Threshold Subsoil Bulk Density for Optimal Soil Physical Quality in Upland: Inferred Through Parameter Interactions and Crop Growth Inhibition

Abstract

Optimal range of soil physical quality to enhance crop productivity or to improve environmental health is still in dispute for the upland soil. We hypothesized that the optimal range might be established by comparing soil physical parameters and their interactions inhibiting crop growth. The parameter identifying optimal range covered favorable conditions of aeration, permeability and root extension. To establish soil physical standard two experiments were conducted as follows; 1) investigating interactions of bulk density and aeration porosity in the laboratory test and 2) determining effects of soil compaction and deep & conventional tillage on physical properties and crop growth in the field test. The crops were Perilla frutescens, Zea mays L., Solanum tuberosum L. and Secale cereael. The saturated hydraulic conductivity, bulk density from the root depth, root growth and stem length were obtained. Higher bulk density showed lower aeration porosity and hydraulic conductivity, and finer texture had lower threshold bulk density at 10% aeration bulk density. Reduced crop growth by subsoil compaction was higher in silt clay loam compared to other textures. Loam soil had better physical improvement in deep rotary tillage plot. Combined with results of the present studies, the soil physical quality was possibly assessed by bulk density index. Threshold subsoil bulk density as the upper value were 1.55 Mg m -3 in sandy loam, 1.50 Mg m -3 in loam and 1.45 Mg m -3 in silty clay loam for optimal soil physical quality in upland.

Changes of Soil Physico-Chemical Properties by Soil Loss of Bare Condition Using Slope Lysimeter

“…표토와 심토의 평균 유기물함량은 식양토에서 각각 8.0, 6.7 g kg -1 , 사양토에서 각각 7.2, 4.2 g kg -1 로 모두 적정범위 (20 -30 g kg -1 ) 미만이었다. 일반적으로 점토함량이 높은 식양 토가 사양토보다 유기물함량이 높은 것으로 보고되고 있는데 (Park et al, 1994;Cho et al, 2016), 본 연구에서도 비 슷한 경향으로 나타났다. 2019년부터 2021년까지 식양토와 사양토의 평균 유기물함량은 각각 6.13 -9.33 g kg -1 과 3.28 -7.80 g kg -1 범위로 (Table 2), 한국 밭토양 화학성 변동 평가에서 보고된 유기물함량 (24 -27 g kg -1 )보다 낮았다 (Kim et al, 2019).…”