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A novel cultivation method that aims to produce high-quality satsuma mandarin (Citrus unshiu Marc.) fruit and other types of citrus fruits was proposed in 2000, in order to meet the market demand for high-quality fruits (i.e., fruits with high sugar content and moderate acidity); this method is called the marudori method. The main feature of this method is the combined drip fertigation with conventional plastic sheet mulching, both of which control tree moisture. Tree moisture management is crucial for the production of high-quality citrus, particularly satsuma mandarins. Therefore, proper active moisture control techniques are required in Japan, where precipitation may vary considerably. Sheet mulching is a conventional technique in which trees are subjected to water stress, which increases the sugar content of fruits. Additionally, drip fertigation is a technique for effective watering and fertilizing, but not commonly used in citrus cultivation in Japan. The combination of these techniques allows this method to provide such benefits as improved fruit quality, efficient fertilization, and enhanced growth of young trees, among others. In this review, we describe this method in detail and discuss the challenges encountered during the improvement and enhancement of the marudori method, with the aim of establishing an objective cultivation system integrated with ICT and other scientific techniques. Discipline: irrigation, drainage and reclamation; horticulture Additional key words: drip irrigation, fruit quality, marudori method, moisture control, satsuma mandarin *Corresponding author: e-mail shima@affrc.go.jp Received 11 May 2015; accepted 7 January 2016. Introduction 1. Importance of tree moisture management in citrus cultivation Citrus is one of the most important crops in fruit cultivation in Japan. While many different types of citrus fruits are cultivated, satsuma mandarin (Citrus unshiu Marc.) has been the predominant fruit cultivated in Japan for many years. The production of high-quality fruits, including citrus fruits, has become critical in the Japanese fruit market. This is because the demand for high-quality fruits has been growing along with the continuing diversification of consumer needs. Moreover, there has been growing demand for the export of high-quality fruits. High-quality citrus fruits are generally defined as those having a high sugar content and moderate acidity. The history of tree moisture during the growth stage strongly affects the quality of mature citrus fruits. Water stress during the growth stage of fruit increases both sugar content and acidity. Notably, trees should be maintained under moderate water stress during certain periods in the summer and autumn, e.g., from late August to early December (Yakushiji et al. 1996). In conventional outdoor citrus cultivation, however, tree moisture is roughly controlled with rain-fed or sprinkler irrigation systems. Thus, in order to produce high-quality citrus fruits, tree moisture management techniques are critical. 2. Instability of precipitation in Japan Japan’s annual precipitation falls within the range of 1000 to 2000 mm, or about twice the world average. However, short-term fluctuations in precipitation are considerably large. For example, while there may be 200 days without rainfall, over 100 mm of rain may fall in one day during an average year in Tokyo. There are two climate factors affecting heavy precipitation in Japan. One is the

A Method for High-Quality Citrus Production Using Drip Fertigation and Plastic Sheet Mulching