Changes in soil organic carbon after more than ten years of continuous organic matter application in orchards in Japan

To clarify the effect of organic matter application on soil carbon sequestration in orchards, long-term field experiments (>10 years) were conducted at three sites (in Tsukuba, Yamanashi, and Omura) characterized by different fruit crop species, soil types, and climate. Three treatments were established in plots at all sites: (i) clean cultivation (CC, the control), in which chemical fertilizer was applied and the ground was kept bare; (ii) sod culture (SC), in which chemical fertilizer was applied and the ground was covered by grass or weeds; and (iii) organic amendment (OA), in which chemical fertilizer and cattle manure (OA(cat)) or bark compost (OA(brk)) were applied and the ground was kept bare. At Tsukuba, annual changes in soil organic carbon concentration (a(soc)) were lowest in CC and highest in OA(cat), and OA(brk) plots. At Yamanashi, CC plots lost soil carbon, and asoc increased the highest in OA(cat) plots. At Omura, a(soc) was negative in CC and SC plots and was positive in OA(brk) plots. Within treatments, annual changes in soil organic carbon were highest in OA plots and lowest in CC plots at all sites; positive differences between control and treatment plots indicated that application of organic matter increased soil carbon sequestration.