Showing papers on "Leaf area index published in 1983"

The red edge of plant leaf reflectance

Abstract: A detailed study of the red edge spectral feature of green vegetation based on laboratory reflectance spectrophotometry is presented. A parameter lambda is defined as the wavelength is defined as the wavelength of maximum slope and found to be dependent on chlorophyll concentration. Species, development stage, leaf layering, and leaf water content of vegetation also influences lambda. The maximum slope parameter is found to be independent of simulated ground area coverage. The results are interpreted in terms of Beer's Law and Kubelka-Munk theory. The chlorophyll concentration dependence of lambda seems to be explained in terms of a pure absorption effect, and it is suggested that the existence of two lambda components arises from leaf scattering properties. The results indicate that red edge measurements will be valuable for assessment of vegetative chlorophyll status and leaf area index independently of ground cover variations, and will be particularly suitable for early stress detection.

Estimating Forest Growth and Efficiency in Relation to Canopy Leaf Area

Abstract: Publisher Summary This chapter demonstrates two structural properties of plant communities—canopy leaf area and growth efficiency. It develops four basic premises that (1) canopy leaf area can be related to competition for light, (2) growth efficiency is responsive to canopy leaf area and other identified environmental factors, (3) potential productivity or site capability can be estimated from knowing maximum canopy leaf area, and (4) canopy leaf areas for trees or stands can be nondestructively estimated by determining sapwood cross-sectional area at a convenient reference height. Canopy leaf area and its vertical distribution can be accurately estimated through correlations with conducting sapwood area throughout the crown. Species within the same genera have widely differing ratios of leaf area to sapwood area. To estimate the canopy leaf area on large trees, the linear taper in sapwood area from breast height (1.37 m) to the base of the crown must be determined.

Spectral estimates of solar radiation intercepted by corn canopies

Abstract: Reflectance factor data were acquired with a Landsat band radiometer throughout two growing seasons for corn (Zea mays L.) canopies differing in planting dates, populations, and soil types. Agronomic data collected included leaf area index (LAI), biomass, development stage, and final grain yields. The spectral variable, greenness, was associated with 78 percent of the variation in LAI over all treatments. Single observations of LAI or greenness have limited value in predicting corn yields. The proportions of solar radiation intercepted (SRI) by these canopies were estimated using either measured LAI or greenness. Both SRI estimates, when accumulated over the growing season, accounted for approximately 65 percent of the variation in yields. Models which simulated the daily effects of weather and intercepted solar radiation on growth had the highest correlations to grain yields. This concept of estimating intercepted solar radiation using spectral data represents a viable approach for merging spectral and meteorological data for crop yield models.

The estimation of percentage light interception from leaf area index and percentage ground cover in potatoes

Abstract: Since Monteith (1977) proposed that growth can be analysed in terms of the amount of energy intercepted by the leaf surface and the efficiency of its use, there has been much interest in the measurement of light interception in potato crops (Scott & Wilcockson, 1978; Milford et al. 1980; Allen & Scott, 1980). This can be measured directly using tube solarimeters placed horizontally above and below the canopy. However, this method suffers from three major drawbacks: (a) in an experiment with many plots it becomes expensive in terms of equipment, (b) a single solarimeter samples only a very small part of the plot canopy, and (c) the solarimeter cannot distinguish between living leaves and other material. Thus, when the crop lodges and/or starts to senesce, visual observations suggest that the area over the solarimeter may not be representative of the plot as a whole.

Agronomical and physiological aspects of the role of nitrogen in yield formation of cereals

Abstract: Nitrogen exerts its influence on crop growth and grain yield in various ways. Early top dressings or a high level of soil nitrogen stimulate tiller formation and leaf growth, which results in an increase of shoot dry weight and leaf area index. Late top dressings promote the survival of ear-bearing tillers, grain set and leaf area duration.

Relation of agronomic and multispectral reflectance characteristics of spring wheat canopies

Abstract: The relationships between crop canopy variables such as leaf area index (LAI) and their multispectral reflectance properties were investigated along with the potential for estimating canopy variables from remotely sensed reflectance measurements. Reflectance spectra over the 0.4 to 2.5 micron wavelength range were acquired during each of the major development stages of spring wheat canopies at Williston, North Dakota, during three seasons. Treatments included planting date, N fertilization, cultivar, and soil moisture. Agronomic measurements included development stage, biomass, LAI, and percent soil cover. High correlations were found between reflectance and percent cover, LAI, and biomass. A near infrared wavelength band, 0.76 to 0.90 microns, was most important in explaining variation in LAI and percent cover, while a middle infrared band, 2.08 to 2.35 microns, explained the most variation in biomass and plant water content. Transformations, including the near infrared/red reflectance ratio and greenness index, were also highly correlated to canopy variables. The relationship of canopy variables to reflectance decreased as the crop began to ripen. the canopy variables could be accurately predicted using measurements from three to five wavelength bands. The wavelength bands proposed for the thematic mapper sensor were more strongly related to the canopy variables than the LANDSAT MSS bands.

Yield variation of wheat and barley in Britain in relation to crop growth and soil conditions—A review

Abstract: Yields of cereals in Britain vary between sites and between years, and average farm yields are less than half of the calculated potential maximum yield. Yield variation is discussed in relation to soil conditions and root growth. An analysis of yield and its components of winter wheat for several sites over several years shows that yield is strongly correlated with number of grains per ear, and number of ears per unit area. These components of yield are influenced by environmental conditions during the reproductive phase of development, particularly light interception, nitrogen absorption and plant water stress. Crop growth analysis shows that total dry matter production is strongly correlated with light absorption, which depends on seasonal variation in leaf area index. Leaf expansion in the field is mainly dependent on temperature, plant water stress, and nitrogen absorption. The environmental factors that are believed to have a strong influence on number of grains per ear, number of ears per unit area, and leaf expansion are discussed. Subjects in which further research is needed are identified. These include: effects of restrictions to root growth on absorption of nutrients and water; effects of soil temperature on leaf expansion and nutrient absorption; the nitrogen requirements of the cereal crop, including the effects of temporary deficiencies of N on the final grain yield.

The relationships between the chlorophyll concentration, LAI and reflectance of a simple vegetation canopy

Abstract: The reflectance of a vegetation canopy is primarily determined by its leaf area index (LAI), the one sided leaf area per unit area of ground, which in turn is usually correlated to the concentration of chlorophyll (the total chlorophyll per unit area of ground) within the canopy|This laboratory experiment on the growth of curled cress Lepedium sativum (L), indicated that during moisture stress there was no correlation between chlorophyll concentration and LAI and therefore no correlation between chlorophyll concentration and canopy reflectance.

Canopy Structure of Mediterranean-Type Shrubs in Relation to Heat and Moisture

Abstract: The similar vegetative characteristics in regions with similar mediterranean-type climates imply that these characteristics should be important for plant survival and optimal resource use within the constraints of irradiance, temperature, annual precipitation and soil moisture. These similar vegetative characteristics include shrub form, moderate leaf area indices and hard, small, evergreen leaves. Usually, where the annual precipitation decreases, the vegetation includes smaller shrubs, lower leaf area indices and drought-deciduous, soft leaves. The links between the vegetative morphological characteristics and soil characteristics involve the physiological characteristics of the species. The vegetation has developed similar forms despite separate phylogenetic histories and different intensities of various selective forces, including climatic factors, low nutrient conditions and frequent fire (Walter 1973; Specht 1979). Regardless of the vegetation histories, differences in distribution and diverse previous selective forces within the regions, the broad similarities between vegetation form and climate in the present mediterranean regions imply current functional-physiological interrelations.

Leaf area index, canopy structure and photosynthesis of red clover (Trifolium pratense L.)

Abstract: . The influence of leaf age, total leaf area and its dispersion in space on canopy photosynthesis were studied using microswards of red clover (Trifolium pratense L.) which were established in the greenhouse. Two varieties, Renova (flowering) and Molstad (non-flowering), were sown in separate plastic boxes at densities of 225, 400 and 625 plants per m2. Vertical distribution of photosynthetically active radiation (PAR), leaf area, leaf age and 14CO2-fixation were determined periodically. Net photosynthesis and dark respiration of canopies were measured. Maximum photosynthetic capacity of individual leaves was measured on plants taken from the intact canopy or from plants where shading of the growing leaves had been prevented. Net photosynthetic rate of canopies increased linearly with leaf area index (LAI) up to an LAI of 3.5 and then declined at higher LAI, independent of variety and sowing density. Below the optimum LAI, net photosynthesis depended mainly on interception of PAR. Decrease in canopy photosynthesis above the optimum LAI was due to a higher proportion of old leaves with decreased photosynthetic capacity, and not to an increase in respiring plant parts. It is concluded that LAI and position of leaf age categories in the canopy are more important than vertical distribution of leaf area in determining canopy photosynthesis of red clover.

On the Quantitative Theory of Resource Partitioning in Rhizomatous Perennial Plants: The Influences of Canopy Structure, Rhizome Branching Pattern, and Self‐Thinning

Abstract: Here I develop a geometry—based quantitative theory of energy partitioning between seed production and rhizome production in energy—limited herbaceous rhizomatous perennial plants. This theory makes two basis predictions. The first prediction concerns species in which additional energy devoted to rhizome production substantially increases the leaf area index of the genet. In such species, the functional relationship between seed production and leaf area index should be well approximated by a steep power law with a slope > 2. The second prediction concerns plants in which increased energy devoted to rhizomes increases the radial growth rate of clones much more strongly than it increases leaf area index and in which genets self—thin in response to crowding. In such plants, the ratio of seed production to rhizome production should be relatively constant across environments and should be strongly influenced by the relationship between the level of investment in rhizomes per ramet and the length of the resulting rhizomes. An investment ratio on the order of 1:2 is often to be expected.

Rice Yield, Biomass, and Leaf Area Related to Evapotranspiration

Abstract: STUDIES on the relationships among evapotranspiration (ET), grain yield, dry biomass, and leaf area index (LAI) of rice were conducted in lysimeters and in the field. Two methods of planting rice were used: transplanting and direct seeding. There were twelve planting combinations involving spring, summer, and fall crops. Three equations involving linear leaf measurements and stem length were developed to estimate the LAI. Peak ET rates occurred during the reproductive stage and coincided well with the maximum LAI value. Two equations involving dry biomass and grain yield in relation to ET were also developed. The relationship between dry biomas (DB) and ET was found to be: DB = 4715.2 + 303.1 ET. Grain yield (rough rice at 12% moisture, GY) was related to ET as: GY = 3995.8 + 174.9 ET. With an average rice yield in the Everglades of Florida, the total ET requirement would be about 54 cm.

Multispectral radiometer to measure crop canopy characteristics

Abstract: A spectroradiometer has been designed for the study of crop reflectance characteristics in the spectral range of 400–1000 nm. Since the instrument records the ratio of incoming to reflected radiation the values obtained are independent of variations in solar elevation, and azimuth angle and atmospheric conditions. A filter wheel with four interchangeable interference filters is used for wavelength selection. The spectroradiometer traverses above a crop canopy on a movable track. This makes it possible to compare measurements from various locations several times in an hour, and to study more than one canopy a day. This instrument provides agronomists with data to estimate crop canopy characteristics such as leaf area index (LAI) rapidly and nondestructively. It also measures the variability of canopy reflectance introduced by temporal and spatial factors.

Hot-spot reflectance measurements applied to green biomass estimation and crop growth monitoring

Abstract: A new ground-based hot-spot reflectance meter (HSM) has been developed and tested for the estimation of green crop biomass and for crop growth monitoring. The concept of the HSM is based on theoretical studies on canopy hotspot reflectance measurements for a selected oblique illumination and view angle of 52° with respect to the vertical. A prototype HSM with a flash lamp as radiant source has been built by the Institute of Applied Physics TPD, Delft. Calibrated near infrared/red and red/green reflectance ratios are acquired which are related to changes of the green leaf area index and the colour characteristics of the canopy leaves. The advantages of the HSM are the independence of solar illumination conditions and the reduced sensitivity to the leaf inclination distribution function. A first measurement programme has been carried out during the 1982 season on winter wheat test fields. A preliminary analysis of the experimental data has demonstrated a good agreement with, reflectance model predictions. A significant relation between the near infrared/red ratio and the development of the leaf area index and the corresponding biomass has been found. This new method can improve the selection of samples for non-destructive assessment of standing biomass for agricultural research and crop production forecasting and estimation.

Description and Application of H20Trans a Stand Level Hydrologic Model for Western Coniferous Forests1

Abstract: A hydrologic model has been developed to study stand level water flow and tree water stress in western coniferous forests. The model, H20TRANS, has an hourly time resolution and is driven by air and soil temperature, humidity, incoming shortwave radiation and precipitation. Required stand parameters include leaf area index, sapwood basal area and soil water storage capacity. The model incorporates rates of snowmelt, canopy interception, litter and soil evaporation. The model predicts leaf conductance as a function of leaf water potential, absolute humidity deficit, incoming shortwave radiation and air temperature, including a special sub-freezing control. Leaf water potential is calculated from soil water content, root water uptake and soil temperature. Primary model outputs are soil moisture depletion, subsurface outflow, transpiration and tree water stress development as measured by leaf water potential and leaf conductance. A validation exercise was done comparing model prediction to field measurements of seasonal soil moisture depletion and tree water stress development. H20TRANS was then used to calculate hydrologic budgets for two lodgepole pine stands in Wyoming differing in leaf area index, density, basal area, and soil storage capacity. Simulation results show large differences between these stands in both magnitude and seasonal timing of transpiration, subsurface outflow and soil moisture depletion.

Relating the radar backscattering coefficient to leaf-area index

Abstract: The relationship between the radar backscattering coefficient of a vegetation canopy, sigma(0) sub can, and the canopy's leaf area index (LAI) is examined. The relationship is established through the development of a model for corn and sorghum and another for wheat. Both models are extensions of the cloud model of Attema and Ulaby (1978). Analysis of experimental data measured at 8.6, 13.0, 17.0, and 35.6 GHz indicates that most of the temporal variations of sigma(0) sub can can be accounted for through variations in green LAI alone, if the latter is greater than 0.5.

Characterization of terrestrial ecosystems for biogeochemical studies using remote sensing

Abstract: Work is in progress to estimate leaf area index (LAI) of temperate closed canopy coniferous forests using transects in Oregon and California. This variable will be measured using remote sensing techniques including correlations of ground dimensional analysis with linear waveband combinations. LAI will be related to important biological variables such as net primary productivity, biomass, and biogenic gas emission fluxes. The spatial variation in LAI, when coupled with species composition, will be used in part to describe the spatial variation and temporal dynamics of biogeochemical cycling.

Studies on the Effects of Relative Humidity of the Atmosphere upon the Growth and Physiology of Rice Plant : II. Relations of relative humidity of the atmosphere to the dry matter production of plant at the seedling stage.

Abstract: This study examined the influence of relative humidity of the atmosphere on the dry matter production of rice at its seedling stage. The plants were grown in a growth cabinet where the relative humidity was maintained at either 60% (dry treatment), 75% (standard treatment), or 90% (wet treatment) with the day/night temperature of 28/24°C and the illumination of 34-30 klux. The plants grown in a more humid atmosphere produced more dry matter when compared over the same growing period after seeding. But, no difference was detected when compared at the same plant age measured in the number of leaves (Fig. 1). We investigated the characteristics of the leaf blade and leaf sheath and conducted grow h analysis. 1. The top to root ratio was greater in the plants grown in a more humid atmosphere when measured either on the same day after seeding or at the same plant age (Fig. 2). 2. Atmospheric humidity had little effect on the weight and length of the leaf blade. On the other hand, the weight and length of the leaf sheath were strongly influenced: the more humid the atmosphere was, the greater the weight and length of leaf sheaths. 3. With increasing atmospheric humidity, the leaf area increased and the specific leaf area increased: the specific leaf area showed a significant positive correlation with the leaf area (Fig. 4). 4. The leaf area index, which strongly influenced crop growth rate, was larger in a more humid atmosphere, which may be why the dry matter production was higher in a more humid condition when compared at the same growing period (Table 2). 5. The plants grown in a more humid condition had a larger leaves. However they were thinner and had a lower photosynthetic rate (Fig. 6). Therefore, it seemed that there was no difference in the dry matter production of the plants grown in the three different humidifies when compared at the same plant age.

Seeding rate recommendations for a winter rye cover crop based on expected leaf area index

Abstract: A direct relationship exists between the leaf area index of winter rye (Secale cereale I.) and its soil erosion protection value. Specific leaf area indexes can be attained by combining heat units or growing degree days and plant density or seeding rate. Seeding rate can be increased to manipulate the leaf area index for a given number of heat units. This relationship and the expected remaining growing degree days from any selected planting date obtained from long-term climate records for selected locations can be used to make sound decisions for planting winter rye during late summer and early fall in a northern climate zone.

Plant spacing in French beans. I. Yield

Abstract: Four cultivars of French beans (Phaseolus vulgaris L.) were grown at a range of plant population densities and rectangularities in two seasons in south-eastern Queensland. Plant population densities two to three times those used commercially increased yields by 25-30%. This increase resulted from a greater number of pods per unit area with only a small reduction in pod size. Rectangularity in the range 1-8 had no effect on yield. These responses are discussed in terms of time courses of leaf area index development, light interception by canopies, crop growth rates and dry matter distribution between vegetative and reproductive growth after flowering.

Biomass of Understorey Plants between 1.5 and 5.0m in aLogged-over Forest

Abstract: The biomass of various comparzents of understorey plants ofa Lowland Dipterocarp Forest, between 1.5 and 5.0 m in height, was determined by harvesting 47 plants from a 0.01 ha plot. The total above ground biomass was equivalent to 2.78 tonnes/ha, and this was made up of 81 percent stem, 7.5 percent branch and 11.5 percent leaf The leaf area index (LAI) of the stratum was 0.36. Individual biomass of plant components and of the total plant was related to their collar girth. Using these regression equations, estimates based on measurements of collar girth in a 0.2 ha plot was found to be very close to that obtained by harvesting. This suggests that regression equations could be suitable for estimating biomass especially where no felling is allowed