Photosynthetically Active Radiation Interception Research Articles

Crop Reflectance as a tool for the online monitoring of LAI and PAR interception in two different greenhouse Crops

Methods for the online monitoring of Leaf Area Index (LAI) and photosynthetically active radiation (PAR) interception of the canopy, in greenhouse conditions, using reflectance measurements of the PAR part of the spectrum for tomato and sweet pepper were investigated. LAI and PAR interception were measured at the same moments as reflectance at six wavelengths at different plant developmental stages in greenhouses. The normalised difference vegetation index (NDVI) was also calculated. Relationships between the measured parameters were established in experimental greenhouses and subsequently tested in commercial greenhouses. The best estimates for LAI and PAR interception for both tomato and sweet pepper were obtained from reflectance at 460 nm. The goodness of the fit was validated with data from the commercial greenhouses was also tested. The divergence of the results from those reported from field experiments can be explained by the special environment that occurs in the greenhouse, where there are more sources of reflectance due to the greenhouse frame and the white plastic that covered the floor. Thus, this new approach to estimating LAI and PAR interception using 460 nm is promising and could play a role in the decision support systems that are used in modern greenhouse management.

Preface

Improving resource-use efficiency is vital for sustainable agricultural production and food security in water-scarce regions such as North China Plain. The aim of this study was to assess the effects of irrigation and straw-mulch on accumulated intercepted photosynthetically active radiation (AIPAR), radiation-use efficiency (RUE) and water-use efficiency (WUE) of wheat. A two-factorial field experiment was carried out at Luancheng Research Station (China) during 2015–16 and 2016–17. The factors included three irrigation levels – full (FI), deficit (DI) and partial root-zone drying (PRD), which besides rainfall received 200, 100 and 100 mm of irrigation, respectively, and two mulching strategies – mulch and no-mulch: ∼8 and 0 Mg ha−1, respectively. The results showed that mulch reduced AIPAR (6–11%) and increased RUE for total aboveground dry biomass (3–9%). Mulch affected intercepted photosynthetically active radiation (IPAR) between the tillering and anthesis stages, largely because of reduced soil surface temperature (0.8–1.5 °C), which led to delayed growth/development and impaired light interception. No significant difference was observed between DI and PRD for grain yield; however, effects on WUE varied during the two seasons. DI led to higher WUE during season I compared to PRD, while PRD resulted in highest WUE during season II. AIPAR was reduced under DI and PRD; however, RUE remained unaffected for irrigation treatments. The complementary effects of mulch were observed only under DI where WUE was increased by 4–6%. The results imply that the PRD irrigation under field conditions is not as effective as it has been anticipated, especially in soils with high clay content. Mulch induced reduction in growth/development tends to nullify its positive effects through water conservation. Taken together, these results reiterate the need to further optimize mulching and PRD irrigation practices before recommending their use under field conditions, especially for small grain cereals.

Development of the gap model ZELIG-CFS to predict the dynamics of North American mixed forest types with complex structures

When the development of gap models began about three decades ago, they became a new category of forest productivity models. Compared with traditional growth and yield models, which aim at deriving empirical relationships that best fit data, gap models use semi-theoretical relationships to simulate biotic and abiotic processes in forest stands, including the effects of photosynthetic active radiation interception, site fertility, temperature and soil moisture on tree growth and seedling establishment. While growth and yield models are appropriate to predict short-term stemwood production, gap models may be used to predict the natural course of species replacement for several generations. Because of the poor availability of historical data and knowledge on species-specific allometric relationships, species replacement and death rate, it has seldom been possible to develop and evaluate the most representative algorithms to predict growth and mortality with a high degree of accuracy. For this reason, the developers of gap models focused more on developing simulation tools to improve the understanding of forest succession than predicting growth and yield accurately. In a previous study, the predictions of simulations in two southeastern Canadian mixed ecosystem types using the ZELIG gap model were compared with long-term historical data. This exercise highlighted model components that needed modifications to improve the predictive capacity of ZELIG. The updated version of the model, ZELIG-CFS, includes modifications in the modelling of crown interaction effects, survival rate and regeneration. Different algorithms representing crown interactive effects between crowns were evaluated and species-specific model components that compute individual-tree mortality probability rate were derived. The results of the simulations were compared using long-term remeasurement data obtained from sample plots located in La Mauricie National Park of Canada in Quebec. In the present study, three forest types were studied: (1) red spruce-balsam fir-yellow birch, (2) yellow birch-sugar maple-balsam fir, and (3) red spruce-balsam fir-white birch mixed ecosystems. Among the seven algorithms that represented individual crown interactions, two better predicted the changes in basal area and individual-tree growth: (1) the mean available light growing factor (ALGF), which is computed from the proportion of light intercepted at different levels of individual crowns adjusted by the species-specific shade tolerance index, and (2) the ratio of mean ALGF to crown width. The long-term predicted patterns of change in basal area were consistent with the life history of the different species.

Environmental Resource Consumption in Wheat (Triticum aestivum) and Bean (Vicia faba) Intercropping: Comparison of Nutrient Uptake and Light Interception

Wheat (Triticum aestivum) and bean (Vicia faba L.) sole crops and their mixture in three planting pattern (M1: alternate-row intercrop, M2: within-row intercrop, M3: mixed intercrop) were used to investigate the amount of resource consumption in terms of PAR interception and nutrient uptake. The experiment was carried out as randomized complete block design with four replications. The results showed that intercropping systems had a significant effect on environmental resources consumption, where intercropping systems had more nutrient uptake and light interception compared to sole crops, suggesting the complementarity effect of intercropping components in resources consumption. The ability of wheat and bean was different in intercropping systems in absorbing nutrients because of their differences in root morphology and cation exchange capacity.

Weed Management in Single- vs. Twin-Row Cotton (Gossypium hirsutum)

Research was conducted to determine the effect of planting pattern, plant density, and levels of weed management intensity on intercepted photosynthetically active radiation (IPAR), weed control, and cotton lint yield in glyphosate-resistant cotton. Twin-row planting pattern canopy IPAR was 55% 7 wk after emergence (WAE) and 76% 9 WAE compared to 48% for single-row planting pattern 7 WAE and 59% 9 WAE. Regardless of cotton density, row spacing, or weed management intensity, control of browntop millet and Florida beggarweed was at least 88% 18 WAE. Benghal dayflower, sicklepod, and smallflower morningglory control was greater in twin-rows compared to single-rows at a cotton density of 7 plants m−2. Control of Benghal dayflower and sicklepod increased when cotton density increased at low weed management intensities; however, cotton density had no effect on weed control at higher levels of weed management input. At a cotton plant density of 7 plants m−2, twin-row cotton yielded 220 kg ha−1more than the single-row planting pattern. Data indicates twin-row cotton production is feasible and that control of various weeds was better in twin-row than single-row pattern at lower cotton density and weed management intensity.

Respostas do capim-Tifton 85 à aplicação de nitrogênio: cobertura do solo, índice de área foliar e interceptação da radiação solar

Estudaram-se os efeitos da adubação nitrogenada sobre o crescimento do capim Tifton 85 (Cynodon spp. cv. Tifton 85), em termos de ocorrência de plantas e altura do dossel, índice de área foliar e interceptação de radiação fotossinteticamente ativa. O estudo foi desenvolvido sobre um planossolo de ocorrência em campo experimental. Os tratamentos consistiram de níveis de N (0; 150; 300; 450 e 600kg/ha de N-ureia, aplicados em duas vezes), arranjados em um desenho experimental de blocos inteiramente ao acaso, com quatro repetições. As avaliações foram realizadas semanalmente, entre 10 e 40 dias após o corte. Tanto a ocorrência de plantas como a altura do dossel responderam à adubação nitrogenada, conforme um padrão de resposta que variou, sazonalmente, em função das doses de N em interação com as condições ambientais. A expansão da área foliar e a interceptação da radiação fotossinteticamente ativa associada, também foram controladas direta e proporcionalmente pelas doses de N aplicadas, sendo maximizadas a valores de índice de área foliar em torno de 4,0.

Effect of sowing date and rate on canopy intercepted photo-synthetically active radiation and yield of winter wheat

小麦适期播种不仅是达到全苗壮苗的关键, 还有利于小麦健壮生长发育, 是提高小麦单产的重要措施。本试验研究了不同播期和播量条件下小麦冠层底部光合有效辐射(<i>TPAR</i>)、叶面积指数(<i>LAI</i>)、冠层截获的光合有效辐射(<i>IPAR</i>)等的变化及播期对冬小麦产量的影响。结果表明, 叶面积指数和冠层截获的光合有效辐射随小麦播种时间的推迟而降低, 小麦冠层底部的光合有效辐射随小麦播种时间的推迟而增大。小麦冠层截获的光合有效辐射与叶面积指数呈显著正相关, 相关系数为0.756; 冠层底部的光合有效辐射与叶面积呈显著负相关, 相关系数为-0.872。小麦产量虽然随播期的推迟呈递减趋势, 但10月20日之前播种的小麦产量间无显著差异。因此, 在冬小麦和夏玉米一年两熟区, 可相应推迟小麦的播种时间, 尽量延长上茬玉米的生长期, 以实现两茬作物的均衡增产。

Relações radiométricas no terço superior da copa de cafeeiro

Com o objetivo de obter os coeficientes de transmissão e de extinção da radiação fotossinteticamente ativa determinou-se o índice de área foliar e mediu-se a radiação fotossinteticamente ativa transmitida no terço superior da copa de cafeeiro variedade Obatã IAC 1669-20, com três diferentes alinhamentos de plantio, em função da trajetória aparente do Sol, em Jaboticabal (SP). Foram três tratamentos, com quatro repetições, no total de doze parcelas, e cada uma com cem cafeeiros; cada tratamento correspondeu a um alinhamento de plantio. O alinhamento 81º-261º, por ser o que mais se aproximava do movimento aparente do Sol desde o nascente até o poente, favoreceu um autossombreamento maior na linha, e assim, ocorre maior disponibilidade de radiação solar difusa, contribuindo para maior índice de área foliar. Os coeficientes de transmissão são menores e os de atenuação são maiores para o alinhamento 81º-261º, revelando maior eficiência na interceptação da radiação fotossinteticamente ativa no terço superior da copa desse alinhamento. Foi possível estimar o coeficiente de extinção (kRFA) em função do índice de área foliar (IAF) por meio do modelo exponencial: κRFA = A + B* exp(-IAF/C); e estimar o índice de área foliar em função da radiação fotossinteticamente ativa interceptada (RFAint) pelo modelo polinomial quadrático: IAF = A(RFAint)² + B(RFAint) + C, onde A, B e C são parâmetros dos modelos.

Does undersowing winter wheat with a cover crop increase competition for resources and is it compatible with high yield?

The sustainability of cropping systems can be increased by introducing a cover crop, provided that the cover crop does not reduce the cash crop yield through competition. The cover crop may be sown at the same time as a cash crop in the crop rotation. We carried out an experiment in 1999–2000 and 2000–2001 in the Paris Basin, to analyze the effects of simultaneously sowing winter wheat ( Triticum aestivum L.) and red fescue ( Festuca rubra L.), a turf grass. Competition between wheat and fescue was analyzed with one variety of red fescue, Sunset, and two varieties of wheat, Isengrain and Scipion, each sown at a density of 150 plants m −2. In this study, we evaluated the effect of undersown fescue on wheat yield and analyzed the competition between the two species in detail. The undersown red fescue decreased wheat yield by about 12% for Isengrain (8.7 t ha −1 for undersown Isengrain versus 9.8 t ha −1 for Isengrain alone) and 7% for Scipion (7.4 t ha −1 for undersown Scipion versus 8.0 t ha −1 for Scipion alone). During the early stages of wheat growth (up to the ‘1 cm ear’ stage, corresponding to stage 30 on Zadoks’ scale), undersown fescue and fescue sown alone grew similarly. However, fescue biomass levels were much lower (5.6 and 4.7 g m −2 for fescue grown alone and undersown fescue) than wheat biomass levels on the undersown plots (120 g m −2 for Isengrain and 111 g m −2 for Scipion). From the e1 stage onwards, the wheat canopy rapidly extended, whereas that of red fescue remained sparse. The time lag between the beginning of the rapid increase in LAI and PAR interception by wheat grown alone and that for fescue grown alone was 590 dd in the second year. This resulted in much slower growth rates for undersown fescue than for undersown wheat. Biomass production rate was therefore low for undersown fescue (12% those of fescue grown alone, on average, at the time of wheat harvest), as were levels of water and nitrogen use. Neither the water deficit that occurred during the second experiment nor the nitrogen nutrition status of the wheat on plots with undersown fescue significantly affected wheat biomass production after anthesis. The global interception efficiency index IG ɛ i indicated that the fraction of the PAR o intercepted by the wheat during its growth (255 days) was 0.35.

Effects of reduced height (Rht) and photoperiod insensitivity (Ppd) alleles on yield of wheat in contrasting production systems

Near isogenic lines (NILs) varying for reduced height (Rht) and photoperiod insensitivity (Ppd-D1) alleles in a cv. Mercia background (rht (tall), Rht-B1b, Rht-D1b, Rht-B1c, Rht8c+Ppd-D1a, Rht-D1c, Rht12) were compared for interception of photosynthetically active radiation (PAR), radiation use efficiency (RUE), above-ground biomass (AGB), harvest index (HI), height, weed prevalence, lodging and grain yield, at one field site but within contrasting (‘organic’ vs. ‘conventional’) rotational and agronomic contexts, in each of 3 years. In the final year, further NILs (rht (tall), Rht-B1b, Rht-D1b, Rht-B1c, Rht-B1b+Rht-D1b, Rht-D1b+Rht-B1c) in Maris Huntsman and Maris Widgeon backgrounds were added together with 64 lines of a doubled haploid (DH) population [Savannah (Rht-D1b) × Renesansa (Rht-8c+Ppd-D1a)]. There were highly significant genotype × system interactions for grain yield, mostly because differences were greater in the conventional system than in the organic system. Quadratic fits of NIL grain yield against height were appropriate for both systems when all NILs and years were included. Extreme dwarfing was associated with reduced PAR, RUE, AGB, HI, and increased weed prevalence. Intermediate dwarfing was often associated with improved HI in the conventional system, but not in the organic system. Heights in excess of the optimum for yield were associated particularly with reduced HI and, in the conventional system, lodging. There was no statistical evidence that optimum height for grain yield varied with system although fits peaked at 85 and 96 cm in the conventional and organic systems, respectively. Amongst the DH lines, the marker for Ppd-D1a was associated with earlier flowering, and just in the conventional system also with reduced PAR, AGB and grain yield. The marker for Rht-D1b was associated with reduced height, and again just in the conventional system, with increased HI and grain yield. The marker for Rht8c reduced height, and in the conventional system only, increased HI. When using the System × DH line means as observations grain yield was associated with height and early vegetative growth in the organic system, but not in the conventional system. In the conventional system, PAR interception after anthesis correlated with yield. Savannah was the highest yielding line in the conventional system, producing significantly more grain than several lines that out yielded it in the organic system.

Simulation on Distribution of Photosynthetically Active Radiation in Canopy and Optimum Leaf Rolling Index in Rice with Rolling Leaves

By replacing leaf area index (LAI) with effective leaf area index (ELAI) through introduction of leaf rolling index (LRI), the distributions of photosynthetically active radiation (PAR) in the canopies of three hybrid rice combinations, Liangyou E32 with high LRI, Liangyoupeijiu with moderate LRI and Shanyou 63 with non-rolling leaves (normal), were simulated. The model based on ELAI could predict more accurately than that based on LAI. The PAR interception, conversion and utilization efficiency in the three combinations were studied to evaluate their optimal LRI and LAI. The PAR utilization efficiency of Liangyou E32 was lower due to excessive rolling leaves and less ELAI, and that of Shanyou 63 was also lower because of the faulty PAR interception and lower photosynthetic rate and saturation point at lower layer in canopy. Compared with the above two combinations, Liangyoupeijiu showed more appropriate distribution of PAR interception and conversion efficiency in canopy, and higher PAR utilization efficiency. The optimal LRI and LAI for Liangyoupeijiu were 0.11 and 7.6, respectively, which were close to the observed value, 0.11 and 7.9, respectively. However, the optimum LAI was 9.8 for Liangyou E32 and 6.2 for Shanyou 63, larger or smaller than those under the current plant density, which led to lower efficiency of PAR utilization. Besides, the optimum LRI for Liangyou E32 and Shanyou 63 were 0.12 and 0.08, respectively, which were close to the actual LRI for Liangyoupeijiu (0.11).

Responses of net ecosystem CO 2 exchange to nitrogen fertilization in experimentally manipulated grassland ecosystems

Nitrogen (N) addition enhances primary productivity of terrestrial ecosystems. However, the effects of N fertilization and/or deposition on net ecosystem CO 2 exchange (NEE) are not fully understood. The effects of N on NEE were investigated in two experimental cheatgrass ecosystems in Ecologically Controlled Enclosed Lysimeter Laboratories (EcoCELLs), Reno, Nevada. In this experiment, no N fertilization was added to the two EcoCELLs in the first year and two different N fertilization regimes were applied in the second year. N fertilizer was applied once to one EcoCELL (pulse fertilization, PF), and the same total amount of N in biweekly increments to the other EcoCell (gradual fertilization, GF). NEE, photosynthetically active radiation (PAR) and canopy green leaf area index (LAI) were continuously measured in the two EcoCELLs during the pretreatment and N-fertilized years. Plant N content and biomass were measured at the end of the growing season in each year. Radiation-use efficiency (RUE CO2) was calculated as the ratio of gross ecosystem photosynthesis (GEP) to the intercepted photosynthetically active radiation (IPAR). The responses of NEE to IPAR were used to estimate the maximum ecosystem photosynthetic capacity ( F max). N fertilization stimulated canopy LAI, plant N content, F max, RUE CO2, NEE and biomass in both methods of N supply applications. PF led to higher LAI, F max and NEE than GF, but both had a similar RUE CO2 during the early growing season. GF maintained higher LAI, F max, RUE CO2 and NEE than PF during the late growing season. At the ecosystem level, N fertilization stimulated daily NEE directly by increasing canopy LAI, plant N content, shoot/root ratio and the maximum ecosystem photosynthetic capacity, and increased the seasonally accumulated NEE indirectly by extending the growing season. PF differed significantly from GF in its effects on NEE and RUE CO2, possibly due to differential rates and timing of N availability. Our study suggested that these changes in the canopy RUE CO2 and growing season under N fertilization or N deposition regimes should be considered in modeling studies of ecosystem C sequestration.

Twin- and Single-Row Corn Production in Northeast Missouri

Producers may consider adopting narrow-row corn (Zea mays L.) due to potential yield advantages; however, variable yield benefits, risk, and costs may limit adoption. Twin-row corn planted in two 7.5-inch spaced rows on 30-inch centers allows farmers to utilize existing harvest equipment. Research was conducted on claypan soils to evaluate the effect of twin-row corn compared to narrow- (≤ 22.5-inch) and 30-inch single-row corn in separate small-plot conventional, no-till, and large-plot no-till trials in Northeast Missouri. This research determined the effect of (i) row spacing on intercepted photosynthetically active radiation (IPAR) and grain yield, and (ii) twin-row plant arrangement and population compared with single rows on grain yield. There was no grain yield increase with narrow-row compared with twin- or single-row corn. Recommendations for plant populations in narrow-, twin-, and singe-row spacings were similar since there was no interaction between row spacing and plant population for the hybrids in this research. Twin- and 30-inch single-row corn grain yield and IPAR was similar regardless of twin-row corn plant placement in all trials except in large-plot, no-till research with a natural European corn borer (Ostrinia nubilalis Hübner) infestation.

Seed yield determination of peanut crops under water deficit: Soil strength effects on pod set, the source–sink ratio and radiation use efficiency

Peanut ( Arachis hypogaea L.) production in Argentina is affected by frequent and unpredictable periods of water deficit that usually overlap the critical period for pod set of early sown crops. An indirect effect of water deficit is reduced pegging due to increased soil strength promoted by surface soil desiccation. There is no knowledge on the associated effects determined by peg production dynamics and variable plant water status. We evaluated the responses of these traits by means of field experiments (Exp 1: 2002–2003; Exp 2: 2005–2006) that included two peanut cultivars (ASEM 485 INTA and Florman INTA) cropped at different sowing dates and water regimes (IRR: irrigated; WS: water stress). Treatments allowed exploring a range of: (i) evaporative demands, (ii) surface soil strength levels, and (iii) soil water contents ( θ). We computed leaf area index (LAI), intercepted photosynthetically active radiation (IPAR), surface soil strength, degree of leaf folding, degree days of stress (SDD), crop (CGR) and pod growth rates (PGR) at critical periods, and radiation use efficiency (RUE). Seed yield and seed yield components (pod number per m 2, seed number per m 2 and individual seed weight) were determined at final harvest. WS promoted a significant decline (average of 73%) in seed yield ( P ≤ 0.022), which was better explained ( r 2 = 0.98) by the decline in seed and pod numbers than by the decline in individual seed weight ( r 2 = 0.67). Seed number responded chiefly to CGR between R 3 and R 6.5, but WS plots of Exp 1 departed from the general model fitted to IRR plots (40–53% decrease respect to predicted values). Biomass partitioning to reproductive sinks was also affected in WS plots. Enhanced soil strength promoted by soil drying reduced normal pegging pattern, and a generic bilinear model indicated a soil strength threshold of ca. 2.23 ± 0.10 MPa ( θ = 0.119 cm 3 cm −3) above which peg penetration decreased dramatically ( r 2 = 0.57, P < 0.001). WS reduced IPAR accumulation (10–30% reduction) and biomass production (34–67% reduction). The former was affected only by direct WS effects (i.e., tissue expansion, leaf movements). The latter was affected additionally by indirect effects (i.e., those determined by reproductive sink activity). The larger response of biomass production than of cumulative IPAR to WS determined a significant ( P < 0.05) decline in RUE with increased water deficit.

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.

Light interception and radiation use efficiency in temperate quinoa ( Chenopodium quinoa Willd.) cultivars

Sea level quinoas are grown at low altitudes in Central and Southern Chile. Both sensitivity to photoperiod and response to temperature largely determine quinoa adaptation, but crop biomass production must be quantified to evaluate agronomic performance. The objectives of this work are: (i) to characterize development effects on leaf area evolution for genotypes of sea level quinoa differing in cycle length, (ii) to quantify the extinction coefficient ( k) for photosynthetically active radiation (PAR) and radiation use efficiency (RUE) from emergence up to the beginning of grain filling and (iii) to identify which crop attributes related to canopy architecture should be considered to improve biomass production. Four cultivars (NL-6, RU-5, CO-407 and Faro) were cropped in Pergamino (33°56′S, 60°35′W, 65 m a.s.l.), Argentina, at three densities (from 22 to 66 plants m −2) in two consecutive years under field conditions with adequate water and nutrient supply. Thermal time to first anthesis and maximum leaf number on the main stem were linearly correlated ( r 2 = 0.87; p < 0.0001). Leaf area continued to increase during the flowering phase, notably in NL-6, the earliest genotype. There were significant differences in maximum plant leaf area between cultivars. Increasing density reduced plant leaf area but effects were comparatively small. Estimated k was 0.59 ± 0.02 across genotypes and was higher ( p < 0.05) for 66 plants m −2. Values for RUE changed as cumulative intercepted PAR (IPAR) increased; at initial stages of development RUE was 1.25 ± 0.09 g MJ IPAR −1, but if cumulative IPAR was higher than 107.5 ± 10.4 MJ IPAR m −2, RUE was 2.68 ± 0.15 g MJ IPAR −1. That change occurred when leaf area index (LAI) and fraction of PAR intercepted were still low and ranged from 0.61 to 1.38 and from 0.33 to 0.51, respectively. No significant association was found with any developmental stage. Our results agreed to the notion that RUE variation during pre-anthesis phases is largely determined by LAI through its effect on radiation distribution within the canopy. Biomass production could be improved if periods of interception below 50% of incoming PAR were reduced to ensure high RUE. This seems to be possible in temperate areas both by the use of late genotypes with a higher number of leaves on the main stem and by early genotypes provided adequate plant density is chosen. Early increment in LAI and overlapping of the leaf area increase period with the flowering phase are desirable strategies for earliest genotypes to maximize yield.

Effects of irrigation and straw mulch on water use and tuber yield of potato in eastern India

Potato, being a temperate crop, its growth and tuber production are limited by high atmospheric temperatures (mean temperature >17 °C). As a result potato is grown in winter season only (November–March) in the eastern plain of India when temperature is favourable. But during winter season, rainfall is erratic and meagre, therefore, potato crop in the region can only be grown with supplemental irrigation. In this study, potato crop was grown with four phenology based irrigation treatments (75 mm water depth with each irrigation) with three replications. Straw mulch at a rate of 6 t ha −1 was applied during the first earthing up in half of the plots to observe the variation of plant growth, water use efficiency and tuber production between mulched and non-mulched plots. The experimental split-plot design consisted of irrigation treatments in the main plots with mulching and non-mulching as subplots. Two years of pooled data with four irrigations resulted in air-dry tuber yields of 14.9 and 11.2 t ha −1 for the mulched and non-mulched plots, respectively. Significantly ( p < 0.05) higher leaf area index, water use efficiency and intercepted photosynthetically active radiation (IPAR) were recorded in the mulched plots compared to the non-mulched plots under the same irrigation treatment. Higher yield and better crop growth were observed in the mulched plots, which might be due to conservation of soil moisture and reduction of soil temperature by 4–6 °C. The highest PAR (89% of the PAR incident above the crop canopy) was found near the crop with mulching and four irrigations. The 77–103 mm less depleted soil moisture in the different treatments was due to the application of straw mulch. Application of straw mulch significantly increased the available phosphorus and potassium in the soil. Water use efficiency and tuber productions differed significantly among irrigation treatments in the non-mulched plots but they did not in the mulched plots with three and four irrigations. Therefore, three irrigations of 75 mm each and mulching were recommended for growing potato in the region when limited water was available.

Vegetative and reproductive plasticity of broccoli at three levels of incident photosynthetically active radiation

To study the effects of shading on the growth, development, dry matter partitioning, and plant architecture of broccoli, "Legacy" hybrid plants were grown in pots in a greenhouse under black shading meshes to generate different levels of photosynthetically active radiation (PAR). The average incident PAR was 23 mol PPF square m/d under control conditions, 15.2 under a 35% mesh, and 6.7 under a 70% mesh. The air temperature was within the range 15-22 deg C. As shading increased so did the duration of the growth cycle and the leaf area (LA). Shading did not affect the number of leaves, although the upper ones were more erect. The stem length and the accumulated intercepted PAR (IPAR) were negatively related. Inflorescence diameter and commercial fresh weight decreased only with the 70% mesh. Shading did not affect stem dry weight (DW) but altered dry matter allocation in the root and spear. The DW of the leaves maintained an average 45.7% of the total DW despite the greater LA developed under shade. The net assimilation rate diminished with the reduction of IPAR, and the LA increased; the plant relative growth rate was therefore practically constant. With increased shading, the leaves and the stem became the dominant photosynthate sinks. The commercial fresh weight achieved with 15.2 mol photosynthetic photon flux (PPF) square m/d was equivalent to that obtained with 23 mol PPF square m/d, but the cycle was extended for 4.5 days. With 6.7 mol PPF square m/d, yield diminished because of the lower DW produced in a cycle extended by 15 days, and because more dry matter was allocated to the stem than to the spear. Based on these results, broccoli could be considered a shade-tolerant plant.

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.

Spatial pattern effect on corn (Zea mays) weeds competition in the humid Pampas of Argentina

The objectives of this study were to determine the effect of spatial pattern on corn above- and below-ground biomass, grain yield, weed above-ground biomass and soil water and photosynthetically active radiation (PAR) dynamics. Field studies were conducted in 2003 and 2004. Three corn hybrids with two spatial pattern (square and rectangular) under weed-free and weedy conditions were tested. Corn grain yield was greater in the square than in the rectangular pattern. This increase was related to better resources use while reducing the competition from weeds. Early in the growing season, there was greater moisture content in the intrarow at square pattern while a lower soil water content was observed at maturity. Conversely, the square pattern registered lower soil water content during the whole corn growing season in the interrow. This soil water profile was an outcome of the uniform corn below-ground biomass distribution. A greater PAR interception with a lower weed above-ground dry matter was obtained in square plant arrangement. The use of uniform spatial pattern appeared as an interesting alternative to increase both the grain yield potential and the corn suppressive ability against weeds in dry-land Argentinean production systems.