Showing papers on "Leaf area index published in 1982"

Environmental Limits on Aboveground Net Primary Production, Leaf Area, and Biomass in Vegetation Zones of the Pacific Northwest

Abstract: Mature vegetation from eight of the 12 major vegetation zones in Oregon and Wash- ington was sampled along a transect from the Pacific Coast to the east slopes of the Cascade Moun- tains. Six stands were in forests, one in woodland, and one in the shrub-steppe. Aboveground-over- story net primary production (NPP, estimated as the sum of annual stem, branch, and foliage production) ranged from 90% of the variation in leaf area index. Although annual precipitation ranged from 20 cm in the shrub-steppe to 260 cm at the coast, it was a relatively poor predictor of stand structure and produc- tion. Biomass and NPP increased linearly up to a leaf area of =30 ha/ha; above this point, biomass continued to increase while NPP decreased. Except in the coastal forest zones, NPP was less than maximum values reported for other mature systems elsewhere in the world for the same range in leaf area indices. Compared to other forested regions of the temperate zone with the same NPP, these systems receive more annual precipitation, and average twice the basal area and biomass.

Effects of Nitrogen Nutrition on the Growth, Yield and Reflectance Characteristics of Corn Canopies

Abstract: Spectral and agronomic measurements were collected from corn (Zea mays L.) canopies under four nitrogen treatment levels (0, 67, 134, and 202 kg/ha) on 11 dates during 1978 and 12 dates during 1979. Data were analyzed to determine the relationship between the spectral responses of canopies and their argonomic characteristics as well as the spectral separability of the four treatments. Red reflectance was increased, while the near infrared reflectance was decreased for canopies under nitrogen deprivation. Spectral differences between treatments were seen throughout each growing season. The near infrared/red reflectance ratio increased spectral treatment differences over those shown by single band reflectance measures. Of the spectral variables examined, the near infrared/red reflectance ratio most effectively separated the treatments. Differences in spectral response between treatments were attributed to varying soil cover, leaf area index, and leaf pigmentation values, all of which changed with N treatment.

The influence of leaf area, light interception and season on potato growth and yield

Abstract: Light interception in the photosynthetically active radiation (PAR) range (400 700 nm) was measured over two years in potato crop canopies. Light interception increased linearly with increasing leaf area index (L) up to values of 2.25, light interception increased at a decreasing rate until L=4.0 was attained when around 95% of the incoming radiation was intercepted. The equation Il=Ioekl accounted for 92% of the variance in the relationship between light interception and L, where Il is the irradiance on a horizontal plane below a leaf area index of L., and k (light extinction co-efficient)=0.335+0.151 (L) 0.0129 (L)2. Crop growth rate was found to be linearly related to the PAR intercepted by the canopy in 1980, in the absence of any apparent water-stress. The photosynthetic conversion efficiency of the canopy (g dry weight MJi PAR intercepted) was 3.42 and 2.49 for 1980 and 1979, respectively. Tuber yields were also found to be linearly related to PAR intercepted by the canopy over the whole season.

Leaf area, light transmission, roots and leaf damage in nine tropical plant communities

Abstract: The vertical distribution of leaf area by species; transmission of photosynthetically active radiation; root biomass and fine-root surface area; and leaf damage were measured in nine tropical ecosystems: six in Costa Rica and three in Mexico. Ecosystems studied included monocultures of maize (young and mature) and sweet potato; year-old natural succession and vegetation designed to mimic succession; a 2.5-year-old mixture of three arborescent perennials (cacao, plantain, Cordia alliodora); 2.7-year-old plantation of Gmelina arborea; coffee shaded by Erythrina poeppigiana; and an old, diverse wooded garden. Leaf area index ranged from 1.0 in young maize to 5.1 in natural succession and the gmelina plantation. The vertical distribution of leaves was most uniform in diverse ecosystems, and most clumped in species-poor ecosystems. Light transmission was inversely proportional to leaf area, and two dense-canopied monocultures (sweet potato and gmelina) were nearly as effective at light capture as were some of the more diverse ecosystems. Optical density of the canopy ranged from 2.0 ( Large roots (> 5 mm diameter) accounted for most root biomass in the older ecosystems at a soil dept of 5–25 cm, and fine roots ( 2.0 m2 m−2 of ground. Total root surface area increased with age and diversity, and the monocultures — even those effective at light capture — had low root surface area. Herbivore damage on leaves of 35 species ranged from 16% of leaf area. Heavily damaged species contributed less to total ecosystem leaf area than did species damaged less than average. Ecosystem-level damage was not well correlated with age or diversity. Leaf damage in all ecosystems ranged from about 2 to 10% of leaf area, or 25 g m−2 of ecosystem. Young monocultures do not necessarily capture less light, provide less soil cover, and experience more herbivory than older, more diverse ecosystems. However, root surface area (and therefore possible nutrient-capture ability) is high only in ecosystems that are diverse or old, and this is an important design consideration for agroecosystems appropriate for the humid tropical lowlands.

Effects of Cultural Practices on Agronomic and Reflectance Characteristics of Soybean Canopies1

Abstract: Understanding the relationship between the reflectance measured and the various cultural practices used in today's soybean production is key for further development and use of remote sensing as a tool for crop monitoring. Field experiments were conducted at the Purdue Agronomy Farm in West Lafayette, Ind. in 1978 and 1979 to study the reflectance factor (RF) of soybean (Glycine max L. Merr.) canopies as affected by differences in row width, population, planting date, cultivar, and soil type (Typic Argiaquoll and Typic Hapludulf). Reflectance factor (RF) data were acquired with a Landsat-band radiometer (Exotech 100), which is a four band radiometer with a 15-degree field of view that measures radiance in the following wavelength regions: 0.5–0.6, 0.6–0.7, 0.7–0.8, and 0.8–1.1 µ. Agronomic measurements included plant height, leaf area index, development stage, total fresh and dry biomass, and percent soil cover. Row width, planting date, and cultivar influenced the percent soil cover, leaf area index, biomass, and development stage of the soybean canopies. Changes in these agronomic variables were manifested in the canopy reflectance. Soil color and moisture were important factors influencing RF in single Landsat bands; however, the near infrared/ red reflectance ratio and the greenness transformation were less sensitive than the single bands to changes in soil background. Variations in spectral responses are strongly associated with planting date during early to mid-season, with the row width during mid-season to near maturity, and with cultivar at maturity. This information should be useful in applications of remote sensing for identifying crops and estimating crop condition and yields.

Intercepted photosynthetically active radiation in wheat canopies estimated by spectral reflectance

Abstract: The interception of photosynthetically active radiation (PAR) was evaluated relative to greenness and normalized difference (MSS 7-5/7+5) for five planting dates of wheat for 1978-79 and 1979-80 in Phoenix. Intercepted PAR was calculated from a model driven by leaf area index and stage of growth. Linear relationships were found between greenness and normalized difference with a separate model representing growth and senescence of the crop. Normalized difference was a significantly better model and would be easier to apply than the empirically derived greenness parameter. For the leaf area growth portion of the season the model between PAR interception and normalized difference was the same over years, however, for the leaf senescence the models showed more variability due to the lack of data on measured interception in sparse canopies. Normalized difference could be used to estimate PAR interception directly for crop growth models.

Sequential analysis of plant growth

Abstract: SUMMARY Plant growth analysis, demographic analysis and yield component analysis are three procedures used to study relationships underlying plant growth and development. Previously, it has been shown that demographic analysis is qualitatively different from plant growth analysis. This paper demonstrates how plant growth analysis and yield component analysis can be merged into a composite procedure, sequential plant growth analysis. The composite approach treats some of the traditional indices of plant growth, including leaf area ratio, leaf area index, unit leaf rate, relative growth rate, crop growth rate and harvest index, as yield components. Regression analysis is used to assess quantitatively the contributions of individual yield components to variations in growth and yield. Fitted curves and trends in coefficients of determination are both used to follow the time course of relationships during development. A study of vegetative growth in bean plants is used to illustrate the composite procedure.

Effect of water gradient on sorghum growth, water relations and yield

Abstract: A field study was conducted during the 1980 growing season to determine the effects of soil moisture gradient on sorghum water relationships, growth, and yield of four hybrids: Sorghum bicolor L. ’G-623 GBR,’ ’RS 626,’ ’RS 671’ and ’A 28+’. June to September was warmer than normal (2.3–4.8 °C), with precipitation of only 16.2 cm during the cropping season. Sprinklers provided a continuously decreasing moisture gradient away from the water source. Plant height, dry matter, and leaf area index (LAI) decreased as watering level decreased. Higher leaf diffusive resistance and lower water potentials were associated with decreasing plant height and decreasing LAI. Canopy temperature (Tc) of the water-stressed sorghum was generally 3.2–3.7 °C warmer than canopy temperatures of well-watered plants. Canopy temperature also correlated well with water use by all hybrids. The average canopy minus air temperature was positive for all hybrids receiving less than 25 cm of irrigation and precipitation during the growing ...

Photosynthetic Recovery of Peanuts to Defoliation at Various Growth Stages1

Abstract: This experiment was designed to study the response of peanut (Arachis hypogaea L.) canopy carbon dioxide exchange rate (CER) to degrees of foliage loss at different dates throughout the season. Peanut plots were manually defoliated 25, 50, and 75 % on different dates during the season for comparison with control plots (0% defoliation). Weekly, CER was measured on control plots and on plots which had been defoliated at different dates. Canopy CER was initially reduced 45 to 70% after 75 % defoliation reduced leaf area index (LAI) to about 1.0, but subsequent measurements revealed considerable CER recovery. Recovery of CER was related to two mechanisms, leaf area production and re-adaptation of previously shaded leaves to full sun. The re-adaptation of leaves to full sun was most apparent from the inability of recently-defoliated canopies to use all the light they intercepted for CER, but after 1 to 2 weeks, efficiency of utilizing photosynthetically active radiation utilization improved without an increase in LAI. The re-adaptation process appeared to be related to increasing specific leaf weight. Recovery mechanisms, especially leaf production, diminished as the peanut plants matured and progressed into pod set and pod fill. Leaf area index increased after early defoliations; however, the rate of LAI increase paralleled that of control plots. For defoliations late in the season, leaf growth had ceased and was not stimulated as a result of defoliation.

Potential Photosynthesis in Trellis-Type Orchard Canopies.

Abstract: The choice of fork angle in orchards of the Tatura trellis design is investigated through simulations of the light relations and resultant photosynthetic response of a variety of structural alternatives. Computations consider a treatment of the penetration of direct solar beam on which is superimposed either a simplified or a complex treatment of the diffuse radiation climate within the orchard canopy. Computations show that, at any leaf area index, the potential seasonal photosynthesis of a flat canopy (fork angle = 180°) sets the upper limit to the productivity of all canopies of lesser fork angle. The diffuse component of radiation has a significant influence on expected absolute harvest yields, reducing the relative differences in yields between canopies of various fork angles which result from the strong interaction between solar trace and canopy geometry. The commonly selected fork angle of 60° cannot be defended on the basis of maximum seasonal potential photosynthetic productivity.

Comparative growth of maize cultivars with different leaf orientation

Abstract: Two maize hybrids, NHYB-1 and NHYB-2 with upright leaf orientation, and two composites, FARZ 27 and 34 with lax leaf orientation, were compared. The crops were grown at three levels of nitrogen (0, 75 and 150 kg N/ha) at Ibadan in the rain forest zone of Nigeria in 1979 and 1980.N application increased leaf area index (LAI) and hastened flowering. The composites had greater LAI than the hybrids. Lodging was greater at harvest than at mid-silk and severer in the hybrids than in the composites. Grain, stover and total dry-matter yields were greater for the composites.The hybrids were more responsive to N application in 1979 but the pattern was not consistent in 1980. More dry matter was partitioned to the grain in the hybrids as shown by their higher harvest index, especially in 1979. The concentration of N in ear leaf and stover increased with increase in N application, but P and K concentrations in the stover were highest in the control treatment.

Growth analysis of poppies (Papaver somniferum L.)

Abstract: A growth analysis study of the effects of two contrasting environments on the yield of field grown poppies (Papaver somnifevum L.) was undertaken using regression techniques. The change in total plant yield during the 1977-78 season was found to be adequately fitted by a cubic polynomial equation. In contrast, the change in total plant yield during the 1976-77 season and the development of leaf area index in both seasons were found to be adequately fitted by quartic polynomial equations. The total plant yield in the 1977-78 season was considerably higher than that in the 1976-77 season from the beginning of December to dry maturity with a maximum difference of 2 200 kg/ha on 15 January. This yield difference can be attributed to the higher crop growth rate in the 1977-78 season from 30 November to 18 January with a maximum difference of 12 g/m2/day on 30 December. Leaf area index was considered to be more important than net assimilation rate in influencing the crop growth rate up to 20 December. The differences in leaf area between the two seasons could be attributed to the climatic conditions. Under Tasmanian conditions, poppy yields could be expected to be reasonably stable from year to year, provided that the crop is encouraged to grow at its optimum during the whole season.

A Case Study in Populus canescens to Estimate the Leaf Area Index

Abstract: SYNOPSIS A 25-year old Populus canescens stand was selected for sampling to estimate the one-side leaf surface area per unit ground area. A portable area meter was used to determine leaf surface areas of a sample of branches of the first order. Different unweighted and weighted regression equations were compared to estimate leaf surface area. The estimated tree leaf areas were regressed on D.B.H., with unit weight being assigned to the single observation.

Studies on Dry Matter and Grain Production of Rice Plants : III. Analysis of dry matter productivity before heading stage

Abstract: In order to analyze the causes of varietal differences in dry matter production before the heading stage, the same varieties used for the experiment, in paper II were examined. The photosynthetic rate of a single leaf (Po), the respiratory rate of each plant organ and the specific leaf area were determined. The extinction coefficient, leaf inclination and the horizontal distribution of leaves in the canopy were also determined. The results obtained are summarized as follows: 1. Varieties with a higher optimum leaf area index showed a smaller value in the decreasing rate (b) of NAR with LAI increase (Fig. 3). 2. All of the variables examined, Po, the mean leaf inclination, the variation coefficient of horizontal leaf distribution in the upper half of the canopy, and the respiratory rate, showed significant positive correlations with b (Table 3 and Table 4). On the other hand, specific leaf area showed a significant negative correlation with b (Table 3). 3. Varieties with a taller plant height and more productive tillers showed thinner leaf blades, a higher leaf area expansion speed, a low Po and lower respiratory rates (Table 4, Table 5, Fig. 5 and Fig. 6). NAR of these varieties was low at the small LAI stage of the canopy, but the decreasing rate (b) of NAR with increase of LAI in the canopy was small. Therefore, dry matter productivity at the increased LAI stage of canopy was high in these varieties (Fig. 2). 4. Varieties with taller plant height and somewhat inclined leaf blades were characterized by a uniform leaf distribution in the upper half of the canopy, so that the b value became smaller (Table 5).

A three-part geometric model to predict the radar backscatter from wheat, corn, and sorghum

Abstract: A model to predict the radar backscattering coefficient from crops must include the geometry of the canopy Radar and ground-truth data taken on wheat in 1979 indicate that the model must include contributions from the leaves, from the wheat head, and from the soil moisture For sorghum and corn, radar and ground-truth data obtained in 1979 and 1980 support the necessity of a soil moisture term and a leaf water term The Leaf Area Index (LAI) is an appropriate input for the leaf contribution to the radar response for wheat and sorghum, however the LAI generates less accurate values for the backscattering coefficient for corn Also, the data for corn and sorghum illustrate the importance of the water contained in the stalks in estimating the radar response

Effects of Ground Cover and Leaf Area on the Spectral Reflectance of Vegetation-Soil Target

Abstract: : The relations between spectral reflectance, percent ground cover, and leaf area index (LAI) for vegetation-soil targets were evaluated for green vegetation against either a light-toned sand and a dark-toned organic loam soil. The percent ground cover and LAI were calculated for the ground area in the radiometer's field of view. The special reflectances of the different targets were measured in the 400 to 1100 nm region. For the vegetation-organic loam targets, the present cover and LAI varied directly with the target reflectance in the green (520-600 nm) and the infrared (700-1100 nm) regions, but varied inversely with reflectance in the red region (650-700 nm). For the vegetation- sand targets, the percent cover and LAI varied inversely with reflectance in the visible region and directly in the IR region. Results show that the major change in reflectance of vegetation-soils was related more to the change in percent cover. For less than 100 percent cover, the LAI varied directly with percent ground cover. A change in LAI produced less change in target reflectance than did a change in percent cover. Once the canopy is closed, i.e., 100 percent cover, variation in LAI had little effect.

Effects of Leaf Area Index, Specific Leaf Area, Nitrogen Content in Leaves and Distribution Ratio of Dry Matter to Pod on Net Assimilation Rate of Peanut Plants in the First Half of Fruiting Stage

Abstract: The author examined effects of leaf area index(LAI), specific leaf area(SLA), nitrogen content in leaves (NL), and distribution ratio of dry matter to pod(PD.R) on net assimilation rate(NAR) in the first half of fruiting stage of peanut plants cultivated under six management factors. The results obtained were as follows.: 1. NAR was affected significantly by mulching, planting date, planting density and number of plants per hill (Table 3). 2. The correlations of NAR with LAI, SLA and PD.R were significantly negative, respectively. But, the correlation between NAR and NL was significantly positive (Fig. 1, Table 4). 3. LAI, PD.R and SLA were selected as independent variables in the best regression equation for determining NAR that accounted for 85 percent of the variation of NAR(Table 5). 4. By comparison of the standard regression coefficients in the equation, it was recognized that the relation of the variables to NAR become stronger in the order of SLA, PD.R and LAI (Table 6). 5. In carrying out growth analysis of peanut plants in the fruiting stage, it is necessary to remark PD.R as an important factor affecting NAR.

Remote sensing of agricultural crops and soils.

Abstract: Research results and accomplishments of sixteen tasks in the following areas are described: (1) corn and soybean scene radiation research; (2) soil moisture research; (3) sampling and aggregation research; (4) pattern recognition and image registration research; and (5) computer and data base services.

Modeling of vegetation canopy reflectance: Status, issues and recommended future strategy

Abstract: Various technical issues related to mapping of vegetative type, condition and stage of maturity, utilizing remotely sensed spectral data are reviewed. The existing knowledge base of models, especially of radiative properties of the vegetation canopy and atmosphere, is reviewed to establish the state of the art for addressing the problem of vegetation mapping. Activities to advance the state of the art are recommended. They include working on canopy reflectance and atmospheric scattering models, and field measurements of canopy reflectance as well as of canopy components. Leaf area index (LAI) and solar radiation interception (SRI) are identified as the two most important vegetation variables requiring further investigation. It is recommended that activities related to sensing them or understanding their relationships with measurable variables, should be encouraged and supported.

Solar radiation attenuation in a hillside jack pine forest

Abstract: A modelling technique for penetration of solar radiation into clumped vegetation canopies is described. It combines Monte-Carlo simulation to determine ray pathlengths through individual plant canopy envelopes with exponential attenuation along these rays. The technique is applied to a hillside forest of randomly located and sized jack pine trees. Scattering effects are incorporated and the model output is compared with field measurements. The results depend on the shape of the tree outline. Attenuation is less rapid with downward cumulative leaf area index than in a randomly dispersed canopy.