Effects Of Ages Of Tea Plantations On Changes Of Nutrient Contents In Soil Aggregates

Tea (Camellia sinensis) is one of the important economic crops in China. Statistics showed that the area of Chinese tea garden reached 258×104 ha and presented an increasing trend. Due to a series of reasons in the ecological system of tea garden soils, such as fertilizer applications, leaf fall returning to soil and root exudates, the concentrations of soil exchangeable Ca and Mg and trace elements decreased gradually, and active Al and F concentrations presented an increasing trend as the increasing of tea plantation age. So far, the changes of nutrients concentrations are still not clear in water-stable aggregates. In this research, the ages of planting tea of 16,23,31 and 53 years in ecological tea plantation of Zhongfeng Village, Mingshan County, Sichuan Province are the research objects to have determination and analysis on effects of ages of tea plantations on. changes of nitrogen, phosphorus, potassium and exchangeable base cation contents in soil aggregates so as to understand the evolution of soil fertility in the process of plantation tea regularly, and promote the sustainable utilization of soil in the tea plantation. The research results indicate:(1) The contents of soil available K and exchangeable K are increased first and then decreased with decrease of particle sizes of the soil non-water-stable aggregates, and higher values which are 38.52-70.32 mg/kg and 0.088-0.174 cmol/kg are found in 0.5-0.25 mm particle size. The distributions of available N, total P and K, and exchangeable Mg are relatively even in soil non-water-stable aggregates of all particle sizes. However, the contents of total N, available P, and exchangeable Na and Ca are increased with decrease of particle sizes of the soil non-water-stable aggregates, and higher values (0.40-0.98 g/kg,8.53-29.32 mg/kg,0.025-0.131 cmol/kg and 0.764-1.840 cmol/kg) are found in <.25 mm particle size. Along with rising ages of the tea plantations, the contents of total N and P and available N and P present increasing trends in soil non-water-stable aggregates of all particle sizes. However, the contents of available K and exchangeable K and Na display decreasing trends, and the contents of exchangeable Ca and Mg show increasing-and-decreasing trends, and higher values are found in tea plantation with ages of 23 and 31 years. The contents of soil non-water-stable aggregates total N and P, available N, P and K, and exchangeable K are greater in 0-20 cm depth than in 20-40 cm depth. However, the contents of soil non-water-stable aggregates exchangeable Na, Ca, and Mg are greater in 20-40 cm depth than in 0-20 cm depth.(2) The contents of soil total N and exchangeable Ca are decreased with decrease of particle sizes of the soil water-stable aggregates, and higher values which are 0.39-0.84 g/kg and 0.647-1.834 cmol/kg are found in>5 mm particle size. The distributions of total P and K, available K, and exchangeable K and Mg are relatively even in soil water-stable aggregates of all particle sizes. However, the contents of available N and P and exchangeable Na are increased with decrease of particle sizes of the soil water-stable aggregates, and higher values (24.20-46.27 mg/kg,5.54-24.85 mg/kg and 0.018-0.125 cmol/kg) are found in<0.25 mm particle size. Along with rising ages of the tea plantations, the contents of total N and P and available N and P present increasing trends in soil water-stable aggregates of all particle sizes. However, the contents of available K and exchangeable K and Na display decreasing trends, and the contents of exchangeable Ca and Mg show increasing-and-decreasing trends, and higher values are found in tea plantation with ages of 23 and 31 years. The contents of soil water-stable aggregates total N and P, available N, P and K, and exchangeable K are greater in 0-20 cm depth than in 20-40 cm depth. However, the contents of soil water-stable aggregates exchangeable Na, Ca, and Mg are greater in 20-40 cm depth than in 0-20 cm depth.(3) The contents of soil total N and P and exchangeable Ca are decreased first and then increased with decrease of particle sizes of the soil micro-aggregates, and higher values which are found in 250-50 μm and<1 μm particle sizes. The distributions of total K. and exchangeable Mg are relatively even in soil micro-aggregates of all particle sizes. However, the contents of available N, P and K and exchangeable K are increased with decrease of particle sizes of the soil micro-aggregates, and higher values (28.83-47.00 mg/kg,6.30-29.02 mg/kg,38.85-61.91 mg/kg and 0.084-0.143 cmol/kg) are found in<1 μm particle size. The higher value of exchangeable Na content is 0.031-0.149 cmol/kg, and is found in 10-5μm particle size. Along with rising ages of the tea plantations, the contents of total N and P and available N and P present increasing trends in soil micro-aggregates of all particle sizes. However, the contents of available K and exchangeable K and Na display decreasing trends, and the contents of exchangeable Ca and Mg show increasing-and-decreasing trends, and higher values are found in tea plantation with ages of 23 and 31 years. The contents of soil micro-aggregates total N and P, available N, P and K, and exchangeable K are greater in 0-20 cm depth than in 20-40 cm depth. However, the contents of soil micro-aggregates exchangeable Na, Ca, and Mg are greater in 20-40 cm depth than in 0-20 cm depth.