Assessment of soil organic carbon stocks differentiation in humus horizons of clay-illuvial soils within young morainic landscapes, northern Poland

Abstract

Clay-illuvial soils (Luvisols or Retisols in WRB) are the most widespread component of soil cover in Poland. Due to common occurrence and relatively high fertility they are crucial for food production. Agricultural use of these soils, however, leads to strong alterations and, in many cases, their degradation. This is especially important in young morainic landscapes of northern Poland. Hummocky and undulating relief combined with agricultural use, leads to truncation of clay-illuvial soils and generally affect the quality of humus horizons and soil organic carbon (SOC) content. The aim of the presented study is to assess the overall SOC stocks in plough horizons of clay-illuviated soils and their differentiation between their most common subtypes (according to Polish Soil Classifi cation 2019). SOC stocks were calculated for 72 soil profi les. The average stocks were low -3.28 kg•m -2 which may be related to both: natural conditions and strong anthropogenic alterations. Based on the obtained results separate subtype attributes, although express the variability of clay-illuvial soils, do not refl ect the diversity of humus pools. However, it can be stated that SOC stocks differ statistically in particular complex subtypes. The highest SOC stocks (4.12 kg•m -2 ) were recorded in the humic stagnogleyic clay-illuvial soils (Stagnic Luvisols/Retisols in WRB) characterized by relatively high soil moisture and a low erosive transformations. Truncated pedons (Ap-Bt-C(k)) were divided into two common subtypes -eroded humic clay-illuvial soils and eroded clay-illuvial soils (Haplic Luvisols). Eroded humic subtype had quite high average SOC stocks -3.61 kg•m -2 , the second subtype had extremely low carbon pools -1.40 kg•m -2 . Such high diversity may result from different pace of erosion in particular profi les and regenerative, sustainable management (e.g. reduced ploughing, vineyards, grassland) leading to the rebuilding of SOC stocks in many of studied eroded humic pedons. Low stocks (2.24 kg•m -2 ) were also noticed in typical clay-illuvial soils which humus horizons were also degraded by erosion. A slight erosional alterations characterized subtype of texturally contrasted humic clay-illuvial soils (Abruptic Luvisols / Haplic Planosols) with average stocks -3.57 kg•m -2 . For further research larger database is necessary. Carbon stocks in the deeper horizons should also be investigated.