A study on nutrient status of microelements in soils of citrus orchards in Chongqing

Abstract：【Objective】The study evaluated the contents of microelements in soils of citrus orchards in Chongqing.【Methods】Soil samples were collected from 567 representative citrus orchards in 15 main counties (districts) of Chongqing.【Results】The range of pH value of orchard soils was 4.1-8.7. Among them, strong acid (pH-1, among them, only0.35% exceeded 30 g· kg-1. The soil available Fe content varied greatly with a range of 0.20-253.68 mg· kg-1, and its average content was 40.91 mg· kg-1. 437 soil samples were rich in available Fe (suitable, high and excessive range) , which accounted for 77.07% of the total samples, and 46.74% of the soil sampleshad excessive available Fe. Among the counties or districts, the content of available Fe in the orchard soils from Wanzhou was the highest, with all the samples in excessive range. The content of available Fe was the lowest in the soils of Wushan, where 32% soil samples were insufficient for citrus growth and 68% of the soil samples were in excess of available Fe. The available Mn content ranged from 0.16 to 100.47 mg· kg-1, and its average content was 3.36 mg· kg-1. Only 0.18% soil samples were suitable for citrus growth, and 99.82% soil samples were in insufficient range. Insufficiency of Mn was common, reaching 83.33% to 100% in different counties or districts. The available Zn content ranged from 0.12 to 14.63 mg· kg-1. 46.38% of the soil samples were deficient in available Zn, and 53.62% of the soil samples were rich in available Zn. Among the counties (districts) , Yubei, Liangping, Banan and Jiang Jin had high levels of available Zn. The soils samples in each of these counties (districts) with rich availabe Zn accounted for more than 70%. The soil available Zn content in Dianjiang, Kaizhou, Fengjie, Fuling, Wushan and Zhongxian counties was low, and the percentage of soil samples with insufficient Zn content was higher than 50%. The available Cu content was 0.17-8.56 mg · kg-1, and only 26.98% of the samples were in low range, and 73.02% of samples were in or above suitable range and 39.86 % samples were in high or excessive ranges. The counties (districts) with low soil available Cu included Banan, Fuling, Yunyang and Wushan. The available Cu content in over 40% of the soil samples was at low level in these 4 counties (districts) . The counties (districts) with high soil available Cu were Yubei, Dianjiang, Kaizhou, Liangping, Fengjie and Wanzhou. More than 80% of the soil samples in these 6 counties (districts) were in rich level. The available B was low, and its average content was 1.06 mg· kg-1.76.72% of the samples had an insufficient content, and only 23.10% were in suitable range. Changshou, Banan, Fengjie, Yunyang, Wushan and Zhongxian had more than 80% of the soil samples with insufficient available B content, which was the highest in Yubei, where only 52.78% of the samples reached the suitable level.【Conclusion】The soils of the citrus orchards in Chongqing had a wide range of pH value and a low organic matter content. The available Fe and Cu contents were medium rich; the available Zn and B contents were low; and the available Mn was deficient. For citrus orchard management, attention should be paid to adjusting soil pH value and based on leaf nutrition diagnosis, appropriate amount of supplementation of Mn, Zn and B containing fertilizers or organic fertilizers should be carried out.