Seasonal Biomass Production Research Articles

Dry Season Biomass Production of Leucaena lecocephala cv Tarramba at 4 months regrowth and from Several Longer Regrowth Plants on Sandy Vertisol Soil at Naibonat, West Timor-Indonesia

Dry Season Biomass Production of Leucaena lecocephala cv Tarramba at 4 months regrowth and from Several Longer Regrowth Plants on Sandy Vertisol Soil at Naibonat, West Timor-Indonesia

Evaluation of water productivity of smallholder irrigation along a Sand River, in the Maigobo watershed of northern Ethiopia

Sand dams are a type of rainwater harvesting technology that can increase groundwater recharge in dry land environments. They are constructed across seasonal sandy rivers and trap sand and water during floods. The sand acts as a natural filter and storage medium for the water, which can be extracted by the local communities through wells, pumps, or scoop holes. This research aims to evaluate agricultural water productivity based on water consumption (ETa) and biomass production of smallholder irrigation schemes along a sand river with a sand dam in the riverbeds of northern Ethiopia. Remotely sensed satellite data, WaPOR (Water Productivity through Open access of Remotely sensed derived data) database was used to estimate water productivity in the arid and semi-arid area. Following the installation of the sand dam at the irrigated parts of the Mai Gobo watershed, both the annual and seasonal values increased over a number of years, according to the spatial analysis of ETa and biomass production. For instance, the maximum seasonal ETa before the dam was about 70 mm/season, whereas after the dam the spatially analysed ETa reached 174 mm/season. Likewise, maximum seasonal biomass production of 1117 kg/ha and 4433 kg/ha were obtained before and after the construction of the sand dam, respectively. Agricultural water productivity at the irrigated plots of the Mai Gobo watershed was also improved from 1.4 kg/m3 to 2.9 kg/m3 before and after the sand dam respectively. Generally, the output of the study can be used as an input for the concerned stakeholder to take measures against the water scarcity problem in the study area. The study also contributes to the scientific knowledge and understanding of the hydrological and agronomical impacts of the sand dam in the arid and semi-arid regions.

Assessing multiple limiting factors of seasonal biomass production and N content in a grassland with a year-round production.

There is little evidence on the extent that multiple factors simultaneously limit ecosystem function of grasslands with year-round production. Here we test if multiple factors simultaneously limit (i.e., more than one factor at a time) grassland functioning in different seasons and how they interacted with N availability. In a Flooding Pampa grassland, we ran a separate factorial experiment in spring, summer, and winter with several treatments: control, mowing, shading, P addition, watering (only in summer), and warming (only in winter), each of them crossed with two nitrogen treatments: control and N addition. Grassland functioning was assessed by aboveground net primary productivity (ANPP), green and standing dead biomass, and N content at the species group level. Out of 24 potential cases (three seasons by eight response variables), 13 corresponded to just one limiting factor, 4 to multiple limiting factors, and the other 7 to no evidence of limitation. In conclusion, grassland functioning in each season was most often limited by just one factor, while multiple limiting factors were rarer. Nitrogen was the prevailing limiting factor. Our study expands our knowledge of limitations imposed by factors associated with disturbance and stress, such as mowing, shading, water availability, and warming in grasslands with year-round production.

Evaluation of the Carry-Over Effect of the “Crop-Forcing” Technique and Water Deficit in Grapevine ‘Tempranillo’

“Crop-forcing” is an effective technique to delay grape maturation to a period of lower temperatures, and in this way, improve grape quality. Because of the aggressiveness of this technique (removal of leaves and fruit to reinitiate a second vegetative cycle), it may affect the level of reserves and could provoke progressive vine exhaustion. The aim of the present work is to evaluate the short- and medium-term evolution of carbohydrate reserves in different plant organs and the effect of “crop-forcing” under different irrigation regimes on seasonal biomass production and its distribution. The study was carried out over a four years period (2017–2020), applying “crop-forcing” in three consecutive years (2017–2019) to the same vines on two different dates and using two irrigation strategies. The application of “crop-forcing” did not decrease root reserve levels in either the year of application or the following year, but did modify starch and soluble sugar levels in shoots and leaves in some moments of the vegetative cycle during the years of “crop-forcing” application. Total biomass production in terms of grams per vine was lower in the “crop-forcing” treatments and continued to be so when “crop-forcing” was no longer applied. The percentage of biomass in vegetative organs increased at the expense of productive organs.

Lipid extraction from some seaweeds and evaluation of its biodiesel production

The present study evaluated the efficiency of seaweeds collected from Abu Qir Bay, Alexandria, Egypt, as a feedstock for biodiesel. A total of 15 macroalgal species were collected overall in the four seasons. The highest seasonal biomass production of 652.1 and 626.3 g m −2 was recorded with Chaetomorpha linum and Ulva compressa in autumn and spring, respectively. While the highest annual biomass production was detected in Ulva fasciata (1056.8 g m −2 ). Lipid content varied among species, with the highest value of 14.66% and 9.94% dw in U. fasciata and U. compressa during spring, which resulted in the highest annual lipid productivity of 67.4 and 63.3 g m −2 , respectively. Palmitic acid (C16:0) showed the highest value among all fatty acids (1.12–19.62 mg g− 1 dw) in all studied species. The biodiesel characteristics of all algae species tested are in agreement with the values of international standards. Overall, the present study recommended U. compressa and U. fasciata as a promising biodiesel feedstock due to the relatively higher lipid productivity and FAMEs characteristics that comply with the international standards and high net energy output that reached 1.24 and 1.30 GJ ton −1 , respectively. • Chaetomorpha linum and Ulva compressa recorded the highest seasonal biomass production. • Possible exploring of 15 macroalgae as biodiesel feedstock species. • Palmitic acid (C16:0) showed the highest proportion in all studied seaweed species. • Ulva compressa and Ulva fasciata are a promising biodiesel feedstock.

Distribución en Chile y colonización del río Cayumapu (Valdivia) por el macrófito acuático invasor Limnobium laevigatum

Limnobium laevigatum is an invasive aquatic herb that increases its range in Chile to displace native species from its place in the coastal zonation of the fresh water bodies. Seasonal biomass production and reproduction of this species are studied in the Sanctuary of Nature “Carlos Anwandter” in Valdivia, Chile. The change experienced by the coastal zonation of the river is established due to the aggressiveness of this invasive species, which was favored by the eutrophication of the waters. The average annual biomass reaches 6,140 kg/ha. The organs with the greatest contribution to biomass are the emergent leaves and the roots. Biomass production was higher in summer and lower in spring, when high values of necromass were also measured, indicating the presence of an unknown deleterious factor. The biomass of roots and emerging leaves has the same seasonal route with a decrease in spring, while the swimming leaves and the necromass show an inverse behavior. The presence of flowers and fruits was confirmed, which supports the hypothesis proposed of sexual reproduction for the Valdivian populations. Finally, a phenological diagram indicates the presence of viable fruits and seeds throughout the year.

Seasonal biomass production, fermentable saccharification and potential ethanol yields in the marine macroalga Ulva sp. (Chlorophyta)

Marine macroalgae (seaweeds) can accumulate high amounts of starch and cellulose in their tissues, hence, offering an attractive potential source of feedstock for bioethanol production. In this study we determined the specific growth rates (SGRs) in the seaweed Ulva sp. (Chlorophyta) during a full year cultured in a land-based facility to estimate sustainable biomass yields. We used 40 and 600 L outdoor tanks that received high and low irradiances, running seawater, aeration and external nutrients. Daily SGRs in 40 L tanks averaged 12 ± 2.04, 15.3 ± 0.8, 19.3 ± 1.8 and 10.3 ± 1.9% biomass increase per day for winter, spring, summer and autumn, respectively, while in 600 L growth averaged 2.5 ± 0.4, 2.2 ± 0.3, 9.8 ± 0.5 and 1.4 ± 0.4% d−1, respectively. In an up-scaled growth trial during summertime in larger culture units of 3400 and 27,000 L growth rates were 4.6 ± 0.8 and 8.7 ± 1.04% d−1, respectively. Altogether, the total biomass potential would yield 1.3 ton FW m−2 y−1. We also optimized enzymatic hydrolysis of dried biomass by means of time-course incubations with cellulase, amyloglucosidase and α-amylase in order to maximize the yields of total reducing sugars (TRS). We measured 163.6 ± 0.3, 179.7 ± 0.1 and 223.9 ± 0.5 mg TRS g−1 DW for summer, spring and winter months, respectively, with an average fermentation of the hydrolysate of 0.3 ± 0.06 g EtOH g−1 TRS. This work underlines the feasibility of seaweed feedstock production in land-based cultivation with respect to ethanol production.

The impact of modifying photosystem antenna size on canopy photosynthetic efficiency-Development of a new canopy photosynthesis model scaling from metabolism to canopy level processes.

Canopy photosynthesis (Ac) describes photosynthesis of an entire crop field and the daily and seasonal integrals of Ac positively correlate with daily and seasonal biomass production. Much effort in crop breeding has focused on improving canopy architecture and hence light distribution inside the canopy. Here, we develop a new integrated canopy photosynthesis model including canopy architecture, a ray tracing algorithm, and C3 photosynthetic metabolism to explore the option of manipulating leaf chlorophyll concentration ([Chl]) for greater Ac and nitrogen use efficiency (NUE). Model simulation results show that (a) efficiency of photosystem II increased when [Chl] was decreased by decreasing antenna size and (b) the light received by leaves at the bottom layers increased when [Chl] throughout the canopy was decreased. Furthermore, the modelling revealed a modest ~3% increase in Ac and an ~14% in NUE was accompanied when [Chl] reduced by 60%. However, if the leaf nitrogen conserved by this decrease in leaf [Chl] were to be optimally allocated to other components of photosynthesis, both Ac and NUE can be increased by over 30%. Optimizing [Chl] coupled with strategic reinvestment of conserved nitrogen is shown to have the potential to support substantial increases in Ac, biomass production, and crop yields.

No precipitation legacy effects on above‐ground net primary production and species diversity in grazed Mediterranean grassland: a 21‐year experiment

AbstractQuestionWhat are the controls on biomass production and species diversity in Mediterranean grasslands? Do medium‐term (i.e. inter‐annual) precipitation legacy effects on biomass production and diversity occur in these grasslands?LocationKarei Deshe Experimental Range Station, Upper Galilee, northern Israel.MethodsWe used a long‐term (21‐r) cattle‐grazing experiment in a Mediterranean grassland to search for evidence of precipitation legacies on herbaceous above‐ground biomass production and species diversity. Biomass production was measured in two seasonal late grazing treatments, in the winter and at peak vegetative production in the spring, while species diversity was determined at peak production. We used ANCOVA to test the effects of residual biomass, previous year's stocking density and previous year's biomass on current biomass production. We ran forward selection and ANCOVA to test for precipitation legacies, using precipitation variables relating to both previous and current year's rainfall. In addition we examined linear regressions of biomass and species diversity on current year's precipitation.ResultsBiomass production and species diversity showed weak to negligible relationships with current year's precipitation. Biomass production, and to a lesser extent, diversity, were affected by inter‐annual fluctuations in growing conditions. However, evidence of inter‐annual precipitation legacies were found only for early season biomass production, and not for peak biomass production or species diversity. We found no effect of grazing on biomass production at the onset of the grazing season, regardless of important differences in previous year's stocking density. Additionally, we found no effect of previous year's biomass production or stocking density on the following year's biomass or diversity, but peak biomass production was strongly related to previous year's residual biomass.ConclusionsThe lack of an inter‐annual precipitation legacy on peak biomass production contributes to a growing body of evidence showing that Mediterranean ecosystems are unique among semi‐arid and sub‐humid ecosystems, where precipitation legacies play an integral role. Mediterranean ecosystems are unique in their combined long‐term high variability in rainfall and long grazing history. This lack of precipitation legacy led to the development of vegetation that is highly resistant to inter‐annual fluctuations in growing conditions. We propose that the high resistance contributes to the lack of inter‐annual, or medium‐term, precipitation legacies on the studied grassland, and may contribute to its persistence under future projected climate change in the region.

A plague of waterfleas (Bythotrephes): impacts on microcrustacean community structure, seasonal biomass, and secondary production in a large inland-lake complex

The spiny cladoceran (Bythotrephes longimanus) is an invasive, predaceous zooplankter that is expanding from Great Lakes coastal waters into inland lakes within a northern latitudinal band. In a large, Boundary Water lake complex (largely within Voyageurs National Park), we use two comparisons, a 2-year spatial and a 12-year temporal, to quantify seasonal impacts on food webs and biomass, plus a preliminary calculation of secondary production decline. Bythotrephes alters the seasonal biomass pattern by severely depressing microcrustaceans during summer and early fall, when the predator is most abundant. Cladoceran and cyclopoid copepods suffer the most serious population declines, although the resistant cladoceran Holopedium is favored in spatial comparisons. Microcrustacean biomass is reduced 40–60 % and secondary production declines by about 67 %. The microcrustacean community shifts towards calanoid copepods. The decline in secondary production is due both to summer biomass loss and to the longer generation times of calanoid copepods (slower turnover). The Bythotrephes “top-down” perturbation appears to hold across small, intermediate, and large-sized lakes (i.e. appears scale-independent), and is pronounced when Bythotrephes densities reach 20–40 individuals L−1. Induction tests with small cladocerans (Bosmina) suggest that certain native prey populations do not sense the exotic predator and are “blind-sided”. Failure of prey to deploy defenses could explain the disproportionate community impacts in New World versus Old World lakes.

Environmental and economic analysis of SolComBio concept for sustainable energy supply in remote regions

The paper attempts to analyse the environmental and economic impacts of the Multi-fuel Solar Hybrid Power Plant concept called SolComBio. An environmental and economic assessment is performed to investigate whether the concept could be suitable for energy source in remote areas compared with the conventional local energy supply systems. The technological concept relies on the combination of a solar thermal receiver and a multi-fuel pulverized biomass burner system to overcome the impediments of local or regional power supply under environmental friendly and economic sound conditions. Through the hybridisation with multi-fuel pulverized burner system, SolComBio concept overcomes the drawbacks of solar systems and offers flexibility of operation time and also possibility of fuel changes, which makes it suitable for areas with seasonal biomass production. Two cases of constructing and operating the plant in a Brazilian and Indonesian remote region are addressed. According to the calculations, SolComBio seems to be promising from the environmental side; nonetheless, depending on the conditions at the local land and feedstock markets the SolComBio concept could be competitive or not. This study offers a reflection how a technological concept can arouse interest of remote regions from the perspective of systems analysis.

Estimating seasonal nitrogen removal and biomass yield by annuals with the extended logistic model.

The Extended Logistic Model (ELM) has been previously shown to adequately describe seasonal biomass production and N removal with respect to applied N for several types of annuals and perennials. In this analysis, data from a corn (Zea mays L.) study with variable applied N were analyzed to test hypotheses that certain parameters in the ELM are invariant with respect to site specific attributes, like environmental conditions and soil type. Invariance to environmental conditions suggests such parameters may be functions of the crop characteristics and certain other management practices alone (like plant population, planting date, harvest date). The first parameter analyzed was Δb, the difference between the N uptake shifting parameter and the biomass shifting parameter. The second parameter tested was Ncm, the maximum N concentration. Both parameters were shown to be statistically invariant, despite soil and site differences. This was determined using analysis of variance with normalized nonlinear regression of the ELM on the data from the study. This analysis lends further evidence that there are common parameters involved in the ELM that do not rely on site-specific or situation-specific factors. More insight into the derivation of, definition of, and logic behind the various parameters involved in the model are also given in this paper.

A simple model to assess the sensitivity of grassland dairy systems to scenarios of seasonal biomass production variability

In recent decades, dairy herds of the peri-Mediterranean area have coped with high climatic variability, which has contributed to weakening their economic equilibrium. Survey studies highlighted that climatic impact depends on the strategies of farmers, related to forage autonomy. To explain this observation precisely and assess the opportunity of changing forage strategy as an adaptation to cope with climatic variability over the long term, a simulator was developed to explore the impact of several biomass production variability scenarios on forage purchases. This approach was applied on dairy cattle farms in a mountain area in the South of France (Ardèche), with forage systems based on grass (hay and pasture), using several levels of forage autonomy. A computer application was developed through a partnership project between our research team and officers of an extension board. We then validated the ability of the simulator to account for the operation of special cases of farms after calibration and studied the model sensitivity to key parameter variations. Then we explored (i) how the simulator can be used to assess the sensitivity of six dairy farms to biomass production variability and (ii) the value of an adaptation strategy with advance forage stockpiling. The sensitivity analysis highlights that the purchase of forage was highly sensitive to production variation during March, April and May. The farms which used grazing the most, exhibited a lower standard deviation than the other farms. Variation obtained for the standard deviation of forage bought was not only explained by the forage autonomy but might depend on other characteristics such as time of turnout and surface allocation. The succession of disadvantageous years was tested. The decrease in the stock differed according to the forage autonomy of farms. Whereas farms which were only just autonomous bought forage as of the first disadvantageous year, farms with forage autonomy of 120% can resist repeated biomass production variability for 8years with the constitution of remaining stocks of forage. The simulator developed here is simple enough both to explore the sensitivity of a dairy system and promote the debate on the results with farmers and advisers.

Energy efficiency of an outdoor microalgal photobioreactor sited at mid-temperate latitude

This work examined the energetic performance of a 6-month semi-continuous cultivation of Scenedesmus obliquus in an outdoor photobioreactor at mid-temperate latitude, without temperature control. By measuring the seasonal biomass production (mean 11.31, range 1.39–23.67 g m −2 d −1), higher heating value (22.94 kJ g −1) and solar irradiance, the mean seasonally-averaged photosynthetic efficiency (2.18%) and gross energy productivity (0.27 MJ m −2 d −1) was calculated. When comparing the solar energy conversion efficiency to the energy investment for culture circulation, significant improvements in reactor energy input must be made to make the system viable. Using the data collected to model the energetic performance of a substitute photobioreactor design, we conclude that sustainable photobioreactor cultivation of microalgae in similar temperate climates requires a short light path and low power input, only reasonably obtained by flat-panel systems. However, temperature control was not necessary for effective long-term cultivation.

Variability in growth, development and reproduction of the non-native seaweed Sargassum muticum (Phaeophyceae) on the Irish west coast

This study compared seasonal growth, development and reproduction of the invasive brown macroalga Sargassum muticum in habitats with different wave exposure on the Irish west coast. Three field sites with different degrees of wave exposure were chosen for monthly observations to reflect different habitats that were characteristic of the Irish west coast. Growth and receptacle development differed considerably between sites. Growth and receptacle development was lower at the most sheltered site. Here, S. muticum showed signs of early fragmentation in April/May during the two years of investigation (2007 and 2008), whilst the population at an exposed site developed normally and plants grew to a maximum average length of 163 cm by July, with the onset of fragmentation in August. Sargassum muticum in a tide pool exhibited a similar seasonal growth cycle as plants at the exposed open shore site. Overall growth however was stunted, with plants reaching a maximum length of only 30–40 cm in July. Receptacle development was also inhibited at the sheltered site, with a maximum of only 10% of plants found to be fertile during spring and summer 2008, while plants at the exposed site and the tide pool exhibited 100% plant fertility by August. An extensive occurrence of the native epiphyte Pylaiella littoralis on S. muticum was noticed during field sampling at the sheltered study site which may have contributed to inhibited development of S. muticum observed in this area. Seasonal biomass production, photosynthetic activity and plant/frond ratio development were contrasted between Sargassum muticum at the open shore and the tide pool. Sargassum muticum biomass production in the tide pool was 3.5 times lower than that of plants on the open shore. Receptacle development and seasonal photosynthetic activity were similar for tide pool and open shore plants, irrespective of morphological differences. Highest photosynthetic rates (fluorescence yield, Y o) were measured during active growth in February and lowest values during development of reproductive tissue and senescence. Numbers of S. muticum plants on the open shore decreased significantly during the year, whilst frond number per plant increased, possibly suggesting self-thinning through shading processes. The high variability in Sargassum muticum productivity and reproductive development between habitats suggests that the degree of competition and impact on native flora could be site-specific, and their local effect on displacements will require further investigations.

Determining grazing capacity in Namibia with the aid of remote sensing

The Namibian rangelands consist of a mixture of herbaceous and woody components. The main source of income is from farming systems with grass production the predominant source of forage. For rangeland managers to utilise this source sustainably, the accurate determination of grazing capacity is vital since it allows for adapting the animal load, and therefore the grazing pressure, to the actual capacity of the land. Various practical approaches and methodologies were investigated to update the existing Namibian grazing capacity map that was compiled more than three decades ago from the expert, but nonetheless subjective, opinion of farmers, extension officers and pasture scientists. The methodologies studied in this paper include the estimation of seasonal herbaceous biomass production using satellite imagery, land cover mapping and the quantitative yield method of determining available forage. It is expected that combining all these methods (information from remote sensing, adjusted with scientifically established coefficients for woody cover, accessibility and palatability and the incorporation of the clipping technique [quantitative yield method] as a ground truthing mechanism) will provide a tool to objectively establish rangeland productivity and thus grazing capacity in Namibia.

Simulation analysis of lucerne–wheat crop rotation on the Loess Plateau of Northern China

The Agricultural Production System Simulator (APSIM) was parameterised and tested against datasets from two field experiments being conducted on Heilu soil at the Qingyang Research Station, Gansu, China as to investigate long-term lucerne productivity and management options of reducing impact of lucerne on winter wheat yield in a lucerne–wheat rotation system. With minimal parameterisation and configuration of the APSIM-Lucerne module, APSIM was able to simulate phenological development and seasonal growth of winter-dormant lucerne cultivar, Longdong compared with the observed data. Flowering date was accurately simulated using the established relationship between accumulated thermal time and mean photoperiod. After the APSIM-Lucerne module was configured for the seasonal variation in RUE (radiation use efficiency), the model simulated lucerne seasonal biomass production over three growing seasons in the continuous lucerne treatment with a root mean squared deviation (RMSD) of 1132 kg/ha (30% of the mean observed biomass). In the treatment where lucerne was removed in August 2001 and two winter wheat crops were sown and harvested in 2001/2002 and 2002/2003 growing seasons, APSIM simulated winter wheat crop biomass in both growing seasons with a RMSD of 1420 kg/ha (20% of the mean observed crop biomass). Wheat grain yield was simulated with a RMSD of 918 kg/ha (27% of the mean observed grain yield). Using measurements of drained upper limit (DUL) and lower limit (LL), and standard soil evaporation and runoff parameters, the model was able to simulate soil water dynamics and water use by lucerne in the lucerne-fallow, continuous lucerne and lucerne–wheat treatments. The long-term simulation suggested that under local climatic conditions, lucerne could produce 11,000 kg/ha biomass annually. The simulation also indicated that integrating lucerne with annual cropping could potentially reduce runoff and early removal improved soil water storage prior to sowing winter wheat and optimise wheat yield following lucerne in a lucerne–wheat rotation system. The findings from these long-term simulations suggest there is need to develop management strategies when lucerne is integrated with annual cropping system to improve soil water use and reduce runoff. There is also need to consider a balance between sustaining wheat yield and providing feed for livestock when developing management strategies for timing of lucerne removal and cropping option in lucerne-based rotation systems. The successful test of APSIM will give local researchers confidence to use the tool exploring cropping system issues in Northern China.

Effect of organic and inorganic fertilizers applied during successive crop seasons on growth and nitrate accumulation in lettuce

Abstract A romaine-type lettuce ( Lactuca sativa L.) cv. Corsica was cultivated during three successive crop seasons (late-spring, late-autumn and late-winter) in the same soil of an experimental greenhouse in S.W. Peloponnese, Greece. Seven long-term fertilization treatments were tested for their effect on plant growth and nitrate concentration in the external lettuce leaves. Treatments included: three different doses of organic fertilization (composted sheep manure) applied at the start of each crop season, three different doses of inorganic N fertilization applied via fertigation during each crop season, and a control treatment in which no fertilizer was applied. A drip irrigation system was used to water all plants. The highest nitrate levels were observed in the medium and maximum inorganic fertilization treatments (572–664 mg kg −1 ) in all crop seasons. They were significantly higher compared to the respective organic fertilization treatments (253–435 mg kg −1 ) and all other fertilization treatments (148–435 mg kg −1 ). Crop season affected lettuce growth more than nitrate accumulation in the lettuce leaves: lettuce biomass production was the smallest and most uniform in the late-autumn season and did not respond to the fertilization treatments tested (ranging from 409 to 439 g plant −1 ), while in the late-spring season biomass production was the highest and most variable (561–841 g plant −1 ), it correlated with nitrate concentration in the leaves and in the medium and maximum inorganic fertilizer doses it significantly exceeded production from all other fertilization treatments (827–841 g plant −1 ). Following the three crop seasons the residual availability of N, P and K was clearly enhanced in the soil receiving the organic compared to the inorganic fertilization. Nitrate concentration in lettuce leaves was far below the upper limits set by the European Commission in all fertilization treatments throughout the three crop seasons, a result attributed mainly to the sufficient level of light intensity and duration throughout the year in Southern Greece.

Evaluating warm-season grass production in temperate-region pastures: A simulation approach

The pasture submodel of the Integrated Farm System Model (IFSM) was modified to simulate the biomass production and nutritive dynamics of a warm-season (C 4) grass monoculture. Predictions of yield and nutritive value were calibrated and evaluated with 5 years of field data from grazed switchgrass ( Panicum virgatum) pastures in Pennsylvania, USA. Uncertainty analysis of biomass at the beginning of each growth cycle showed that each estimated yield was sensitive to the amount of biomass that started its growth cycle but not to those of previous growth cycles. Sensitivity analysis showed that predicted yield was most sensitive to physiological parameters such as proportion of photosynthate partitioned to shoots, specific leaf area, structural growth per unit carbohydrate, leaf photosynthetic efficiency, and the light extinction coefficient. Sensitivity of yield to maximum rooting depth increased during periods of drought. For 10 of 13 simulated sampling dates, confidence intervals of field-observed and predicted mean yield overlapped, and half of predicted mean annual yields were within ±32% of observed values. The model predicted seasonal crude protein (half of predictions within ±25%), neutral detergent fiber (all within ±12%), and in vitro true digestibility (all within ±16%) more accurately. Refining the model’s representation of warm-season grass phenology and calibrating it to simulate other field experiments may improve predictions of seasonal biomass production. The whole-farm model with a warm-season grass component will provide a useful research and teaching tool for evaluating the long-term economic and environmental sustainability of dairy and beef production systems in warm temperate regions.

Seasonal growth of submersed macrophytes in lakes: The effects of biomass density and light competition

The long-term growth and succession of aquatic plant species in lakes have been documented in many field studies, but there has been little insight to quantify the mechanisms which determine the outcome of competitive growth. In this paper, a process-based macrophyte growth model is formulated and used to investigate the light limited growth of individual macrophyte species and of two species in competition. Closed form solutions for integral biomass production over 1 day are derived, reducing the time and depth resolution required for seasonal growth calculations. For growth in monoculture, seasonal biomass production is found to be most sensitive to the base growth and respiration rate coefficients and the temperature dependence of growth, and relatively insensitive to biomass density, and the half-saturation constant for light. The sensitivity of seasonal biomass production to basic physiological, morphological, and physical lake parameters is found to be significantly higher for growth in competition compared to growth in monoculture. For published growth parameter values, invasive species are predicted to suppress the growth of native species over a well-defined range of water depths and turbidities, largely by reaching the water surface early in the season and subsequently forming a dense surface canopy.