Distribution Of Fluoride And Aluminum Fractions In Soil Aggregates And The Relationship With Soil Chemical Properties Under Tea Plantation

Tea (Camellia sinensis) is known to absorb a great deal of the fluoride and aluminum, and the amounts of fluoride and aluminum of tea leaves are larger than that of other plants. Soil acidification of tea plantation has exacerbated with the increase of tea plant life. Moreover, soil acidification has influenced the distribution and bioavailability of fluoride and aluminum fractions. Thus, studying on the changes of fluoride and aluminum fractions within soil aggregates in the different tea plantation ages has a role of significant instruction to sustainable development of such tea plantations. In this research, the ages of planting tea of 16,23,31 and 53 years in ecological tea plantation of Zhongfeng Township, Mingshan County, Ya'an City, Sichuan Province, Southwest China are the research objects to have determination and analysis on effects of ages of tea plantation on changes of fluoride and aluminum and its fractions concentrations in soil aggregates to understand the evolution of fluoride and aluminum in the process of plantation tea, and provide evidence for scientific management of soils in the tea plantation. The research results indicate:(1) The contents of soil total and residual fluoride mainly distributed in<0.25 mm particle size aggregate, with 444.40-566.98 and 437.16-557.06 mg/kg, respectively. The contents of soil water-soluble and exchangeable fluoride increased with decreasing of particle sizes of the soil aggregates, and higher values 0.72-1.22 and 0.89-1.86 mg/kg were found in<1 mm particle sizes. However, the contents of Fe/Mn oxide-bound and organic matter-bound fluoride decreased with decreasing of particle sizes of the soil aggregates, and higher values 3.60-5.27 and 5.53-7.99 mg/kg were found in>2 mm particle sizes. The contents of soil total and residual aluminum mainly distributed in<1 mm particle size aggregates, with 81.19-98.35 and 79.58-93.69 g/kg, respectively. The contents of soil water-soluble and exchangeable aluminum increased with decreasing of particle sizes of the soil aggregates, and higher values 3.46-5.34 and 62.78-228.85 mg/kg were found in<0.25 mm particle size. However, the contents of soil Fe/Mn oxide-bound and organic matter-bound aluminum mainly distributed in>5 mm particle size aggregate, with 397.17-432.04 and 22.76-35.08 mg/kg, respectively. The contribution rates of soil aggregates to fluoride and aluminum and its fractions showed that the dominant size fraction was>2 mm particle sizes with values 45.53%-90.35% and 63.37%-91.67% at the two soil depths. Moveover, the fluoride and aluminum and its fractions contents in>2 mm aggregate size fractions had a highly significant positive correlation relation with the fluoride and aluminum and its fractions contents in tea plantation soils.(2) The concentrations of residual fluoride and aluminum comprised most of the total fluoride and aluminum, respectively. The distribution ratios of residual fluoride and aluminum accounted for more than 90%. In addition, the distribution of other fluoride fractions were governed by Fe/Mn oxide-bound fluoride (2.55-5.27 mg/kg)? organic matter-bound fluoride (1.91-7.99 mg/kg)> water-soluble fluoride (0.54-1.22 mg/kg)> exchangeable fluoride (0.27-1.86 mg/kg). However, the distribution of other aluminum fractions were governed by Fe/Mn oxide-bound aluminum (342.43-432.04 mg/kg)> exchangeable aluminum (33.45-228.85 mg/kg)> organic matter-bound aluminum (7.27-35.08 mg/kg)> water-soluble aluminum (1.63-5.34 mg/kg) in four tea plantations. Along with rising ages of the tea plantations, the contents of soil total fluoride, residual fluoride, water-soluble fluoride, exchangeable fluoride, water-soluble and exchangeable aluminum presented increasing trends in soil aggregates of all particle sizes, and higher values were 433.12-566.98,421.33-557.06,0.66-1.22,0.42-1.86,1.82-5.34,102.72-228.85. The contents of soil total aluminum, residual aluminum, Fe/Mn oxide-bound aluminum and fluoride displayed decreasing trends, with lower values were 78.38-92.73,72.44-87.30 g/kg, 342.43-410.01,254.64-368.84 mg/kg. The contents of organic matter-bound fluoride and aluminum showed increased first and then decreased, and higher values were found in tea plantation with age of 23 years with 3.90-7.99 and 11.06-35.08 mg/kg, respectively.(3) The water-soluble fluoride, residual fluoride, and aluminum fractions had a significant correlation relation with soil pH, organic carbon, water-soluble organic carbon, nitrogen, and phosphorus within macro-aggregates. Organic matter-bound fluoride only had a significant correlation relation with water-soluble organic carbon within>2 and 1-0.5 mm aggregates. However, exchangeable fluoride and Fe/Mn oxide-bound fluoride had a significant correlation relation with soil pH, organic carbon, water-soluble organic carbon, nitrogen, and phosphorus within micro-aggregates. The results indicated that soil pH, organic carbon, water-soluble organic carbon, nitrogen, and phosphorus had a great influence on water-soluble fluoride, residual fluoride, and aluminum fractions within macro-aggregates, and exchangeable fluoride and Fe/Mn oxide-bound fluoride within micro-aggregates. In addition, organic matter-bound fluoride was the most likely to be affected by water-soluble organic carbon within macro-aggregates.