Radiation Use Efficiency Values Research Articles

Clash of the Titans: Comparing Productivity Via Radiation Use Efficiency for Two Grass Giants of the Biofuel Field

The comparative productivity of switchgrass (Panicum virgatum L.) and Miscanthus (Miscanthus × giganteus) is of critical importance to the biofuel industry. The radiation use efficiency (RUE), when derived in an environment with non-limiting soil water and soil nutrients, provides one metric of relative productivity. The objective of this study was to compare giant Miscanthus to available switchgrass cultivars, using established methods to calculate RUE of the two species at two disparate sites. Measurements of fraction intercepted photosynthetically active radiation (PAR) and dry matter were taken on plots at Elsberry, MO (Miscanthus and the switchgrass cultivars Alamo, Kanlow, and Cave-in-Rock) and at Gustine, TX (Miscanthus and Alamo switchgrass, irrigated with dairy wastewater and a non-irrigated control). In MO, Miscanthus mean RUE (3.71) was less than Alamo switchgrass mean RUE (4.30). In TX under irrigation, Miscanthus mean RUE was 2.24 and Alamo switchgrass mean RUE was 3.20. In MO, the more northern lowland switchgrass cultivar, Kanlow, showed similar mean RUE (3.70) as Miscanthus. In MO, the northern upland cultivar Cave-in-Rock had a mean RUE (3.17) that was only 85% of that for Miscanthus at MO. Stress (water and nutrients) had a greater effect on Miscanthus RUE than on switchgrass RUE in TX. These results provide realistic RUE values for simulating these important biofuel grasses in diverse environmental conditions.

Canopy stay-green and yield in non-stressed sunflower

Delayed leaf senescence during the grain filling phase, or stay green (SG), may be functional or cosmetic; the first being considered a valuable trait in breeding of many crop species. To establish whether canopy senescence patterns exhibited by two sunflower ( Helianthus annuus L.) hybrids visually selected for slow post-anthesis canopy leaf area index (LAI) loss reflected functional, rather than cosmetic, SG, LAI dynamics and total biomass increase between anthesis and physiological maturity were followed in three separate experiments in which the putative SG hybrids were compared with standard (i.e., non stay green, NSG) hybrids exhibiting normal rates of canopy senescence under non- or minimal-water stress conditions. In two experiments, pairwise (i.e., one SG vs. one NSG) comparisons were made at two crop population densities. In the third experiment, grown at a single crop population density, four NSG hybrids were contrasted with the two SG hybrids. Canopy senescence dynamics were well described by fitted bilinear functions which discriminated between an initial, slow phase of leaf area loss and a second phase of rapid canopy senescence. No differences between hybrids in the rate of senescence during the first phase were found, but the putative SG hybrids exhibited a significantly slower rate of senescence during the second phase and a significantly higher LAI at physiological maturity (as % of LAI at anthesis). One NSG hybrid showed a greater rate of second-phase senescence than the remaining three hybrids in this category. Across experiments, the anthesis-physiological maturity increment in total oil-corrected biomass and radiation use efficiency (RUE) were significantly greater in the SG hybrids. Cluster analysis based on these four attributes, using data from Exp. 3, clearly discriminated between SG and NSG hybrids. Examination of specific leaf N (SLN) dynamics suggests that the lower RUE values observed in one of the NSG hybrids could be attributable to lower SLN values, but this was not the case for the remaining NSG hybrids. It is also possible that very rapid canopy LAI loss in another NSG hybrid may underlie its lower RUE. The failure of SG hybrids to translate greater post-anthesis biomass increment into grain yield across experiments was associated with their slightly shorter times to anthesis and their significantly lower biomass at anthesis. Grain number, the component of yield most strongly associated with yield, was associated with biomass at anthesis. A further contributing factor was that the duration of grain-filling tended to be shorter in SG hybrids. In the one experiment in which this variable was measured, resistance to stalk breakage was greater in the SG hybrids than the NSG one to which they were compared. We conclude that the SG observed in the hybrids with slower canopy senescence is functional and not cosmetic, and that for this to be translated into a yield advantage all hybrids need to reach anthesis at the same time and grain-filling duration also has to be the same across hybrids. Stay green is an interesting secondary trait to select for and should lead to higher and more stable yields in environments in which stem breakage (lodging) is a problem.

Radiation-use efficiency of irrigated biomass sorghum in a Mediterranean environment

Mathematical crop simulation models are useful tools in predicting the potential yield of field crops in a specific environment. The main driving parameter used to estimate biomass accumulation in most of these models is radiation-use efficiency (RUE). Biomass sorghum (Sorghum bicolor L. Moench) is a crop that can be used for energy production (thermal and bioethanol chains) and a knowledge of its RUE in different water supply conditions can help to improve model simulations and evaluate crop diffusion. A 3-year field experiment was carried out in Southern Italy where sorghum was submitted to four irrigated regimes based on actual crop evapotranspiration (ETc). In the first year ETc was measured with weighted lysimeters, while in the other 2 years it was estimated by means of estimated crop coefficient (Kc) and the reference evapotranspiration ET0. The RUE, calculated as the slope of the first-order equation between dry biomass and intercepted photosynthetically active radiation along a crop cycle, showed an average of 2.91 ± 0.54 g MJ–1, even if the RUE proved to be closely correlated with crop water consumption. The latter ranged between 891 and 454 mm and the RUE increased 4.2 mg MJ–1 per mm of water used. A high crop interception of solar radiation was observed in sorghum, reaching its maximum efficiency 40 days after sowing. To obtain high yielding yield biomass sorghum requires a large supply of water, as confirmed by the Kc calculated during the crop cycle, which resulted higher (especially in the development and middle stages) when compared with those reported in the FAO 56 Paper. The obtained RUE values also confirmed a high efficiency in biomass production of this crop, allowing for the introduction of biomass sorghum in the cropping systems of Mediterranean environments as an alternative crop for energy purposes, but with adequate irrigation water supply.

Effects of Reduction in Plant Height Induced by Chlormequat on Radiation Interception and Radiation-Use Efficiency in Wheat in Southwest Japan

The effects of reducing plant height by the growth retardant chlormequat on radiation interception and radiation-use efficiency in field-grown wheat were studied in southwest Japan. Chlormequat was applied to wheat cultivar Sanukinoyume 2000 at the beginning of jointing. The cumulative total solar radiation intercepted by the plant canopy (Si) was determined by continuous measurements of total solar radiation above the canopy with a dome pyranometer and below the canopy with tube solarimeters. Nondestructive measurement of leaf area index (LAI) and mean tip angle of the canopy (MTA) using a plant canopy analyzer was performed weekly. Chlormequat application shortened the culm length by 12.6% compared with the control, but did not affect the aboveground dry matter (AGDM), LAI, yield or yield components except for the harvestindex (HI). The extinction coefficient in canopy (K) was not affected by chlormequat, so that Si at heading and anthesis were not significantly different. Radiation-use efficiency (RUE) of chlormequat treated plants estimated from the slope ofalinearregression of Si vs AGDM was 1.34 g MJ-1 for the period up to heading and 1.57 g MJ-1 for theperiod up to anthesis. The RUE values were not significantly different between chlormequat-treated and control plants. Although the effect may be restricted to the duration from heading to the premature ripening stage, a higher MTA in chlormequat should provide a more even distribution of radiation within the canopy, which should increase the photosynthetic performance. These results suggested that shortening the culm length of this wheat cultivar by about 12% is beneficial in reducing the risk of lodging without affecting light interception characteristics or RUE.

Solar radiation use efficiency by soybean under field conditions in the Amazon region

The objective of this work was to evaluate the efficiency of soybean (Glycine max) in intercepting and using solar radiation under natural field conditions, in the Amazon region, Brazil. The meteorological data and the values of soybean growth and leaf area were obtained from an agrometeorological experiment carried out in Paragominas, Pará state, during 2007 and 2008. The radiation use efficiency (RUE) was obtained from the ratio between the above-ground biomass production and the intercepted photosynthetically active radiation (PAR) accumulated to 99 and 95 days after sowing, in 2007 and 2008, respectively. Climatic conditions during the experiment were very distinct, with reduction in rainfall in 2007, which began during the soybean mid-cycle, due to the El Niño phenomenon. An important reduction in the leaf area index and biomass production was observed during 2007. Under natural field conditions in the Amazon region, the values of RUE were 1.46 and 1.99 g MJ-1 PAR in the 2007 and 2008 experiments, respectively. The probable reason for the differences found between these years might be associated to the water restriction in 2007 coupled with the higher air temperature and vapor pressure deficit, and also to the increase in the fraction of diffuse radiation that reached the land surface in 2008.

<b>EFISIENSI PENGGUNAAN RADIASI SURYA DAN SEBAGAI DASAR DALAM MODEL JARAK PAGAR</b><br>(RADIATION USE EFFICIENCY AS BASIS THE CROPS MODELING OF JATROPHA)

Plant growth interpretation in term of accumulated intercepted solar radiation and the radiation use efficiency (RUE) was used to study the growth and analysis of Jatropha (Jatropha curcas L.). A number of crop growth simulation models have been developed using the RUE concept to predict crop growth and yield in various environments. These models generally calculate daily biomass production as the product of the quantity of radiation intercepted and RUE. This research was carried out to quantify the RUE, biomass and leaf area index on Jatropha under rainfall condition, four levels of nitrogen fertilizer (N) and three population densities (P) planted twice. The experiments used a systematic Nelder fan design with 9 spokes and 4 – 5 rings were conducted at SEAMEO-BIOTROP field experiment in 2007. Data from the first experiment were used for parameterization and calibration and the second experiment data for model validation. Values of RUE were determined by nitrogen fertilizer and plant density. Based on parameterization, we found that RUE for prediction above ground biomass accumulation of Jatropha were 0.94 (r=0.83) g MJ-1 to 1.3 (r=0.75) g MJ-1. Validation between model prediction and field experimental data showed that model can simulate crop growth and development of Jatropha.

Productivity and radiation use efficiency of tea grown under different shade trees in the plain land of West Bengal

Tea is grown under shade trees at higher elevation to attain better quality and higher productivity of the leaf. Hence, a field study was carried out to study the influence the shade trees on productivity and radiation use efficiency of the tea, when grown under plain at the Krishi Ban (Tea garden) of Bidhan Chandra Krishi Viswavidyalaya, Gayespur, West Bengal (Latitude 220 58/ N, Longitude 880 31/ E, altitude 9.75 m amsl). Different shade trees namely Acacia auriculiformis, Albizia lebbeck, Dalbergia sissoo, Glyricidia sepium, Casuarina equisetifolia, Gmelina arborea and Eucalyptus hybrid were taken for screening. Observation on yield and components of Photosynthetic Active Radiation (PAR) were taken at four periods. Each period began from one day after a plucking date and continued to the next plucking date. In total there were four periods as: Period I (7.9.01-3.10.01), Period II (4.10.01-13.11.01), Period III (14.11.01-22.2.02) and Period IV (23.2.02-19.3.02). Irrespective of periods, maximum productivity level (398.1 Kg ha-1) of tea was attained under Dalbergia sissoo and it was minimum (271.7 Kg ha-1) under Glyricidia sepium. Irrespective of periods the highest level (0. 438 g MJ-1) of radiation use efficiency (RUE) was attained under Gmelina arborea. Tea grown under Glyricidia sepium and Casuarina equisetifolia resulted lowest RUE value.

Radiation Use Efficiency of Arrowleaf, Crimson, Rose, and Subterranean Clovers

Parameters describing the growth of cool‐season annual clovers are necessary for potential growth simulations, but have not yet been determined. Accordingly, the objective of this study was to quantify and compare the key parameter for biomass production, radiation use efficiency (RUE), for arrowleaf (Trifolium vesiculosum Savi.), crimson (T. incarnatum L.), rose (T. hirtum All.), and subterranean (T. subterraneum L.) clovers. Data on the fraction of light intercepted and biomass were collected biweekly over 2 yr at Overton, TX, and were used to calculate the RUE. Radiation use efficiency was calculated for biomass as a function of cumulative intercepted photosynthetically active radiation (IPAR) for aboveground biomass and for total biomass including roots. Similarly, RUE was calculated for regrowth following one or two cuttings. Over the 2 yr of this study, the mean RUEs for aboveground biomass original growth were 2.92, 2.52, 1.94, and 1.86 g MJ−1 for rose, arrowleaf, crimson, and subterranean, respectively. The mean RUEs for the total biomass including roots, during this time were 3.01, 2.59, 2.00, and 1.98 g MJ−1, respectively. Relative to the original growth aboveground RUE values, the RUE of aboveground regrowth following one cutting averaged 92% across the four species. Likewise, the mean RUE of aboveground regrowth of the four species following two cuttings was 119%. These values of RUE will aid modelers in simulating these important N2 fixing species.

Environmental effects on seed yield determination of irrigated peanut crops: Links with radiation use efficiency and crop growth rate

In Argentina, delayed sowing causes a decrease in seed yield and in radiation use efficiency (RUE) of peanut crops ( Arachis hypogaea L.), but it is not known if RUE reduction is mainly due to reduced temperature during late reproductive stages or to a sink limitation promoted by decreased seed number in these conditions. We analyzed seed yield determination and RUE dynamics of two cultivars (Florman and ASEM) in four irrigated field experiments (Exp n ) grown at three sites and five contrasting sowing dates (between 17 October and 21 December) in three growing seasons. An additional field experiment was performed with widely spaced plants ( i.e. with no interference among them) to evaluate the effect of peg removal on RUE and leaf carbon exchange rate (CER). Seasonal dynamics of mean air temperature and irradiance, biomass production (total and pods), and intercepted photosynthetically active radiation (IPAR) were followed. Seed yield and seed yield components (pod number, seeds per pod, seed number and seed weight) were determined at final harvest. Crop growth rate (CGR) and pod growth rate (PGR) were computed for growth phases of interest. RUE values for crops sown until 14 November were 1.89–1.98 g MJ −1 IPAR, within the usual range. RUE decreased significantly for cv. Florman in the late sowing of Exp 1 (29 November) and for both cultivars in Exp 3 (21 December sowing). Across experiments, seed yield (4.5-fold variation relative to minimum) was strongly associated ( r 2 = 0.87, P < 0.0001) with variations in seed number (3.5-fold variation relative to minimum), and to a lesser extent ( r 2 ≤ 0.54, P ≤ 0.001) to variations in seed weight (1.9-fold variation relative to minimum). Seed number was positively related ( P < 0.01) to CGR ( r 2 = 0.66) and to PGR ( r 2 = 0.72) during the R 3–R 6.5 phase (seed number determination window), while crop growth during the grain-filling phase ( i.e. between R 6.5 and final harvest) was positively associated with grain number ( r 2 = 0.80, P < 0.001). No association was found between RUE and mean air temperature, neither for the whole cycle nor for the phase between R 6.5 and final harvest, which showed the largest temperature variation (16.4–22.4 °C) across experiments. Use of mean minimum temperature records (range between 13.8 and 18.5 °C) did no improve the relationship. However, grain-filling phase RUE showed a positive ( r 2 = 0.69, P = 0.003) linear response to seed number across experiments. This apparent sink limitation of source activity was consistent with the reduced RUE (from 2.73 to 1.42 g MJ −1 IPAR) and reduced leaf CER at high irradiance (from ca. 30 to 15 μmol m −2 s −1) for plants subjected to 75% peg removal.

Radiation-use efficiency of modern and old spring cereal cultivars and its response to nitrogen in northern growing conditions

The typical features of high latitude growing seasons, particularly the short and intensive growth period and intense solar radiation during early growth, limit crop development and yield formation. A field study was conducted over two years to assess the differences between old and modern spring cereal cultivars in radiation-use efficiency (RUE), to characterise the traits contributing to the differences and to gauge the effect of nitrogen on the traits. Field experiments were conducted with wheat ( Triticum aestivum L.), barley ( Hordeum vulgare L.) and oat ( Avena sativa L.) under two nitrogen regimes (90 kg N ha −1 and control with 0 kg N ha −1). RUE was reduced at 0 kg N ha −1. Pre-heading RUE was not influenced by year, but post-heading RUE was, with values being either higher or nearly the same in comparison with pre-heading values. RUE values for barley, wheat and oat were similar to those reported elsewhere. Old two- and six-row barley cultivars had higher pre-heading RUE than modern cultivars. After heading, under decreasing light levels biomass accumulation was high due to the high RUE values. Old oat and six-row barley cultivars had higher post-heading RUE than modern cultivars. In intensive northern growing conditions, RUE varied seasonally and increased at increasing N application rate.

Decline in the growth of a sugarcane crop with age under high input conditions

In Australian sugarcane crops, growth in terms of radiation use efficiency (RUE) can appear to slow down well before final crops are harvested, despite conditions that are considered favourable for growth. In order to assess the extent and cause of this reduced growth phenomenon (RGP), 14 experiments conducted in Australia were examined. From these experiments, 34 treatments were selected where nutrients and water were likely to be non-limiting and consequently the yields obtained were likely to be limited only by temperature and radiation. Radiation use efficiency is defined as the measured amount of net biomass accumulated above ground per unit radiation intercepted. Accumulated biomass may have been lost through loss of stalks. In almost half of the treatments RUE significantly declined between approximately 223 and 665 days after crop start. The high incidence of RGP found in the analyses (a) challenges the previously held assumption that a constant value of RUE can be used to adequately describe biomass accumulation in sugarcane as a function of cumulative radiation interception and (b) suggests that relatively low growth rates during the later phases of the cropping season are frequently experienced throughout the Australian sugar industry. Reduced growth phenomenon resulted in actual biomass at final harvest being on average 21% less than potential yield, compared with 5% in crops that did not display a slowdown in growth. Mean maximum RUE in the plant crop was greater than in ratoon crops, at 1.37 and 1.19 g MJ −1, respectively. As there was no effect of location, cultivar, crop duration, ratoon crop class or fumigation treatment on RUE for the periods either before or after the onset of reduced growth, it would appear that the value of RUE is predominantly influenced by crop class. Despite the differences in RUE between the two crop classes, RGP occurred at a similar frequency in both plant and ratoon crops. In order to gain a greater mechanistic understanding of the factors likely to be associated with the onset of the RGP, the relative time of lodging, specific leaf nitrogen (SLN), number of stalks and seasonal temperature were all considered individually. Whilst declining SLN and increasing stalk loss were associated with reductions in growth during the later periods of crop growth, it is likely that lodging also contributed to the widespread slowdown in biomass accumulation, whereas photosynthetic stress, as a result of extreme temperatures, did not play a substantive role in reducing growth.

Maize Radiation Use Efficiency under Optimal Growth Conditions

Accurate measurement of crop growth and radiation use efficiency (RUE) under optimal growth conditions is required to predict plant dry matter accumulation and grain yield near the genetic growth potential. Research was conducted to quantify the biomass and leaf area index (LAI) accumulation, extinction coefficient, and RUE of maize (Zea mays L.) under conditions of optimal growth. Maize was grown in two environments over five growing seasons (1998–2002). Total aboveground biomass at maturity ranged from 2257 g m−2 in 1998 to 2916 g m−2 in 2001; values that are considerably greater than the biomass achieved in most previous studies on RUE in maize. Peak LAI ranged from 4.8 to 7.8. Maize extinction coefficients during vegetative growth (k) were within the range of recently published values (0.49 ± 0.03), with no clear pattern of differences in k among years. Seasonal changes in interception of photosynthetically active radiation (PAR) were similar across all but one year. Estimates of RUE were obtained using the short‐interval crop growth rate method and the cumulative biomass and absorbed PAR (APAR) method. Values of RUE obtained using the two methods were 3.74 (±0.20) g MJ−1 APAR and 3.84 (±0.08) g MJ−1 APAR, respectively, and did not vary among years. This compares to a published mean RUE for maize of 3.3 g MJ−1 of intercepted PAR (Mitchell et al., 1998). Moreover, RUE did not decline during grain filling. Differences in biomass accumulation among years were attributed in part to differences in observed radiation interception, which varied primarily due to differences in LAI. Maize simulation models that rely on RUE for biomass accumulation should use an RUE of 3.8 g MJ−1 APAR for predicting optimum yields without growth limitations.

Peanut leaf area index, light interception, radiation use efficiency, and harvest index at three sites in Texas

Stability of parameters describing crop growth of peanut ( Arachis hypogaea L.) is important because of the diversity of climatic conditions in which peanuts are grown and is valuable when developing simulation models for this species. In contrast, variability in the same parameters is desirable for plant breeders working to develop improved cultivars. This study seeks to quantify key parameters for biomass and yield production of some common peanut cultivars at three sites in Texas. We measured leaf area index (LAI), light extinction coefficient ( k) for Beer's law, and harvest index (HI) for four cultivars at Stephenville, TX and one cultivar near Gustine, TX, and for LAI and biomass on four cultivars at Seminole, TX. Mean radiation use efficiency (RUE) values were 1.98 g MJ −1 at Stephenville, 1.92 at Gustine, and 2.02 at Seminole. Highest RUE values were for the Low-Energy Precise Application (LEPA) irrigation treatment at Seminole. Maximum LAI values ranged from 5.6 to 7.0 at Stephenville, from 5.0 to 6.2 at Seminole, and was 5.3 at Gustine. Mean k values ranged from 0.60 to 0.64 at Stephenville and was 0.77 at Gustine. The overall mean HI was 0.36, with a mean of 0.33 for Stephenville, 0.44 for Gustine, 0.53 for spray irrigation at Seminole, and 0.58 for LEPA irrigation at Seminole. Values of RUE, k, and HI for the cultivars in this study and similarities between this study and values reported in the literature will aid modelers simulating peanut development and yield and aid breeders in identifying key traits critical to peanut grain yield improvement.

Maize yield potential: critical processes and simulation modeling in a high-yielding environment

Understanding processes of maize ( Zea mays L.) growth and production of grain in high-yielding, irrigated conditions offers hope to understand yield potential in many other environments. In this study we investigated such processes at the plant level, and attempted to simulate maize yields at the field level and county level in the high yielding region of the High Plains of Texas. In addition, we used the normalized difference vegetation index (NDVI) from satellite data of year 2000 to update leaf area index for yield simulation in three counties. In the field study, we measured maize leaf area index (LAI), the fraction of photosynthetically active radiation intercepted (FIPAR), and the harvest index (HI) in irrigated plots near Dumas, Texas. The light extinction coefficient ( k) for Beer's law was calculated with the FIPAR and the LAI. The radiation use efficiency (RUE) was determined with sequential measurements of the fraction of photosynthetically active radiation (PAR) intercepted and biomass harvests. The RUE was 3.98 g of above-ground biomass per MJ of intercepted PAR in 1999 and 3.41 in 2000 for three sampling dates prior to silking. These values are 106 and 93% of the expected RUE values at the measured vapor pressure deficits, using a previously published response function. The mean k value was −0.46 in 1999 and −0.47 in 2000, similar to the expected value of −0.43 reported in the literature for this row spacing. The mean HI measured in 2000 was 0.52, similar to values of 0.53 and 0.54 in the literature. Application of these parameters to maize simulation with the Agriculture Land Management Alternatives with Numerical Assessment Criteria (ALMANAC) model for 13 center pivot irrigated fields near Dumas in 1999 provided simulations within 1.0 Mg ha −1 with a mean error of 0.03 Mg ha −1 and a mean square error of 0.10. For five years of grain yields reported for each of four counties in this region of Texas, ALMANAC simulations were within 5% of the mean measured yields. Introduction of PAR interception, based on the satellite-derived normalized difference vegetation index (NDVI), into ALMANAC resulted in slight increases in accuracy of yield prediction for two counties and a slight decrease in accuracy in one county for year 2000. Consistency in values of RUE, k, and HI in this study as compared with values reported in the literature will aid modelers simulating maize growth and grain yields in similar high-yielding, irrigated conditions.

Interception of photosynthetically active radiation and radiation-use efficiency of wheat, field pea and mustard in a semi-arid environment

Fractional ground cover, fractional PAR interception ( f), canopy extinction coefficient ( k) and radiation-use efficiency (RUE) for wheat, pea and mustard were examined in a field experiment conducted over 5 years in a semi-arid environment in Australia. Two crop sequences were compared: fallow–wheat–pea and mustard–wheat–pea. Significant periods of water stress occurred in some years. Complete ground cover was not achieved and f ranged to maxima of 0.77, 0.80 and 0.80 in wheat, pea and mustard, respectively. For wheat, fallow increased f under both average growing season and drought conditions, but pea PAR interception was not influenced by crop sequence. Estimates of k for wheat, pea and mustard were 0.82 (±0.05), 0.76 (±0.03) and 0.68 (±0.12), respectively. Estimated RUE (aboveground biomass) of 1.81 (±0.05), 1.52 (±0.05) and 1.92 (±0.12) g MJ −1 intercepted PAR for wheat, pea and mustard, respectively, was measured over the vegetative phase. Seasonal conditions had minimal impact on k and RUE, and RUE was generally lower than the maxima reported in the literature, but they were similar to others reported in comparable environments and matched predicted unstressed RUE for C 3 plants. This calls into question the application, in simulation models for crops that rarely reach full cover in such arid environments, of water supply or stress factors to RUE values established elsewhere on unstressed crops.

Yield improvements through modification of planting density and harvest frequency in short rotation coppice Salix spp.—2. Resource capture and use in two morphologically diverse varieties

In the second paper in this series factorial combinations of two short rotation coppice (SRC) willow varieties ( S. viminalis cv. Jorunn and S. x dasyclados) and five planting densities (10,000–111,000 plants ha −1 ) were compared at a site in Cambridgshire, UK. Frequent measurements of above-ground and below-ground biomass accumulation (AGBA and BGBA), canopy radiation interception ( I), green leaf area index (GLAI), radiation use efficiency (RUE), and attenuation coefficient ( k) were made in 1997, 1998 and 1999 in order to explain density, variety and harvest interval related yield effects. At full canopy, the highest GLAIs attained, usually by the highest plant density, were in the range 5–6.5. GLAI declined rapidly once this peak had been attained. GLAI decreased following canopy closure (radiation interception >90%), due to loss of leaves lower down the canopy profile. Despite a more rapid loss of leaf area by the highest planting density, GLAD values were consistently greater at the highest planting density ( P>0.05), and GLAD for S. dasyclados was significantly greater than S. viminalis in each year ( P<0.05). GLAD was related to final dry matter production. Higher planting densities also had earlier dates of canopy closure, which were correlated with increased final yield. k values were in the range −0.2–−0.51, indicating differences in morphology between the varieties although no consistent trends could be determined. Patterns of AGBA mirrored canopy development. Peak AGBA in the first season was 19 and 14 t ha −1 for S. viminalis and S. x dasyclados, respectively. End of season yield was significantly lower (11.5 and 12.9 t ha −1 for S. viminalis and S. x dasyclados, respectively) due to leaf fall and carbohydrate movement. End of season yields followed a clear, significant trend of increased yield with increasing plant density in the case of S. viminalis. This trend was not apparent with S. x dasyclados after the first season. RUE values were significantly increased ( P<0.05) by planting density and variety, ranging from 1.55 to 2.55 g MJ −1 for 10,000 and 111,000 plant ha −1 , respectively, in S. viminalis, which had significantly higher RUE values than S. x dasyclados. Plant mortality, after three seasons, was approximately 15% at the highest density but less than 5% at the three lowest densities. The two varieties behaved similarly. Thus, very high plant populations were sustained at the high planting densities. An inverse relationship between individual plant weight and planting density was evident, but there was no linear relationship. Higher plant densities supported larger plants than would have been expected from a linear relationship. As a consequence, yields at high densities were higher than yields at low densities.

Seasonal variation in radiation use efficiency of irrigated rice

Radiation use efficiency (RUE), the amount of carbon assimilated per unit intercepted photosynthetic photon flux density ( Q i), is important in understanding and modeling the relationship between plant growth and the physical environment. Field experiments were conducted in 1998 and 1999 to evaluate RUE as a function of growth and development in a commercial rice field near El Campo, TX. Half-hourly averages of carbon assimilation were obtained from tower-based conditional sampling (CS), and Q i was measured with quantum sensors. We found a high correlation between half-hourly averages of CO 2 exchange rate (CER) and Q i. RUE steadily declined during growth of the primary crop, from 3.18 to 2.65 μg μmol −1 quanta, in 1998 and 1999, respectively, for leaf area index (LAI) between 1 and 2, to 1.57 and 1.55 μg μmol −1 quanta, respectively, for LAIs exceeding 5. Post-anthesis values of RUE were substantially lower than pre-anthesis values at comparable LAIs. Post-anthesis RUE in the ratoon crop was also lower than pre-anthesis RUE. Daily totals of CER and Q i values were also strongly correlated. We concluded that when RUE is used as a model parameter, it must be changed for differing LAI and for pre- and post-anthesis periods.

Rice Parameters Describing Crop Performance of Four U.S. Cultivars

Parameters describing processes of crop growth and yield production provide modelers with the means to simulate crops and provide breeders with a system of comparing cultivars. Such values for rice (Oryza sativa L.) are especially important for some regions in the southern USA. Accordingly, the objective of this study was to quantify key biomass and yield production processes of four rice cultivars common in this region. We measured the leaf area index (LAI), the light extinction coefficient (k) for Beer's law, N concentrations, and the harvest index (HI) for the main and ratoon crops in 1999 and 2000 at Eagle Lake, TX. Dry matter was linearly related to intercepted photosynthetically active radiation (IPAR) for all of the data sets. The mean radiation use efficiency (RUE) was 2.39 g aboveground biomass MJ−1 IPAR. Maximum LAI values ranged from 9.8 to 12.7, and the mean k value for the main crop was 0.37. The highest main crop yields were 7.04 Mg ha−1 for Cocodrie in 1999 and 7.22 Mg ha−1 for Jefferson in 2000. Yield differences among cultivars were due to HI differences and were not related to RUE values. The mean HI was 0.32 for all four cultivars over the two harvests in each of the 2 yr. Consistency in values of RUE, k, N concentrations, and HI among the cultivars in this study and between this study and values reported in the literature will aid modelers simulating rice development and yield and aid breeders in identifying key traits critical to rice grain yield improvement.

Physiological responses of argentine peanut varieties to water stress.: Light interception, radiation use efficiency and partitioning of assimilates

In Argentina, peanut production is concentrated in areas where unpredictable and intermittent periods of water deficit occur almost every year especially, during the pod growth period. Florman INTA is the most popular variety among peanut producers, but it is highly sensitive to drought. Manfredi 393 INTA was released as a drought-tolerant variety. Differences between these varieties in radiation interception and crop mass accumulation relative to light levels, as well as in allocation of assimilate to economic yield under water deficit, have not been previously studied. An experiment was set with two different regimes of water supply. Half of the crop was irrigated (IRR) from sowing to maturity, while the other half received no water between 47 and 113 days after sowing. The fraction of PAR intercepted, ( f), leaf area, pod and vegetative above-ground biomass and leaf carbon dioxide exchange rate (CER) were measured periodically during the water deficit period. The leaf area index, degree of leaf folding, canopy extinction coefficient, radiation use efficiency (RUE), partitioning factor, ( p), and harvest index (HI) were calculated from the measurements. Under water stress, f was reduced in both varieties with respect to their controls, and the reduction was proportionally higher in Florman INTA as a consequence of a higher leaf area reduction and degree of leaf folding. However, f remained higher in Florman INTA than in Manfredi 393 INTA due to the enhanced capacity of the former to generate leaf area under non-limiting water supply. RUE values were higher in Manfredi 393 INTA than in Florman INTA, both under irrigation as well as under severe water deficit, where they were obtained using a two-parameter exponential model. The reason for the higher RUE values in Manfredi 393 INTA was its ability to maintain a higher leaf CER. Partitioning to pods under irrigation was greater in Manfredi 393 INTA than in Florman INTA, as a result of a longer pod filling period and higher p. Towards the end of podfill, there was a rapid increase of p in Florman INTA, but too late to improve its HI. Under water stress, the time course of p for both varieties was lower than in the IRR treatments and consequently, HI at harvest was reduced. Low HI values could be attributed to some extent to the mechanical impedance of the upper soil layer, caused by water deficit. Mechanical impedance alters the relation among p and HI values obtained under irrigation and water stress. However, even if it is accounted for, cultivars with high HI under IRR conditions usually have high HI under water deficit.

Modeling radiation- and carbon-use efficiencies of maize, sorghum, and rice

A previously developed model for radiation-use efficiency (RUE) for gross photosynthesis and net carbon accumulation by wheat before anthesis [Agric. Forest Meteorol. 101 (2000) 217], with some improvement, has been applied to maize, sorghum, and rice during their vegetative period under unstressed conditions. The objective of the present study is to assess the extent to which the model can provide RUE for net carbon accumulation and carbon-use efficiency (CUE; the ratio of daily net carbon accumulation and gross photosynthesis) for a range of incident irradiance and leaf area indices of maize, sorghum and rice, recognizing that (a) these crops are grown in substantially different environmental conditions than those for wheat, and (b) while rice is a C 3 crop like wheat, maize and sorghum are C 4 crops. The calculated RUE values for net carbon accumulation differed from observations (five for maize, two for sorghum and three for rice) by −24% to +19%, with an average ( n=10) of −4% (underestimation), while the calculated CUE values are found to be within the range of observations. The model parameters have not been calibrated or adjusted for these comparisons. Calculations suggest that there is much room to increase the RUE of sorghum over the currently available measurements, although it might not attain the potential maximum value for maize. The effects of variations in the maximum rate of leaf photosynthesis among cultivars, changes in the relationship between maximum rate of photosynthesis by leaves and its nitrogen content, and uncertainties in the input canopy parameters on RUE and CUE are assessed by sensitivity analysis.