奄美大島の商業パッションフルーツ園における施肥管理，土壌化学性，葉内ミネラルおよび果実品質の調査

抄録

High-quality passion fruit （Passiflora edulis） with low acidity for fresh consumption is demanded recently. Some recent basic findings have not been fully utilized in commercial passion fruit orchards, and so an understanding of the current situation of commercial orchards is necessary. Therefore, cultivation managements, such as fertilizer application, were interviewed and soil chemical properties, leaf mineral contents, and fruit qualities were measured at 12 commercial orchards on Amami-Oshima Island, a major production area in Japan. The annual and cumulative amounts of N, P２O５, and K２O fertilizer were calculated based on the interview data. Soil samples were collected to determine soil pH, electrical conductivity （EC）, exchangeable Ca, Mg, and K, and available P２O５ content. Leaves were collected to determine the leaf mineral content and SPAD values. Fruits were collected to determine the fruit weight, size, the juice weight, Brix, and titratable acid content. The soil in eight of the 12 orchards had excess available P２O５, and eight orchards had excess exchangeable K compared to the standard values published by Kagoshima Prefecture. The excess available P２O５ decreased Brix. The greater the amount of cattle manure compost applied, the higher the available P２ O５ content, suggesting that excessive compost application was the main cause of available P２ O５ accumulation. Leaf N content was lower than the standard value for high-quality fruit in previous studies. Therefore, increasing the amount of N applied and reducing the amounts of P and K is necessary for producing high-quality fruit. Reducing the amount of cattle manure compost and increasing chemical fertilizer containing N as ammonium sulfate and urea would be effective to this end. In four orchards, the high soil pH might have suppressed vegetative growth. Excess chemical fertilizer and/or the application of topsoil containing shells might have increased soil pH. Yields and fruit diameter decreased with increasing years of passion fruit cultivation. Interveinal yellowing leaves were observed in some orchards, though the cause could not be determined from the soil chemical properties and leaf mineral contents.