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

Publication date: January 2015
Source:Geoderma, Volumes 237–238
Author(s): Ai Leon , Kazunori Kohyama , Yusuke Takata , Kazuyuki Yagi , Yoshiaki Umemiya , Toshiaki Ohkura , Hiroshi Obara
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 20years of survey data. A rolling nationwide survey was conducted four times between 1979 and 1998. Each complete survey required approximately 5years. In the tea gardens (n=191), the proportion of strongly acidified soils (pH<4) increased from 31% (1979–1983) to 69% (1994–1998). Large C inputs mainly resulted from trimmed branches in the spaces between the hedges. The concentration of C in the topsoils increased significantly, regardless of the initial soil C concentration, in the strongly acidic soils when mineral fertilizers containing nitrogen (N) were added at rates of 0.6 to 0.9Mgha⁻¹ N. The soil C concentration increased by 2.0, 2.2, and 2.5gkg⁻¹ yr⁻¹ at the non-Andosol sites with ‘low pH’ (soil pH was <4 over time), ‘decreasing pH’ (soils had a pH>4 at the beginning of the survey but a pH<4 at the end of the survey), and ‘fluctuating pH’ (soils had a pH that fluctuated above and below pH 4 over time), respectively. Soil C increased by 1.9 and 2.2gkg⁻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 0.2–0.3gkg⁻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.