Migration of Chlorine in Plant–Soil–Leaching System and Its Effects on the Yield and Fruit Quality of Sweet Orange

Abstract

Chlorine (Cl) is indispensable for the growth of plants. While rarely systematic reports are available for the effect of Cl-containing fertilizers on citrus production. This study aimed to investigate the impacts of various Cl-containing fertilizers on the nutrients in the leaves, the yield and quality of sweet orange, and the Cl migration in the plant–soil–leaching system. A 5-year field experiment (2016–2020) with five Cl treatments (0, 75, 150, 450, and 900 kg ha−1), and soil core lysimeter test with five Cl levels (0, 150, 225, 300, and 450 kg ha−1) were carried out. The results showed that 77.0% of Cl leached into above 60 cm deeper soil layer, with calcium as the main accompanying ions, resulting in less Cl being absorbed by the citrus plants. The content of Cl in the leaves and soil was enhanced by the increasing input of Cl-containing fertilizer, without yearly increased characteristics, under a mean annual rainfall of 1,474 mm. Chlorine significantly increased the yield (13.24–37.8 9%), fruit weight, and vitamin C (Vc), in addition to enhancing the flavor and the juice yield of sweet orange via improving the absorption of N and K. Moreover, the long-term application of potassium sulfate has elevated the accumulation of sulfur in the soil and in leaves; it is becoming a potential risk factor for citrus production. Taken together, the application of Cl-containing fertilizer in sweet orange is feasible, and trace absorbance of Cl could improve the yield and fruit quality of sweet orange.

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“…These processes are most common during the rainy season, which lasts from March to August [53]. During the months of June to September, the Cl dissolving rate was higher than the leaching rate, but the converse was true from September to December, which helps to explain why the soil Cl concentration was highest in September [53]. There was a difference (although minor) in SO4 2− concentration between CF and Cl − treatments (Table 2).…”

“…Thus, it indicated that Cl and S contents were remarkably greater compared to other cations in the leachate [53]. In addition, the bioavailable form of S in the soil was SO4 2− , thus fluctuation in cationic migration might be due to the lower solubility of CaSO4, causing a slower migration of SO4 2− in the soil than Cl [53]. Another reason is the strong absorption capability of iron and aluminum oxides for SO4 2− , which may be higher in acidic soil [57].…”

“…Due to the heavy rains, Cl-containing fertilizer disintegrated quickly, causing diffusion and leaching. These processes are most common during the rainy season, which lasts from March to August [53]. During the months of June to September, the Cl dissolving rate was higher than the leaching rate, but the converse was true from September to December, which helps to explain why the soil Cl concentration was highest in September [53].…”

“…Thus, Cl movement in soil is mostly influenced by water fluxes [52]. Liu et al reported that the Cl level in soil enhanced significantly after being fertilized with Clborne fertilizer at depth (0-60 cm), but the Cl concentration in the soil could not rise during continuous addition over 5 years with an average precipitation of 1475 mm in the field trial [53]. Due to the heavy rains, Cl-containing fertilizer disintegrated quickly, causing diffusion and leaching.…”

“…The discharge of cations rose, thus leach loss further improved in the acidic soil [55] containing Cl, N-NO3, as well as S as the key concomitant anions [56]. Thus, it indicated that Cl and S contents were remarkably greater compared to other cations in the leachate [53]. In addition, the bioavailable form of S in the soil was SO4 2− , thus fluctuation in cationic migration might be due to the lower solubility of CaSO4, causing a slower migration of SO4 2− in the soil than Cl [53].…”