Canopy Light Transmission Research Articles

Effect of sowing date and density on sink/source relationship and canopy light transmission of summer maize (<I>Zea mays</I> L.)

通过播种期和密度两因素耦合试验(3个播期, 各播期下设3个密度)研究不同播期、密度组合对夏播玉米群体源库关系及冠层透光率的影响。结果表明: 适宜播期(6月22日之前)与适当密度(半紧凑型品种“金海5号”为6.00~7.50万株·hm^-2, 紧凑型品种“郑单958”为6.75~8.25万株·hm^-2)组合的各源库指标表现较优。叶面积指数(LAI)在吐丝期达到4.88~5.97, 成熟期仍保持在2.73~4.48; 群体透光率在吐丝期和成熟期分别达21.09%~34.82%和27.97%~35.29%; 吐丝期穗位叶片<i>Pn</i>较高, 达34.4~41.7 μmol(CO₂)·m^-2·s^-1; “金海5号”6月15~17日播种、播种密度为7.50万株·hm^-2, “郑单958”6月15~17日播种、播种密度为8.25万株·hm^-2时, 均产量达到最大, 分别为14 863.50 kg·hm^-2和15 123.30 kg·hm^-2。

Impact of invasion of Acer platanoides on canopy structure and understory seedling growth in a hardwood forest in North America

Invasion by exotic plant species is known to affect native communities and ecosystems, but the mechanisms of the impacts are much less understood. In a field study, we examined the effects of a tree invader, Acer platanoides (Norway maple, NM), on canopy structure and seedling growth in the understory of a North American deciduous forest. The experimental site contains a monospecific patch of A. platanoides and a mixed patch of A. platanoides with its native congener, A. rubrum (red maple, RM). In the study, we examined canopy characteristics of three types of trees in the forests, i.e., RM trees in the mixed forest, NM trees in the mixed forest, and NM trees in its monospecific patch. Height growth and biomass production of RM and NM seedlings under intact canopies and newly created gaps of the three types of trees were followed for two growing seasons. We found that removal of half of the canopy from focal trees increased canopy openness and light transmission to the forest floor, but to a greater extent under NM trees than under RM trees. Seedlings of these two Acer species varied greatly in biomass production under canopies of the same type of trees and in their responses to canopy opening. For example, seedlings of the exotic NM grown under the native RM trees in the mixed forests increased biomass production by 102.4% compared to NM seedlings grown under conspecific trees. The native RM seedlings grown under NM trees, however, reduced biomass production by 23.5% compared to those grown under conspecific trees. It was also observed that RM was much more responsive in biomass production to canopy opening than NM. For instance, total seedling biomass increased by 632.2% in RM, but by only 134.6% in NM in response to the newly created gaps. In addition, we found that NM seedlings allocated a greater portion of biomass below-ground as canopy openness increased, whereas the same trend was not observed in RM seedlings. Our results thus demonstrated that invasion of NM significantly altered canopy structure and community dynamics in the hardwood forest. Because the exotic NM seedlings are able to grow well under the native RM trees, but not vice versa, NM will likely expand its distribution in the forests and make it an ever increasingly serious tree invader in its non-native habitats, including North America.

Spatial structure of bryophyte communities along an edge-interior gradient in an Atlantic Forest remnant in Northeast Brazil

The species richness and diversity of epiphytic and epiphyllous bryophytes were investigated along an edge-interior gradient in a large Atlantic Forest remnant in Northeast Brazil. Bryophyte samples were collected at 60 geographically randomised points, which were distributed among five zones located at different distances in from the forest edge. In each site the altitude was recorded and a hemispherical photograph was taken to determine the degree of canopy opening and light transmittance. There was no statistically significant variation of species-richness and diversity in relation to the forest edge, even at 1084 m from the edge. Instead, among the microenvironment variables studied, only altitude supported the most diverse bryophyte floras, especially epiphyllous and shade-tolerant species that are sensitive to disturbance. Besides this, the degree of canopy cover was also relevant, albeit with less significance. These results show that bryophytes respond better to scattered and unique conditions, within moderate microclimates, in the remnant itself than they do to the edge-interior gradient distances alone.

A simple net ecosystem productivity model for gap filling of tower-based fluxes: An extension of Landsberg's equation with modifications to the light interception term

Net ecosystem productivity (NEP) is a key ecological variable in forestry and carbon sequestration sciences. Advances in eddy-covariance instrumentation in recent years have improved the accuracy to which productivity in ecosystems can be measured. However, equipment failure, power outages, system maintenance shutdowns, and inclement weather frequently introduce gaps in the measurement data stream, which can reduce the integrity, usefulness, and interpretation of the data. To compensate for these limitations, a simple NEP model with few automatically adjustable parameters is developed to improve gap filling of discontinuous time series. Initial model formulation and parameter-value determination are founded on 2004 growing-season NEP measurements collected at eight Fluxnet-Canada (FCRN) stations (i.e., eight ecosystems) from across Canada's southern commercial forest zone. A preliminary inter-equation comparison of three commonly used flux equations, all with photosynthetically active radiation (PAR) as the independent variable, revealed that the three equations provided similar mean description of NEP. In this paper, we use Landsberg's equation [Landsberg, J.J., 1977. Some useful equations for biological studies. Exp. Agric. 13, 272–286] in modelling NEP. Initial parameter values of the Landsberg's equation were shown to depend on forest species composition, stand age, and existing site conditions. Further analysis indicated that on average for a 9-day period for the Atlantic Maritime balsam fir site in New Brunswick, Landsberg's equation represented mean NEP very well for cloudy days, but performed poorly when light conditions deviated from average conditions. We hypothesized that variation in the level of diffuse and direct radiation contributed to differences in light response. As Landsberg's equation does not explicitly address (i) light quality, i.e., level of diffuse to direct illumination, and (ii) vertical canopy structure, a simple NEP model combining Landsberg's equation with a two big-leaf (sunlit versus shade leaf model concept) and multiple-layer canopy light transmission formulation was developed for modelling the day-to-day variation in NEP and for gap filling. Results from these enhancements captured more of the NEP peaks (coefficient of determination, r 2 = 0.70) than were previously modelled with the unaltered form of Landsberg's equation ( r 2 = 0.63). Model sensitivity analysis suggested partitioning the canopy in four canopy layers provided the best overall improvement in NEP calculations; beyond four layers, model improvement was minor.

Growth rate responses of Lobaria pulmonaria to canopy structure in even-aged and old-growth cedar–hemlock forests of central-interior British Columbia, Canada

The ability of cyanolichens to sustain growth in even-aged forests that develop after clear-cut harvesting is a major conservation biology concern in British Columbia's inland rainforest. This and other conservation issues have led to proposals advocating partial-cut rather than clear-cut harvesting to better maintain the structures that support biodiversity in old-growth forest stands. However, evaluating the potential impacts of alternative harvesting practices cannot occur without first understanding lichen growth responses to the existing range of natural variability in canopy structure. Using transplant experiments with thalli of Lobaria pulmonaria (a tripartite foliose cyanolichen), we evaluate growth responses to canopy structure in both naturally occurring 120 year old small-patch even-aged stands and in adjacent old-growth uneven-aged forest stands. Canopy microclimate was also measured in old-growth reference trees, allowing calculation of energy conversion efficiency for old-growth L. pulmonaria thalli. Growth rates of L. pulmonaria transplants showed a strong correlation with canopy light transmission (CLT). Mean annual lichen dry matter gain over the 2-year measurement period ranged from less than 5% on branches in closed canopy even-aged stands (<1 mol m −2 day −1 CLT) to near 20% on branches under canopy gaps in old-growth stands (>18 mol m −2 day −1 CLT). Intercepted irradiance of hydrated L. pulmonaria thalli ( I wet) under old-growth stand conditions was 24.7 and 45.5 MJ m −2 annually in years 2 and 3 of the study, resulting in an energy conversion efficiency of 1.33 and 0.61%, respectively. Open sky (gap fraction) above lichen transplants in old-growth stands was much greater than that found in even-aged stands, allowing for longer duration sunfleck events in the lower canopy of the old-growth forest stands. These findings suggest that the creation of small openings by partial-cut harvesting in the inland rainforest may result in conditions favourable to continued growth of the dominant canopy cyanolichen, L. pulmonaria. They also support existing concerns about future cyanolichen growth in even-aged forests regenerating after clear-cut harvesting.

Description and test of a simple process-based model of forest growth for mixed-species stands

Process-based models of forest growth have been discussed for decades, but their utility as management tools has only recently begun to increase. Ideally this type of model would be tested by treating it as a complex hypothesis that relates independently measured parameters to predicted responses. This approach provides a test of the structure and the parameterization of the model that is not possible if the model has been calibrated (or tuned). We conduct such a test of a new model of forest production and allocation. The test uses a series of plots located across complex terrain in northern Idaho, USA. The production model scales leaf-level gas exchange to the canopy, and is parameterized with foliar nitrogen, leaf area index (LAI), and canopy structural parameters. New biomass is allocated such that tree allometry is maintained while foliage and branches turn over. A simple approach combines allometric equations across species in mixed-species stands. Predictions of volume increment for a 10-year period were higher than measurements, but the two were significantly correlated. The discrepancy was reduced when leaf area index was estimated from canopy light transmission rather than allometric equations. We argue that one likely reason for the overprediction is the occurrence of soil water deficits in the summer. A sensitivity analysis showed that estimates of production were most sensitive to leaf area index and canopy average foliar nitrogen content, but much less to other parameters. We conclude that comparing the model to observed data reveals shortcomings that might have been hidden if the parameters had been tuned. The mixed-species allometric constraint provides a new tool for modeling biomass allocation in mixed-species stands.

Déterminants botaniques de l’agrégation du feuillage et de l’interception de la lumière pour des taillis de peupliers âgés de deux ans : caractérisation à partir de maquettes 3-D

Botanical parameters (e.g., shoot and branch inclination, petiole length, leaf phyllotaxy, size and shape) that influence light interception and foliage clumping in dense two-year-old monoclonal poplar (Populus spp.) coppice crops were analysed with a three-dimensional simulation model. Crop LAI varied from 1 to 2 for clone Ghoy and from 2.5 to 7.4 for clone Trichobel from May to September. Canopies were strongly clumped, with a clumping index (μ) about 0.5. Canopy light transmittance (τ) varied from 0.59 in May to 0.41 in September for clone Ghoy and from 0.42 to 0.08 for clone Trichobel, and was strongly associated with LAI. The overall effect of a simulated shift in botanical parameters was relatively small and resulted in limited changes in μ and τ by ± 0.05 and ±0.1, respectively. Petiole length had the most notable effect on μ and τ, while the other parameters were less effective. However, biomass cost analyses showed that actual petiole length optimised the efficiency of biomass investment into light capture.

Confronto tra tecniche di ripresa ottiche e digitali per la descrizione del clima luminoso nella foresta di Paneveggio (TN)

Hemispherical photography is a widely used tool for the indirect estimation of forest light environment and quantification of canopy openness, LAI, and direct and diffuse canopy light transmittance. Several comparisons have been made in existing literature between digital and film systems and their performance under different stand structures and light intensity levels, but the conclusions are not always in agreement. The aim of this research is to compare the light estimates coming from analysis of digital- and film-based hemispherical photographs taken in a mountain Norway spruce (Picea abies (L.) Karst.) forest in the Valbona forest reserve (Paneveggio - Pale di S. Martino Regional Park, Trent, Italy). Two 100x100m permanent plots were established in a previous study (Motta 2002), one each in a single- and a multi-storied stand. The images were taken from grid points 12.5 m apart using a digital camera equipped with a Nikon FC-E8 fisheye adapter, immediately followed by a film camera shot (Sigma 8mm F4 fisheye lens). Images were digitized and analyzed using Gap Light Analyzer (Frazer et al. 1999). The output variables (canopy openness, LAI, total, direct and diffuse transmitted PAR) were compared by statistical means across the full sample (48 photos) and for the two sites independently. The ratio between digital and film output was analyzed in its relationship to canopy cover, local tree density, spatial pattern of canopy gaps and zenith angle. Under the dense, even-aged cover the results were similar, while the digital images provided significantly lower transmittance estimates (up to 32% less than film-based estimates) in the uneven-aged stand. We addressed different sources of error for the two techniques; some corrective strategies are proposed herein.

魚眼デジタルカメラ画像による林冠の開空域の自動識別と葉面積指数の推定

We propose an automatic and nearly versatile method for detecting forest canopy gaps using the digital fish-eye camera images. By analyzing data obtained by a field research during the entire growing-season in a cool-temperate deciduous broad-leaf forest in Takayama, Japan, we found the following criteria mostly applicable except for canopies with autumn-color : 1. The pixels with the digital number of the blue band less than 150 were at the vegetation (leaves and stems) . 2. The pixels with the digital number of the blue band more than 200 were at the canopy gaps. 3. The pixels with the digital number of the blue band between 150 and 200 were at the canopy gaps if their digital numbers of red were less than those of blue. Otherwise they were at the vegetation. Estimated canopy gap fraction by these criteria corresponded well with those estimated by the conventional and subjective approach. We compared gap fraction by these criteria with gap fraction by the other approaches and a transmittance by LAI2000. These comparisons indicated necessity of consideration about sensitivity and exposure of the digital cameras. The values of the leaf area index estimated from those gap distributions were much less than the estimation by the canopy light transmittance approach but the pattern of their seasonal changes (except for autumncolor) were close to each other.

Plant species diversity and composition along an experimental gradient of northern hardwood abundance in Picea mariana plantations

Maintenance of biodiversity in managed forest ecosystem is an increasing concern, particularly in plantation forests. To test the two hypotheses that (i) past vegetation treatments modify species diversity and that (ii) a trade-off exists between plantation productivity and diversity, we measured plant species diversity in the upper, intermediate and lower strata of 16–17-year-old Picea mariana plantations along a gradient of hardwood abundance. The gradient was obtained with various intensities of non-chemical release and thinning treatments. P. mariana productivity linearly decreased as the proportion of hardwoods within the canopy increased. As the proportion of P. mariana increased, total species richness and plant diversity (Shannon index [ H′]) first increased up to an intermediate level, and then decreased. Proportion of non-crop to crop tree species explained 66% of the variation in species diversity of the upper strata, 0% of the intermediate strata, and 20% of the lower strata. Intensity of past vegetation treatments slightly affected species composition, as evaluated by the Sørensen’s index of similarity. Maintaining an almost exclusive cover of P. mariana had marginal effects on species richness and understory diversity. But, a large increase in hardwoods proportion occurred at the expense of species richness and diversity of the understory stratum. Differences in canopy light transmission between covers could not explain this result. Variation in species richness and diversity along the gradient of hardwood abundance had a hump shape, a characteristic of the classic disturbance-diversity hypothesis. But, the intensity of past vegetation control had a weak predictive capability for plant species richness and diversity. Thus, vegetation control to maximise crop tree productivity in P. mariana plantations is not likely to affect understory plant diversity or composition. It may however contribute to an increase in stand structural diversity.

Light Transmittance Estimates in a Longleaf Pine Woodland

Abstract While the importance of canopy structure in open woodlands and savannas on regulating the flow of energy and matter is well known, few studies have investigated how variation in overstory abundance influences canopy light transmission and the extent that estimates vary in their ability to characterize the light environment in these ecosystems. Canopy light transmittance (% photosynthetic photon flux density, or %PPFD) was measured with gallium arsenide phosphide (GaAsP) photodiodes and was monitored throughout the growing season in an open-canopy longleaf pine (Pinus palustris Mill.) woodland across an overstory abundance gradient. Several estimates of canopy light transmittance were also measured, including 10 minute averages of %PPFD under clear and overcast sky conditions during summer, fall, and winter, as well as light estimates derived from hemispherical photographs (gap fraction, GF: gap light index, GLI; and weighted canopy openness, WCO). Linear and curvilinear regression were used to analyze the relationship between (1) light measurements and canopy structure and (2) light estimates and growing-season % PPFD measured by light diodes. Of all light measurements in this study, ten-minute average % PPFD measurements during clear days were the most variable: only a small proportion in the 10-minute average of light reaching the understory was correlated to either overstory structure or growing-season canopy transmittance. While measures on overcast days improved the correlations, they tended to overestimate transmittance. Gap fraction (GF) and gap light index (GLI) were strongly correlated with % PPFD and overstory structure, and the relationship between GLI and % PPFD was improved by using a direct light setting of 60%. In addition to strong correlation, hemispherical photographic estimates of light fell along a 1:1 line with % growing-season PPFD; thus, estimates were relatively unbiased. Measures of light in this ecosystem need to incorporate the large spatial and temporal variation in light transmittance that is characteristic of this ecosystem if investigators are to understand the relationship between open-canopy woodlands and their light environments.

Leaf area index inferred from solar beam transmission in mixed conifer forests on complex terrain

Forest process models are used to predict forest growth in a broad range of conditions. Because more than a quarter of the world’s forests are in mountainous regions, leaf area index (LAI) must frequently be estimated for forests in complex terrain. LAI is often inferred from canopy light transmission using various canopy models. Choice of a canopy model becomes especially problematic in complex terrain because the complex topography changes the path length of the solar beam through the canopy. For example, if solar elevations are expressed relative to the inclined surface, low elevations can occur on steep slopes at any time of the day, especially on surfaces facing north (in the northern hemisphere). We inferred LAI with various models at 36 plots in a mixed conifer forest in northern Idaho, USA, over a wide range of altitude and solar insolation. We compared these inferences to allometric estimates of LAI. We also tested a theoretical solution for path length on complex terrain. We conclude that the use of this path length correction does not improve agreement between ceptometer LAI and allometric LAI. However, residuals of the fit between transmission and allometric LAI were weakly related to path length ( P=0.052) and squared path length ( P=0.049) in a quadratic multiple linear regression. The best fits between ceptometer LAI and allometric LAI were both based on extinction coefficients corrected only for solar zenith angle; we recommend the Beer–Lambert model for its simplicity. We analyzed residuals of ceptometer estimates of LAI and determined that they were correlated with species composition. These results suggest that species composition might be used to predict extinction coefficients, though the current data set will not support such prediction. Thus, terrain complexity had only a minor influence on model predictions of leaf area index in these stands, simplifying the prediction of LAI in mountain forests.

Description of development, light interception and growth of sunflower at two sowing dates and two densities

The relationship between dry matter production and solar radiation interception by plant canopies is well known for several crops including sunflower. The effects of temperature environment on sunflower development have also been subject of much research. However, under seasonal rainfall, management strategies, such as the choice of sowing dates and of plant densities may change crop responses to temperature and radiation, preventing the use of standard relationships. The object of this work is to study the influence of two sowing dates on crop development and two plant densities on light interception and growth of sunflower crops grown on stored soil water in the semi-arid Mediterranean region of southern Portugal. The cultivar “Florassol” was sown at Évora, Portugal on 13 March 1997 (S1) and on 5 May 1997 (S2) and in each sowing date at the densities of 11.4 plants m −2 (D 1) and 4 plants m −2 (D 2). Leaf number, leaf area and above-ground dry matter were measured weekly throughout the crop cycle. Meteorological parameters and canopy light transmission were measured continuously. Crop development was slower in S1 than in S2 because of cooler temperatures during crop cycle in S1 but thermal requirements for each development phase were similar. Temperature, though affecting the duration of phenological phases, did not affect maximum leaf area per plant, which was similar for the same plant density in both sowing dates. For the first sowing, significant differences in dry matter production and light interception were found between the two densities. Crop dry matter production and solar radiation interception were smaller in D 2 than in D 1 owing to a greater leaf area index in D 1, although leaf area and above-ground dry mass per plant were higher in the lower density (D 2). Leaf number, canopy light extinction coefficient and the radiation use efficiency were similar in both densities.

5545897 Optically-based chemical detection system : Jack Michael Goleta, CA, United States assigned to Santa Barbara Research Center

The amount of green leaf area, quantified by the leaf area index (LAI), is one of the key factors determining ecosystem net primary production and energy exchange between land surfaces and the atmosphere. LAI can be measured indirectly using optical methods that are based on the tight relationship between LAI and canopy light transmittance, or through allometric regression models. Until now there has been very little research to compare LAI estimated by the two different approaches. In this study we compare optically-based estimates of LAI to estimates produced using local foliage biomass models for three boreal tree species. Our study is based on 661 Scots pine, Norway spruce and Silver birch stands in the southern boreal zone in Finland. Routine stand inventory and LAI-2000 Plant Canopy Analyzer measurements were performed in all stands. We used three allometric foliage mass models to calculate foliage masses for each stand. The foliage mass estimates were then converted to LAI using specific leaf area (SLA) values. A theoretical stem diameter distribution was also used together with the only diameter-dependent foliage mass models. Optical LAI was corrected for shoot-level clumping (i.e., the clumping of needles into shoots). Finally, we estimated LAI from measured canopy gap fractions by inverting a canopy radiation model. Allometric foliage mass models produced significantly different foliage mass estimates (and the LAI estimates based on them). Among the allometric methods, however, the most sophisticated in terms of input tree variables agreed fairly well with each other and also with the clumping-corrected optical methods. The results indicate a need for caution when using foliage biomass or LAI estimates calculated using different models, especially if the estimates are to be used as an input for other models. The simple shoot-level clumping correction of optical LAI showed the best fit with allometric LAI. Our results support the use of a simple shoot-level clumping correction instead of more complicated correction methods in optical LAI estimation in coniferous forests.

A Comparison of Seeding Rate, Spacing, and Weed Control Methods in the Virginia Tech Transplanted Meadow

Combinations of seeding rate, spacing, and weed control treatments were evaluated for their effect on the performance of the Virginia Tech transplanted meadow technique. The treatments consisted of seeding at 112 or 56 g·90 m−2; within-row transplant spacing of 30, 45, or 60 cm; and mulching, oryzalin application, or no weed control measures. Plant competition alone was insufficient, whereas oryzalin was the most effective for weed control but also reduced the plant stand and floral display. Mulch provided effective weed control with maximum floral display. Close transplant spacing within rows resulted in quick site coverage initially, but this advantage disappeared after 8 weeks compared to wider spacing. Seeding rate did not affect site coverage until the meadow reached maturity at 12 weeks. The lower seed rate allowed more lodging, resulting in a more open appearance and greater canopy light transmission. Chemical name used: 4-(dipropylamino)-3,5-dinitrobenzenesulfonamide (oryzalin).

Canopy light transmittance in a chronosequence of mixed-species deciduous forests

We measured the photosynthetically active radiation transmitted through the canopies of 24 Maryland forest stands, each around midday in midsummer. We then compared the observed values of PAR transmittance with stand age and measures of canopy structure. Generally, transmittance was low, with positively skewed frequency distributions. The geometric mean transmittance followed a distinct pattern with stand age. It was lowest (about 1%) in the youngest stands, increased to about 2.5% as forests approached ages of about 50 years, and then declined with age in the oldest sites (65–340 years). Transmittance was not significantly correlated with many simple measures of forest structure, including estimated aboveground biomass and leaf area index. Better predictions of transmittance used information on the vertical arrangement of the canopy, such as leaf area density. The results are contrary to the common assumptions that forests get consistently darker through time, and that transmittance is inversely proportional to the sheer mass or leaf area of the canopy. The Beer–Lambert extinction coefficient, k, changed with stand age and structure and was especially high in very young stands. We suggest that the variation in light transmittance, and k, can be explained by successional changes in the three-dimensional structure of the canopy.

Radiation Use Efficiency among Cotton Cultivars

AbstractCotton (Gossypium hirsutum L.) cultivars have diverse growth rates and fruiting characteristics that may be due to differences in radiation use efficiency. Potential growth rates were measured to see if differences could be attributed to radiation use efficiency or canopy light transmission coefficients. An irrigated field study was conducted at the Blackland Research Center using three diverse cotton cultivars; Acala SJ‐2, Deltapine 5O, and Tamcot CD3H. Plant densities ranged from 10 to 14 plants m−2. Transmitted, incoming, and reflected photosynthetically active radiation and leaf area index were measured weekly from 3 wk after emergence to boll opening. Dry matter accumulation and leaf area index were significantly different among cultivars both years. Light transmission coefficients were not different, but cultivars differed in radiation use efficiency through the reproductive period. Values for radiation use efficiency ranged from 1.5 g MJ−1 photosynthetically active radiation for Acala to 1.3 g MJ−1 for Tamcot. Values were not significantly different during the vegetative period. These differences during the reproductive period are likely due to differences in boll number and photosynthetic efficiency among cultivars. Tamcot had 50 to 100% more bolls than Acala both years. These results suggest that crop models should account for these cultivar differences in radiation use efficiency.

Nitrogen Fertilizer Effects on Growth, Flowering, Oil Yield, and Yield Components in Meadowfoam1

AbstractMeadowfoam (Limnanthes alba Benth.) seed is a source of oil for use in industrial products and processes. Nitrogen fertilization typically has not increased seed yields of meadowfoam. Data are lacking for characterizing plant growth responses, flowering, honey bee (Apis mellifera L.) foraging, oil yield, and yield components of meadowfoam when fertilized with N. Thus, this field study was conducted in 1981 and 1982 on a Woodburn silt loam soil (fine‐silty, mixed, mesic Aquultic Argixeroll) to determine the effects of ammonium sulfate applied at 0 (control), 50 (50N), and 100 (100N) kg N ha−1. Increased vegetative growth of meadowfoam in response to spring application of N appears to be consistent. Nitrogen fertilization lowered canopy light transmittance and caused a differential flowering response from nonfertilized plants. Seeds per flower in the N‐fertilized treatments were not increased. Flower densities in N‐fertilizedtreatments in 1982 averaged 135% higher than in the control. Seed yields were not increased by N in 1981, but in 1982, seed and oil yields were increased by 113 and 99%, respectively, when N was applied. Oil content was consistently lower when N was applied, but this effect was more than offset by the higher seed yield in 1982. Because of the similar response of agronomic characters in 50N and 100N treatments, applications of 100 kg N ha−1 do not appear to be advantageous. Spring N fertilization of meadowfoam increased seed yield primarily through increased flower number.

Irrigation Effects on Agronomic Characters of Meadowfoam1

AbstractMeadowfoam (Limnanthes albaBenth.), a winter annual adapted to Mediterranean climates, produces a seed oil that has potential uses in industry. Insufficient water during flowering and seed development of meadowfoam might cause the highly variable seed yields previously experienced. The effects of irrigation on oil yield, seed yield and yield components, plant growth and development, and honey bee (Apis melliferaL.) foraging were determined. Irrigation treatments included: none (control), early irrigation (EI) during flowering, and continued irrigation (CI) from flowering until maturity. The soil was a fine‐silty, mixed, mesic Aquultic Argixeroll. Seed yield was not increased with irrigation in 1981, probably because above‐average precipitation occurred during May and June, but in 1982 seed yield in the irrigated treatments averaged 32% higher than in the control. Seed yield differences between the El and CI treatments were not significant. Seeds per flower and 1000‐seed weights in the irrigated treatments in 1982 were 9 and 5% higher than in the control, respectively. Bee foraging at late flowering was greater in the irrigated treatments than in the control. Greater bee activity in the irrigated treatments may account for more seeds per flower in these treatments than in the control. The seed oil content in the irrigated treatments was significantly lower than in the control; however, meadowfoam in the irrigated treatments in 1982 yielded 29% more total oil than in the control. Compared with the control, irrigated plants were taller in both years and in 1982 produced more dry matter and had a smaller canopy light transmittance. In some years meadowfoam can be successfully grown in Mediterranean climates without irrigation; however, in other years irrigation during flowering and seed development, particularly during flowering, may be required to achieve high seed and oil yields.

Leaf Water Potentials and Light Transmission of Intercropped Sorghum and Soyabeans

SUMMARYIn a field experiment to estimate water needs of intercropped sorghum and soyabeans, leaf water potential (LWP) and canopy light transmission were measured. Sorghum had 8–11% lower LWP when grown in mixture than alone, but soyabeans, shaded by sorghum had a higher LWP than in monoculture. Absolute LWP values suggest that only about 10% additional water would be required by the mixture compared with individual requirements of the aggressor species in a two-species mixture of this nature.