Necessidades Hídricas e Resposta da Oliveira (olea europaea l.) Ao Deficit Hídrico na Região da Terra Quente
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Data
2008
Autores
Silva, Anabela Afonso Fernandes
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A oliveira (Olea europaea L.) tem sido tradicionalmente cultivada em condições de sequeiro. Contudo, nos últimos anos tem-se assistido a uma expansão do olival em condições de regadio, o que tem suscitado uma série de questões, nomeadamente sobre as necessidades hídricas e a resposta produtiva resultante. Foi neste sentido que se traçaram os objectivos gerais desta desta Tese: quantificar as necessidades de rega e caracterizar a resposta produtiva da oliveira na cv. “Cobrançosa” em função de diferentes dotações de água de rega. Assim, o estudo experimental realizou-se durante três anos consecutivos (2004-06) num olival comercial da cv. “Cobrançosa” (12 anos,
6x6 m) nas condições edafoclimáticas da região da Terra Quente em Trás-os-Montes. A parcela experimental foi constituída por três subparcelas adjacentes, as quais foram submetidas a três tratamentos de rega: T0-sequeiro, T1-rega deficitária (30-50%ET) e T2-rega máxima (100%ET).
O estudo focou o efeito da rega no crescimento vegetativo, na utilização da água, na produtividade (frutos e azeite), na composição química e qualidade do azeite, nas eficiências do uso da água (WUE) e da radiação (RUE) e na resposta fisiológica. A evapotranspiração anual (ET) variou de 295 mm no tratamento de sequeiro (T0) a 700 mm no de rega máxima (T2). Os valores da ET para o tratamento de rega deficitária (T1) variaram entre 64% a 80% da ET do T2, dependendo do ano. As necessidades estacionais de rega, para o tratamento bem regado (T2) foram cerca de 1900 m3 ha-1, o que representa em média 1,46 mm d-1 para um período de rega cerca de 130 dias (finais de Maio a finais de Setembro). A relação ET/ET0 obtida neste estudo revelou que a utilização de água pela oliveira é apenas influenciada pelo deficit de água no solo (DAS) quando este é superior a 60%.
Em todos os anos a rega aumentou o crescimento vegetativo, reflectindo-se num aumento da quantidade de radiação interceptada e, consequentemente, na produção. De facto, a produção foi fortemente incrementada pela rega, sendo superior no T2 47% a
88% ao T0, e 33% a 55% ao T1; enquanto no T1 foi 45% a 73 % superior ao T0.
Devido à tendência da oliveira para a alternância de produções, a resposta da produtividade (Y) em função da ET foi calculada para os dados bienais, o que resultou numa resposta do tipo linear: Y = 1,05x - 304 (r2 = 0,95) e Y = 0,35x -93 (r2 = 0,90), quer para a produtividade de frutos e quer para a de azeite, respectivamente. Este tipo de resposta mostrou a existência de um equilíbrio delicado entre a disponibilidade de águae a intercepção da radiação solar, consolidada pelos resultados das eficiências do uso da água e do uso da radiação que revelaram um aumento com a quantidade de água utilizada.
A quantidade de água aplicada afectou alguns parâmentros relacionados com a qualidade e a composição do azeite. Assim, observou-se que a rega provocou uma diminuição dos polifenóis e da estabilidade oxidativa, e um aumento do índice de peróxidos. A composição em ácidos gordos não foi influenciada pela dotação de rega, mas respondeu às variações climáticas inter-anuais. Contudo, as variações destes parâmetros não foram importantes ao ponto de condicionar a qualidade do azeite. A relação entre o potencial hídrico de base do ramo (ΨB) e o teor de água disponível (TAD) no solo permitiu identificar os seguintes valores críticos: ausência de deficit hídrico quando o ΨB>-0,70 MPa; deficit hídrico moderado para valores de ΨB que variaram entre -0,70 MPa a -2,0 MPa; deficit hídrico severo quando o ΨB<-2,0 MPa e extremamente severo quando o ΨB<-4,0 MPa (o que corresponde a TAD<10%).
As medições das trocas gasosas indicaram que, em ambos os tratamentos de rega a taxa de fotossíntese aparente (A) aumentou, enquanto que a depressão da taxa de fotossíntese e da condutância estomática (gs), observada durante os períodos do meio-dia e da tarde diminuiu. Em condições de ausência de stresse hídrico, os valores mais elevados da A e gs foram observados no Outono e os menores em dias caracterizados por elevada demanda evaporativa. Em condições de elevado deficit de pressão de vapor do ar (VPD), a oliveira previne a perda excessiva de água através da diminuição do grau de abertura dos estomas, com um decréscimo proporcional da gs com o aumento do VPD, pelo menos até 3,2 kPa no T1 e 3,9 kPa no T2. Em contraste, no T0 observou-
-se uma menor sensibilidade dos estomas com o VPD. Por outro lado, verificou-se que nas plantas do T0 em condições de deficit hídrico muito severo, a gs decresceu drasticamente quando TAD< 20%, ao contrário das plantas regadas, onde a gs mostrou-se insensível para valores de TAD> 20%. Em adição, foi observada uma ausência de, relação entre a gs e o potencial hídrico do ramo, independentemente do tratamento de rega, indicando que o efeito do estado hídrico do solo nos estomas não é mediado pelo potencial hídrico da folha. Assim, nas oliveiras em condições de deficit hídrico severo os resultados sugerem que a existência de sinais químicos e hidráulicos das raízes para as folhas podem controlar a resposta da condutância estomática ao meio ambiente.
The olive tree (Olea europaea L.) has been traditionally cultivated in the dry conditions. However, irrigated olive orchards have expanded in recent years, which has raised a number of questions, particularly about the water requirements and the resulting productive response. The general objectives of this thesis were to quantify the irrigation requirements and to characterise the response of olive cv. "Cobrançosa" to water supply. An experimental study was carried out for three consecutive years (2004-06) in an olive commercial grove of cv. "Cobrançosa" (12 years, 6x6 m) under the edaphoclimatic conditions of the Terra Quente (“Hot land”) region of Trás-os-Montes, Portugal. The experimental plot was made up of three adjacent subplots, which were submitted to three irrigation treatments, namely: T0-the drought treatment, T1-deficit irrigation (30-50% ET) and T2- full irrigation (100% ET). The study focused on the effect of irrigation supply on growth, water use, productivity (fruit and oil), the chemical composition and quality of olive oil, the water-use (WUE) and radiation-use (RUE) efficiencies and the physiological responses. The annual evapotranspiration (ET) ranged from 295 mm in the drought treatment (T0) to 700 mm with full irrigation (T2). Depending on the year, the values of ET of the deficit irrigation treatment (T1) varied from 64% to 80% of that of T2. The seasonal irrigation requirement for the full irrigation treatment (T2) was close to 1900 m3 ha-1, which on average, represents 1.46 mm d-1 for the irrigation period, which is around 130 days (end of May to late September). The ET/ET0 values obtained in this study indicate that the water-use of olive trees is only influenced by soil water deficit (DAS) above 60%. Irrigation promoted vegetative growth in all years, leading to an increase in intercepted radiation and therefore in yield. Indeed, production was strongly enhanced by irrigation, so that in the T2 treatment, it was 47% to 88% higher than in T0 and 33% to 55% than in T1, whereas yield in T1 was 45% to 73% higher than in T0. Due to the tendency of the olive tree to alternate bearing, the production function yield-ET was calculated for biennial data, resulting in Y = 1.05 x - 304 (r2 = 0.95) and Y = 0.35 x -93 (r2 = 0.90), for fruit and oil yield, respectively. This type of response showed that there is a delicate balance between the availability of water and the interception of solar radiation, strengthened by the results of the water-use and radiation-use efficiencies which showed an increase with the amount of water used. Water supply affected some parameters related to the oil quality and composition. Irrigation promoted a decline of phenolic compounds and oxidative stability and an increase of the peroxide value. Fatty acid composition was not affected by water supply but responded to inter-annual climatic variability. However, the variations of these parameters were always within the range of high quality olive oil. The relationship between the predawn shoot water potential (ΨB) and the available soil water content (TAD) allowed the identification of the following threshold values: no water deficit when ΨB>-0.7 MPa; moderate water deficit for values of ΨB ranging between -0.7 MPa and -2.0 MPa; severe water deficit for values of ΨB<-2.0 MPa and extremely harsh or severe soil water deficit when ΨB<-4.0 MPa (TAD <10%). Measurements of gas exchange indicated that in both irrigation treatments the rate of apparent photosynthesis (A) increased, while the depression of photosynthesis and stomatal conductance (gs) during the midday and afternoon period were reduced. Under no water stress conditions the higher values of A and gs were observed in autumn and the lowest in days characterised by high evaporative demand. Under high vapour pressure deficit of the air (VPD), the olive tree was able to prevent excessive loss of water through the reduction of the degree of stomata aperture, with a decrease proportional to the increase of VPD at least up to 3.2 kPa on T1 and to 3.9 kPa on T2. By contrast, in T0 there was a lower sensitivity of stomata to VPD. Furthermore, it was found that in rain-fed trees under severe soil water deficit, gs decreased dramatically when TAD <20%, unlike in the irrigated plants, where gs proved to be insensitive to TAD >20%. Additionally, no relationship was observed between gs and shoot water potential, regardless of treatment irrigation, indicating that the effect of soil water status in the stomata is not mediated by the leaf water potential. Thus, in olive trees under severe water deficit conditions, the results suggest that chemical and hydraulic signals from the roots may control the response of leaf conductance to the environment.
The olive tree (Olea europaea L.) has been traditionally cultivated in the dry conditions. However, irrigated olive orchards have expanded in recent years, which has raised a number of questions, particularly about the water requirements and the resulting productive response. The general objectives of this thesis were to quantify the irrigation requirements and to characterise the response of olive cv. "Cobrançosa" to water supply. An experimental study was carried out for three consecutive years (2004-06) in an olive commercial grove of cv. "Cobrançosa" (12 years, 6x6 m) under the edaphoclimatic conditions of the Terra Quente (“Hot land”) region of Trás-os-Montes, Portugal. The experimental plot was made up of three adjacent subplots, which were submitted to three irrigation treatments, namely: T0-the drought treatment, T1-deficit irrigation (30-50% ET) and T2- full irrigation (100% ET). The study focused on the effect of irrigation supply on growth, water use, productivity (fruit and oil), the chemical composition and quality of olive oil, the water-use (WUE) and radiation-use (RUE) efficiencies and the physiological responses. The annual evapotranspiration (ET) ranged from 295 mm in the drought treatment (T0) to 700 mm with full irrigation (T2). Depending on the year, the values of ET of the deficit irrigation treatment (T1) varied from 64% to 80% of that of T2. The seasonal irrigation requirement for the full irrigation treatment (T2) was close to 1900 m3 ha-1, which on average, represents 1.46 mm d-1 for the irrigation period, which is around 130 days (end of May to late September). The ET/ET0 values obtained in this study indicate that the water-use of olive trees is only influenced by soil water deficit (DAS) above 60%. Irrigation promoted vegetative growth in all years, leading to an increase in intercepted radiation and therefore in yield. Indeed, production was strongly enhanced by irrigation, so that in the T2 treatment, it was 47% to 88% higher than in T0 and 33% to 55% than in T1, whereas yield in T1 was 45% to 73% higher than in T0. Due to the tendency of the olive tree to alternate bearing, the production function yield-ET was calculated for biennial data, resulting in Y = 1.05 x - 304 (r2 = 0.95) and Y = 0.35 x -93 (r2 = 0.90), for fruit and oil yield, respectively. This type of response showed that there is a delicate balance between the availability of water and the interception of solar radiation, strengthened by the results of the water-use and radiation-use efficiencies which showed an increase with the amount of water used. Water supply affected some parameters related to the oil quality and composition. Irrigation promoted a decline of phenolic compounds and oxidative stability and an increase of the peroxide value. Fatty acid composition was not affected by water supply but responded to inter-annual climatic variability. However, the variations of these parameters were always within the range of high quality olive oil. The relationship between the predawn shoot water potential (ΨB) and the available soil water content (TAD) allowed the identification of the following threshold values: no water deficit when ΨB>-0.7 MPa; moderate water deficit for values of ΨB ranging between -0.7 MPa and -2.0 MPa; severe water deficit for values of ΨB<-2.0 MPa and extremely harsh or severe soil water deficit when ΨB<-4.0 MPa (TAD <10%). Measurements of gas exchange indicated that in both irrigation treatments the rate of apparent photosynthesis (A) increased, while the depression of photosynthesis and stomatal conductance (gs) during the midday and afternoon period were reduced. Under no water stress conditions the higher values of A and gs were observed in autumn and the lowest in days characterised by high evaporative demand. Under high vapour pressure deficit of the air (VPD), the olive tree was able to prevent excessive loss of water through the reduction of the degree of stomata aperture, with a decrease proportional to the increase of VPD at least up to 3.2 kPa on T1 and to 3.9 kPa on T2. By contrast, in T0 there was a lower sensitivity of stomata to VPD. Furthermore, it was found that in rain-fed trees under severe soil water deficit, gs decreased dramatically when TAD <20%, unlike in the irrigated plants, where gs proved to be insensitive to TAD >20%. Additionally, no relationship was observed between gs and shoot water potential, regardless of treatment irrigation, indicating that the effect of soil water status in the stomata is not mediated by the leaf water potential. Thus, in olive trees under severe water deficit conditions, the results suggest that chemical and hydraulic signals from the roots may control the response of leaf conductance to the environment.
Descrição
Dissertação para obtenção do grau de Doutor em Engenharia Agrícola
Palavras-chave
Olea europaea L. , Relação planta água , Relação planta solo , Fisiologia vegetal