Showing papers on "Leaf area index published in 1975"

Relations of Photosynthetic Rates and Leaf and Canopy Characters to Sugarcane Yield 1

Abstract: Simple correlations showed photosynthetic rates at low air velocities to be closely associated with leaf width, porosity, and specific leaf weight, and less closely associated with stomatal number, plant fresh weight, and, probably spuriously, leaf thickness Photosynthetic rates/unit of leaf area did not increase with increasing yield, and selection of cultivars for these or for leaf characters related to high photosynthetic rates would be of little practical value to the sugarcane (Saccharum sp) breeder Photosynthetic rates/unit of land area are more likely to be related to yield Leaf-area index was positively associated with tonnage in two field tests Leaf arrangement was associated with higher sugar/metric ton in one test, but not in a second Selection by breeders for higher leaf-area indices and for optimum leaf arrangement is recommended

Characteristics of the Canopy, Root System and Grain Yield of a Crop of Lupinus angustifolius cv. Unicrop

Abstract: The time course of development of a lupin crop was studied at Bakers Hill, Western Australia. The aim was to gain insight into the crop factors influencing yield. Weekly measurements were made of numbers and weights of plant parts, and profiles of roots, leaf area and light interception. A profile of carbon dioxide in the crop atmosphere was taken at the time of maximum leaf area, and the net carbon dioxide exchange (NCE) of pods was estimated for three successive weeks. The crop took 10 weeks to attain a leaf area index (LAI) of 1 and a further 9 weeks to reach a maximum LAI of 3.75, at which time only 33% of daylight reached the pods on the main axis. Once the maximum LAI was attained at week 19, leaf fall accelerated and rapid grain filling commenced almost simultaneously on all of the three orders of axes which had formed pods. Measurements of NCE between pods on the main axis and the air suggest that the assimilation of external carbon dioxide by the pods contributed little to grain filling. Grain dry weight was 2100 kg ha-1 of which 30%, 60% and 10% came from the main axis, first and second order apical axes respectively. Only 23% of the flowers set pods and this constitutes an important physiological limitation to grain yield.

Studies of grain production in Sorghum bicolor (L. Moench), 5. Effect of planting density on growth and yield

Abstract: Growth analysis was applied to grain sorghum (cv. RS610) grown at low, medium and high population densities, i.e. 14,352, 143,520 and 645,836 plants ha-1 respectively. The medium densities had two arrangements of plants, square (S) and rectangular (R). Crop growth rates, inflorescence growth rates, leaf area indices, net assimilation rates and leaf growth rates were calculated from growth functions of plant dry matter and leaf area over time. Differences in crop growth rate between populations in the early stages were attributed to leaf area development—specifically to the initial leaf area (dependent on seedling number) and not to differences in leaf growth rates. Peak crop growth rates were 15.0, 27.5, 26.0 and 45.8 g m-2 day-1 for the low, medium (S), medium (R) and high populations respectively. The large difference between the growth rates of the medium (S) and the high populations was not explained by differences in the amount of radiation intercepted. Although leaf area indices were 4.6 and 10.2 respectively for the two populations, both canopies intercepted almost all of the noon radiation. Light extinction coefficients were 0.45 and 0.29 respectively. The relationship between net assimilation rate and leaf area index was such that for comparable leaf area indices above 2, plants at higher densities showed greater improvement in yield per unit increment in leaf area index. A maximum grain yield of 14,250 kg ha-1 was obtained at the high population density as a result of higher dry matter production, but a similar harvest index to that of the crops grown at the other densities. Inflorescence growth rate (g m-2 day-l) slightly exceeded crop growth rate in the latter part of grain filling, which indicated that there was some retranslocation to the grain of previously assimilated material. The maximum grain yield represents an efficiency of utilization of short-wave solar radiation during crop life of 2.5 x 10-6g cal-1. *Part IV, Aust. J. Agric. Res., 26: 25 (1975).

Productivity of Vegetable Crops in a Region of High Solar Input. IV. Field Chamber Measurements on French Beans (Phaseolus vulgaris L.) And Cabbages (Brassica oleracea L.)

Abstract: Net CO2 uptakes have been measured for crop canopies of French beans and cabbages, sown at two plant densities, using a large field assimilation chamber and a semi-closed gas-analysis system. For both species, the maximum rates of uptake were a little less than 40 mg CO2 dm-2 (ground area) h-1, and light saturation of the canopy occurred at 600-650 W m-2 (French beans) or about 800 W m-2 (cabbages). Net CO2 uptake decreased with leaf area index at values below about 5, but was relatively insensitive to temperature over the range used. Once this leaf area index was reached, the relationship between net uptake and solar radiation remained fairly constant throughout the growth period. For both species, dark respiration rates were markedly dependent on temperature, and also were lower at night than during the day when measured at the same temperature. For both French beans and cabbages, growth analyses showed the maximum growth rates to be 18-19 g dry weight m-2 (ground area) day-1. The mean growth rate from emergence to harvest for an overwintered cabbage crop was 5.5 g m-2 day-1. It is suggested that the main advantage of the region in terms of plant productivity lies in the long frost-free growing season and the ability of frost-tolerant crops to maintain fairly high growth rates throughout a mild and comparatively sunny winter.

Measurement of Leaf Areas and Leaf Angles of Plants at Hardangervidda, Norway

Abstract: The leaf areas and leaf angles of vascular plants were measured in 1972 and partly in 1971 at Norwegian IBP Tundra sites, lichen heath, dry meadow, wet meadow and willow thicket in the low-mid alpine zones and at the subalpine birch forest site described by Sonesson et al. (1975).

Reflectant Induced Modification of Soybean Canopy Radiation Balance. II. A Quantitative and Qualitative Analysis of Radiation Reflected from a Green Soybean Canopy1

Abstract: This report is one of a series of papers describing reflectant-induced modification of the canopy radiation balance. Water-saving effects are expected since net radiation, which is the driving force for evapotranspiration, should be reduced by the reflectant treatment. The experiments were planned to establish reflection patterns over soybeans (Glycine max. [L.] Merr. ‘Amsoy’) at Mead, Nebraska. This study was undertaken to determine reflection coefficients at various solar elevations and at two values of leaf area index (LAI = 2.5 and 5.5) of a normal, unreflectorized soybean canopy so as to develop a base line against which to evaluate the effectiveness of various factorial treatments of reflectant materials, times and amounts of application. Therefore, net radiation, incoming and reflected radiation (300 to 3,000 nm) and the corresponding energy spectra within the 380 to 1,550 nm wavelength band were measured using a net radiometer, an upright and inverted pyranometer and a spectroradiometer, respectively. The shortwave reflection coefficient, αₛ as well as the coefficients for photosynthetically active radiation α(PAR) and near-infrared radiation α(NIR) remained nearly constant throughout most of the day, but increased significantly when solar altitude was less than 35° The dependence of albedo on LAI was a function of wavelength. At medium to high solar elevations α(PAR) decreased with increasing LAI while α(NIR) increased sharply. At lower solar altitudes both α(PAR) and α(NIR) increased with increasing LAI. The radiant energy reflected from the soybean crop showed a strong spectral shift toward NIR wavelengths with the increase in leaf area.

Distribution of Carbon Dioxide Released in a Field Crop

Abstract: A model to deal with the two-dimensional diffusion of carbon dioxide, released at ground level, within and above a crop canopy was developed and tested experimentally. The CO2 was released from a uniform area source at ground level and at a constant rate. The crop canopy was assumed to be horizontally uniform and infinite. The steady-state CO2 distribution was obtained as a solution of the two-dimensional diffusion equation by the forward finite-difference approximation, using a digital computer. Theoretical wind and eddy diffusivity profiles for above and within the canopy were incorporated. Crop assimilation was neglected.The crop canopy was characterized by its aerodynamic parameters: crop height, zero-plane displacement, roughness length and exponential coefficient of the within-canopy wind profile. The model calculated the CO2 profile as a function of down-wind distance, wind speed in the crop surface boundary layer, CO2 release rate, and CO2 concentration at the upwind edge of the source. The influence of crop canopy structure on the CO2 profile was found by changing the aerodynamic canopy parameters.A series of CO2 diffusion field experiments was conducted in a cotton canopy. All input parameters in the model, except the exponential coefficient of the within-canopy wind profile, were measured. The CO2 profiles at a fixed down-wind distance were determined and compared with those predicted by the model.The model overestimated the CO2 concentration in the lower layer of the canopy by about 50% when the leaf area index was 2.33 and the canopy was open. The difference between predicted and measured values was 20 to 30% when the leaf area index was 2.74 and the canopy was denser due to branching in the upper layers. It was concluded that the model can give a useful approximation of the distribution of CO2 in a dense and uniform canopy, when wind fluctuations are small, and under thermally neutral conditions.

Evapotranspiration of Dryland Barley with Different Plant Spacing Patterns1

Abstract: Standard row, grid, and paired-row plant spacing patterns were compared at the same plant population for their effect on barley (Hordeum vulgare L.) leaf area index (LAI), crop canopy, evapotranspiration (ET), and yield under dryland conditions in the field. The minimum unit area of equal plant population density for all spacing patterns was 240 cm². Crop canopy was defined as the percentage of soil surface covered by the crop when viewed from a direction normal to the surface. Crop canopy and LAI were lowest for the grid spacing pattern, largely because of less tillering. During the vegetative phase with adequate water availability, the barley crop planted in the paired-row pattern had the highest LAI but intermediate crop canopy. Evapotranspiration was more closely related to crop canopy as achieved with these spacing patterns than to LAI. Slightly greater ET during the first two-thirds of the growing season by barley in the standard row pattern resulted in more water stress and lower ET later in the season, but this did not reduce grain yield below that for the other spacing patterns.