Green Area Index Research Articles

Understanding the effect of a triazole with anti-gibberellin activity on the growth and yield of oilseed rape (Brassica napus)

SUMMARYThe effects of the anti-gibberellin triazole metconazole on yield, lodging resistance, seeds/m2 (sink size) and rooting in the presence of negligible amounts of disease were investigated using five multi-site experiments carried out in the UK between 1999 and 2007. The green area index (GAI) of the crop at the time of application had the greatest influence on the yield response across 173 comparisons between metconazole-treated and untreated crops. Crops with a GAI in March (growth stage (GS) 3·3–3·5 ‘green bud’) of 0·8–2·8, which represented moderate to large sized UK commercial crops, had an average response of +0·21 t/ha to metconazole applied at the full recommended rate of 1·2 litres/ha. Crops with a GAI of less than 0·8, which represented small commercial crops, had an average response of −0·14 t/ha. Applications between green bud and early flowering gave the greatest yield increase. Positive yield responses were associated with a reduction in lodging, or more seeds/m2, or a combination of both. The proportional area lodged was reduced by 0·1 for each 50 mm reduction in crop height (R2=0·60; P<0·001). Across six field trials, metconazole applied in spring increased root length density between soil depths of 0·40 and 1·00 m from an average of 0·478 to 0·601 cm/cm3 (P<0·05). It was estimated that this could increase yield by 0·2–0·3 t/ha in a dry season. The results show that the growth regulatory properties of metconazole can be used to improve several key aspects of growth that are believed to restrict current farm yields.

Durum wheat (Triticum durum Desf.) in rotation with faba bean (Vicia faba var. minor L.): long-term simulation case study

The aim of this work was to apply the CropSyst simulation model to evaluate the effect of faba bean cultivation as a break crop in the continuous durum wheat cropping system in southern Italy. The model was previously calibrated and validated for durum wheat and faba bean on data derived from experiments carried out in southern Italy (for different years and treatments), comparing observed and simulated crop growth, yield, soil water, and nitrogen output variables. The validation showed good agreement between simulated and observed values for cumulative above-ground biomass, green area index, and soil water content for both crops and grain yield for durum wheat; a negative correlation for grain yield in faba bean was observed due to a reduction in harvest index in the well-watered crop, which the model does not simulate well. Subsequently, a long-term analysis was carried out to study the effects on durum wheat of introducing a legume crop in rotation with the cereal in 2 and 3-year sequences. A long-term simulation, based on 53 years of daily measured weather data, showed that faba bean, due to a lower level of transpirated water (on average 247 mm for durum wheat and 197 mm for faba bean), allowed for greater soil water availability at durum wheat sowing for the cereal when in rotation with a legume crop (on average, +84 mm/m for durum wheat following the faba bean), with positive effects for nitrogen uptake, above-ground biomass, and grain yield of wheat. The yield increase of wheat when following a faba bean crop was on average +12%, but this effect was amplified in drier years (up to 135%). In conclusion, the case study offered the potential to confirm the positive results previously obtained in long/medium-term field experiments on the introduction of faba bean in rotation with durum wheat, as well as reduction in the chemical application of nitrogen.

Analysis of vegetation indices derived from hyperspectral reflection measurements for estimating crop canopy parameters of oilseed rape ( Brassica napus L.)

Vegetation indices (VIs), which are derived from hyperspectral measurements, may be useful non-destructive measures to estimate crop canopy parameters. A systematic analysis of the reflectance spectrum of winter oilseed rape (OSR) for the derivation of VIs has not been conducted yet. We therefore derived in our study VIs from 61 available wavebands of the spectral range from 400 nm to 1000 nm systematically and compared the best ones to commonly used indices. Hyperspectral reflectance and destructive measurements of crop canopy parameters were therefore carried out in 2005 and 2006 in northern Germany for calibration and in 2006 for validation at the same location. For the derivation of VIs for OSR, three different approaches were tested. The approaches differed in the way of the waveband combinations by combining two wavebands in a simple ratio (SR) form λ 1 / λ 2 , a normalized difference index (NDI) form ( λ 1 − λ 2 )/( λ 1 + λ 2 ) or by using a stepwise forward multiple regression (MR), which identifies the best linear combination of all available bands in a linear combination. The derived VIs were tested for their predictive power for crop canopy parameters like green area index (GAI), shoot dry matter (DM shoot ) and total nitrogen amount in the shoot (N shoot ) and were compared to commonly used indices. Waveband combinations of two near infrared bands resulted in the best prediction of the tested crop canopy parameters for calibration and validation data sets. Correlation coefficients ( r 2 ) yielded values up to 0.82 between new indices and N shoot . Especially, NDI 750,740 was best predicting GAI, whereas either NDI or SR forms of 740 nm and 780 nm showed best results predicting DM shoot and N shoot and outperformed commonly used indices. Predicting crop canopy parameters by MR showed good results for calibration, but highest variation for validation among all newly derived indices.

Interannual Ecosystem CO2 Dynamics in The Alpine Zone of The Eastern Alps, Austria

ABSTRACTInformation about the annual carbon fluxes of fen and meadow ecosystems in alpine environments is rare. We studied the influence of photosynthetic active radiation (PAR), plant green area index (GAI), soil temperature, and water-filled pore space (wfps) on the net CO2 emission at four alpine sites (one meadow and three fen sites) differing in water balance and plant community. Measurements over two years were made in the Eastern Alps, Austria, including two snow-free periods and two snow periods. During snow-free periods, net CO2 gain during daylight periods (NEElight , PAR > 0) depended on PAR and GAI. The net CO2 emission rate at night (Rtot , PAR = 0) was positively related to soil temperature, while low wfps reduced the carbon loss via Rtot of the meadow and driest fen study site but reinforced carbon loss of the wetter fen sites. Daily average ecosystem net CO2 gain (NEEday ) during snow-free periods (averaged over both years) at the meadow was 3.5 g CO2 m−2 d−1 and ranged from 1.5 to 3.4 g CO2 m−2 d−1 at the fen sites. Mean average daily wintertime CO2 emission was low, being only −0.9 g CO2 m−2 d−1 for meadow and between −0.2 and −0.7 g CO2 m−2 d−1 for all fen sites. All sites function as significant annual net carbon sinks, with a net carbon gain from 50 to 121 g C m−2 a−1 (averaged over both years) irrespective of water balance. Our results indicate that these alpine fen sites that have built up a large carbon stock in the past do not gain a further carbon surplus compared with the meadow under the current climate.

Disentangling leaf area and environmental effects on the response of the net ecosystem CO2 exchange to diffuse radiation

There is an ongoing discussion about why the net ecosystem CO2 exchange (NEE) of some ecosystems is less sensitive to diffuse radiation than others and about the role other environmental factors play in determining the response of NEE to diffuse radiation. Using a six-year data set from a temperate mountain grassland in Austria we show that differences between ecosystems may be reconciled based on their green area index (GAI; square meter green plant area per square meter ground area) - the sensitivity to diffuse radiation increasing with GAI. Our data suggest diffuse radiation to have a negligible influence on NEE below a GAI of 2 m2 m-2. Changes in air/soil temperature and air humidity concurrent with the fraction of diffuse radiation were found to amplify the sensitivity of the investigated temperate mountain grassland ecosystem to diffuse radiation.

Seasonal and inter‐annual variability of the net ecosystem CO2 exchange of a temperate mountain grassland: Effects of weather and management

The role and relative importance of climate and cutting for the seasonal and inter-annual variability of the net ecosystem CO2 (NEE) of a temperate mountain grassland was investigated. Eddy covariance CO2 flux data and associated measurements of the green area index and the major environmental driving forces acquired during 2001-2006 at the study site Neustift (Austria) were analyzed. Driven by three cutting events per year which kept the investigated grassland in a stage of vigorous growth, the seasonal variability of NEE was primarily modulated by gross primary productivity (GPP). The role of environmental parameters in modulating the seasonal variability of NEE was obscured by the strong response of GPP to changes in the amount of green area, as well as the cutting-mediated decoupling of phenological development and the seasonal course of climate drivers. None of the climate and management metrics examined was able to explain the inter-annual variability of annual NEE. This is thought to result from (1) a high covariance between GPP and ecosystem respiration (Reco) at the annual time scale which results in a comparatively small inter-annual variation of NEE, (2) compensating effects between carbon exchange during and outside the management period, and (3) changes in the biotic response to rather than the climate variables per se. GPP was more important in modulating inter-annual variations in NEE in spring and before the first and second cut, while Reco explained a larger fraction of the inter-annual variability of NEE during the remaining, in particular the post-cut, periods.

Breeding Effects on Grain Filling, Biomass Partitioning, and Remobilization in Mediterranean Durum Wheat

This work assesses the changes resulting from durum wheat (Triticum turgidum L. var. durum) breeding in Italy and Spain during the 20th century on grain filling, biomass production, and allocation at anthesis, and the remobilization of preanthesis photosynthates to the grain of main stems. Field experiments, involving 12 Italian and 12 Spanish cultivars released at different periods, were conducted at two Spanish sites during three growing seasons. Breeding activities did not modify final grain weight (WG), the maximum rate of grain filling (R), nor grain filling duration (D) of central grains of main spikes. Genetic variability existed for WG and R within countries and periods. Cycle length (expressed as days from sowing to anthesis [DSA]) was reduced by 2 and 8 d in Italian and Spanish cultivars, respectively. Crop dry weight (CDW) decreased by 21% (0.51% yr−1) and green area index (GAI) by 28% (–0.33% yr−1) in Spanish cultivars. Green area index at anthesis did not differ between old and modern Italian cultivars, while CDW decreased by 9%. Leaf area index (LAI) remained unchanged in cultivars from both countries, while the spike:stem ratio increased by 8 and 10% in Italian and Spanish cultivars, respectively. Changes over time in DSA were positively associated with changes in CDW and GAI. Dry matter translocation (DMT) efficiency switched from 9% in old cultivars to 20% in modern ones. The contribution of preanthesis assimilates to grain yield (CPA) increased to values of 31 and 27% in Italian and Spanish modern cultivars, respectively. Opportunities for further increases in genetic yield potential in Mediterranean‐type environments are discussed.

Breeding Effects on Grain Filling, Biomass Partitioning, and Remobilization in Mediterranean Durum Wheat

This work assesses the changes resulting from durum wheat (Triticum turgidum L. var. durum) breeding in Italy and Spain during the 20th century on grain filling, biomass production, and allocation at anthesis, and the remobilization of preanthesis photosynthates to the grain of main stems. Field experiments, involving 12 Italian and 12 Spanish cultivars released at different periods, were conducted at two Spanish sites during three growing seasons. Breeding activities did not modify final grain weight (WG), the maximum rate of grain filling (R), nor grain filling duration (D) of central grains of main spikes. Genetic variability existed for WG and R within countries and periods. Cycle length (expressed as days from sowing to anthesis [DSA]) was reduced by 2 and 8 d in Italian and Spanish cultivars, respectively. Crop dry weight (CDW) decreased by 21% (0.51% yr−1) and green area index (GAI) by 28% (–0.33% yr−1) in Spanish cultivars. Green area index at anthesis did not differ between old and modern Italian cultivars, while CDW decreased by 9%. Leaf area index (LAI) remained unchanged in cultivars from both countries, while the spike:stem ratio increased by 8 and 10% in Italian and Spanish cultivars, respectively. Changes over time in DSA were positively associated with changes in CDW and GAI. Dry matter translocation (DMT) efficiency switched from 9% in old cultivars to 20% in modern ones. The contribution of preanthesis assimilates to grain yield (CPA) increased to values of 31 and 27% in Italian and Spanish modern cultivars, respectively. Opportunities for further increases in genetic yield potential in Mediterranean-type environments are discussed.

Drought stress effects on wheat are mitigated by atmospheric CO2 enrichment

The atmospheric CO2 concentration is predicted to increase and to generate a rise in the global surface temperature, and change the seasonal precipitation pattern. This could aggravate the severity of summer drought conditions and affect crop yield. We studied the effect of the interaction of CO2 and water supply on seasonal absorption of photosynthetically active radiation and radiation-use efficiency of aboveground biomass production to understand the processes contributing to final yield. Wheat was grown over two years in open-top chambers at present or future (+280 ppmv) atmospheric CO2 concentration and under sufficient water supply or drought stress in lysimeters with a soil depth of 0.4 m (first year) or in the field with unrestricted root growth (second year). Drought stress was started after the first node stage by halving the water supply. Our results show that under sufficient watering, CO2 enrichment did not affect the green area index or seasonal radiation absorption. Drought stress always decreased the green area index and accelerated canopy senescence, which in the second year resulted in a decrease of 23% in the seasonal radiation absorption under the present atmospheric CO2 concentration. CO2 enrichment stimulated the green area index under drought stress in the second year and seasonal radiation absorption was only decreased by 16%. Radiation-use efficiency was reduced by drought and increased by CO2 elevation and the CO2 effect was higher under restricted (+60%) than under sufficient watering (+32%). This implies that CO2 enrichment enhanced final biomass and grain yield by less than 10% under well-watered conditions and by more than 44% under drought stress conditions, respectively. This study indicates that the increase in atmospheric CO2 concentration will attenuate the effects of summer drought on wheat grain yield.

Carbon dioxide dynamics of a restored maritime peatland

The restoration of cutaway peatlands provides an opportunity to return the carbon (C) sink function and to examine the influence of climate on peat formation and C accumulation. We studied CO2 exchange dynamics in 2002 and 2003 at a rewetted cutaway peatland located within the temperate maritime climatic zone. Gross photosynthesis (PG), ecosystem respiration (RTOT), and net ecosystem exchange (NEE) were observed in a range of microsites representing a hydroseral succession gradient: Typha latifolia—Phalaris arundinacea, Eriophorum angustifolium—Carex rostrata, and Juncus effusus—Holcus lanatus vegetation communities and areas of bare (unvegetated) peat. Annual rainfall was 26% higher in 2002 and 4% lower in 2003 than the long-term average and influenced water table position at all microsites. Observed instantaneous CO2 fluxes varied temporally and spatially at all microsites. Modelled PG was strongly dependent on irradiation (Photosynthetically Active Radiation) and the Vascular Green Area index (VGA). RTOT was influenced by the soil temperature at 5 cm depth (T5cm) and the water table position. All microsites were net sources of CO2 in both years of the study, and higher losses (with the exception of Juncus/Holcus) were observed in 2003 at all microsites. In general, losses followed the trend Juncus/Holcus > Phalaris > Typha > bare peat > Eriophorum—Carex in 2002 and Phalaris > Juncus—Holcus > Typha > Eriophorum/Carex > bare peat in 2003. Losses ranged from -163 to -651 g CO2 - C·m−2.y−1 in 2002 and -308 to -760 g CO2 - C·m−2.y−1 in 2003. Considerable wintertime losses were observed at all microsites. The results from this study suggest that these peatlands are vulnerable to interannual variations in climatic inputs and that future predictions of climatic change may make restoration of the C sink function in cutaway peatlands in the temperate maritime climatic zone a considerable challenge in the years ahead.

A SIMULATION MODEL FOR DYNAMIC GREEN AREA INDEX IN WINTER RAPESEED (BRASSICA NAPUS)

Aims Accurate simulation of green area index is critical for reliable prediction of crop growth and yield using a crop growth model.Our study was undertaken to develop a process-based simulation model for predicting dynamic green area index,including leaf area index(LAI) and pod area index(PAI),in winter rapeseed(Brassica napus).Methods Leaf area expansion was simulated through the relationship between LAI and source-or sink-limited dry matter.Daily leaf expansion rate increased in an S-shaped growth curve under source limitation,as influenced by temperature,water and nitrogen levels.Under the sink limitation,leaf area expansion was quantified on the basis of specific leaf area.Pod area was calculated from specific pod area and pod dry matter.The specific leaf area and specific pod area were determined from physiological development time and genotype.We calibrated and validated the model using experimental data from different varieties,sowing dates and nitrogen fertilization rates.Important findings Root mean square error(RMSE) values of LAI were 11.15%,15.57% and 16.87% at three N levels,and the average RMSE value of PAI in two varieties was 12.92%.Plotting the 1∶1 relationship between the simulated and observed values in LAI and PAI growth dynamics indicated a good fit.Our model of green area index in winter rapeseed shows a high accuracy and applicability under different conditions.

Is barley yield in the UK sink limited?: I. Post-anthesis radiation interception, radiation-use efficiency and source–sink balance

Source or sink limitation of grain filling in cereals is often inferred from experiments in which the source:sink ratio is manipulated by shading, defoliation or grain removal. However, interpretation of this type of experiment is usually qualitative rather than quantitative in nature and the extent of any imbalance between the source and sink is not known. The objectives of the current work were: (1) to provide a detailed analysis of radiation interception, radiation-use efficiency (RUE) and carbohydrate storage reserves in winter barley in order to quantify the potential supply of photosynthates for grain filling; (2) to estimate the variation in source–sink balance between environments. Field experiments were conducted on cv Pearl at six sites in the UK and over 3 years. Crops were grown under a comparable husbandry regime at each site and received a full fertilizer and crop protection programme. When the cumulative interception of post-anthesis photosynthetically active radiation (PAR) was plotted against the increase in biomass to determine RUE, the pattern of response differed between sites and years; for some site/years the response was linear, for others it was non-linear where RUE decreased during the latter stages of grain filling. The extent and statistical significance of non-linearity was determined from the quadratic term of fitted 2nd order polynomials. There was no significant association between climatic variables, such as temperature, radiation or rainfall, and the value of the quadratic term of RUE. Neither could non-linearity of RUE be explained in terms of the shedding of leaf tissue during canopy senescence. There were weak associations ( r 2 < 0.3) between the extent of non-linearity and green area index (GAI), above-ground biomass, and specific leaf N, at ear emergence (Zadoks GS 59). A much stronger relationship ( r 2 = 0.63) was found between the source:sink ratio (green area per grain) at GS 59 and non-linearity of RUE. These results suggest that a major factor leading to the reduction in RUE during the second half of grain filling at some sites was feedback inhibition from a limited sink capacity. This conclusion is supported by a fairly strong positive association between RUE non-linearity and the apparent contribution of stem carbohydrate reserves to grain yield ( r 2 = 0.47). The potential assimilate supply for grain filling was estimated as (maximum post-anthesis RUE × PAR intercepted) + stem soluble carbohydrate reserves at GS 59. The potential supply exceeded the measured yield at all sites except one implying that crops were predominantly sink limited. The size of the excess, which is a measure of the relative source–sink balance during grain filling, differed widely between site/years.

Radiation- and water-use associated with growth and yields of wheat and chickpea in sole and mixed crops

A renewed interest in mixed cropping for its potential to boost yields through increased capture and use of solar radiation and soil-water by the component species. This led to the present study, in which we assessed the performance of wheat and chickpea, grown as sole crops or mixed at half their sole crop populations for their capacity to capture and use solar radiation and soil-water. Trials were conducted in the drought season of 1994 and with or without supplementary irrigation in an average rainfall season of 1995. For the rainfed crops in both years, there was no advantage of mixed crops over wheat grown as a sole crop (wheat-s) either in terms of green area index (GAI), fraction of photosynthetically active radiation intercepted by the canopy ( i PAR), dry matter (DM) or grain yield produced. The lack of a yield advantage of mixed cropping was associated with poor canopy development and low yielding capacity of chickpea; it was unable to compensate for its reduced population density in the mixture. Grain yield for chickpea in the mixed crop (chickpea-m) averaged just 29% that of its sole crop (chickpea-s), whereas wheat grown in mixture (wheat-m) produced 72% the yield for wheat-s. Supplementary irrigation from early spring onwards in 1995 increased yield for chickpea-m by 44% over that of chickpea-s, while yield for wheat-m fell to 65% that for wheat-s. Every millimetre of irrigation water increased yield by 10.0, 3.8 and 12.5 kg ha −1 for wheat-s, mixed crop and chickpea-s, respectively. Mixed cropping did not affect the time taken by either wheat or chickpea to attain maximum growth rate, flowering or maturity. The land equivalent ratio (LER) based on grain yields for wheat–chickpea intercropping were 1.01 in 1994, 1.02 without irrigation in 1995, and 1.10 with irrigation in 1995. Neither radiation-use-efficiency nor water-use-efficiency was improved by mixed cropping compared with wheat-s. The poor performance of the mixed crop was ascribed to its poor canopy development early in the season, especially by the chickpea that resulted in low i PAR and transpiration. It is concluded that there was no advantage of growing wheat and chickpea in mixed crops in southern cereal belts of Australia if total biomass or grain yield is the primary purpose.

A high resolution green area index for modelling the seasonal dynamics of CO2 exchange in peatland vascular plant communities

We studied vegetation dynamics at peatlands, differing in their climate, land use management history and vegetation community in Ireland and Finland over a two-year period. Our aim was to develop a species-specific method to be used to (1) describe the seasonal dynamics of green (photosynthetic) area (GA) of the vegetation and (2) incorporate these changes into CO2 exchange models. The extent of temporal and spatial variation between and within communities indicated the need for a two-step calculation approach for each community. Firstly, at biweekly to monthly intervals, GA of all species within a range of vascular plant communities was estimated by non-destructive field measurements. Gaussian or log-normal models were fitted to describe the seasonal dynamics of each species. Secondly, an estimate of community vascular green area (VGA) was obtained by summing the modelled daily GA of all species within the community. The highest values of VGA (2.1–6.0 m2 m−2) occurred within the reed communities at the rewetted cutaway peatland in Ireland and the lowest at the ombrotrophic lawn communities in Finland (0.5–1.0 m2 m−2). The relationship between light saturated gross photosynthesis (PG) and VGA was either linear or hyperbolic depending on the degree of self-shading that occurred within each community. The addition of the VGA term into PG models improved the explaining power of the model by 57.6, 24.5 and 23% within the Typha latifolia, Phalaris arundinacea and Eriophorum angustifolium/Carex rostrata communities, respectively. VGA proved useful in recording the seasonal development of a wide range of peatland vascular plant communities over geographically and climatically different regions.

Durum Wheat under Mediterranean Conditions as Affected by Seed Size

AbstractThis study was carried out in order to determine the effect of seed size on the growth and yield of durum wheat. Four field experiments, composed of six durum wheat (Triticum turgidum L. var. durum) varieties and three seeding sizes were conducted in north‐east Spain in 2000 and 2001 in randomized complete block designs. The growth of seedlings was dramatically affected by seed size. Large seeds produced greater plot stands, but the plants had fewer tillers, leaves and spikes and less green area and dry weight than plots from small seeds. Grain yield was 16 % greater in plots from large seeds, which resulted in greater biomass, green area index, spikes per m2 and heavier kernels than in plots from small seeds. Kernel weight was the yield component most related to grain yield in the three seed sizes. The percentage of yield variation explained by kernel weight increased as the weight of kernels increased. This was a consequence of the use of larger seeds, the same effect being observed when the comparison was made between varieties with different kernel weights. Selection for heavy kernel varieties may help to improve the yield of durum wheat in Mediterranean environments similar to that prevailing in north‐east Spain.

Near-Ground Remote Sensing of Green Area Index on the Shortgrass Prairie

Accurate and efficient leaf area measurements of shortgrass prairie vegetation are difficult to obtain. Few studies have considered the green area index (GAI) as an approximation of the total area of photosynthetically active tissue per unit of ground area. The main objective of this study was to evaluate several near-ground remote sensing methods as reliable and cost efficient measures of GAI on the shortgrass prairie. GAI measured with a standard leaf area meter was compared to 1) spectral vegetation indices calculated from multispectral radiometer data, 2) GAI obtained from laser point-frame measurements, and 3) green cover estimates derived from digital camera images. All methods were assessed for accuracy, time, and cost efficiency. Data were collected in 2001 at the Central Plains Experimental Range in northern Colorado. The standard leaf area meter method was neither time nor cost efficient in comparison with the other methods evaluated in this study. The cost of GAI measurement with the traditional leaf area meter method ($225 per plot) was 20 times greater than GAI estimation with the multispectral radiometer ($11 per plot). Comparison of GAI obtained with the standard leaf area meter method with red-band reflectance index values (0.63‐0.69 lm) obtained with a portable multispectral radiometer resulted in the best model predictions (R 2 ¼ 0.76, Akaike’s information corrected criterion [AICC] ¼ 182.9) and the most cost efficient method for GAI estimation. Green cover estimates from digital image analysis resulted in a good correlation with the leaf area meter GAI (R 2 ¼ 0.72, AICC ¼ 178.1). However, classification accuracies of digital images were decreased by limited spectral separability between green vegetation, brown vegetation, and soil background. Further calibration and refinement of near-ground remote sensing techniques for vegetation might establish these methods as efficient ground-truth alternatives to satellite-based remote-sensing applications of rangelands such as the shortgrass prairie.

Irrigation of grapevines with saline water: I. Leaf area index, stomatal conductance, transpiration and photosynthesis

In the Negev Desert of Israel, saline water is used to irrigate grapevines (Cabernet Sauvignon grafted on Roggeri) with the premise that the vine is only moderately salt sensitive. The objectives of the research were to study the effect of salinity on major production factors of the grapevine. Irrigation was applied with water of three salinity levels: 1.8, 3.3 and 4.8 dS m −1 in four replications. Seasonal water application was 633 mm for all treatments. Biweekly measurements were taken from April to October. Green area index (GAI: the ratio of total leaf surface to the unit of land area allocated to each vine), photosynthesis, leaf conductance and transpiration fluxes were determined and the measurements were combined to form an exponential relationship between plant canopy and effective light interception. The effect of salinity was most pronounced on GAI and leaf conductance. Its maximal value (GAI = 5.2) was reduced by about 40% with increased salinity. Gas exchange rates per unit area of individual leaves were less affected by salinity. The extrapolation of the data from daily to seasonal values yielded a total of 9.0, 7.4 and 6.8 Mg ha −1 for the respective low, medium and high salinity levels. Hence, total grapevine productivity, based on the product of leaf area and the photosynthesis rate declined with increased salinity. Total yield of berries was not reduced by salinity and hence it was concluded that in addition to yield other factors should be studied. For example, the quality of the berries and life expectancy of the vines under saline conditions.

Near-Ground Remote Sensing of Green Area Index on the Shortgrass Prairie

Drought is an inherent trait of most rangelands and sound management necessitates managers address two fundamental questions when facing a drought situation. The first question is, ‘‘what is the probability that a useful amount of precipitation will be received over the period of concern?’’ and the second question is, ‘‘if it does rain, what will the impact be in terms of quantity and quality of herbage produced?’’ The objective of this study was to address the second question. Our hypothesis was that herbage growth response to above normal summer precipitation (i.e., 23 in July and August) would be limited in the northern Great Plains because of a general absence of productive warm-season species. Study plots were twelve 5 X 10-m non-weighing lysimeters. Treatments were: 1) simulated (i.e., rainout shelter imposed), severe spring drought (i.e., 1 May - 1 July) followed by ambient precipitation thereafter; 2) simulated, severe spring drought followed by ambient precipitation thereafter plus summer irrigation (i.e., July and August); 3) ambient precipitation only; and 4) ambient precipitation plus summer irrigation. Results indicated substantial herbage production can be expected in this region during summer when precipitation is well above average because of the positive growth response of blue grama (Bouteloua gracilis [H.B.K.] Lag. ex Griffiths), the dominant warm-season grass growing in this region. However, results also showed that level of production in the study situation (i.e., spring drought, wet summer) was only about 50% of that attained in a normal (i.e., wet spring/dry summer) year. Moreover, long-term weather data shows the probability of receiving 23 normal precipitation in both July and August (i.e., our irrigation treatments) is &lt; 1%. Thus, although these rangelands possess the capacity to respond favorably to summer precipitation, the low probability of receiving substantial levels of summer precipitation ensures levels of ecological and economic risk remain high.

Growing season evapotranspiration from Tamarix ramosissima stands under extreme arid conditions in northwest China

Given the increasing threat of water shortages in the extremely arid regions (rainfall<50 mm year−1) of northwestern China, growing season evapotranspiration (ET) associated with native species such as Tamarix ramosissima is of particular interest. Consequently, this study sought to evaluate the accuracy of daily ET estimates using Bowen ratio data, as well as measuring seasonal ET and development of an energy balance for a stand of T. ramosissima. Bowen ratio apparatus measurements of ET were carried out on a stand of T. ramosissima in a 2.04 km2 field, which are all covered with T. ramosissima near Erdaoqiao, Ejina Province, Inner Mongolia Autonomous Region, China. Soil moisture content and green area index were also monitored. Daily ET could be accurately estimated from Bowen ratio data on a continuous basis over the 153-day growing season. The mean daily T. ramosissima ET over this period was 1.62 mm day−1, for a seasonal total of 248.20 mm. In this extremely arid locale, the great majority of available energy dissipated over the growing season was a result of sensible rather than latent heat fluxes. While the heat storage term was the main source of energy at night and a considerable sink of energy during the daytime, the magnitude of the daily mean soil heat flux was small. Such a determination of temporal and ecosystem-specific ET patterns allows an improved prediction of ET in the desert riparian zone.

Regional simulation of ecosystem CO 2 and water vapor exchange for agricultural land using NOAA AVHRR and Terra MODIS satellite data. Application to Zealand, Denmark

While accurate information on ecosystem CO 2 and water vapor exchange is available at eddy covariance flux tower sites, methods to expand predictions of CO 2 and energy exchange to regional or global scales with high fidelity are lacking. The main objective of this study was to examine the applicability of land surface and atmospheric products from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Advanced Very High Resolution Radiometer (AVHRR) for assessing the spatial variation in CO 2 and water vapor fluxes for cloudless agricultural land pixels at the Island of Zealand, Denmark. The spatial distribution of green leaf area index, direct-beam and diffuse solar radiation and air humidity was inferred on the basis of late morning MODIS data that was combined with afternoon AVHRR data to resolve the diurnal variation in air and surface temperature. These variables were used in a coupled “two-leaf” ecosystem model operating at an hourly time scale. The enhanced vegetation index (EVI) was strongly correlated with field measurements of green leaf area index ( r 2=0.91) and remained sensitive to variations in green biomass up to green leaf area indices of 4–5. Evaluation against standard meteorological data showed that instantaneous estimates of air temperature, actual vapor pressure and incoming solar radiation could be retrieved with overall root mean square errors of 2.5 °C, 138.3 Pa and 47.7 W m −2, respectively. The combination of late morning and afternoon inferences made it possible to resolve the diurnal course in key model parameters, and predicted rates of ecosystem CO 2 and water vapor exchange were comparable to eddy covariance measurements at a single flux tower. A large spatial diversity in CO 2 and water vapor exchange was maintained throughout the study period due to significant regional variations in meteorological input variables and large spatial differences in canopy development. The results of this study stress the necessity of pixel based estimates for an accurate evaluation of regional budgets of CO 2 and water vapor exchange.