Photosynthetically Active Radiation Interception Research Articles

Development of a dynamic model to estimate canopy par interception

Models of the shadows cast by orchard trees can provide useful information to assist in canopy and nutrient management, estimation of potential yield and water use. In this study, an analytical model was developed that calculates the shape, size, position and orientation of the shadows cast by the tree canopy and described the diurnal and seasonal changes in those shadows. The objective of this study was to derive analytical expressions to describe the positions and potential effects of shadows in time and space based on shape and size of the canopy, row and tree spacing, row orientation, and the latitude and the longitude of the orchard to compute canopy PAR interception considering the shading from neighbouring trees. The model was based on the assumption that canopies have spherical or ellipsoidal shape. Simulations were performed at different times of the day to study the shading patterns of trees and evaluated in terms of solar radiation received, transmitted and intercepted. The model was calibrated using field data to assist orchard design and canopy management based on lightbar scans obtained at different times of the day. The calibration procedure was tested on an almond orchard by comparing the shadows scanned and estimated by the model. The maximum average values between precision and recall were 87.50% and 87.75%, respectively.

Row orientation effects on potted-vines performance and water-use efficiency

The relation between water-use and intercepted solar radiation depends on many factors involved in vine canopy architecture and physiology. In addition, vine productivity is related to the efficiency with which the intercepted photosynthetically active radiation (IPAR) is used, which in turn depends mainly on water availability and transport. In hedgerow-managed vines it exists the possibility to modulate IPAR by orienting their rows, influencing water-use efficiency (WUE), defined as dry matter produced by water used. Aiming to unravel the effects of row orientation on WUE, a three-year experiment was carried out in Valencia (Spain) on potted Vitis vinifera (L.) cv. Bobal and Verdejo with vine rows oriented either north-south (NS) or east-west (EW), under no-water restrictions. Simulated radiation interception over the growing seasons at the experimental plot showed an average 39% reduction in daily IPAR when EW was compared to NS. Vine transpiration was quantified by water balance, decreasing by 16% in Bobal and 8% in Verdejo when comparing EW against NS. In both cultivars, this reduction was 18% when considered relative to the total leaf area. Carbon assimilation was not markedly affected by row orientation. Therefore, since in both cultivars minor differences in vine performance occurred between orientations, WUE tended to increase by orienting the rows to the EW compared to NS. This resulted in most of the seasons an increase in water productivity calculated as grape yield/water-use ratio. Leaf gas exchange measurements partially agreed with the radiation interception simulations, suggesting a more complex regulatory mechanism and highlighting the importance of canopy microclimatic conditions in the physiological processes of hedgerow-managed crops. These findings encourage further research under field conditions and different soil water availabilities, aiming to optimize grapevine water productivity.

Solar radiation effects on growth, anatomy, and physiology of apple trees in a temperate climate of Brazil.

The aim of study was to characterize patterns of interception and distribution of photosynthetically active radiation (PAR) in an apple orchard and to examine its relationship with morphophysiological characteristics of "Royal Gala" and "Fuji Suprema" apple trees. The experiments were conducted during three production cycles in two distinct orchard areas, one covered by black anti-hail netting and another uncovered (control). We analyzed PAR characteristics with data from meteorological sensors installed on the canopy, as well as growth, anatomical, and physiological variables of apple trees. The reduction of PAR by netting influenced the components of radiation balance. PAR intercepted, absorbed, transmitted, and reflected by the canopy under netting decreased by 33%, 31%, 32%, and 46%, respectively, in comparison to uncovered canopy. When leaf area index (LAI) was 1.5 (under netting) and 2.5 (uncovered), maximum PAR interception efficiency was reached. During the three production cycles, a light extinction coefficient of 1.09 and 0.76 was found under netting and in the control, respectively. Plant height was greater under netting in all three cycles for both cultivars. Number of leaves, LAI, and shape index did not differ between treatments. At stage 85, leaves of "Royal Gala" under netting showed lower chlorophyll content and thinner parenchymas in comparison to the control. However, physiological and anatomical characteristics of Fuji "Suprema" did not change under anti-hail netting.

High radiation use efficiency improves yield in the recently developed elite hybrid rice Y-liangyou 900

Yield potential in super hybrid rice has continued to increase in recent decades through morphological improvements and the use of inter-subspecific heterosis. Radiation use efficiency (RUE) has been singled out as an important determinant of grain yield in cereal species. However, it is not known whether yield increases in super hybrid rice breeding programs have involved improvements in RUE. Three-year field experiments evaluated the effects of breeding on grain yield and its physiological determinants, including RUE, intercepted photosynthetically active radiation (IPAR), aboveground biomass production, and harvest index (HI), in three representative super hybrid rice varieties released between 1999 and 2015 and grown under three N regimes (N0: 0 kg ha–1, N1: 210 kg ha−1, N2: 300 kg ha–1). Grain yield in the recently developed super hybrid rice cultivar Y-liangyou 900 (YLY900) increased significantly, relative to Liangyoupeijiu (LYPJ) and Y-liangyou 2 (YLY2), reaching more than 11 t ha–1 in the N2 treatment each year. Yield improvements in YLY900 were primarily due to increased aboveground biomass production resulting from a higher RUE, being 10.6 % (biomass) and 12.1 % (RUE) higher than those in LYPJ and YLY2. Unlike YLY900, aboveground biomass accumulation in LYPJ and YLY2 mostly resulted from increased IPAR. Nitrogen supply significantly increased intercepted radiation and intercepted percentage but not RUE. The N treatments had no effect on HI, within or between varieties. Grain yield had a significant (P < 0.01) positive correlation with both intercepted radiation and RUE in all three cultivars. The multiple regression analysis showed that the higher grain yield in YLY900 was more closely related to RUE, while those in LYPJ and YLY2 were highly dependent on intercepted radiation. Considering that YLY900 had a significant yield advantage, we conclude that RUE plays a more prominent role than HI in yield progress in super hybrid rice. Crop breeders should focus on breeding for improved solar radiation properties as a sustainable means of increasing yields in super hybrid rice.

Resource use efficiency in a cotton-wheat double-cropping system in the Yellow River Valley of China

AbstractThe cotton-wheat double-cropping system is widely used in the Yellow River Valley of China, but whether and how different planting patterns within cotton-wheat double-cropping systems impact heat and light use efficiency have not been well documented. A field experiment investigated the effects of the cropping system on crop productivity and the capture and use efficiency of heat and light in two fields differing in soil fertility. Three planting patterns, namely cotton intercropped with wheat (CIW), cotton directly seeded after wheat (CDW), and cotton transplanted after wheat (CTW), as well as one cotton monoculture (CM) system were used. Cotton-wheat double cropping significantly increased crop productivity and land equivalent ratios relative to the CM system in both fields. As a result of increased growing degree days (GDD), intercepted photosynthetically active radiation (IPAR), and photothermal product (PTP), the capture of light and heat in the double-cropping systems was compared with that in the CM system in both fields. With improved resource capture, the double-cropping systems exhibited a higher light and heat use efficiency according to thermal product efficiency, solar energy use efficiency (Eu), radiation use efficiency (RUE), and PTP use efficiency (PTPU). The cotton lint yield and biomass were not significantly correlated with RUE across cropping patterns, indicating that RUE does not limit cotton production. Among the double-cropping treatments, CDW had the lowest GDD, IPAR, and PTP values but the highest heat and light resource use efficiency and highest overall resource use efficiency. This good performance was even more obvious in the high-fertility field. Therefore, we encourage the expanded use of CDW in the Yellow River Valley, especially in fields with high fertility, given the high productivity and resource use efficiency of this system. Moreover, the use of agronomic practices involving a reasonably close planting density, optimized irrigation and nutrient supply, and the application of new short-season varieties of cotton or wheat can potentially enhance CDW crop yields and productivity.

Effects of seeding pattern and phosphorus application on population structure, photosynthe-tic characteristics and yield of winter wheat

Under Xinjiang winter wheat seeding pattern, in order to sort out proper phosphorus application (PA) and find out the effects and mechanism of PA on population structure, photosynthesis characteristics and yield and provide reliable evidence for PA management of winter wheat, we arranged a two-factor complete split-plot design of wheat variety "Xindong 22". The main area consisted of two seeding ways: drill seeding pattern (D) and uniform seeding pattern (U), while in the sub-area there were four levels of PA(P2O5): 0, 60, 120, and 180 kg·hm-2(represented by P0, P60, P120 and P180 for those treatments, respectively). The results showed that the earbearing percentage in U was 15.9% higher than that in D, and the other features (PAR interception rate, extinction coefficient, leaf area index, SPAD and photosynthetic parameters) were more optimal in 120 kg·hm-2 treatment. Our results showed that the 120 kg·hm-2 treatment in U would be the optimal option with respect to population structure, photosynthetic characteristics, and yield.

Photoselective coverings influence plant growth, root development, and buddability of citrus plants in protected nursery

Use of protective coverings can be an economically viable option in fruit nurseries than in fully mature commercial orchards. In protected nurseries, photoselective coverings can influence the growth of rootstocks, budding success, and budding growth of the budded scion cultivar. The effect of photoselective coverings (white, silver, green, red and stainless steel net house) along with open conditions (control) was studied on plant growth, nutrient uptake and root growth of rough lemon and Carrizo citrange rootstock seedlings which were subsequently budded with Kinnow and Daisy mandarin cultivar buds, respectively. The rough lemon plants under red net had better height, internodal length and budding success, while in open conditions, higher seedling diameter, root diameter, shoot and root dry weight, leaf number and secondary root number were recorded in rough lemon seedlings. The Carrizo seedlings in red net had better seedling diameter, internodal length, leaf area and number, shoot dry weight and budding success. The higher nitrogen, phosphorus, potassium and zinc levels were recorded in the leaves of rough lemon and Carrizo citrange under red shade net. The plant height of rough lemon seedlings was positively correlated to internodal length, budding success and leaf areaas well as leaf phosphorus and iron levels. The highest buddable seedlings were recorded in open conditions but, budding success in red shade net house. The highest sprout lengths of Kinnow and Daisy mandarin saplings were recorded in red net followed by green net and white net. Higher photosynthesis and stomatal conductance were recorded under red shade net, whereas lowest PAR interception was recorded in open conditions.

Effect of rice straw biochar and irrigation on growth, dry matter yield and radiation‐use efficiency of maize grown on an Acrisol in Ghana

AbstractIn order to determine whether the current low productivity associated with rainfed cultivation on degraded soils in Ghana can be improved by biochar amendment and irrigation, field experiments with maize were conducted over two seasons in 2017 and 2018. Rice straw biochar at rates of 0 t/ha (B0), 15 t/ha (B15) and 30 t/ha (B30) was combined with irrigation regimes of full irrigation (I100), deficit irrigation (I60) and no irrigation (I0). The I100 treatment was irrigated to field capacity every 3–4 days according to time domain reflectometry measurements while the I60 treatment received 60% of the irrigation amount given to I100 but with the same irrigation frequency. The I0 treatment was not irrigated. In both seasons, the B30 treatment recorded the highest total dry matter yield (TDMY), intercepted photosynthetically active radiation (IPAR) and radiation‐use efficiency (RUE) and these were significantly (p ≤ .05) higher than B0 except for RUE in 2017. Irrigation regimes did not significantly affect TDMY, IPAR and RUE in 2017 but compared to I100, I0 significantly reduced TDMY, IPAR and RUE in the relatively dryer 2018 season. Measured ratio vegetation indices differentiated biochar treatments earlier in the 2018 season than during 2017 and increase of leaf chlorophyll content indices with biochar rate in both seasons indicated that biochar amendment improved nitrogen uptake. Our study demonstrated that rice straw biochar is capable of increasing TDMY, IPAR and RUE of maize grown on degraded soils in Ghana. The study further showed that TDMY, IPAR and RUE of deficit irrigated maize for two seasons were similar to the counterpart fully irrigated maize and may be a viable water management option for farmers in Ghana to save irrigation water resources.

Comparison of SHD and Open-Center Training Systems in Almond Tree Orchards cv. ‘Soleta’

The increase in the demand for almonds, the development of novel self-fertile and late-flowering varieties, and the establishment of plantations in new irrigated areas have led to significant progress in the productive techniques of almond tree cultivation. One of the most important has been the increase in planting density, due to the development of dwarfing rootstocks. This paper presents a comparison between two training systems with ‘Soleta’ almond cultivar: a super high density (SHD) system using Rootpac-20 dwarfing rootstock versus an open-center training system using GF-677 rootstock. To this end, several parameters related to chlorophyll content (fluorescence and SPAD) and light interception (from photosynthetically active radiation (PAR) measurements) were monitored throughout two vegetative cycles, and other productive conditions (flowering, fruit set and production) were tracked at specific times of the cycle. The open-center system resulted in higher PAR interception than the SHD system, but also in the presence of poorly illuminated fractions of the canopy. Differences were observed between both systems in terms of average fruit weight and yield per canopy volume. Lower yields were obtained in SHD system than in open-center, which may be significantly increased by adapting the inter-row spacing. However, the degree of efficiency in the use of resources or productive inputs, such as irrigation, was favorable to the new SHD training system, so its potential to become a reference system in modern plantations (using over-the-row harvesters similar to those used for vine and olive trees) seems promising.

Influence of integrated crop management practices on yield, PAR interception, resource-use-efficiency and energetics in pigeonpea in North Indian Plains

Influence of integrated crop management practices on yield, PAR interception, resource-use-efficiency and energetics in pigeonpea in North Indian Plains

Effects of intercropping on light energy utilization characteristics and productivity of diffe-rent feed crops

To explore light energy utilization characteristics and yield effect of different legume-gramineae intercropping patterns, we set up five kinds of monocropping patterns including alfalfa, triticale, oats, maize and sorgo as reference in a field experiment. The light energy utilization chara-cteristics and productivity of four kinds of intercropping patterns including alfalfa-triticale, alfalfa-oats, alfalfa-maize and alfalfa-sorgo were examined. The contribution degree of each light energy index to yield formation was analzyed using path analysis method. The results showed that the contribution of each index of light energy to yield from large to small was as follows: leaf area index (LAI)=1.236, net photosynthetic rate (Pn)=0.519, canopy openness (DIFN)=0.302, intercellular CO2 concentration (Ci)=-0.026, stomatal conductance (gs)=-0.116, transpiration rate (Tr)=-0.188, PAR interception rate (FIPAR)=-1.708. Light use efficiency (LUE) as a comprehensive indicator of light energy utilization had the largest value (1.367). Compared with monoculture, the values of LAI, Pn, gs, Tr and FIPAR of four kinds of gramineae grasses increased under intercropping and the values of DIFN and Ci decreased, while alfalfa showed an opposite trend. Compared with monoculture, the LUE of four kinds of gramineae grasses under intercropping was significantly increased. The increase rates of triticale and oats (35.2% and 30.4%) were higher than that of maize and sorgo (28.7% and 26.3%). The decrease rates of alfalfa intercropping with triticale and oats (6.1% and 8.3%) were obviously lower than that of maize and sorgo (21.8% and 24.5%). The values of land equivalent ratio (LER) of four kinds of intercropping patterns was all greater than 1. The LER values of alfalfa-triticale and alfalfa-oat were significantly higher than those of alfalfa-maize and alfalfa-sorgo. It could be seen that LAI had the largest direct contribution to yield, followed by Pn. Among the four intercropping patterns, two patterns, alfalfa-triticale and alfalfa-oats, had greater improvement potential of light energy utilization and yield.

Impact of rice straw biochar and irrigation on maize yield, intercepted radiation and water productivity in a tropical sandy clay loam

Continuous cultivation of staple crops to feed a growing population in the semi-deciduous agro-ecological zone of eastern Ghana (SDAG) has led to degraded soils and decreased crop yields. Biochar constitutes a potential remedy as it is often reported to improve soil health and increase crop yield of infertile soils. We thus conducted an experiment over two seasons to evaluate the impact of rice straw biochar on yield, radiation interception and water productivity of maize grown in the SDAG. The biochar was incorporated into the soil at rates of 0, 15 and 30 t ha−1 under irrigated and non-irrigated conditions. Maize grain yield (GY), accumulated intercepted photosynthetic active radiation (IPAR) and water productivity (WP) were compared among treatments. Regardless of season, the highest GY, IPAR and WP were achieved in plots amended with 30 t ha−1 biochar. A biochar rate of 30 t ha−1 increased grain yield by 17% and 36% and IPAR by 19% and 25% in 2017 and 2018 seasons, respectively, compared to a no biochar control. For both seasons, maize GY for the 15 t ha−1 treatment was statistically similar to that of 0 t ha−1 treatment whether irrigated or not. Irrigation increased grain yield by 9% and IPAR by 3% in 2017 and with 30% and 17%, respectively, in the dryer 2018 season. The effects of biochar and irrigation were additive. Water productivity from the 30 t ha−1 treatment was significantly higher in the non-irrigated than in the irrigated plots. Overall, in the SDAG, a biochar soil amendment rate of 30 t ha−1 might be a viable solution for farmers to increase yield and enhance water productivity of maize. Future studies should focus on the effect of biochar on the soil and crops over a longer time span in order to recommend viable management options to the farmers in SDAG.

Effects of Severe Water Stress on Maize Growth Processes in the Field

In this study, we investigated the effects of water stress on the growth and yield of summer maize (Zea mays L.) over four phenological stages: Seedling, jointing, heading, and grain-filling. Water stress treatments were applied during each of these four stages in a water-controlled field in the Guanzhong Plain, China between 2013 and 2016. We found that severe water stress during the seedling stage had a greater effect on the growth and development of maize than stress applied during the other three stages. Water stress led to lower leaf area index (LAI) and biomass owing to reduced intercepted photosynthetically active radiation (IPAR) and radiation-use efficiency (RUE). These effects extended to the reproductive stage and eventually reduced the unit kernel weight and yield. In addition, the chlorophyll content in the leaf remained lower, even though irrigation was applied partially or fully after the seedling stage. Severe and prolonged water stress in maize plants during the seedling stage may damage the structure of the photosynthetic membrane, resulting in lower chlorophyll content, and therefore RUE, than those in the plants that did not experience water stress at the seedling stage. Maize plants with such damage did not show a meaningful recovery even when irrigation levels during the rest of the growth period were the same as those applied to the plants not subjected to water stress. The results of our field experiments suggest that an unrecoverable yield loss could occur if summer maize were exposed to severe and extended water stress events during the seedling stage.

Response of photosynthetic active radiation interception, dry matter accumulation, and grain yield to tillage in two winter wheat genotypes

ABSTRACT To examine the effects of winter wheat genotypes on dry matter (DM) accumulation and grain yield (GY) under no-tillage conditions in North China Plain (NCP), a field experiment was conducted using the genotypes Tainong 18 (F) and Jimai 22 (J). Two tillage systems were tested, conventional tillage (CT) and no-tillage (NT) during the 2015/2016 and 2016/2017 winter wheat growing seasons. Genotypes and tillage systems were compared regarding DM accumulation, GY, leaf area index (LAI), photosynthetic active radiation (PAR) interception, and flag leaf fluorescence parameters. LAI, PAR interceptions, and flag leaf fluorescence parameters were significantly higher under CT than under NT conditions. This suggests that the efficiency of light harvesting by the PSII reaction center of leaves can increase due to CT. DM accumulation was significantly higher under CT than under NT. Spike DM accumulation was higher in F than in J in the heading and the filling stages. In both growing seasons, GY was significantly higher under CT than under NT, GY of NTF was significantly higher than that of NTJ, which was due to a significantly higher number of kernels per spike. This indicates that genotype F can compensate for a low GY due to NT.

On-farm diagnosis for greenhouse tomato in south Uruguay: Explaining yield variability and ranking of determining factors

• Greenhouse tomato yield was primarily determined by cumulated PAR intercepted. • Average yield gap was 5.4 kg m −2 and 34% relative to attainable. • Potassium nutrition was the main factor explaining yield gaps differences. Knowledge about contributing factors to yield loss is essential for sustainable intensification of agriculture, which has the objective to increase both, yield and environmental sustainability. This study aimed to identify strategies to reduce the distance between under-performing and best-yielding greenhouse tomato crops in the south region of Uruguay. Gap to attainable yield was described and main causes of yield variability were explored by combining regional agronomic diagnosis and yield gap analysis. A sample of 110 tomato greenhouses within 23 farms during 2014/15 and 2015/16 were assessed. The variables assessed were classified in four groups: growth defining, growth limiting, growth reducing factors and yield components. Yield ranged from 0.9 to 24.3 kg m −2 . Cumulated photosynthetically active radiation (PAR) intercepted was the most correlated with yield. We analyzed two complementary ways of increasing yield: (1) modifying growth-defining factors to increase cumulated PAR intercepted and attainable yield, and (2) modifying growth-limiting and reducing factors responsible for the gap to attainable yield at a given level of cumulated PAR. PAR interception could be increased by adjusting transplanting dates to modify daily incident radiation, improving transmissivity of greenhouses and fraction PAR intercepted by canopy. We classified crops in three groups of cumulated PAR intercepted and yield. The average gap between actual and attainable yield was 34%. The strategy to close that gap differed among groups, but K nutrition was common to all. Results from this study allowed us to deliver relevant and actionable information to better inform discussions among farmers and their technical advisors.

Effects of directional planting on light environment and leaf photosynthesis of summer maize population

To improve light environment, photosynthetic capacity, and thus the yield of maize, the effects of directional planting on light distribution in canopy and photosynthetic characteristics of ear leaves, as well as the performance of PSII that closely related with photosynthetic characteristics and reflected by the rapid chlorophyll fluorescence kinetic curves were examined in Zhengdan 958 maize variety. The results showed that the orientation of leaves remarkably affected photosynthetically active radiation (PAR) interception of ear leaves, with PAR interception of ear leaves in southward treatment being 271.8% higher than that under northward treatment. The orientation of leaves affec-ted photosynthetic light use efficiency of ear leaves under high and low light conditions. The southward treatment increased net photosynthetic rate (Pn) under saturated light in ear leaves, indicating that the use efficiency to high light was enhanced in leaves of southward treatment. In contrast, the northward treatment increased the apparent quantum yield (α) of ear leaves, indicating leaves in southward treatment adapted the light-limited environment. During the early stage after anthesis, the performance of PSII electron donor side and electron acceptor side was significantly improved, and thus enhanced the performance of PSII reaction center (PIABS) and fluorescence photochemical quenching coefficient (Ψo) in ear leaves of southward treatment. The increase of quantum yield of electron transfer (φEo) indicated the enhancement of transfer performance of electrons from photosystem 2 (PSII) to photosystem 1 (PSI) in leaves of southward treatment. The photosynthetic performance of ear leaves showed a trend of southward > eastward > westward > northward during the early stage after anthesis. Forty days after anthesis, the use efficiency to high light decreased in ear leaves of southward treatment, but the ear leaves of southward treatment showed high use efficiency to low light, which changed the trend of photosynthetic performance of ear leaves to northward > westward > eastward > southward. In summary, northward and eastward treatments improved the light distribution in canopy, the PAR interception of ear leaves, the capacity of photosynthesis and dry matter production, and consequently increased the yield of summer maize.

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.

In sink-limited spring barley crops, light interception by green canopy does not need protection against foliar disease for the entire duration of grain filling

Disease management in cereals is heavily reliant on the use of fungicides, but development of anti-microbial resistance, effects on non-target organisms and persistence of active ingredients in the environment and food chain challenge the sustainability of this approach. Better targeting of fungicides according to crop need within an integrated pest management (IPM) programme could improve the sustainability of disease management. The objectives of the present study were to determine 1) the duration of protection of post-anthesis canopy light interception required to maximise the yield of spring barley and 2) to relate this to the response of crops to timing of fungicide applications. As the yield of spring barley is considered to be sink-limited (limited by the number and storage capacity of grains) rather than source-limited (limited by the amount of carbon assimilates available for grain filling) in many environments, we hypothesised that the canopy would not need to be protected for the entire grain filling period. Field experiments were conducted at two sites in the UK (Edinburgh and Herefordshire) over four years, providing contrasting climates and soil types. Shading was used to determine the response of grain filling to reductions in light interception over defined intervals, thereby mimicking effects of foliar disease on light interception, as shading is easier to control than the onset and duration of disease epidemics. Shades giving ˜67% reduction in photosynthetically active radiation (PAR) were erected over plots of disease-free crops at weekly intervals commencing at flowering and leaving them in place until harvest. The required duration of protection of light interception was estimated as the period from flowering to the time at which the onset of shading had no effect on yield. In a separate experiment the response to five fungicide timing treatments was determined on three relatively disease-susceptible varieties. Timings were the start of stem extension (referred to here as T1 only) and T1 followed by a second application at either flag leaf emergence (early T2), flowering (mid T2) or the start of rapid grain growth (late T2); untreated plots served as controls. Results showed that canopy PAR interception does not need to be protected for the entire grain filling period in order to maximise yield. The critical period determined from shading was 3–5 weeks after 50% ear emergence depending on the site year, or the first 72–90% of grain filling. There was a significant yield response to fungicide treatment in all site-years of 0.33−0.74 t ha−1 irrespective of the disease severity and yield potential of the site. Where disease severity was low to moderate a T1 application on its own gave sufficient protection during grain filling to maximise yield. Later applications increased healthy area PAR interception further, but effects occurred late during grain filling and did not increase yield. When disease was severe a T1 plus mid T2 application was required to protect PAR interception during the critical early to mid- grain filling period. These results provide the necessary physiological understanding to help target fungicide applications according to crop need.

Selection of shade trees in forest restoration plantings should not be based on crown tree architecture alone

The planting of tree seedlings is a common restoration technique in the tropics, and using large‐crowned, fast‐growing shade species is recommended to suppress invasive grasses and accelerate forest succession. We analyzed the effectiveness of shade species in shading the forest floor during the rainy and dry seasons at young forest restoration sites, whether shade changes according to site for a given species, and whether crown architecture can predict the shade level. We measured the photosynthetically active radiation (PAR) intercepted by the tree crowns of 14 species in two 3‐year‐old restoration plantings. The ability to predict shade based on crown architecture traits was evaluated using multiple linear regressions. The interception of PAR varied according to species, site, and season for seven species and was generally higher during the rainy season. Low values of tree and first branch height and high values of trunk diameter and mean area of a leaf predicted greater light interception. For the dry season, the ability to predict PAR interception was weaker than that for the rainy season and affected by a shorter tree height and a greater crown area. The crown architecture of shade species did not completely predict their shading ability, and the preselection of shade species for forest restoration purposes based only on crown architecture traits is not effective. Therefore, it is important to consider other factors, such as how long trees retain their leaves throughout the year and the soil and management conditions of the sites undergoing restoration, during the selection of species.

Inter-relationship between intercepted radiation and rice yield influenced by transplanting time, method, and variety.

Photosynthetically active radiation (PAR) is one of the most important environmental factors that determine the productivity and grain quality of the crops. Continuous rainy days or cloudy weather throughout crop growth especially at critical stages often resulted in great loss of grain quality and yield in rice. Low light stress has rigorously constrained the rice production in various rice-growing regions, especially in Southeast Asia. Method and time of planting are the major management factors contributing to the higher yield potential of rice by influencing light harvesting and use efficiency. Present study was executed consecutively for 5years (kharif seasons of 2012-2016) to determine whether planting time improves the radiation absorption and use efficiency in different duration rice cultivars. We evaluated the difference in plant growth and development leading to yield formation under different planting time which related to radiation incidence and interception. The results of the study revealed that PAR interception depends on morphological characters of cultivars and also with agronomic management such as transplanting time and method. Long duration cultivar intercepted more PAR but interception decreased due to late planting (3rd week of July), whereas short duration cultivars (Naveen) when planted earlier (1st week of June) could not effectively utilize intercepted PAR constraining the biomass accumulation and yield formation. Effect of planting density and crop architecture on PAR absorption was apparent among establishment methods as light interception at crop canopy was highest in the system of rice intensification and lowest in that of wet direct seeding. In general, Pooja as a long duration cultivar intercepted more PAR per day but when compared on same date of planting, the comparative absorption of radiation was 30.6% higher in Naveen. The lower yields in the wet season are attributed mostly to reduction in grain number per panicle or per unit land area, which is a consequence of high spikelet sterility. Grain yield of rice planted in July third week was reduced by 3.8, 12.3, and 6.9% over June first and third week and July first week, respectively, mainly due to spikelet sterility (26%) and lower grains per panicle (18%). Our results indicated that agronomic management like optimum time of sowing, cultivar duration, and establishment methods should be followed for yield improvement in tropical lowlands where light intensity is limiting due to prevailing weather situations.