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Crop Canopies (crop + canopy)
Selected AbstractsSimulation of the three-dimensional distribution of the red:far-red ratio within crop canopiesNEW PHYTOLOGIST, Issue 1 2007Michaėl Chelle Summary ,,It is widely recognized that the red:far-red ratio (,) acts as a signal that triggers plant morphogenesis. New insights into photomorphogenesis have been gained through experiments in controlled environments. Extrapolation of such results to field conditions requires characterization of the , signal perceived by plant organs within canopies. This paper presents a modeling approach to characterize this signal. ,,A wheat (Triticum aestivum) architectural model was coupled with a three-dimensional light model estimating the irradiances of virtual sensors. Architectural parameters and , values were measured on two contrasting spring wheat canopies under outdoor conditions. Light simulations were compared with measurements, and an analysis of sensitivity to measurement conditions was carried out. ,,The model results agreed well with measurements and previously published data. The sensitivity analysis showed that , strongly depends on canopy development as well as on sky conditions, sensor orientation, and sensor field of view. ,,This paper shows that modeling enables investigation of , distribution in a canopy over space and time. It also shows that the characterization of light quality strongly depends on measurement conditions, and that any discrepancies in results are likely attributable to different experimental set-ups. The usefulness of this modeling approach for crop photomorphogenesis studies is discussed. [source] Would transformation of C3 crop plants with foreign Rubisco increase productivity?PLANT CELL & ENVIRONMENT, Issue 2 2004A computational analysis extrapolating from kinetic properties to canopy photosynthesis ABSTRACT Genetic modification of Rubisco to increase the specificity for CO2 relative to O2 (,) would decrease photorespiration and in principle should increase crop productivity. When the kinetic properties of Rubisco from different photosynthetic organisms are compared, it appears that forms with high , have low maximum catalytic rates of carboxylation per active site (kcc). If it is assumed that an inverse relationship between kcc and , exists, as implied from measurements, and that an increased concentration of Rubisco per unit leaf area is not possible, will increasing , result in increased leaf and canopy photosynthesis? A steady-state biochemical model for leaf photosynthesis was coupled to a canopy biophysical microclimate model and used to explore this question. C3 photosynthetic CO2 uptake rate (A) is either limited by the maximum rate of Rubisco activity (Vcmax) or by the rate of regeneration of ribulose-1,5-bisphosphate, in turn determined by the rate of whole chain electron transport (J). Thus, if J is limiting, an increase in , will increase net CO2 uptake because more products of the electron transport chain will be partitioned away from photorespiration into photosynthesis. The effect of an increase in , on Rubisco-limited photosynthesis depends on both kcc and the concentration of CO2 ([CO2]). Assuming a strict inverse relationship between kcc and ,, the simulations showed that a decrease, not an increase, in , increases Rubisco-limited photosynthesis at the current atmospheric [CO2], but the increase is observed only in high light. In crop canopies, significant amounts of both light-limited and light-saturated photosynthesis contribute to total crop carbon gain. For canopies, the present average , found in C3 terrestrial plants is supra-optimal for the present atmospheric [CO2] of 370 µmol mol,1, but would be optimal for a CO2 concentration of around 200 µmol mol,1, a value close to the average of the last 400 000 years. Replacing the average Rubisco of terrestrial C3 plants with one having a lower and optimal , would increase canopy carbon gain by 3%. Because there are significant deviations from the strict inverse relationship between kcc and ,, the canopy model was also used to compare the rates of canopy photosynthesis for several Rubiscos with well-defined kinetic constants. These simulations suggest that very substantial increases (> 25%) in crop carbon gain could result if specific Rubiscos having either a higher , or higher kcc were successfully expressed in C3 plants. [source] A model of the effect of fungicides on disease-induced yield loss, for use in wheat disease management decision support systemsANNALS OF APPLIED BIOLOGY, Issue 1 2007A. Milne Abstract A model of the effect of foliar-applied fungicides on disease-induced yield loss is described, parameterised and tested. The effects of fungicides on epidemics of Septoria tritici (leaf blotch), Puccinia striiformis (yellow rust), Blumeria graminis f.sp. tritici (powdery mildew) and Puccinia triticina (brown rust) on winter wheat were simulated using dose,response curve parameters. Where two or more active substances were applied together, their joint action was estimated using an additive dose model where the active substances had the same mode of action or a multiplicative survival model where the modes of action differed. By coupling the model with models of wheat canopy growth and foliar disease published previously, it was possible to estimate disease-induced yield loss for a prescribed fungicide programme. The difference in green canopy area and, hence, interception of photosynthetically active radiation between simulated undiseased and diseased (but treated) crop canopies was used to estimate yield loss. The model was tested against data from field experiments across a range of sites, seasons and wheat cultivars and was shown to predict the observed disease-induced yield loss with sufficient accuracy to support fungicide treatment decisions. A simple method of accounting for uncertainty in the predictions of yield loss is described. Fungicide product, dose and spray timing combinations selected using the coupled models responded appropriately to disease pressure and cultivar disease resistance. [source] Effect of spray application technique on spray deposition in greenhouse strawberries and tomatoesPEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 2 2010Pascal Braekman Abstract BACKGROUND: Increasingly, Flemish greenhouse growers are using spray booms instead of spray guns to apply plant protection products. Although the advantages of spray booms are well known, growers still have many questions concerning nozzle choice and settings. Spray deposition using a vertical spray boom in tomatoes and strawberries was compared with reference spray equipment. Five different settings of nozzle type, size and pressure were tested with the spray boom. RESULTS: In general, the standard vertical spray boom performed better than the reference spray equipment in strawberries (spray gun) and in tomatoes (air-assisted sprayer). Nozzle type and settings significantly affected spray deposition and crop penetration. Highest overall deposits in strawberries were achieved using air-inclusion or extended-range nozzles. In tomatoes, the extended-range nozzles and the twin air-inclusion nozzles performed best. Using smaller-size extended-range nozzles above the recommended pressure range resulted in lower deposits, especially inside the crop canopy. CONCLUSIONS: The use of a vertical spray boom is a promising technique for applying plant protection products in a safe and efficient way in tomatoes and strawberries, and nozzle choice and setting should be carefully considered. Copyright © 2009 Society of Chemical Industry [source] |