Showing papers on "Leaf area index published in 1971"

A physiological analysis of the growth of oilseed rape

Abstract: For seed crops other than cereals there have been comparatively few comprehensive field studies which have analysed the physiological basis of the effects of genotype and agronomic treatments on growth, development and yield. Milbourn & Hardwick (1968), working on vining peas (Pisum sativum L.), have recently shown that pod growth rate and the yield of seeds are not simple functions of leaf area index and that sourc es of materials other than the leaves are important in affecting the yields of pods and seeds. Furthermore, Flinn & Pato (1970) have shown that the pods themselves can contribute to assimilation in the field pea (Pisum arvense L.). Field experiments carried out at Cambridge in 1968 and 1969 have produced evidence on the relative importance of leaves and other photosynthetic tissues in determining the yields of pods and seeds in another seed crop, namely oilseed rape. The experiment in 1969 is described and discussed below.

Productivity of the Oil Palm ( Elaeis guineensis Jacq. ) in Malaysia

Abstract: Crop Growth Rate, Leaf Area Index, Net Assimilation Rate and Harvest Index were estimated for oil palms in nine age groups growing on coastal alluvial soils in Malaysia. The mean Crop Growth Rate of mature palms was 29·83 t./ha./yr, with a Leaf Area Index of 3·61, and Net Assimilation Rate was 0·16 gm./dm.2/wk. Photosynthetic efficiency was about 2·2 per cent. Oil constituted about 17 per cent of total dry matter production. Possibilities for improving the yield of oil are briefly discussed.

Photosynthesis of wheat under field conditions. III. Seasonal trends in carbon dioxide uptake of crop communities

Abstract: Photosynthesis of two wheat cultivars grown in the field was examined during three seasons by use of a portable field assimilation chamber. There were large differences in dry weight, leaf area, and carbon dioxide uptake between seasons. Variations in carbon dioxide uptake by the community were related mainly to changes in leaf area index (LAI). There were changes in carbon dioxide uptake per unit LAI with time, and between the two cultivars in the first season, but the effects of these changes were small compared with the effects of LAI. Differences in grain yield were correlated with LAI and carbon dioxide uptake in the period after anthesis.

Photosynthesis of wheat under field conditions. IV. The influence of density and leaf area index on the response to radiation

Abstract: The photosynthesis of two cultivars of wheat at three densities of sowing was measured during the growing season of 1968 When the data were plotted as carbon dioxide uptake versus leaf area index (LAI) (leaf laminae and green stem) for a fixed value of solar radiation, it was found that all of the data could be fitted by a single curve, irrespective of variety, sowing density, or time of season when the measurements were made Since the curve was of continuously decreasing slope, the carbon dioxide uptake per unit LAI was highest for the low values of LAI and was reduced with the increased light interception at high LAI For a solar radiation of 06 cal/cm2/min the approximate maximum net photosynthesis was 45 g CO2/m2/hr for an LAI of 6 A mathematical model for photosynthesis was found to give good prediction of carbon dioxide uptake versus solar radiation for most of the period of measurement For each plot, a rectangular hyperbola was fitted to the data When the parameters of the model were subsequently plotted as a function of LAI, then within a given variety, it was found that lines of common slope but differing intercepts could be drawn through the points for different sowing densities From these fitted lines together with the measured values of LAI and respiration, carbon dioxide uptake was then predicted as a function of solar radiation by employing the rectangular hyperbola model Good agreement between predicted and measured values of photosynthesis was obtained

Soybean Canopy Structure and Some Radiant Energy Relations 1

Abstract: Measurements were made of canopy outline, leaf area index and the radiation environment of a soybean row crop at several stages of growth. The major change with time in canopy geometry occurred in the uppermost hemicylinder of leaves which increased in height and lateral spread. The proportion of energy reflected and reradiated from the top of the canopy increased during the season and this may be related to increases in both leaf area index and lateral spread of the crop.A nonlinear relationship between the incoming radiation and the energy received at a plane within the crop indicated that changes in leaf inclination during periods of high insolation gave a more open canopy.Measurements of energy in the 310- to 2750-nm waveband showed that from 65 to 85% of the radiation received at a plane in the crop came from the upper hemisphere and the remainder was reflected to the under surface. Extinction coefficients, calculated for solar radiation, showed large changes with height in the canopy, indicating that the assumptions made in applying the Bouguer-Lambert law to energy relations in a soybean canopy are not valid. Any model of the radiation relations of row crop canopies must account for energy changes in both the vertical and lateral directions.

Net photosynthesis and leaf area index relationships in swards of dactylis glomerata under contrasting defoliation regimes

Abstract: Net photosynthesis per unit area of ground surface was determined at saturating light energy levels in Dactylis glonwrata swards over a wide range of leaf area indices (LAI). The relationship between net photosynthesis and LAI was influenced by the particular defoliation regime to which the sward was subjected. In most instances net photosynthesis and LAI were linearly related, with defoliation regime influencing both the slope and intercept of the regression. However, a defoliation regime which left leaves below 3 inches (7.5 cm) resulted in a curvilinear relation. The net photosynthesis-LAI relationships were compared with the DM production of the swards on which they were obtained. Differences in these relationships did not entirely explain the differences in sward yield. The significance of these findings is discussed with reference to the theories of light interception and pasture growth.

Studies on the productivity of tropical pasture plants. III.* Stand structure, light penetration, and photosynthesis in field swards of Setaria and green leaf Desmodium

Abstract: Inclined point quadrat analysis was applied to pure swards of two pasture species, Desmodium intortum and Setaria sphacelata. Canopy structures are described in terms of the denseness and inclination of foliage and stems. Light penetration patterns throughout the day were calculated. The two species differed greatly in these characteristics. Desmodium leaf was oriented at a uniform mean angle to the horizontal throughout the height of the canopy, but leaf occurred predominantly in the upper layers. In contrast, leaf angles in Setaria varied down the profile, with most of the leaf in the middle layers. There were diurnal variations between and within the species in the amounts and distribution of sunlit leaf area index. Diurnal patterns of canopy photosynthesis were estimated from calculated leaf and light profiles, photosynthesis-illuminance data, and records of incident radiation. There was an overall 1.8 : 1.0 advantage in sward photosynthesis by Setaria, arising from a greater than two-fold superiority at high angles of the sun, falling to a 1.6 : 1 .0 advantage at low angles. This trend follows the diurnal patterns of light penetration into the two canopies. From calculated sward photosynthesis, concurrently measured dry matter production, and other data it was concluded that the relative magnitude of productivity corresponded very closely to the relative photosynthetic capacities of the leaves. Therefore, canopy structures were comparatively unimportant as determinants of yield differences. ________________ *Part II, Aust. J. Agric. Res., 21: 183 (1970)

Determining density of maize canopy. 2: Airborne multispectral scanner data

Abstract: Multispectral scanner data were collected in two flights over a light colored soil background cover plot at an altitude of 305 m Energy in eleven reflective wavelength band from 045 to 26 microns was recorded Four growth stages of maize (Zea mays L) gave a wide range of canopy densities for each flight date Leaf area index measurements were taken from the twelve subplots and were used as a measure of canopy density Ratio techniques were used to relate uncalibrated scanner response to leaf area index The ratios of scanner data values for the 072 to 092 micron wavelength band over the 061 to 070 micron wavelength band were calculated for each plot The ratios related very well to leaf area index for a given flight date The results indicated that spectral data from maize canopies could be of value in determining canopy density