The operation of the soil dressing using Pumice Flow Deposit (Pfld) has been spreading in recent years to improve productivities of upland crops. However, quantitative date to evaluate this type of soil dressing were still lacking. In this study, field experiment were conducted at three site of different soil origins in Abashiri district. The amount of applied Pfld were 50 and 100mm for Fine Brown Lowland soil, and 36,70 and 100mm for Fine Brown Forest soil and for Kuroboku soil. As Pfld, which is a kind of volcanic ash, is composed of high rate of pumice sand, its fertilities are very poor except for phosphorus. Pfld has pH of about 7. Some physical properties of these soils were ameliorated by application of Pfld. These were an increase of sand fraction, a convergence of solid ratio to 0.4m3m-3 and of bulk density to 1.0Mg m~3, an increase of easily available moisture when its value of original soil was under 0.lm3m~3, an increase of saturated hydraulic conductivity of the order of 10_6m s—1,and an improvement of soil tilth for fine soils with the decrease of soil stickiness. However, soil pH was unchanged, and CEC, exchangeable cation and available nitrogen were decreased slightly by the soil dressing. Pot experiments showed that mixing 0.6m3m-3 of Pfld with fine lowland soil suppressed crust formation and the rate of emergence increased up to 80%. Crop yields except of potatoes and sugar beet in Fine Brown Forest soil decreased with the increase of the Pfld applied. The cause of lower yields were considered by the decrease of soil chemical fertilities. However the facts that lower inner quality of crops and higher T/R ratio with higher yield at the 70 or 100mm dressing plot, indicate the higher release of soil nitrogen in a latter growth stage. While in the Kuroboku soil, outer color of potatoes became to light due to decrease of the adhhesion of soil particles. Above results indicate that application of Pfld as the soil dressing does not always increase crop yields but improves some physical properties of the soils which enhances efficiency of field operations. Therefore we have to estimate not only crop yields but various factors such as workabilitiy or crop quality when we judge the effect of soil dressing.
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