Changes in soil properties following conversion of forests into intensively managed Camellia sinensis L. plantations along a chronosequence

Abstract

Tea in Kenya was introduced in the beginning of the 20th Century, although commercial cultivation commenced in 1924. The total acreage of tea plantations has steadily increased and currently covers approx. 0.15 million ha, i.e. ~5% of the total area in the world. Usually, highest yields are obtained when plantations are 20-40 years old, but remain in production till 100 years. Plantations older than 40 years start degrading slowly, but the real cause of this degradation is unclear. This article reports on changes in soil characteristics as a possible feedback of degradation in ageing tea plantations using results of analyses of soils sampled from a natural forest and a chronosequence of tea plantations (14, 29, 43 and 76 years old). The effects of long-term tea monocropping on soil acidity, exfractable aluminium and manganese, and how they affect the ratios of the base nutrients (K, Ca, Mg), phosphorus and sulphur, were tested. The soils were classified as Nitisols with 46-59% clay and 33-38 g kg-1 of organic carbon. There were small differences in soil characteristics between the natural forest soil and the tea plantations. Soil pH ranged from 3.5 to 4.7, and was lower in tea plantations than in the natural forest. The C:N ratio in the tea soils was found fairly constant and ideal along the chronosequence which helps in increase of microbial biomass C and N and total microbial activity (TMA) in ageing tea plantations. Thus, liming and balanced fertilization of K and Mg is required for sustainable tea plantations.