CHANGES IN SOIL PHYSICAL-PROPERTIES OF 4 DIFFERENT FIELDS DURING AND AFTER UPLAND RECLAMATION THAT INVOLVED GRADING

In four fields reclaimed with grading (Shari: coarse Stratic Regosolic Andosols; Kyowa: fine Brown Andosols; Hokuryu: Acid Brown Forest soil s with medium texture; and Toma: Acid Brown Forest soils with Dark Epi pedon and medium texture), changes in the physico-chemical and structu ral properties of soil strata subjected to surface layer handling (her eafter referred to as ''surface layer handled soil strata'' (SLHS)) we re investigated during and after reclamation. 1) SLHS were estimated t o be derived mainly from the A and B horizons of each pre-reclaimed fo rest soil except for the Shari field where buried horizons were also t reated in the same way as the surface soil layer. 2) During surface la yer handling (SLH), SLHS were structurally degraded in all the fields 3) During SLH, the compaction (increase in bulk density and decrease i n coarse-size pore volume (CP: from 0 to -6.23 kPa) and easily-availab le water-holding pore volume (EAW: from -6.23 to -100kPa)) of SLHS pro ceeded except for coarse textured soils (Shari). 4) In the Kyowa and T oma fields, bulk density of SLHS decreased, CP increased after a singl e plowing and harrowing, unlike EAW, even when SLH was performed at a low soil moisture level. In both fields, the recovery of EAW was small er than that of CP during the several years after SLH. Countermeasures for the recovery of EAW should be investigated further. 5) In the Hok uryu field where SLHS contained swelling clay and the soil moisture wa s 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-y ear period after SLH. Shrinkage with dehydration proceeded in the lowe r SLHS during this period. Reclamation procedures should thus be condu cted when the soil moisture is low. 6) The effects of subsoiling condu cted after SLH differed with the soil types and soil moisture levels.