1,721,200 research outputs found
Leaf and canopy photosynthesis models for cocksfoot (Dactylis glomerata L.) grown in a silvopastoral system
Full text linkThe aim of the research reported in this thesis was to construct leaf and canopy photosynthesis models for understorey cocksfoot pasture grown in a 10-11-year old Pinus radiata silvopastoral system. From these models, dry matter (DM) production was predicted based on a numerical description of the biological mechanisms involved in canopy photosynthesis.
To do this, a wide range of environmental and management conditions were created through changes in light intensity and regime, temperature, soil moisture, nitrogen (N) and regrowth duration. A unique component of a silvopastoral system is the fluctuating light regime experienced by the understorey plants. The daily photosynthetic photon flux density (PPFD) integral was 55-62% of the open, with periods of full sunlight (1700-1900 µmol m⁻² s⁻¹ PPFD at midday) and severe shade (129-130 µmol m⁻² s⁻¹ PPFD) that changed within 45-120 minutes depending on the solar angle elevation. A similar pattern obtained from artificial slatted structures, also provided a bimodal light regime but with lower light intensity.
The resulting DM growth rates ranged from 2 to 154 kg DM/ha/d. These differences were related to differences in canopy leaf area index (LAI) from 0.5 to 8.2 units caused by a reduced tiller population, canopy etiolation and canopy leaf angle.
Net photosynthesis rate from seven light intensities (0, 100, 250, 500, 750, 1000 and 2000 µmol m⁻² s⁻¹ PPFD) were measured in the field using an open infrared gas analysis system. These were used to construct light curves for the youngest fully expanded intact leaves. The prediction of DM production was based on an integrated leaf photosynthesis model that uses a non-rectangular hyperbola function to estimate the saturated leaf photosynthetic rate (Pmax), the photosynthetic efficiency (α) and the degree of curvature (θ) in the photosynthetic response of individual leaves. The highest Pmax was 27.4 µmol CO2 m⁻² s⁻¹ in non-limited conditions. This decreased to a minimum of -0.5 µmol CO₂m⁻² s⁻¹ under severe water stress (Ψlp= -16 bar). Values of α ranged from 0.036 µmol CO₂/µmol PPFD in non-limiting conditions to 0.020 µmol CO₂/µmol PPFD at 1.5% N. The degree of curvature of the leaf response curve θ was unaffected by the range of environmental factors and regrowth duration and had a mean value of 0.96 ±0.02. The response of these parameters to different temperature, N, moisture, regrowth and shade conditions were predicted using a multiplicative model for predicting Pmax, a 'law of the minimum factor' model for α and a constant for θ.
These parameters were then incorporated into a canopy photosynthesis model with coefficients for respiration, partitioning and the main canopy characteristics that affect light interception (LAI and leaf angle). Based on this model, cocksfoot DM production was predicted for silvopastoral systems in non-limiting situations and where a single, two, three, four or all five factors were limiting for: air temperatures from 2 to 37 °C, water status from Ψlp -0.1 to -16.0 bar (corresponding to a soil volumetric water content to 500 mm depth of 8.5 to 34%), foliage N content from 1.5 to 5.9%, regrowth duration from 20 to 60 days, and time course of shade (severe shade: 5% of open PPFD or moderate shade: 50% of open PPFD) from 1 to 180 minutes and the correspondent induction process (lag in the rise of photosynthesis rate to the maximum value) from 30, 60 and 180 minutes of severe shade.
Using this model, it was shown that the continuous light regime of 50% transmissivity throughout a day had higher canopy photosynthesis than for the same intensity but a fluctuating light regime with periods of 90-120 minutes of full sunlight and severe shade (10.4 vs 8.4 g CO₂ m⁻² d⁻¹). This was due to (i) a faster decrease in Pmax and α for plants experiencing 5% of open PPFD compared with 50% of open PPFD; (ii) the lack of an induction process under continuous shade. These results indicate that artificial shade cloth gives a biased representation of the response of understorey pastures in silvopastoral systems. Validations from observed DM production data (from 9 to 134 kg DM/ha/d) were obtained from different environmental and management conditions and indicated that approximately 86% of the variation in cocksfoot growth rate was accounted for by using the model proposed. Therefore, the canopy photosynthesis model proposed in this study provides a powerful and useful tool for understanding and predicting DM production of cocksfoot understorey pastures in silvopastoral systems
Yield and botanical composition of lucerne, cocksfoot or ryegrass based pastures over six years
No full textObjective: To quantify annual yield and botanical composition from lucerne, cocksfoot and ryegrass based pastures. The presentation focuses on results from the MaxClover Grazing Experiment and lucerne grazing management strategies.Meat & Wool NZ Ltd/ Pastoral21, The Cocksfoot Growers Association, Lincoln Universit
Legumes for hill country
No full textIn drought prone hill country, legumes can be introduced to increase nitrogen transfer to companion grasses which increases both the quality and quantity of feed available for grazing livestock. This powerpoint presentation accompanied an oral presentation by Professor Derrick Moot in Wairoa. Topics covered included species selection, and livestock and grazing management practices to aid establishment and ensure persistence. References are included.The New Zealand Merino Company & Sustainable Farming Fund, Ministry of Agriculture and Forestr
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Pasture and forage options for store lamb and beef production from South Island hill and high country.
No full textIn 2005 the Lees Valley Farmers Group applied for a MAF Sustainable Farming Fund (SFF) Grant to investigate pasture and forage options for the intensification of South Island Hill and High Country. At the beginning of the project the site was low producing browntop with matagori and sorrel. Over the three years the project looked at a wide range of topics. Questions were answered by Lincoln University dryland research and technical staff who set up, and measured, a range of experiments which covered >10 ha area in the driest, stoniest part of the valley bottom. These experiments looked at:
• methods of establishment and their cost,
• the effect of lime on the establishment and growth of the introduced pasture species,
• forage production,
• identification of grass and legumes suited to the environment
• which mixtures performed best and when
• nitrogen response of grasses
• quality of pasture/forage produced.
This booklet reports the research results presented at the 2007 field day.Research sponsored by Lincoln University and the Sustainable Farming Fund (SFF), Ministry of Agriculture and Forestry
Harvest index variability within and between field pea (Pisum sativum L.) crops
No full textThe association between individual plant performance and seed yield variability within
and between field pea crops was investigated. In 1988/89 six F8 genotypes with
morphologically distinct characteristics were selected from a yield evaluation trial.
Analysis of the individual plant performance within these crops indicated an association
between low seed yields and the location and dispersion of plant harvest index (PHI) and
plant weight (PWT) distributions. The analyses also showed there was a strong linear
relationship between the seed weight (SWT) and PWT of the individual plants within each
crop, and that the smallest plants tended to have the lowest PHI values.
A series of 20 simulations was used to formalize the relationships between SWT, PWT
and PHI values within a crop into a principal axis model (PAM). The PAM was based
on a principal axis which represented the linear relationship between SWT and PWT, and
an ellipse which represented the scatter of data points around this line.
When the principal axis passed through the origin, the PHI of a plant was independent
of its PWT and the mean PHI was equal to the gradient of the axis. However, when the
principal axis had a negative intercept then the PHI was dependent on PWT and a MPW
was calculated.
In 1989/90 four genotypes were sown at five plant populations, ranging from 9 to 400
plants m⁻². Significant seed and biological yield differences were detected among
genotypes at 225 and 400 plants m⁻². The plasticity of yield components was highlighted,
with significant genotype by environment interactions detected for each yield component.
No relationship was found between results for yield components from spaced plants and
those found at higher plant populations.
The two highest yielding genotypes (CLU and SLU) showed either greater stability or
higher genotypic means for PHI than genotypes CVN and SVU. Despite significant
skewness and kurtosis in the SWT, PWT, and PHI distributions from the crops in this
experiment, the assumptions of the PAM held. The lower seed yield and increased
variability in PHI values for genotype CVN were explained by its higher MPW and the
positioning of the ellipse closer to the PWT axis intercept than in other genotypes. For
genotype SVU, the lower seed yield and mean PHI values were explained by a lower
slope for the principal axis.
Both low yielding genotypes were originally classified as having vigorous seedling growth
and this characteristic may be detrimental to crop yields. A method for selection of field
pea genotypes based on the PAM is proposed. This method enables the identification of
weak competitors as single plants, which may have an advantage over vigorous plants
when grown in a crop situation
An overview of dryland legume research in New Zealand
No full textWith limited funds, and the relatively low importance of dryland pastures in New Zealand, research has been targeted at the species most likely to induce transformational change on-farm. Lucerne research into biophysical influences on plant growth and development has added flexibility to spring grazing management. Coupled with additional agronomic research and extension, farmers now have the confidence to use lucerne as a direct feed source for sheep, beef and deer. Research on Caucasian clover seedling development identified the long duration to secondary leaf production as the physiological basis for slow clover establishment in mixed swards. Despite agronomic strategies to overcome this, its use is now limited by commercial constraints. A 10-year ‘MaxClover’ grazing experiment at Lincoln University demonstrated the superiority of subterranean clover with cocksfoot over perennial ryegrass and white clover for pasture persistence, quality and animal performance. Pastures with high legume content had higher water-use efficiency and produced greater animal and pasture production. Balansa and gland clovers both show a strong influence of photoperiod on time of flowering, which suggests they may be suitable for oversowing into areas of winter wet and summer dry hill and high country. Further research into their ecological niche and ability to regenerate each autumn is required. For all legumes, the role of inoculation requires further research with recent results suggesting indigenous, rather than commercially introduced, bacterial populations are dominant in root nodules. Uptake of dryland pasture species for on-farm use has only been successful when research, extension and agribusiness interests have been aligned
Lucerne agronomy, Sheparton, Victoria
No full textPresentation on Lucerne agronomy, Sheparton, Victoria, Australia
Dryland pastures
No full textThe aim of this research was to quantify annual yield and botanical compositionfrom lucerne, cocksfoot and ryegrass based pastures for dryland situations.Research sponsored by Lincoln University, the Sustainable Farming Fund (SFF) Ministry of Agriculture and Forestry, Meat and Wool New Zealand Ltd, and The Cocksfoot Growers Association
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