We estimated the phosphorus (P) budgets for all 212 cities, towns and villages of Hokkaido, Japan. We also carried out water sampling from all major rivers flowing in the respective areas during the snowmelt season and measured total P (TP) concentration. Surplus P in the agricultural land was estimated by subtracting the amount of crop uptake from the input sources, such as the amount of chemical and compost fertilizers, crop residues, rainfall and irrigation. The livestock excreta P not utilized on farmland was assumed to be disposed P. Total P concentrations in most of the river water ranged from undetectable to 1 mg L-1, rarely reaching up to 2.32 mg L-1, and the areas surrounding the Funka Bay had comparatively higher concentrations. More than two-thirds of the areas had surplus P in farmland ranging from negative values to 30 kg ha-1 of farmland, and areas with mixed farmland and livestock husbandry had higher surplus values ranging from 31 to 72 kg ha-1, indicating that the source of the residual P was applied chemical and manure fertilizers. Total P concentration in river water was not correlated with the proportion of upland field and urban area or with the farmland surplus P resulting from the P cycling and the municipal waste P that mixes into the river water. However, TP concentration was positively correlated with the proportion of Andisol area occupied by farmlands (r = 0.25, P < 0.01). The TP concentration was also correlated with the topographic factors in areas (r = 0.49, P < 0.01) that possess more than 50% Andisols in farmlands. Multiple regression analysis showed that TP concentration was best explained by a combination of disposed excreta, the Andisol area occupied by farmland, the application rate of chemical fertilizers and topographic factors (r2 = 0.21, P < 0.001). Thus, P losses from farmlands to river water during the snowmelt season could mainly be attributed to fertilizer management and soil type along with the topographic condition of the area
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 waterholding 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.
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