Leaf photosynthesis and respiration of three bioenergy crops in relation to temperature and leaf nitrogen: how conserved are biochemical model parameters among crop species?

Given the need for parallel increases in food and energy production from crops in the context of global change, crop simulation models and data sets to feed these models with photosynthesis and respiration parameters are increasingly important. This study provides information on photosynthesis and respiration for three energy crops (sunflower, kenaf, and cynara), reviews relevant information for five other crops (wheat, barley, cotton, tobacco, and grape), and assesses how conserved photosynthesis parameters are among crops. Using large data sets and optimization techniques, the C3 leaf photosynthesis model of Farquhar, von Caemmerer, and Berry (FvCB) and an empirical night respiration model for tested energy crops accounting for effects of temperature and leaf nitrogen were parameterized. Instead of the common approach of using information on net photosynthesis response to CO2 at the stomatal cavity (An–Ci), the model was parameterized by analysing the photosynthesis response to incident light intensity (An–Iinc). Convincing evidence is provided that the maximum Rubisco carboxylation rate or the maximum electron transport rate was very similar whether derived from An–Ci or from An–Iinc data sets. Parameters characterizing Rubisco limitation, electron transport limitation, the degree to which light inhibits leaf respiration, night respiration, and the minimum leaf nitrogen required for photosynthesis were then determined. Model predictions were validated against independent sets. Only a few FvCB parameters were conserved among crop species, thus species-specific FvCB model parameters are needed for crop modelling. Therefore, information from readily available but underexplored An–Iinc data should be re-analysed, thereby expanding the potential of combining classical photosynthetic data and the biochemical model

Growth and biomass productivity of kenaf (Hibiscus cannabinus, L.) under different agricultural inputs and management practices in central Greece

The growth and biomass productivity of kenaf (Hibiscus cannabinus, L.) cultivars Tainung 2 and Everglades 41 were determined under three irrigation applications (low: 25%, moderate: 50% and fully: 100% of maximum evapotranspiration; ETm), four nitrogen dressings (0, 50, 100 and 150 kg hat), two sowing dates, and two plant densities (20 and 30 pl m(-2)) in two field experiments carried out on an representative aquic soil of western Thessaly plain (central Greece), in the period 2003-2005. The results demonstrated a paramount effect of sowing time (and thus the availability of the vegetative growing period) on crop growth and biomass productivity; delayed sowings (after mid-May) may reduce biomass production by 38%. Irrigation water had a significant effect (P 0.05) on biomass accumulation. Cultivars performed similar growth rates (no significant differences), which under full water and nitrogen inputs reached maximum growth rates of 180-220 kg ha(-1) day(-1) which may serve as reference for the assessment of crop performance under production situations at hierarchically lower input and management levels for central Greek conditions. (C) 2010 Elsevier B.V. All rights reserved

Switchgrass (Panicum virgatum L.) nutrients use efficiency and uptake characteristics, and biomass yield for solid biofuel production under Mediterranean conditions

Switchgrass produces high amounts of biomass that can be used for solid biofuel production. In this study, the dry biomass yield vs. N-P-K nutrient uptake relations as well as the N-mineralization and the N-fertilization recovery fraction for switchgrass (cv. Alamo) were determined under field conditions for three N-fertilization (0, 80 and 160 kg ha(-1)) and for two irrigation (0 and 250 mm) levels, in two soils in central Greece with rather different moisture status over the period 2009-2012. It was found that dry biomass yield on the aquic soil may reach 27-30 t ha(-1) using supplemental irrigation, and remain at high levels (19-24 t ha(-1)) without irrigation. In the xeric soil, however, lower biomass yields of 14 -15 t ha(-1) may be produced with supplemental irrigation. The average N-concentration varies between 0.23% in stems and 1.10% in leaves, showing the very low needs in N. P-content varies between 0.16% in leaves and 0.03% in stems, whereas K-content fluctuates between 0.67% and 0.78%. Linear biomass yield-nutrient uptake relationships were found with high R-2, pointing to nutrient use efficiencies of 240 and 160 kg kg(-1), for N and K respectively. The base N-uptake ranged 70-84 kg ha(-1) in the aquic to 60 kg ha(-1) or less in the xeric soil. N-recovery fraction was about 30% in the aquic soil and lower in the xeric. Therefore, switchgrass is very promising for biomass production and its introduction in land use systems (especially in aquic soils of similar environments) should be seriously taken into consideration. (C) 2014 Elsevier Ltd. All rights reserved

Assessing interrill erosion rate from soil aggregate instability index, rainfall intensity and slope angle on cultivated soils in central Greece

In order to develop anew formula for assessing interrill erosion rate by incorporating the soil aggregate instability index, beta, erosion plots at seven sites in central Greece were used to measure interrill erosion rate under natural rainfall conditions during, a 39-month period. Soils classified as Alfisols, Inceptisols and Entisols with slopes 7-21%. moderately well to excessively drained, clay to loamy textured. were Studied. Runoff and total sediment were collected after each ponding rainfall event. The equation E-i = 0.628 beta S-t(1.3) e(0.6967/30) was finally proposed (R-2 = 0.939. P < 0.001) to describe interrill erosion rate. The term, S-t represents the tangent of the slope angle, and 130 represents the maximum rainfall intensity in 30 min. The addition of the aggregate instability index to improve existing methodologies provide was considered to provide an easy to determine and reliable measure of soil erodibility. Validation with independent data showed that the model predicted interrill erosion well (R-2 = 0.766. P < 0.001). Therefore, the proposed model based on the aggregate instability index, beta, has the potential to improved methodology for assessing interrill erosion rate. (C) 2004 Elsevier B.V. All rights reserved

The effect of land parameters on vegetation performance and degree of erosion under Mediterranean conditions

Important land parameters such as soil texture, soil depth, topography, parent material, and climatic conditions were studied in a semi-detailed soil survey conducted in the island of Lesvos, and were related to the vegetation performance and degree of erosion. Rainfall data indicated that the island could be divided into two major climatic zones: a semi-acid (western part) and a dry sub-humid (eastern part). A 45% rainfall gradient has been recorded in the above two climatic zones. The great reduction in rainfall combined with the higher evapotranspiraton demands in the semi-arid zone has significantly affected vegetation performance and degree of erosion in the area. Due to the general lack of available water, the semi-arid part of the island is dominated by poor marquis vegetation, while olive trees, oak and pine forests prevail in the dry sub-humid part under similar topogaphical and geomorphological conditions. Vegetation cover increases with increasing rainfall and soil depth. Slope grade has a variable effect on soil erosion in the various climatic zones. Erosion is decreasing with increasing rainfall for the same slope classes. Severely eroded soils prevail in the semi-arid zone with slopes greater than 12%, while slightly to moderately eroded soils are found in the dry sub-humid zone under similar slope classes. The highest rates of land degradation have been measured in areas with soils formed on pyroclastic formations. Areas with soils formed on basic igneous rocks, shale and lava are well vegetated and protected from erosion under a broad range of slopes and weather conditions. (C) 2000 Published by Elsevier Science B.V. All rights reserved

Creation of a remote sensing unmanned aerial system (UAS) for precision agriculture and related mapping applications

Our goal is to create a fully autonomous airborne remote sensing platform, for the production of various vegetation indices to determine growth, development, yield crop and provide considerable information in real time and at low cost (compared with existing methods) for the study area. The primary tool for extraction and production of the information is an unmanned aerial system (UAS) that carries sensors and cameras flying over the study area, transmitting real time data that has been programmed to collect. The collected data is land cover, geographic location, weather data, geomorphologic and cadastral data, ortho-corrected derivatives and qualitative data type coverage, biomass and other parameters that have been introduced to the platform via computational GIS routines. This idea emerged during the analysis of the functional ecology in Greek agro-ecosystems within spatial information and mapping. To take full advantage of dynamic tools of IT, such as Geographic Information Systems and Expert Systems, Global Positioning Systems, Remote Sensing and Agriculture Engineering tools. The platform named "Skiptrovamon" has numerous applications and is used as a tool in many scientific fields, such as; precision agriculture, geography, geomorphology, topography, urban geography, and remote sensing. Skiptrovamon was designed and has been tested as remote sensing platform for precision agriculture. As the aircraft flies over the study area it collects information from cropland and outputs, yield crop, current biomass, indicate the stressed plants and possible lack or adequate irrigation and fertilization in real time through computational routines. Copyright © (2013) by the American Society for Photogrammetry & Remote Sensing

Potential growth and biomass productivity of Miscanthus x giganteus as affected by plant density and N-fertilization in central Greece

The potential growth and biomass productivity of Miscanthus x giganteus was investigated under constraint-free conditions during two years with appreciable different climatic conditions in central Greece, and under three different plant densities (0.66, 1, 2 pl m(-2)) and two different nitrogen dressings (N-0 = 50, N-1 = 100 kg N ha(-1)). The field experimental design was a 3 x 2 factorial split plot in four blocks. Plant height, tiller number, leaf area index and dry weight per plant component were measured in subsequent harvests throughout the growing periods of 2001 and 2002. It was found that fertilisation within the studied rates did not affect growth and biomass productivity of the crop, and no interaction between fertilization and plant density was observed in any of the samplings. Contrary to fertilization, a significant effect of plant density was found, with the denser populated plants (10,000-20,000pl ha(-1)) performing growth rates of 250-350kg ha(-1) d(-1) for large parts of the growing period, reaching maximum dry biomass yields in excess of 38t ha(-1) in the more favorable year, 2002, and 28 tha(-1) in the warmer and drier year 2001. Such high yield potentials were explained by the particularly great assimilation rates of this crop that were also measured under light saturation and optimum temperature and water regimes. With such biomass yields (11.2-15.2 t ha(-1) oil equivalent), obtainable particularly under modest fertilisation needs, Miscanthus sinensis should be considered as a very promising crop for biomass production in Greece in the near future. (c) 2006 Elsevier Ltd. All rights reserved

The effect of water vapour adsorption on soil moisture content under Mediterranean climatic conditions

The effect of water vapour adsorption on the soil moisture content of different soils under semi-arid climatic conditions (Greece) was evaluated. Time domain reflectometers were used for continuously monitoring soil moisture content at various depths. Water vapour adsorption by the soil was measured using weighing lysimeters. The obtained data indicated that nighttime water vapour adsorption is very important for areas characterised by high oscillation of air humidity. In a period of 8 months, viz. from February to August 1996, a total amount of 226 mm of water vapour was adsorbed by the soil, while the total rainfall was only 179 mm in the same period. Water vapour adsorption was found to be responsible for the diurnal fluctuations of the volumetric soil moisture content. This fluctuation was related to the clay content, the depth and the initial moisture content of the soil, Water vapour adsorption could be related to the soil moisture tension of the uppermost soil layer, the daily minimum value, and the amplitude of air humidity. Rock fragments restricted water vapour adsorption, but their contribution to the reduction in evaporation was greater under certain climatic conditions. (C) 1998 Elsevier Science B.V

Effects of Pea Cultivation as Cover Crop on Nitrogen-Use Efficiency and Nitrogen Uptake by Subsequent Maize and Sunflower Crops in a Sandy Soil in Central Greece

The long-term positive effects of cropping systems involving rotation with cover crops on soil properties and the environment are well recognized. The present work concerns a 3-year field experiment focusing on two cropping systems including two energy crops [maize (Zea mays L.) and sunflower (Helianthus annuus L.)] cultivated May-September on an infertile sandy soil, and Pisum sativum cultivated as cover crop after the harvest of the energy crop. Soil samples from two soil layers, 0-20 cm and 20-40 cm deep, were collected at the beginning and end of the experiments; they were analyzed for soil physical and chemical properties such as soil moisture properties, total nitrogen (N), phosphorus (P), potassium (K), pH, organic matter, and organic carbon (C). The results demonstrated the effect of pisum intercropping on the performance of the subsequent energy crop. These results are particularly important for the cultivation of less fertile soils such as sandy soils, which can be put in use for the production of energy crops such as maize and sunflower, which are characterized by high nutrientparticularly Ndemand

Assessing the efficiency of switchgrass different cultural practices for pellet production

Switchgrass is a perennial crop producing high amounts of biomass for good quality pellet production. The objective of this study is to examine the efficiency of different cultural practices of switchgrass for pellet production under field conditions for four different N-fertilization (0, 80, 160 and 240 kg ha(-1)) and two different irrigation levels (0 and 250 mm), in two soils in central Greece with rather different moisture status over the period 2009-2012. Moreover, comparison between three harvest methods (two different types of bales and silage) was made. The results derived from this study revealed that the bale at 22 kg is the harvesting practice with the highest costs while there was reduction of efficiency scores when nitrogen levels increased. At both environments the efficiency scores followed the same trend, confirming that low levels of nitrogen fertilization enhance the economic competitiveness of switchgrass production. Palamas site is the area where switchgrass for pellet production had positive income ranging from 400 to 1600 (sic)ha(-1), while Velestino site had always negative. Therefore, places like Velestino with non-aquic soil should be avoided for switchgrass. These data suggest that growing switchgrass for solid biofuel production as energy crop is a worthwhile decision only in areas with a moderately shallow groundwater table (aquic soil) or maybe in high precipitation regions. (C) 2014 Elsevier Ltd. All rights reserved