Long-term impact of sustained-deficit irrigation on yield and fruit quality in sweet orange cv. Salustiana (SW Spain)

Long-term impact of different sustained-deficit irrigation (SDI) treatments on a 13-year-old orange orchard (Citrus sinensis L. Osbeck, cv. Salustiana) was studied from 2004 to 2008. The experiment consisted of a control irrigation treatment which was applied at 100% of the crop evapotranspiration (ETc) values for the whole season, and three SDIs imposed as a function of different water-stress index (WSI) values, defined as the ratio of the actual volume of water supply to the ETc rate. The values defined by the WSI were 0.75, 0.65, and 0.50. The plant-water status was measured through the midday stem-water potential (ΨStem). Yearly, yield and fruit quality were evaluated at harvest in each treatment, and a global analysis was carried out using the whole dataset. Overall, no significant differences were found in fruit yield between SDIs and control treatments, although significant differences appeared in some of the fruit-quality parameters (total soluble solids and titrable acidity) which also showed significant relationships with integrated stem-water potential (ΨInt) and irrigation water applied. These findings lead us to conclude that SDIs have important and statistically significant effects on fruit quality. Thus, the application of sustained-deficit irrigation (SDI with WSI of 50) provides promising possibilities for optimising citrus irrigation and boosting the water productivity for citrus orchards in a semiarid Mediterranean climate.Long-term impact of different sustained-deficit irrigation (SDI) treatments on a 13-year-old orange orchard (Citrus sinensis L. Osbeck, cv. Salustiana) was studied from 2004 to 2008. The experiment consisted of a control irrigation treatment which was applied at 100% of the crop evapotranspiration (ETc) values for the whole season, and three SDIs imposed as a function of different water-stress index (WSI) values, defined as the ratio of the actual volume of water supply to the ETc rate. The values defined by the WSI were 0.75, 0.65, and 0.50. The plant-water status was measured through the midday stem-water potential (ΨStem). Yearly, yield and fruit quality were evaluated at harvest in each treatment, and a global analysis was carried out using the whole dataset. Overall, no significant differences were found in fruit yield between SDIs and control treatments, although significant differences appeared in some of the fruit-quality parameters (total soluble solids and titrable acidity) which also showed significant relationships with integrated stem-water potential (ΨInt) and irrigation water applied. These findings lead us to conclude that SDIs have important and statistically significant effects on fruit quality. Thus, the application of sustained-deficit irrigation (SDI with WSI of 50) provides promising possibilities for optimising citrus irrigation and boosting the water productivity for citrus orchards in a semiarid Mediterranean climate. Impacto em longo prazo do déficit de irrigação-sustentada na produtividade equalidade dos frutos em laranjeira doce cv. Salustiana (SW Espanha)ResumoO impacto em longo prazo de diferentes tratamentos de irrigação-sustentada (SDI) em um pomarde laranjas de 13 anos de idade (Citrus sinensis L. Osbeck, cv. Salustiana) foi estudado de 2004 a2008. O experimento consistiu de um tratamento de irrigação controle que foi aplicado a 100%da evapotranspiração de cultura (ETc) para toda a temporada e três SDIs impostas em funçãode diferentes valores de estresse hídrico (WSI), definidos como a relação do volume real de águarequerido com relação à taxa de ETc. Os valores definidos pela WSI foram 0,75, 0,65 e 0,50. O statusplanta-água foi medido através do potencial de tronco-água a meio-dia (ΨStem). Anualmente, aprodução e a qualidade dos frutos foram avaliadas no momento da colheita em cada tratamento,e uma análise global foi realizada utilizando o conjunto inteiro de dados. Em geral, não foramencontradas diferenças significativas na produção de frutos entre os SDIs e os tratamentos controle,embora diferenças significativas apareceram em alguns dos parâmetros de qualidade de fruto(sólidos solúveis totais e acidez titulável), que também mostraram relações significativas compotencial tronco-água integrado (ΨInt) e água de irrigação aplicada. Essas observações levam aconcluir que as SDIs têm efeitos importantes e estatisticamente significativos na qualidade dos frutos.Assim, a aplicação do déficit de irrigação-sustentada (SDI com WSI de 50) oferece possibilidadespromissoras para otimizar a irrigação de citros e aumentar a produtividade da água para pomaresde citros em um clima semi-árido Mediterrâneo