Effects of ages of tea plantations on changes of nitrogen,  phosphorus and potassium contents in soil aggregates

Through field investigation and laboratory analysis, effects of ages of tea plantations on changes of nitrogen, phosphorus and potassium contents in soil aggregates were studied. Results show that the contents of soil available K are increased first and then decreased with the increase of particle sizes of soil aggregates, and higher values which are from 38.52 to 70.32 mg/kg are found in 0.5-0.25 mm particle size. The distributions of total P and total K and available N are relatively even in soil aggregates of all particle sizes, and their coefficients of variation are 2.77%-11.58%, 0.82%-3.72% and 5.98%-10.62% separately. However, the contents of total N and available P are increased with decrease of particle sizes of the soil aggregates, and higher values(0.40-0.98 g/kg and 8.53-29.32 mg/kg) are found in 0.25 mm particle size. Along with rising ages of the tea plantations the contents of total N and total P and available N and P present increasing trends in soil aggregates of all particle sizes. However, the contents of available K display decreasing trends, and the contents of total K show no significant changes. The contribution rates of nitrogen, phosphorus and potassium contents in soil aggregates(5 mm) are 45%-72%. Along with rising ages of the tea plantations, the contribution rates of 5 mm aggregates nutrient contents present increasing first and then decreasing trends, and higher values are found in tea plantations with ages of 23 and 31 years(60%-72%). The nitrogen, phosphorus and potassium retaining capacities and supplying capacities are significantly different in soil aggregates with different particle sizes. Long-term cultivation of tea is beneficial to soil aggregates total N and P and available N and P accumulations. However, the contents of available K are decreased year by year, and the contribution rates of 5 mm aggregates nutrient contents are found to be higher in tea plantations with ages of 23 and 31 years, and declined somewhat afterwards. Therefore, in management of tea gardens, it is essential to adopt balanced application of nitrogen and potassium fertilizers, and in tea plantations which are older than 23 years, to use organic manure in addition, so as to promote the increase of soil aggregates content and improve the capacity of tea garden soil fertilizer conservation and fertilizer supply.