Change in soil carbon in response to organic amendments in orchards and tea gardens in Japan

Abstract Changes in total carbon (C) concentrations in topsoil were examined in response to organic amendments (OAs) in Japanese orchards and tea gardens at the farm level using 20 years of survey data. A rolling nationwide survey was conducted four times between 1979 and 1998. Each complete survey required approximately 5 years. In the tea gardens (n = 191), the proportion of strongly acidified soils (pH  − 1  N. The soil C concentration increased by 2.0, 2.2, and 2.5 g kg − 1  yr − 1 at the non-Andosol sites with ‘low pH’ (soil pH was  4 at the beginning of the survey but a pH  − 1  yr − 1 at Andosol sites with ‘decreasing pH’ and ‘fluctuating pH,’ respectively. In contrast, in the orchards (n = 787) where the soil pH was adjusted to maximize plant growth, the long-term changes in soil C varied depending on the initial soil C concentrations. The initial topsoil C concentrations differed depending on the soil type and soil temperature. The soil C concentration increased by 0.2–0.3 g kg − 1  yr − 1 in the non-Andosol sites where the initial soil C level was low, but this increase was not significant. However, the soil C concentrations did not change at the Andosol sites where the initial soil C concentrations were high. The application of OAs did not differ significantly among the sites and did not vary significantly with time (with a few exceptions). Strongly acidic tea soils can potentially sequester large quantities of applied C, mainly from trimmed branches. Thus, tea soils are important for alleviating greenhouse gas emissions from tea gardens where large amounts of nitrous oxide have been emitted. Moreover, orchard soils with low initial soil C concentrations have the potential to increase soil C.