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Phenological models applied to grapevines are valuable tools to assist in the decision of cultural practices related to winegrowers and winemakers. The two-parameter sigmoid phenological model was used to estimate the three main phenological stages of the grapevine development, i.e., budburst, flowering, and veraison. This model was calibrated and validated with phenology data for 51 grapevine varieties distributed in four wine regions in Portugal (Lisboa, Douro, Dão, and Vinhos Verdes). Meteorological data for the selected sites were also used. Hence, 153 model calibrations (51 varieties × 3 phenological stages) and corresponding parameter estimations were carried out based on an unprecedented comprehensive and systematized dataset of phenology in Portugal. For each phenological stage, the centroid of the estimated parameters was subsequently used, and three generalized sigmoid models (GSM) were constructed (budburst: d = −0.6, e = 8.6; flowering: d = −0.6, e = 13.7; veraison: d = −0.5, e = 13.2). Centroid parameters show high performance for approximately 90% of the varieties and can thereby be used instead of variety-specific parameters. Overall, the RMSE (root-mean-squared-error) is < 7 days, while the EF (efficiency coefficient) is > 0.5. Additionally, according to other studies, the predictive capacity of the models for budburst remains lower than for flowering or veraison. Furthermore, the F-forcing parameter (thermal accumulation) was evaluated for the Lisboa wine region, where the sample size is larger, and for the varieties with model efficiency equal to or greater than 0.5. A ranking and categorization of the varieties in early, intermediate, and late varieties was subsequently undertaken on the basis of F values. These results can be used to more accurately monitor and predict grapevine phenology during a given season, thus supporting decision making in the Portuguese wine sector.

Key words:Preparedness measures to cope with droughts and water scarcity in semi-arid climates in irrigated agriculture include the identification of irrigation scheduling strategies that minimize the water demand with acceptable impacts on yields. Those strategies may be produced by simulation and focus on different levels of water demand. The irrigation scheduling simulation model ISAREG, validated for Tunisia, is used to simulate those strategies. The generated irrigation scheduling strategies are applied to deficit irrigation of winter wheat, tomato and potato crops under semi-arid conditions in Central Tunisia. The alternative schedules are evaluated through the combined use of indicators relative to the reduction in demand for irrigation water, the consequent yield reduction and the impacts on farmer's income. The economic evaluation of those strategies is performed with the help of a linear programming model. Results indicate that, when there is limited water availability, each crop reacts differently to the water restrictions applied in terms of yield decrease and gross margin per unit surface and unit of water applied. For average demand, the adoption of deficit irrigation is generally feasible for all crops considered. However, for the tomato crop, there is a trend to restrict the cultivated surface when water scarcity increases. Under high and very high demand conditions, the gross margin per unit of water applied decreases for the potato and the tomato crops but increases for the wheat crop. Then, adopting deficit irrigation is not feasible for the tomato and potato crops, the option being to decrease the cultivated surface. On the contrary, the wheat crop responds wen to deficit irrigation, with a good water valorisation, including under drought conditions. A. Zairi et al.The frequent occurrence of droughts requires pro-active and rational water management approaches that could be helpful to both managers and farmers. Those measures include the reinforcement of the hydraulic infrastructures, increased waste water reuse, the enforcement of restrictions on water volumes supplied for irrigation, and changes in water prices . However, their application require s better knowledge of the climatic variability and respective impact on crop yields.A recent study shows that a decrease of 10 % in water supply to cereal s and fodder crops would result in a reduction of about 2 % in the net agricultural product, mainly as a consequence of a reduction in the irrigated area (DGIRE, 1997). Irrigated wheat surface (60 000 ha) is less than 5 % of the total cereal cropped area in Tunisia but, when drought occurs, the irrigated wheat area contributes with 20 % to the total cereal production, while also playing a main role in seed production (El Amami, 1995).In order to prepare appropriate irrigation strategies for wheat and main field horticultural crops, tomato and potato, when water supply restrictions have to be imposed, the present study was performed to assess how deficit irrigation (English and Raja, 1996) could...

In the present study, we calibrated and validated thermal models to predict the DOY date at which the grape maturity index, potential alcohol/total acidity (PA/TA), reaches 0.75 (MS0.75), 1.0 (MS1), 1.5 (MS1.5), and 2.0 (MS2) for two grapevine Portuguese varieties, Touriga Nacional (TN) and Encruzado (EN), growing in the Dão wine region, Portugal. Daily rates of forcing calculated with the Sigmoid function (SM) and the Degree Day function (DD) were used. The outcomes show that the best performance of the models was obtained for the heat accumulation starting at flowering (tx = EL23). The analysis of model sensitivity to changes in forcing rate coefficients (T0, e, and d) enabled the selection of the same models for all maturity stage of each variety. The selected models revealed significant predictability, though dependent on the grape maturity stage and variety (EFF > 0.81 for TN and EFF > 0.75 for EN). The non-linear regression analyses of sugar concentration (SC) and total acidity (TA) with heat accumulation, calculated using the select models, demonstrated that a high fraction of SC and TA variance was explained by the variation of these temperature-based indices. Comparatively to SC and TA, the results highlight that the thermal conditions accumulated from flowering had a lower influence on pH juice variance.

RESUMOQuando bem aproveitados, os resíduos orgânicos conduzem a grandes benefícios disponibilizando matéria orgânica e nutriente ao solo. Neste contexto, objetivou-se, no presente estudo, verificar o efeito da aplicação de doses de composto orgânico em dois solos submetidos a diferentes compactações na biomassa seca do milho. Para isto se aplicaram, em 54 vasos, três doses de composto orgânico nas quantidades 0 (testemunha), 40 e 80 g dm -3 , em um Argissolo Vermelho Escuro e em um outro Argissolo Vermelho-Amarelo, coletados no horizonte A p , no perfil de 0 a 0,20 m, conduzidos em três diferentes densidades (1,3; 1,5 e 1,7 kg dm -3 ) e três repetições. A cultura utilizada no experimento foi o milho (Zea mays), cultivar Itapuã 700. As variáveis avaliadas foram biomassa seca da parte aérea do milho (MS) e os teores de N, P, K, Ca, Mg e carbono orgânico total (COT) do solo. Os resultados obtidos indicaram que a aplicação do composto orgânico causou efeito significativo sobre os teores dos macronutrientes disponíveis e COT e a compactação do solo pouco afetou as variáveis estudadas. Palavras-chave: aproveitamento de resíduos, adubação, densidade do solo, Zea maysEffect of compaction and organic compost application on corn biomass and macronutrient contents in soil ABSTRACT When well utilized, organic residues lead to great benefits making organic matter and nutrients available in soils. In this context, the present study had the objective to evaluate the effect of organic compost doses on two soils submitted to different compactions and on corn biomass. Thus, in 54 pots were added three doses 0, 40 or 80 g dm -3 of organic compost in a Dark Red Argisoil or Red Yellowish Argisoil, collected from the Ap horizon (depth of 0 to 0.20 m), submitted to three compaction degrees (1.3, 1.5 and 1.7 kg dm -3 ), with three replications. The crop used in the experiment was corn (Zea mays), cultivar Itapuã 700. The plant growth, and content of N, P, K, Ca, Mg and organic carbon (TOC) in soil were evaluated. The results point out that the organic compost application significantly affected soil OC and macronutrients, but little effect was induced by the soil compaction on these variables.