Showing papers on "Leaf area index published in 1981"

Plant self-thinning and leaf area dynamics in experimental and natural monocultures

Abstract: The gradient of the relationship between mean plant weight and density for many species in self-thinning monocultures is known to be -3/2. There is evidence in the literature that this gradient may decline as light intensity falls. A recent controversy has centred upon whether or not the -3/2 gradient can be restored at low light intensities by graphing mean leaf area per plant against density. An experiment was conducted, using Trifolium pratense L. grown at three light intensities, to establish the gradient of this relationship. Whereas the mean weight vs. density gradient remained near -3/2 at all light intensities, the mean leaf area vs. density gradient approximated to -1.0, indicating that leaf area index stays constant as thinning proceeds. Thus, the results do not support the proposal that alterations in leaf area ratio act to restore the -3/2 gradient to the mean leaf area vs. density graph at low light intensities. Support for these findings is discussed, including data from field monocultures of Mercurialis perennis L.

Increased growth of ryegrass exposed to ammonia

Abstract: Fluxes of ammonia (NH3) between the soil/plant system and the atmosphere are components of the nitrogen cycle, but knowledge of them is inadequate1,2. Grassland in the UK annually receives 8.4 ×l05 tonnes of fertilizer nitrogen3 and 5 × 105 tonnes of nitrogen through the excreta of grazing ruminants4. Emissions of NH3 from these sources may be 105 tonnes annually5 and, apart from the loss of a plant nutrient, they may pollute the air. We report here that NH3 has beneficial effects on growth of perennial ryegrass (Lolium perenne L.), apparently through leaf sorption. In air containing NH3 at 16µgm−3, similar to the level above a grazed pasture6, sorption would be 48–224 ng m−2 leaf area s−1, depending on the density of leaves in the canopy. For grass with a leaf area index of 4, this process would add nitrogen at 6–28 g ha−1 h−1. These results support the suggestion7 that some of the flux of NH3 from soil may be sorbed by overlying plants.

The influence of light and temperature during winter on growth and death in simulated swards of Lolium perenne

Abstract: Two growth experiments were carried out in January-March 1978 in which simulated swards of perennial ryegrass were (1) heated by soil warming cables to give soil surface temperatures of approx. 7·5-9·C above ambient temperature, (2) shaded with netting to reduce light levels by approx. 50%, or (3) both heated and shaded. Heating alone increased leaf appearance, death, extension, lamina size, leaf area index (LAI), tillering (month 1)and whole plant weight (month 2) and reduced stubble water-soluble carbohydrates and specific leaf weight (SLW). Shading alone increased leaf extension, lamina size and LAI but to a lesser extent than did heating. Shading decreased SLW, leaf death rate, tillering (month 2), stubble carbohydrates and whole plant weight, but not herbage weight. The effects of heating plus shading were similar to those of heating alone, except that the increases in leaf size, extension and LAI were even greater, and shoot bases and roots had low or negative growth rates. In general the heating treatments caused a rapid turnover of leaf material, but net herbage growth was relatively insensitive. It is concluded that (1) temperature rather than light was limiting whole plant growth, especially from mid-February to mid-March and (2) mild, dull weather in winter is likely to induce tiller death associated with reduced investment in carbohydrate reserves.

Bulk stomatal resistance control on evaporation

Abstract: Bulk stomatal resistances of a soybean crop were evaluated throughout a growing season as residuals in both the combination model and an Ohm's Law analogue. For a leaf area index exceeding unity, bulk stomatal resistances from the combination model compared well with estimates derived from leaf stomatal resistance and leaf area index measurements. Employing independent bulk stomatal resistances in the combination model yields evaporation estimates which agreed well with estimates from the Bowen ratio method. Leaf resistance was found to be related to global solar radiation during non-limiting soil moisture conditions. Although leaf resistance varied inversely with soil moisture, the relationship could not be used to provide predictive procedures. Procedures used by other workers which relate stomatal resistance to environmental influences were found to be of limited application.

Crop identification and leaf area index calculations with Landsat multitemporal data

Abstract: Formulas are given to convert land-based vegetative canopy spectral reflectance measurements into Landsat digital counts in the four channels for a clear standard atmosphere. These formulas are shown to predict the curves found by plotting multitemporal Landsat trajectories. With correct interpretation, plots of channel 3 versus channel 4 Landsat data for crops are shown to yield information on both crop identification and crop leaf area index.

Modeling Biomass Production of Sweet Sorghum1

Abstract: Sweet sorghum (Sorghum bicolor (L.) Moench) is a leading contender in biomass production energy systems because of its high biomass yield, high percentage of easily fermentable sugars and combustible organics, tolerance to water stress, and low fertilizer requirements. However, scientific information on growth factors is limited and precludes establishing valid inter-relationships for predicting biomass production. With that objective in mind, a field study on sweet sorghum was conducted to investigate the relationships among stalk length, leaf area index and dry biomass. Cultivar Mer 71-7 was planted using two row configurations of single rows on 71-cm centers and double rows on 142 cm centers on Pahokee muck (Lithic Medisaprist). The spacing between double rows was 30 cm. Leaf area, stalk length, and dry leaf biomass were periodically monitored. Six equations involving leaf area were developed. The first equation estimated leaf area (A) from the length of leaf (L) and the maximum width of leaf (W), i.e., A = 0.741 LW. The second equation estimated leaf area from the length of leaf alone, i.e., A = 0.083 L squared. The third equation estimated leaf area per stalk (Y) from stalk length (X), i.e., Y = Exp (X/(2.106 + 0.093X + 0.629X Xmore » 10-4X squared). The fourth equation showed the dry leaf biomass accumulation (DAR) as a function of time (T), i.e., DAR = 0.764 X 10-3T0.481. The fifth equation predicted the leaf dry biomass (LDB) from DAR and leaf area index (LAI), i.e., LDB = DAR X LAI. The sixth equation estimated total dry biomass (TDB) from LDB and ratio of dry leaf biomass to total dry biomass (DBPL), i.e., TDB = LDB/DBPL. The relationships developed appeared to be useful for estimating sweet sorghum biomass. However, further testing is needed to evaluate the effects of diverse growing conditions and varieties and to determine the utility of the method in comparison to determining the mean plant weights and populations. (Refs. 16).« less

Floristic and leaf structure patterns along a shallow elevational gradient

Abstract: The floristic and leaf structure changes occurring on an elevational gradient in the Yule Brook Botany Reserve at Kenwick, W.A. are described. Species compositional changes observed included both apparent discontinuous and continuous elements. A major change in the floristic gradient appeared to correlate with a zone of winter soil saturation, although the major elevational gradient seemed to be one of increasing soil moisture availability. This same discontinuity was indicated by the average leaf size response. Leaf area index, specific leaf weights, leaf length : width ratios. leaf thickness, leaf margin and surface characteristics as well as leaf stomatal, cuticle, palisade and epidermal characters, however, did not show patterns relating to the environmental gradient, but did indicate, on the basis of leaf morphology, a vegetation generally adapted to hot, dry conditions.

Azimuthal radiometric temperature measurements of wheat canopies.

Abstract: The effects of azimuthal view angle on the radiometric temperature of wheat canopies at various stages of development are investigated. Measurements of plant height, total leaf area index, green leaf area index and Feeks growth stage together with infrared radiometric temperature measurements at 12 azimuth intervals with respect to solar azimuth and at different solar zenith angles were obtained for four wheat canopies at various heights. Results reveal a difference on the order of 2 C between the temperatures measured at azimuths of 0 and 180 deg under calm wind conditions, which is attributed to the time-dependent transfer of heat between canopy component surfaces. The azimuthal dependence must thus be taken into account in the determination of radiometric temperatures.

Structure and seasonal distribution of litterfall in young plantations of Populus ‘Tristis#1’

Abstract: Litterfall was sampled in 3- to 7-year-old irrigated and fertilized plantings of Populus ‘Tristis#1’ in northern Wisconsin. Leaves accounted for more than 90 per cent of the total litter and reached an asymptotic value of about 4,000 to 4,200 kg/ha. Leaf litterfall culminated in late September or first half of October. Inadequate light appeared to be responsible for an early (June) leaf fall in dense plantings. The maximum cumulative leaf area index ranged from 8.4 to 8.7. The pattern of foliation and defoliation was similar: it started with small leaves in the lower canopy and ended with large leaves of the upper canopy. Longevity of the small leaves was shorter than that of the large leaves. Leaf size was positively affected by fertilization but was not affected by a discontinuation of irrigation by mid-July during the droughty 1976. The specific leaf weight ranged from 2.6 mg/cm2 in the lower canopy to 10.2 mg/cm2 in the upper canopy. The specific leaf weight of litter leaves was 4 to 38 per cent lower than that of green leaves of the same size.

Spectral-agronomic relationships of corn, soybean and wheat canopies

Abstract: During the past six years several thousand reflectance spectra of corn, soybean, and wheat canopies were acquired and analyzed. The relationships of biophysical variables, including leaf area index, percent soil cover, chlorophyll and water content, to the visible and infrared reflectance of canopies are described. The effects on reflectance of cultural, environmental, and stress factors such as planting data, seeding rate, row spacing, cultivar, soil type and nitrogen fertilization are also examined. The conclusions are that several key agronomic variables including leaf area index, development stage and degree of stress are strongly related to spectral reflectance and that it should be possible to estimate these descriptions of crop condition from satellite acquired multispectral data.

Water stress, transpiration and leaf area index in eucalypt plantations in a bauxite mining area in south‐west Australia

Abstract: The clearing of native forests for open cut mining for bauxite is a potential cause for severe modification of the hydrological cycle. In the Darling Range, Western Australia, jarrah (Eucalyptus marginata Sm.) woodlands are being cleared for mining and are being replaced with plantations of other eucalypts. The plantation trees, which were up to 8 years old, showed no greater water stress than those of the original forest. The leaf area index of older plantation trees was usually higher than that of the original, mature forest. Transpiration rate was estimated on twigs enclosed briefly in a transpiration chamber. Prior test showed that this method was appropriate for comparisons in field grown eucalypts. Field measurements of stratified samples showed little difference in transpiration rate per unit leaf area between plantation forests and original forests. For the last 3 months of the dry season, however, transpiration per unit area of leaves was depressed by 25% in the plantation forest.

Seasonal changes in leaf area index and chlorophyll in an indian grassland

Abstract: SUMMARY (1) Seasonal variation in the leaf area index in grassland at Berhampur, India, showed a minimum of 0 5 in March and a maximum of 5.0 in late September. For most species, the maximum occurred between July and November. (2) There were seasonal changes in chlorophyll concentration, with maximum per unit dry weight of plant of 3 5 mg g-' in late August and maximum per unit area of 1.2 g m-2 in late September. Newbould (1967) and Milner & Hughes (1968) recommended that the estimation of chlorophyll concentration and leaf area indices should be utilized in all International Biological Programme projects as quantitative measures of the photosynthetic system. Although stems, petioles, leaf-sheaths and a few other green organs of plants show some light interception, which may be very important at certain times of the year, leaves are the main organs for photosynthesis and community production. Watson (1947) formulated the concept of leaf-area index (LAI) which is the quotient of the total leaf area (one surface only) divided by the total ground area. The community chlorophyll concentration per unit area was cited by Odum (1971) as an example of 'community homeostasis'. Several ecological processes, particularly (primary) production, are influenced by the amount of leaf area and the chlorophyll concentration (Brougham 1960; Bray 1960; Black 1963; Bliss 1966, 1970; Ovington & Lawrence 1967; Knight 1973; Mall & Billore 1974; Misra & Mall 1975; Billore & Mall 1975; Redmann 1975). This paper describes an attempt to evaluate the magnitude of the seasonal changes in LAI and chlorophyll concentration in terms of both dry weight of plant material and of ground area in a grassland community.

The Energy and Mass Exchange Characteristics of a Loblolly Pine Plantation

Abstract: (1) Energy balance measurements based on Bowen ratio techniques were used in conjunction with the big-leaf model to characterize energy and mass exchange between the atmosphere and the forest canopy in a loblolly pine plantation. (2) The partitioning of net radiation into latent and sensible heat by the Bowen ratio varied greatly with time of day and from day to day even when measured at the same time of day. Such variation results from variations in net radiation, canopy resistance, and air vapour density deficit. The maximum Bowen ratio during daylight hours was 2.3 and the minimum 0.1 1. (3) Canopy conductance was significantly correlated with solar radiation flux density in the canopy. (4) Significant correlations were found between average stomatal conductance (calculated from canopy resistance and leaf area index) and leaf temperature, vapour density deficit, and solar radiation flux in the canopy.

Soybean canopy reflectance as influenced by cultural practices

Abstract: Experiments were conducted at West Lafayette, Indiana in 1978 and 1979 to study the reflectance factor of soybean canopies as affected by differences in row width, population, planting date, cultivar and soil type. Reflectance factor data were acquired throughout the growing season with a LANDSAT-band radiometer. Agronomic data included plant height, leaf area index, development stage, total fresh and dry biomass, percent soil cover, and grain yield. The results indicate that row width, planting date, and cultivar influence the percent soil cover, leaf area index, and biomass present, which are in turn related to the multispectral reflectance. Additionally, the reflectance data were quite sensitive to the onset of senescence. Soil color and moisture were found to be important factors influencing the reflectance in single LANDSAT bands, but the near infrared/red reflectance ratio and the greeness transformation were less sensitive than the single bands to the soil background present.

Spectrally Derived Inputs to Crop Yield Models

Abstract: Solar radiation as an energy source for plants is available only when it interacts with leaves. The ratio of total solar radiation intercepted (SRI) by a corn canopy has been described as a function of leaf area index (LAI) using Bouguer's Law, and is included in models which predict final corn grain yield. LAI for corn may vary greatly pver large areas due to differences in planting dates, hybrids, stresses, and plant populations. Measurement of LAI is tedious and time consuming, which limits the use of models requiring LAI to relatively small areas. Spectrallyderived estimates of SRI may more accurately depict conditions in large crop production areas, and permit the application of crop models to large areas. Agronomic and spectral data were collected in 1979 and 1980 at the Purdue University Agronomy Farm, West Lafayette, Indiana. Agronomic data acquired from several planting dates of corn (Zea mays L.) included LAI and final grain yieI'd." Reflect~nce measurements were made in four wavelength bands using a Landsat band radiometer (Exotech ~OOA) . In addition to the data collected at the Agronomy Farm, in 1978 Landsat MSS data were acquired for nine 5 x 6 n. mile segments with commercial corn fields in five states. Ten fields per segment were identified, and their spectral data analyzed. Crop development stages were monitored and final yield estimated for each of these fields. Agronomic variables studied at the Purdue Agronomy Farm including LAI and calculated SRI were regressed on spectral data. In both years studied, SRI was better predicted than LAI, by the Greenness transformation. Spectrally estimated SRI, linearly interpolated and summed from planting to maturity was found to be oositively correlated with final grain yield. Measured LAI, however, performed better in two crop yield models than spectrally predicted SRI. The relationships developed from the data acquired at the Purdue Agronomy Farm were applied to the commercial corn fields using Landsat MSS data. In six of the nine cases examined, spectrally estimated SRI, summed from six weeks prior to six weeks post silking, was found to be positively correlated with final grain yield. The use of spectrally estimated SRI alone to predict crop yields is not recommended. Spectrally estimated SRI used in conjunction with ancillary data, including meteorological data, is recommended in applications over large areas where it is not feasible to directly measure LA!. 1981 Machine Processing of Remotely Sensed Data Symposium 52

Field spectrometer to measure percent ground coverage and leaf area index of agriculture crops

Abstract: Measurement of percent ground cover (PGC) and leaf area index (LAI) are required for crop modelling, yield estimation and for ground truth data in remote sensing studies. An instrument which traverses on a track above a crop and continuously measures the ratio of incident and reflected radiation at various wavelengths was developed and tested. Spectral irradiance and reflectance measurements were made at four wavelengths (647.8, 675.5, 739.9, 790.4 nm) at eight stages of growth of wheat and barley for three crop densities. Data provided information on the relations between spectral properties at selected wavelength and leaf area expansion at different growth stages. The spectral data were highly correlated with leaf area index measurements.

Selection of Concomitant Variates Affecting Regrowth, Yield, and Digestibility in Forage Sorghums 1

Abstract: Numerous environmental factors and plant characteristics, and interactions among them and with management practices, affect growth and composition of summer annual forage sorghums (Sorghum bicolor (L.) Moench). Thirty-eight plant and environment characteristics were estimated concurrently with the dry matter (DM) yield, DM regrowth rate (DM yield/day since emergence or since preceding harvest), and in vitro dry matter digestibility of three cultivars grown in the field on a fine-loamy, siliceous, thermic Humic Hapludults and subjected to 19 different defoliation regimes in 2 different years. The selection of a subset of the 38 observed concomitant variates could be useful for planning future research. The purpose of this paper is to report on the sequential use of factor analysis and multiple regression techniques to decrease the number of independent variables without appreciable loss in the explanation for variability in the dependent variables. Factor analysis was used first to reduce possibly redundant concomitant variables or select proxy variables for a whole dimension. Fifteen of the original 38 variates were selected. multiple regression was then used to reduce further the concomitant variables to nine variables (days of growth since planting, days of regrowth since previous harvest, height of standing crop, leaf area index (LAI) of whole plant, DM yield of stubble at previous harvest, cumulative precipitation, degree days since previous harvest, percent leaf in DM harvest, LAI of whole plant at previous harvest). Six or fewer of these variates were associated with a large portion of the variability in the three dependent variables. The goal of parsimoniously identifying the variables which affected the dependent variables within a genotype in these experiments was attained. The strategy employed—sequential use of factor analysis and multiple regression for reduction in number of concomitant variables—may have merit for investigations in many agronomic disciplines