Changes in soil physical properties of four different fields during and after upland reclamation that involved grading

Abstract

Abstract In four fields reclaimed with grading (Shari: coarse Stratic Regosolic Andosols; Kyowa: fine Brown Andosols; Hokuryu: Acid Brown Forest soils with medium texture; and Toma: Acid Brown Forest soils with Dark Epipedon and medium texture), changes in the physico-chemical and structural properties of soil strata subjected to surface layer handling (hereafter referred to as “surface layer handled soil strata” (SLHS)) were investigated during and after reclamation. 1. SLHS were estimated to be derived mainly from the A and B horizons of each pre-reclaimed forest soil except for the Shari field where buried horizons were also treated in the same way as the surface soil layer.2. During surface layer handling (SLH), SLHS were structurally degraded in all the fields.3. During SLH, the compaction (increase in bulk density and decrease in coarse-size pore volume (CP: from 0 to -6.23 kPa) and easily-available water-holding pore volume (EAW: from -6.23 to -100 kPa)) of SLHS proceeded except for coarse textured soils (Shari).4. In the Kyowa and Toma fields, bulk density of SLHS decreased, CP increased after a single plowing and harrowing, unlike EAW, even when SLH was performed at a low soil moisture level. In both fields, the recovery of EAW was smaller than that of CP during the several years after SLH. Countermeasures for the recovery of EAW should be investigated further.5. In the Hokuryu field where SLHS contained swelling clay and the soil moisture was estimated to have been high when SLH was performed, bulk density, CP, and EAW of the upper SLHS did not recover appreciably during the 8-year period after SLH. Shrinkage with dehydration proceeded in the lower SLHS during this period. Reclamation procedures should thus be conducted when the soil moisture is low.6. The effects of subsoiling conducted after SLH differed with the soil types and soil moisture levels.