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- O que fazem as oliveiras de noite ou redistribuição hidráulica num olival de sequeiro no AlentejoPublication . Ferreira, Maria Isabel; Conceição, N.; Pacheco, C.A.; Green, S.Hydraulic redistribution is a mechanism that ensures the survival of superficial roots in dry soil during late summer, as they are submitted during part of the day to a negative flux, coming from roots with access to deep water. This mechanism also enables the plant to continue exploring these upper soil layers, richer in minerals and organic matter and has been observed in many ecosystems, including Montado, in Portugal. A critical question arises: to which extent is the survival of traditional rainfed ecosystems dependent on the water table condition? In order to identify the importance and dynamic of this process in olive groves, a study was conducted in South Portugal using two different, independent methods to follow sap flow in roots. We report the first results obtained with a modified heat pulse method, in a rainfed olive grove. By following roots sap flow from wet spring, 6 months without significant rain and early autumn, we found experimental evidence of hydraulic redistribution from some roots to others
- Medição da evapotranspiração de um coberto vegetal por métodos micrometeorológicos: o método das flutuações instantâneasPublication . Valente, Fernanda; Paço, Teresa Afonso do; Ferreira, Maria IsabelA quantificação do consumo de água pelos diversos cobertos vegetais é fundamental para uma gestão sustentável dos recursos hídricos. Neste artigo é apresentado o método das flutuações instantâneas (eddy covariance na terminologia anglo-saxónica), um método direto para a medição da evapotranspiração. Para além da descrição do método e dos instrumentos necessários à sua aplicação, apresentam-se alguns aspetos práticos a ter em consideração na implementação desta técnica e as principais correções a efetuar na fase de processamento dos dados. Descreve-se ainda a medição de outras componentes do balanço energético, em particular, do fluxo de calor sensível à superfície do solo e aborda-se resumidamente o problema do fecho do balanço de energia. No final é feita uma síntese dos ensaios experimentais onde este método foi aplicado por equipas do Instituto Superior de Agronomia, da Universidade de Lisboa.
- Seasonal variation of water uptake of a Quercus suber tree in Central PortugalPublication . Nadezhdina, Nadezhda; Ferreira, Maria Isabel; Silva, R.; Pacheco, C.A.Hydraulic redistribution (HR) is the phenomenon where plant roots transfer water between soil horizons of different water potential. When dry soil is a stronger sink for water loss from the plant than transpiration, water absorbed by roots in wetter soil horizons is transferred toward, and exuded into dry soil via flow reversals through the roots. Reverse flow is a good marker of HR and can serve as a useful tool to study it over the long-term. Seasonal variation of water uptake of a Quercus suber tree was studied from late winter through autumn 2003 at Rio Frio near Lisbon, Portugal. Sap flow was measured in five small shallow roots (diameter of 3–4 cm), 1 to 2 m from the tree trunk and in four azimuths and at different xylem depths at the trunk base, using the heat field deformation method (HFD). The pattern of sap flow differed among lateral roots as soil dried with constant positive flow in three roots and reverse flow in two other roots during the night when transpiration ceased. Rain modified the pattern of flow in these two roots by eliminating reverse flow and substantially increasing water uptake for transpiration during the day. The increase in water uptake in three other roots following rain was not so substantial. In addition, the flux in individual roots was correlated to different degrees with the flux at different radial depths and azimuthal directions in trunk xylem. The flow in outer trunk xylem seemed to be mostly consistent with water movement from surface soil horizons, whereas deep roots seemed to supply water to the whole cross-section of sapwood. When water flow substantially decreased in shallow lateral roots and the outer stem xylem during drought, water flow in the inner sapwood was maintained, presumably due to its direct connection to deep roots. Results also suggest the importance of the sap flow sensor placement, in relation to sinker roots, as to whether lateral roots might be found to exhibit reverse flow during drought. This study is consistent with the dimorphic rooting habit of Quercus suber trees in which deep roots access groundwater to supply superficial roots and the whole tree, when shallow soil layers were dry.
- Nota introdutóriaPublication . Ferreira, Maria Isabel; Lopes, João Rui Rolim Fernandes Machado; Paço, Teresa Afonso do; Paredes, Paula Cristina Santana; Fernandes, Maria Rosário
- Within-row advection and stomatal conductance of an irrigated cropPublication . Ferreira, Maria IsabelThe effects of soil water deficit (edaphic stress) and air vapour-pressure-deficit (atmospheric stress) on stomatal conductance of tomato (Lycopersicon esculentum Mill.) were separately analysed for the range of predawn leaf water potential (Ψp) normally observed in an irrigated crop. Three separate experiments under field conditions were used. In this respect, the main experimental results were: (i) noon stomatal conductance (gs) correlated well with Ψp but poorly with leaf water status expressed via noon leaf water potential; (ii) the scattering sometimes obtained in the relationship between Ψp and gs, for high values of Ψp (above -0.4 MPa) can be explained by a preponderant effect of air vapour-pressure-deficit on stomatal behaviour, compared to the effect of soil water deficit; (iii) the reason for the change on leaf-to-air VPD, responsible for the stomatal closure seems to be the clothesline effect i.e. the positive within-row advection from dry inter-row space. The discussion suggests that the slope of the relationship Ψp - gs can change with the soil cover, the size of the plots and their surrounding conditions. What we observed for this crop and irrigation system is extendable to other crops with important dry soil around, to analyse the implications of the air humidity near the leaves on the stomatal behaviour and water fluxes. This hypothesis can also explain opposite tendencies on the transpiration versus evapotranspiration efficiency.
- Medições de fluxo de seiva pela equipa de Engª Rural do ISA - balanço de 30 anos de experiências e aspectos metodológicosPublication . Ferreira, Maria Isabel; Paço, Teresa Afonso do; Silvestre, José; Silva, Rodolfo; Conceição, NunoAs técnicas de medição do fluxo de seiva (FS) são apresentadas como a alternativa viável para obter longas séries contínuas do uso da água pelas plantas lenhosas, embora não apresentem a fiabilidade das técnicas micrometeorológicas, designadamente a mais apropriada para cobertos altos, a das flutuações instantâneas (conhecida como de eddy covariance) que exige grandes extensões uniformes e em que as medições nem sempre são contínuas devido a condições meteorológicas adversas, mas que serve de referência em articulação com medições de evaporação do solo. Com estas técnicas de FS obtêm-se valores que, à escala diária, aproximadamente correspondem à transpiração, a principal componente da evapotranspiração. Existem muitas abordagens diferentes, sendo que a técnica de dissipação de calor designada por de Granier se tornou popular pela sua aparente simplicidade e baixo custo, embora a sua aplicação em comparação com técnicas de referência tenha evidenciado a necessidade de resolver vários problemas. Esta contribuição apresenta uma visão geral da aplicação desta técnica, seu desenvolvimento e resultados desde 1992, pela equipa de Engenharia Rural (ER) do ISA. Inclui-se a breve descrição do princípio, sensores, instalação, tratamento de dados, identificação das principais dificuldades e algumas soluções encontradas para minimizar erros, bem como a comparação com as técnicas de referência mencionadas, permitindo uma calibração caso-a-caso, de forma a obter longas séries fiáveis. Usou-se ainda uma simulação do campo das temperaturas pelo método das diferenças finitas e simulações em laboratório, para lidar com questões como a que foi designada por gradiente natural, a heterogeneidade azimutal e radial, a mudança de escala espacial, as equações de calibração. Este intenso trabalho pioneiro permitiu quantificar o uso da água por longos períodos em muitos e representativos cobertos florestais e agrícolas, em regadio ou em sequeiro, obtendo-se ainda a informação complementar para diagnosticar o estado hídrico, para interpretar os resultados e assim contribuir para afinar modelos de uso da água para a respectiva gestão, designadamente os coeficientes culturais e de stress para uso na rega.
- Evaluation of the effect of irrigation on biometric growth, physiological response and essential oil of Mentha spicata (L.)Publication . Marino, Stefano; Ahmad, Uzair; Ferreira, Maria Isabel; Alvino, ArturoA field experiment was performed on spearmint (Mentha spicata L.) under different irrigation regimes in a hilly area of Southern Italy. Objectives of the study include evaluating the physiological and biometrical response of mint from plant establishment up to its complete maturation, as well as the yield composition in essential oil at two different dates. Increasing levels of water stress affected later developing leaves and plant’s water status and net photosynthesis (from the beginning of stress (DAT 63), while affecting negatively the biometric response very soon and significantly from 35 DAT. Photosynthesis limitation played a critical role from DAT 53 on, namely later, in the harvest period (DAT 35–70). Under severe water stress, crop restricted water losses by modulating stomatal closure and, at harvest, showing lowered mesophyll conductance. Irrigation treatments did not affect the concentration of organic compounds, while the yield of essential oils was negatively affected by water stress due to reduced crop growth, in terms of total and leaf biomass, leaf area index (LAI) and crop height
- The N-P-K soil nutrient balance of portuguese cropland in the 1950s: the transition from organic to chemical fertilizationPublication . Carmo, Miguel; Garcia-Ruiz, Roberto; Ferreira, Maria Isabel; Domingos, TiagoAgricultural nutrient balances have been receiving increasing attention in both historical and nutrient management research. The main objectives of this study were to further develop balance methodologies and to carry out a comprehensive assessment of the functioning and nutrient cycling of 1950s agroecosystems in Portugal. Additionally, the main implications for the history of agriculture in Portugal were discussed from the standpoint of soil fertility. We used a mass balance approach that comprises virtually all nitrogen (N), phosphorus (P) and potassium (K) inputs and outputs from cropland topsoil for average conditions in the period 1951–56. We found a consistent deficit in N, both for nationwide (−2.1 kg.ha−1.yr−1) and arable crops (−1.6 kg.ha−1.yr−1) estimates, that was rectified in the turn to the 1960 decade. P and K were, in contrast, accumulating in the soil (4.2–4.6 kg.ha−1.yr−1 and 1.0–3.0 kg.ha−1.yr−1, respectively). We observed that the 1950s is the very moment of inflection from an agriculture fertilized predominantly through reused N in biomass (livestock excretions plus marine, plant and human waste sources) to one where chemical fertilizers prevailed. It is suggested that N deficiency played an important role in this transition
- Transpiration reduction as an answer to water stress: models versus measurements for irrigated olive trees in South PortugalPublication . Lourenço, S.; Conceição, N.; Losada, H.P.; Silvestre, J.; Siqueira, J.; Santos, F.; Rolim, J.; Ferreira, Maria IsabelThe so-called stress functions, allowing quantification of transpiration or evapotranspiration reduction, as an answer to water deficit stress (stress coefficient, Ks), are useful tools for irrigation scheduling. It is known that this coefficient depends on several variables and parameters, such as evapotranspiration rate, root patterns/density and soil properties. However, the most common Ks models with practical applicability do not include some of these factors and the experimental work on this matter is not abundant. A well-known model proposed in the FAO 56 manual uses two parameters: the allowable depletion (p) and the total available soil water (TAW) in the root zone, the input variable being the soil water depletion (SWD). We discuss the application of this model in olive trees under specific natural conditions. Two studies were conducted in Alentejo, South Portugal (2011 and 2017), in one intensive and one super intensive drip irrigated olive orchards (Olea europaea 'Arbequina'). Transpiration reduction was obtained from sap flow measurements. For both experiments, Ks was related to the estimated SWD. The experimental relationship was compared with modelling outputs. Experimental results show that, in both experiments, the Ks FAO 56 model only fits using parameters such as p= 0.05 and TAW = 350 mm. The suggested p in that manual is 0.7. Furthermore, for such soils, anisotropic canopy and small wetted area (drippers), 350 mm is much more than first approach estimates would suggest. The results can be related with the root system functioning and resilience of olive trees
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