Temporal Variation of SOC Enrichment from Interrill Erosion over Prolonged Rainfall Simulations

Yaxian Hu,Wolfgang Fister,Nikolaus Kuhn

doi:10.3390/agriculture3040726

Abstract

Sediment generated by interrill erosion is commonly assumed to be enriched in soil organic carbon (SOC) compared to the source soil. However, the reported SOC enrichment ratios (ERSOC) vary widely. It is also noteworthy that most studies reported that the ERSOC is greater than unity, while conservation of mass dictates that the ERSOC of sediment must be balanced over time by a decline of SOC in the source area material. Although the effects of crusting on SOC erosion have been recognized, a systematic study on complete crust formation and interrill SOC erosion has not been conducted so far. The aim of this study was to analyze the effect of prolonged crust formation and its variability on the ERSOC of sediment. Two silty loams were simultaneously exposed to a rainfall simulation for 6 h. The ERSOC in sediment from both soils increased at first, peaked around the point when steady-state runoff was achieved and declined afterwards. The results show that crusting plays a crucial role in the ERSOC development over time and, in particular, that the conservation of mass applies to the ERSOC of sediment as a consequence of crusting. A “constant” ERSOC of sediment is therefore possibly biased, leading to an overestimation of SOC erosion. The results illustrate that the potential off-site effects of selective interrill erosion require considering the crusting effects on sediment properties in the specific context of the interaction between soil management, rainfall and erosion.

Highlights

The on-site soil loss by interrill erosion is many times smaller than that from rill erosion, it literally affects all arable land [1]
The runoff of conventionally-farmed soil (CS) started after 60 min and kept increasing until a steady state was achieved at 180 min (Figure 3a), indicating the completion of structural crust formation [27,30]
The enrichment of soil organic carbon (SOC) in interrill sediment observed in several studies is a potentially crucial parameter for assessing soil-climate interaction, as well as the off-site impacts of interrill erosion on water courses

Summary

Introduction

The on-site soil loss by interrill erosion is many times smaller than that from rill erosion, it literally affects all arable land (globally, 14.2 million km2) [1]. Due to the limited raindrop kinetic energy and lack of concentrated runoff, interrill erosion is associated with selective entrainment and transport of sediment [2]. Fine and/or light particles and associated substances (e.g., soil organic carbon, phosphorus and nitrogen) are entrained and transported away from eroding sites in greater proportions than their concentration in the source soil suggests. Globally a potentially significant amount of between 0.6 to 1.3 petagram of organic carbon is affected annually by interrill erosion processes, including aggregate breakdown, crust formation, rainsplash and rainwash [1]. The susceptibility of soil organic carbon in interrill sediment to mineralization [8] emphasizes the necessity to improve our understanding of the role of interrill erosion and the associated crust formation in interrill

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