the effect of N application on dry matter accumulation of Choy Sum.

Photosynthesis rate, radiation and water use efficiencies of irrigated potato in a semi-arid climate using Eddy covariance techniques

AbstractUnderstanding the photosynthetic behaviour, radiation use efficiency (RUE) and water use efficiency (WUE) of potatoes in response to diurnal and seasonal fluctuations in weather, is important for optimizing growth and production. The net ecosystem exchange (NEE) of carbon dioxide (CO2), is a parameter used to measure the balance between gross CO2 assimilation (also referred to as gross primary production (GPP)) and ecosystem respiration (Reco). The objectives of this study were (i) to quantify the NEE of potato grown in two contrasting agro-ecologies and partition NEE into Reco and GPP; (ii) to describe seasonal patterns in daily photosynthesis, RUE and WUE in potato; and (iii) to analyse the variability in photosynthesis rate, RUE and WUE as affected by weather and crop growth stage. We measured CO2 and water vapour fluxes using eddy covariance techniques in potato fields in two production regions of South Africa. The winter crop had higher mean RUE and WUE values, whereas the summer crop absorbed more CO2. RUE had a negative relationship with incident radiation. To optimize dry matter production, WUE and RUE, potato crops must be well established and develop a full canopy early during the season. Maintaining the crop for a longer period in the field has yield benefits, although they appear to decline over time due to reduced efficiencies as the crop matures. The RUE observed over the growing period in the present study was high, relative to findings by other field studies, despite relatively warm growing conditions that were likely sub-optimal for potato.

Effects of plant density on the aboveground dry matter and radiation-use efficiency of field corn.

The amount of solar radiation intercepted by the plant canopy drives crop plant photosynthesis and the formation and development of plant organs. Radiation-use efficiency (RUE) is an index used to quantify the relationship between solar radiation and biomass, and crop yield can be increased by increasing RUE. The main goals of this study were to initially investigate the effects of plant densities on the aboveground dry matter of corn, and subsequently examine the effects of plant densities on RUE and leaf area index (LAI), and the effects of LAI on RUE. Finally, we provide a comparative assessment of the approaches used to determine RUE. Analyses were conducted using growth and meteorological data obtained for two field corn varieties (TNG1 and TNG7) grown under four different plant density conditions in central Taiwan in 2017. The RUE values obtained in this study were primarily estimated from the slope of the linear relationship between aboveground dry matter measured at periodic harvests and the corresponding cumulative intercepted photosynthetically active radiation up to the time of harvest. TNG1 and TNG7 with a row spacing of 37.5 cm × 20 cm had the largest amounts of aboveground dry matter and highest RUE values of 4.41 and 4.55 g MJ-1, respectively. We established that the higher the plant density, the higher were the values obtained for RUE and LAI. We also compared the different methods of estimating RUE and make recommendations in this regard. Our findings in this study will enable farmers to gain information on the dynamics of crop yield variation at an early stage of growth, and also provide reference values that can be incorporated in future crop yield models.

Eco-physiological yield determinants in four potato genotypes grown in a temperate environment

The eco-physiological yield determinants of four potato genotypes suitable for processing into French fries were studied. Field trials were carried out during the growing seasons 2016/17 and 2017/18 at Balcarce, Argentina (−37.85 S, −58.19 W). Genotypes, identified as Bal1, Bal2, Bal3 and Bal4, have growing cycles of 95–105, 100–110, 110–120, and 120–130 days after emergence, respectively. Intercepted photosynthetic active radiation (PARint), radiation use efficiency (RUE), harvest index (HI) and tuber yield were evaluated during both growing seasons. Bal4 achieved the highest dry matter tuber yield in both growing seasons, with 1412 and 1879 g mˉ² for 2016/17 and 2017/18, respectively. Due to a combination of a high PARint and RUE values, tuber dry matter in Bal4 was 20–30 % higher than that achieved by other genotypes. PARint throughout the growing cycle was 1025 and 1121 MJ mˉ² for Bal4, for 2016/17 and 2017/18 seasons, respectively; these values were 10–22 % higher than those observed for the other genotypes. RUE was 1.66 and 2.02 g MJˉ 1 for Bal4 in 2016/17 and 2017/18 growing seasons, respectively, these values are 14–18 % higher than those observed for the other genotypes. HI varied between 0.81 and 0.87 for all genotypes, in both seasons. PARint, and RUE were the two most critical yield determining factors that explained the differences in tuber dry matter yield between the potato genotypes. Bal4 showed highest yields due to a particular combination of high PARint and high RUE, not reported in the literature, so far. These results could contribute to improve early selection in future breeding programs, to better adjust growth models and to establish specific management strategies for a particular genotype. • The eco-physiological yield determinants of four potato genotypes were studied. • Genotypes differed in cycle length and in intercepted radiation. • Genotypes also differed in radiation use efficiency and in harvest index. • One genotype combined high radiation interception and high radiation use efficiency.

The Effect of Planting Time and Plant Density on Radiation Use Efficiency (RUE) on Lowland Rice (Oryza sativa L.) Cv. Inpari 30

The right planting time and plant density in rice cultivation in the rainy season affect the generative phase, where absorption of solar radiation intensity more efficiently increases productivity. This study aims to improve the absorption of energy efficiency of solar conversion with differences in planting time and planting density. The experiment was carried out from January to June 2019 in the experimental garden of Brawijaya University, Malang City, East Java. The research design used is a nested design with three replication. The main factor is planting time which consists of 3 levels, namely: January (B1); February (B2); March (B3). The nested factor is plant density which consists of 3 levels, namely: 111.111 plant ha-1 (T1); 166.667 plant ha-1 (T2); 226,667 plant ha-1 (T3). Data analysis used variance (ANOVA). If the results are significantly different, then the honest significant difference test (HSD) is continued at the 5% level. The results showed the differences in total leaf area index, plant dry weight, panicle weight every clump, grain weight every clump, grain weight every harvest plot, yield per hectare, and radiation use efficiency (RUE). The planting time in March has a higher RUE value than the planting time in January or February. The yield per hectare shows the planting time in March is higher than the planting time in January or February planting time. Plant density of 30x30 cm shows yields per hectare higher than planting density of 30x20 cm and planting density of 40x20x12.5 cm.Â

Radiation use efficiency and biomass production of maize under optimal growth conditions in Northeast China.

Accurate crop growth and radiation use efficiency (RUE) measurements under optimal growth conditions are required to predict grain yield near the genetic growth potential and estimate climate change effects on crop production. Research was conducted to quantify RUE of maize during the whole growth period, vegetative period (VP, phenological development stage DVS < 1.0), and reproductive period (RP, DVS ≥ 1.0) under the optimal growth condition in Northeast China. Maize was grown in three population density treatments (9.0, 7.5, and 6.0 plants m-2, referred to HD, MD, and LD respectively) over three growing seasons (2017-2019). The maximum Leaf Area Index (LAI) was observed after the anthesis period (DVS = 1.2), ranged from to 4.9 to 6.9, and then gradually decreases. Photosynthetically active radiation (PAR) intercepted by the canopy of maize was approximate 10% during the early stage of the vegetative period (DVS < 0.3). Then greatest differences occurred during the late vegetative period (DVS = 0.3 to 0.8). When DVS > 1.0, there is no significant difference between the three population density conditions. Estimates of RUE were obtained based on the intercepted PAR (IPAR) and absorbed PAR (APAR). RUE value was 3.97 g MJ-1 APAR or 3.73 g MJ-1 IPAR in the whole growth period, and did not vary among density treatments. Moreover, maximum RUE occurred during VP (4.11 g MJ-1 APAR) and declined during RP (3.95 g MJ-1 APAR). Therefore, we recommend that maize models that rely on RUE for aboveground biomass accumulation should be using a value of 3.97 g MJ-1 APAR for predicting optimum maize grain yield in Northeast China, especially for the potential yield.

Effect of Varieties and Spacing on Radiation Efficiency, Growth and Yield of Sweet Corn (Zea mays saccharata Sturt.) in The Lebak Swamp Land

Corn is an important food crop in Indonesia which has a function as a source of food, a source of feed and the main ingredient for industry. Corn production in Hulu Sungai Utara Regency has increased from 2018-2020. However, it has not been able to meet market demand for corn because it is constrained by several factors such as lowland swamp land which is used as a place of cultivation with all the problems, namely periodically inundated land, low soil fertility, high soil acidity, toxic substances, lack of micro nutrients, organic matter still raw and others. From the aspect of cultivation technology, the use of superior varieties and proper spacing is influenced by environmental factors, especially climatic factors. The objectives of the study were: 1) Analyzing the interaction of varieties and planting distance on radiation efficiency and growth component of sweet corn (Zea mays saccharata Sturt.) in the lebak swamp land. 2) Analyzing the best varieties and the best planting distance for radiation efficiency and growth component of sweet corn (Zea mays saccharata Sturt.) in the lebak swamp land. This research was conducted in the lebak swamp land of ​​the STIPER Amuntai Experimental Garden, Muara Tapus Village, Hulu Sungai Utara Regency, South Kalimantan Province. At an altitude of ± 2 meters above sea level with coordinates of -2o28' South Latitude and 115o13"' East Longitude from May 2021 to August 2021. This study used a factorial randomized block design (FRBD) method. The first factor is the sweet corn variety (V) consisting of four levels, namely exsotic variety (v1), jambore variety (v2), talenta variety (v3) and ganebo variety (v4). The second factor is sweet corn planting distance (J) consisting of three levels, namely 75 cm x 20 cm (j1), 75 cm x 25 cm (j2) and 75 cm x 30 cm (j3). The results showed that the interaction between varieties and spacing did not affect all observation variables. Varieties affect the observed variables of plant height, number of leaves, leaf area index, plant growth rate, relative growth rate and number of seeds per row. Plant spacing affects the observed variables of plant height, leaf area index and plant growth rate. The best variety is the talent variety (v3) and the best spacing is 75 cm x 20 cm (j1) and the value of radiation use efficiency is 1,5584 g.MJ-1.

Radiation Use Efficiency and Agronomic Performance of Biomass Sorghum under Different Sowing Dates

Accurate estimation of radiation use efficiency (RUE) at variable timed sowing dates will enhance the prediction of plant dry matter accumulation. The objectives of this study were to (1) determine the impact of three sowing dates on the productivity, performance, and economic feasibility of three biomass sorghum hybrids and (2) evaluate the variability of RUE in the production of biomass sorghum under the effects of variable timed sowing dates. Over a two-year experiment, biomass sorghum hybrids were grown and monitored at different sowing seasons under optimal growth conditions. Average dry biomass (DB) productivity at harvest ranged from 22.71 to 32.77 Mg ha−1. Higher leaf area index (LAI) values (&gt;4.0) represented an intercept of over 95% of incident photosynthetically active radiation (PAR). RUE obtained from the slope of the linear relationship between DB produced and accumulated intercepted photosynthetically active radiation (IPAR) ranged from 2.92 to 4.157 g MJ−1 across growing seasons. Higher RUE values were observed for the energy hybrids in the early and mid-season. They converted IPAR efficiently into DB. Lastly, the economic feasibility of each sorghum hybrid and sowing date was evaluated in terms of their expected net returns. Economic results suggest that the sorghum hybrids considered could be a viable source of biomass season long, with net returns ranging from USD 560.55 ha−1 to USD 1255.06 ha−1.

Regionalizing crop types to enhance global ecosystem modeling of maize production

Improving the prediction of crop production is critical for strategy development associated with global food security, particularly as the climate continues to change. Process-based ecosystem models are increasingly used for simulating global agricultural production. However, such simulations often use a single crop variety in global assessments, implying that major crops are identical across all regions of the world. To address this limitation, we applied a Bayesian approach to calibrate regional types of maize (Zea mays L), capturing the aggregated traits of local varieties, for DayCent ecosystem model simulations, using global crop production data from 2001 to 2013. We selected major cropping regions from the FAO Global Agro-Environmental Stratification as a basis for the regionalization and identified the most important model parameters through a global sensitivity analysis. We calibrated DayCent using the sampling importance resampling algorithm and found significant improvement in DayCent simulations of maize yields with the calibrated regional varieties. Compared to a single type of maize for the world, the regionalization of maize leads to reductions in root mean squared error of 11%, 31%, 27%, 30%, 19%, and 27% and reductions in bias of 59%, 59%, 50%, 81%, 32%, and 56% for Africa, East Asia, Europe, North America, South America, and South and Southeast Asia, respectively. We also found the optimum parameter values of radiation use efficiency are positively correlated with the income level of different regions, which indicates that breeding has enhanced the photosynthetic efficiency of maize in developed countries. There may also be opportunities for expanding crop breeding programs in developing countries to enhance photosynthesis efficiency and reduce the yield gap in these regions. This study highlights the importance of representing regional variation in crop types for achieving accurate predictions of crop yields.

Impact of Foliar Fungicides on Frogeye Leaf Spot Severity, Radiation Use Efficiency and Yield of Soybean in Iowa

Frogeye leaf spot, caused by Cercospora sojina K. Hara, is a major soybean (Glycine max L. Merr.) disease that has become more prevalent in the upper Midwest and can be managed with foliar fungicides. Incorporating disease severity into a parameter directly related to yield may better relay the impact of disease on yield and yield components than severity alone. Experiments during the 2018 and 2019 growing seasons in fields located in north central and southwestern Iowa were completed to (i) determine how foliar fungicides affected frogeye leaf spot, remotely sensed plant health indicators, and soybean yield, and (ii) compare the relationship and impact of foliar fungicides and frogeye leaf spot on radiation-use efficiency (RUE) estimated using unmanned aerial vehicle reflectance data. Fungicides affected frogeye severity and yield in one of the three locations; in Lewis 2018, the flutriafol + fluoxastrobin treatment reduced frogeye leaf spot severity by over 50% and increased yield by 19% compared to non-treated controls. Applications of foliar fungicides increased canopy coverage compared to non-treated controls (p = 0.012), but NDVI, SPAD values, and RUE values did not differ between fungicide treatments at all three locations. Estimated soybean RUE values (1.05 to 1.66 g Mj−1) were within the range of known values. Overall, this study indicates that RUE can be a valuable resource to estimate the impact of the disease on yield, however, additional research will be needed to use RUE within certain pathosystems.

Quantifying the interaction of water and radiation use efficiency under plastic film mulch in winter wheat

Local natural resources, (e.g., precipitation, solar radiation) are important for developing environmentally and scientifically sound management practices in dryland agroecosystem. Maximizing water use efficiency (WUE) in dryland farming systems remains a challenge. The objectives of this study were to assessing the robustness of radiation use efficiency (RUE) during different periods and investigate the interaction between RUE and WUE from water loss pattern and canopy development during wheat growth under different agricultural practices (non-mulched control, CK; transparent film mulching, TF; and black film mulching, BF) from 2013 to 2016 on the Loess Plateau, Northwest China. Results showed that RUE was mainly improved during post-anthesis under PM treatments. PM treatments contributed to elevated canopy photosynthesis and a delayed RUE peak during the reproductive period. Due to the increased spike number and ratio of plant transpiration to soil evaporation, TF and BF treatments had relatively stable photosynthetic activity relative to the CK treatment even those during dry periods. Initially, no relationship was found between WUE and RUE under the CK treatment. On the other hand, RUE and WUE were positively related in TF and BF treatments following a power function. RUE values increased with WUE rapidly to stabilize at a plateau value of 5.5 g MJ−1 under TF and BF treatments, and thus, the wheat WUE had a higher improvement potential than RUE as it did not have an apparent plateau value. PM treatments enhanced the wheat production by taking full advantage of local solar radiation and precipitation (improving RUE and WUE). This higher use efficiency of resources produced more photoassimilates for wheat than that under the CK management, increased source size (LAI) and sink size (spike number) during wheat growth seasons, and thus increased the final grain yield.

Cultivar selection can increase yield potential and resource use efficiency of spring maize to adapt to climate change in Northeast China

Northeast China (NEC) is one of the major maize production areas in China. Agro-climatic resources have obviously changed, which will seriously affect crop growth and development in this region. It is important to investigate the contribution of climate change adaptation measures to the yield and resource use efficiency to improve our understanding of how we can effectively ensure high yield and high efficiency in the future. In this study, we divided the study area into five accumulated temperature zones (ATZs) based on growing degree days (GDD). Based on the meteorological data, maize data (from agro-meteorological stations) and the validated APSIM-Maize Model, we first investigated the spatial distributions and temporal trends of maize potential yield of actual planted cultivars, and revealed the radiation use efficiency (RUE) and heat resource use efficiency (HUE) from 1981 to 2017. Then according to the potential growing seasons and actual growing seasons, we identified the utilization percentages of radiation (PR) resource and heat resource (PH) for each ATZ under potential production from 1981 to 2017. Finally, we quantified the contributions of cultivar changings to yield, PR and PH of maize. The results showed that during the past 37 years, the estimated mean potential yield of actual planted cultivars was 13 649 kg ha–1, ranged from 11 205 to 15 257 kg ha–1, and increased by 140 kg ha–1 per decade. For potential production, the mean values of RUE and HUE for the actual planted maize cultivars were 1.22 g MJ–1 and 8.58 kg (°C d)–1 ha–1. RUE showed an increasing tendency, while HUE showed a decreasing tendency. The lengths of the potential growing season and actual growing season were 158 and 123 d, and increased by 2 and 1 d per decade. PR and PH under potential production were 82 and 86%, respectively and showed a decreasing tendency during the past 37 years. This indicates that actual planted cultivars failed to make full use of climate resources. However, results from the adaptation assessments indicate that, adoption of cultivars with growing season increased by 2–11 d among ATZs caused increase in yield, PR and PH of 0.6–1.7%, 1.1–7.6% and 1.5–8.9%, respectively. Therefore, introduction of cultivars with longer growing season can effectively increase the radiation and heat utilization percentages and potential yield.

Estimating Soybean Radiation Use Efficiency Using a UAV in Iowa

Radiation use efficiency (RUE) is difficult to estimate and unreasonable to perform on a small plot scale using traditional techniques. However, the increased availability of Unmanned Aerial Vehicles (UAVs) provides the ability to collect spatial and temporal data at high resolution and frequency, which has made a potential workaround. An experiment was completed in Iowa to (i) demonstrate RUE estimation of soybean [Glycine max (L.) Merr.] from reflectance data derived from consumer-grade UAV imagery and (ii) investigate the impact of foliar fungicides on RUE in Iowa. Some fungicides are promoted to have plant health benefits beyond disease protection, and changes in RUE may capture their effect. Frogeye leaf spot severity did not exceed 2%. RUE values ranged from 0.98 to 1.07 and 0.96 to 1.12 across the entire season and the period post-fungicide application, respectively, and fell within the range of previously published soybean RUE values. Plots treated with fluxapyroxad + pyraclostrobin had more canopy cover (p = 0.078) compared to the non-treated control 133 days after planting (DAP), but yields did not differ. A “greening effect” was detected at the end of the sample collection. RUE estimation using UAV imagery can be considered a viable option for the evaluation of management techniques on a small plot scale. Since it is directly related to yield, RUE could be an appropriate parameter to elucidate the impact of plant diseases and other stresses on yield.

Air temperature is the main driving factor of radiation use efficiency and carbon storage of mature Norway spruce stands under global climate change.

Plant growth is affected by light availability, light capture, and the efficiency of light energy utilisation within the photosynthetic uptake processes. The radiation use efficiency (RUE) of four even-aged, fully stocked mature Norway spruce stands along a temperature, precipitation, and altitudinal gradient of the Czech Republic was investigated. A new straightforward, methodological approach involving an analysis of digital hemispherical photographs for RUE estimation was applied. The highest annual RUE value (0.72 g MJ-1) was observed in the stand characterised by the lowest mean annual air temperature, the highest annual amount of precipitation, located at the highest altitude, and with the lowest site index reflecting site fertility. From the viewpoint of global climate change mitigation, this stand fixed 4.14 Mg ha-1 and 13.93 Mg ha-1 of carbon units and CO2 molecules into above-ground biomass, respectively. The lowest RUE value (0.21 g MJ-1) within the studied growing season was found in the stand located at the lowest altitude representing the site with the highest mean air temperature and the lowest amount of precipitation where 1.27 Mg ha-1 and 4.28 Mg ha-1 of carbon units and CO2 molecules, respectively, were fixed. From the tested meteorological variables (mean air temperature, the monthly sums of temperature, precipitation, and air humidity), RUE was only significantly dependent on air temperature. Therefore, global warming can lead to diminishing RUE and carbon sequestration in Norway spruce stands, especially at low altitudes.

Intercepted radiation and radiation-use efficiency in sunflower crops grown at conventional and wide inter-row spacings: Measurements and modeled estimates of intercepted radiation

The underlying eco-physiological principle behind row spacing choice in many field crops is that early and complete ground cover will maximize yield via greater crop photosynthesis during the critical period for grain number determination in environments with no major water limitations. Recently this principle has been put in doubt: wide row-spacing (1.40 m instead of 0.7 m) did not reduce oil or biomass yield in sunflower at plant densities of between 2 and 7 pl m−2, in spite of incomplete ground cover at the wider row spacing. Here, we report the effect of two row spacings (0.7 and 1.4 m), in sunflower crops of equal plant density, on interception of radiation, radiation use efficiency (RUE), crop biomass and oil yields in three experiments. Two approaches were used to estimate interception of radiation by the crops: i) periodic diurnal measurements during the crop cycle of interception in the inter-row space and on the sides of the hedgerows; and ii) the use of a olive hedgerow model, adapted to sunflower, to estimate radiation intercepted by the two crop arrays. Biomass at anthesis, at physiological maturity, and oil yield in crops grown in the two row-spacings did not differ. The results show that the increased RUE of the 1.4-m spaced crops in pre-anthesis phase was able to compensate for the delay of these crops in achieving close to full interception of irradiance. The daily patterns of irradiance incident on the hedgerow faces, especially the sunlit face, in the pre-anthesis phase and in the early and late hours of the day, were strongly affected by row-spacing. A more favorable irradiance in these periods of the day in the mid- and upper portions of the sunlit face of the 1.4-m spaced hedgerows may have contributed to the greater RUE values of these crops in the pre anthesis phase.The hedgerow model provided descriptions of the seasonal dynamics of intercepted radiation that were fully consistent with measured values for both row spacings.

Different determinants of radiation use efficiency in cold and temperate forests

AbstractAimTo verify which vegetation and environmental factors are the most important in determining the spatial and temporal variability of average and maximum values of radiation use efficiency (RUEann and RUEmax, respectively) of cold and temperate forests.LocationForty‐eight cold and temperate forests distributed across the Northern Hemisphere.Major taxa studiedEvergreen and deciduous trees.Time period2000–2011.MethodsWe analysed the impact of 17 factors as potential determinants of mean RUE (at 8 days interval, annual and interannual level) and RUEmax (at annual and interannual level) in cold and temperate forests by using linear regression and random forests models.ResultsMean annual RUE (RUEann, c. 1.1 gC/MJ) and RUEmax (c. 0.8 gC/MJ) did not differ between cold and temperate forests. However, for cold forests, RUEann was affected by temperature‐related variables, while for temperate forests RUEann was affected by drought‐related variables. Leaf area index (LAI) was important for both forest types, while N deposition only for cold forests and cloud cover only for temperate forest. RUEmax of cold forests was mainly driven by N deposition and LAI, whereas for temperate forests only a weak relationship between RUEmax and CO2 concentration was found. Short‐term variability of RUE was strongly related to the meteorological variables and varied during the season and was stronger in summer than spring or autumn. Interannual variability of RUEann and RUEmax was only weakly related to the interannual variability of the environmental drivers.Main conclusionsCold and temperate forests show different relationships with the environment and vegetation properties. Among the RUE drivers observed, the least anticipated was N deposition. RUE is strongly related to short‐term and seasonal changes in meteorological variables among seasons and among sites. Our results should be considered in the formulation of climate zone‐specific tools for remote sensing and global models.

Radiation Use Efficiency of Forage Resources: A Meta‐Analysis

Core Ideas This is the first meta‐analysis of radiation use efficiency (RUE) of forage resources.RUE was most responsive to genotype, followed by N, water and light availability.Mean intraspecific differences were as large as interspecific ones.Most responses of RUE to the environment depended on the level of other factors.These results will enhance the accuracy of radiation‐based plant growth models. Forage production is increasingly monitored through models based on remote sensing. Radiation use efficiency (RUE) is a key input to these models. However, no study has synthesized the published values of RUE of forage resources. Our objective was to quantitatively synthesize through a meta‐analysis the variation of RUE of forage resources and its main controls. We gathered 496 RUE values and assessed their variation according to genotype, resource availability and phenological stage. Mean RUE was 1.93 ± 1.2 g of dry matter (DM) per megajoule of intercepted photosynthetically active radiation (IPAR) (±SD). The RUE was most responsive to genotype and to direct and indirect manipulations of resource availability. Within genotype treatments, mean effect size of C4 species identity, cultivar identity and C3 species identity was 61, 58, and 42%, respectively. Within resource availability treatments, mean effect size was 43% for N fertilization, 40% for shading and inter‐annual environmental variation and 23% for irrigation and defoliation frequency. For the phenology treatment, mean effect size of reproductive vs. vegetative stage did not differ from zero. This large variability implies a challenge to select RUE values as input to estimate productivity through plant‐growth models, such as those based on remote sensing, but also highlight the margin for increasing RUE through breeding and management practices.

Radiation use efficiency and biomass partitioning to storage roots in fodder beet crops

Abstract Intercepted photosynthetic active radiation (IPAR), radiation use efficiency (RUE) and partitioning of dry matter (DM) to storage roots (proot, %) were quantified for fodder beet crops subjected to contrasting water (irrigated or rain-fed) and nitrogen (N; 0, 25, 50, 100 and 200 kg/ha) supply conditions in Canterbury, New Zealand. The objectives were to enhance the understanding of physiological processes controlling fodder beet response to abiotic stresses and also to estimate parameters for biophysical models that simulate crop growth. Data from three field experiments showed a wide range of fodder beet yield (14–29 t DM/ha) in response to water and N stress. These yield differences were mostly explained by the treatments effect on IPAR (650–1050 MJ PAR/ha), with relatively smaller responses in RUE and proot. For unconstrained (fully irrigated; ≥100 kg N/ha) growth conditions, maximum values were 3.6 g DM/MJ PAR for RUE and 78% for proot for total biomass at final harvest. The RUE for the rain-fed, 0 kg N/ha crops was reduced by up to 25%, while proot was only marginally reduced (∼3% in rain-fed crops) compared with crops under unconstrained growth conditions. While the RUE responded linearly to additional N supply in irrigated crops, rain-fed crops showed a more consistent decline in RUE across N fertiliser rates with 65–70% of unstressed values. High RUE values were observed across a wide range of crop N status (Nitrogen Nutrition Index [NNI] from 0.8 to 1.6) in irrigated crops. In contrast, RUE in rain-fed was low at high NNI estimates because of high N concentration in a smaller canopy area. The lower RUE in rain-fed crops was aligned with reduced leaf photosynthetic rates (Pnleaf) although there was a high variability in Pnleaf measurements. These results give a first quantification of IPAR, RUE, proot and Pnleaf in fodder beet. They provide insights on the relative sensitivity of fodder beet to water and N stresses. These results are valuable for the interpretation of crop responses and for setting parameters for biophysical models to simulate fodder beet growth.