High Soil pH and Plastic-Shed Lead to Iron Deficiency and Chlorosis of Citrus in Coastal Saline–Alkali Lands: A Field Study in Xiangshan County

Citrus are one of the most important fruit crops in the world, and the citrus hybrid cv. Beni-Madonna (BM) is widely cultivated in Xiangshan County in China because of its profitability. However, due to the lack of technical guidance and management, nutritional unbalances of trees occur frequently and are a major constraint for fruit quality and yield. In this study, the soil and fruit nutritional status of 62 citrus orchards in three diverse landforms (mountain, flat, and coastal saline–alkali land) located in Xiangshan County has been investigated. Higher pH, calcium, and magnesium content but lower soil organic matter, nitrogen, iron, and boron content were observed in orchards of the coastal saline–alkali land compared with the mountain and flat lands. Compared to Citrus x unshiu, another major hybrid citrus cultivar in Xiangshan county, the Fe deficiency in fruits of BM in coastal saline–alkali lands was more severe, leading to chlorosis symptoms. In addition, long-term cultivation under plastic housing increased soil salinization and affected the absorption of Fe and other nutrients by BM. In conclusion, organic fertilizers, acidic fertilizers, and micronutrient fertilizers should be applied in citrus orchards located in coastal saline–alkali lands. Especially, BM orchards should be supplemented with iron fertilizer and not rely excessively on protection with plastic films.