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Th e modeling of yield response to water is expected to play an increasingly important role in the optimization of crop water productivity (WP) in agriculture. During 3 yr (2004)(2005)(2006)(2007), fi eld experiments were conducted to assess the crop response to water stress of quinoa (Chenopodium quinoa Willd.) in the Bolivian Altiplano (4000 masl) under diff erent watering conditions (from rain fed, RF, to full irrigation, FI). Crop physiological measurements and comparisons between simulated and observed soil water content (SWC), canopy cover (CC), biomass production, and fi nal seed yield of a selected number of fi elds were used to calibrate the AquaCrop model. Subsequently, the model was validated for diff erent locations and varieties using data from other experimental fi elds and from farmers' fi elds. Additionally, a sensitivity analysis was performed for key input variables of the parameterized model. AquaCrop simulated well the decrease of the harvest index (HI) of quinoa in response to drought during early grain fi lling as observed in the fi eld. Further-on, the procedure for triggering early canopy senescence was deactivated in the model as observed in the fi eld. Biomass WP (g m −2 ) decreased by 9% under fully irrigated conditions compared with RF and defi cit irrigation (DI) conditions, most probably due to severe nutrient depletion. Satisfactory results were obtained for the simulation of total biomass and seed yield [validation regression R 2 = 0.87 and 0.83, and Nash-Sutcliff effi ciency (EF) = 0.82 and 0.79, respectively]. Sensitivity analysis demonstrated the robustness of the AquaCrop model for simulation of quinoa growth and production, although further improvements of the model for soil nutrient depletion, pests, diseases, and frost are also possible. available water in the soil between fi eld capacity and permanent wilting point; WP, water productivity; WP*, water productivity, normalized for ET o ; Y, total seed yield; Z x , maximum rooting depth.

Different chemical forms of cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), lead (Pb), nickel (Ni), and zinc (Zn) were determined in agricultural soils cultivated with lettuce and celery. These soils have been irrigated for several decades with nontreated wastewaters. The chemical forms of the metals were characterized by sequential extraction analysis in five steps, the extracting solutions of which contained 200 mg L -1 nitrilotriacetic acid (NTA). The results showed that Cd, Pb, and Cu exhibited the highest values of extracted metal, and Cr exhibited the lowest value. Almost all of the metals in these soils are bound to iron oxides, followed by the metal complexed to organic matter. The form bound to manganese oxides is equally important to Co. Cadmium is the most mobile metal and its available forms account for 40% of the total extracted. When these metals were determined in plants, both shoots and roots, a greater concentration of Cr, Zn, and Cu was found in celery, and Cu, Ni, and Zn in lettuce, most of the metals being in roots. Only Cd and Co are similarly distributed in shoots and in roots. The relation between the metal contents in plants and the different fractions of the metal in soil was evaluated through linear correlations. Different results were obtained, the forms accounting for the metal in celery are those of the metal bound to iron oxides, while the metal content in lettuce would be related to the exchangeable, bound to manganese oxide, and carbonate forms.

X-ray crystallography, variable temperature 1H NMR and nuclear Overhauser effect experiments, and ab initio calculations provided evidence of the s-trans preferential conformation of captodative olefin 1-acetylvinyl p-nitrobenzoate (1a) in solid, solution, and gas phases. The reactivity of 1a in cycloaddition reactions was rationalized under the basis of experimental ionization energy and electron affinity parameters. Correlation of the latter with the frontier molecular orbitals, calculated at the ab initio 3-21G and 6-31G* levels, suggests a nonsignificant effect of the electron-donor group upon control of the reactivity and regioselectivity of these olefins in Diels−Alder reactions.

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