Enumeration of carbon and nitrogen contents of water-stable aggregates in layers of topsoils from cultivated and adjacent bush-fallow loamy soils

C.A Igwe,C.B Okebalama,A.O Onunwa

doi:10.4314/as.v21i1.16

Abstract

Soil organic carbon (SOC) and total soil nitrogen (TSN) dynamics have both pedological and agronomic basis. Knowledge of their retention within aggregate hierarchies of varying soil textures as influenced by land use change is limited. The capacity of loam (L), clay loam (CL), sandy loam (SL) and sandy clay loam (SCL) soils to retain SOC and TSN in water-stable aggregate (WSA) at 10-cm intervals of 0-30 cm topsoil depths under cultivated and bushfallow/ uncultivated systems was investigated. The soils showed high dispersion ratio and great variations in aggregate silt and clay indices (CL > L > SCL > SL) under both land uses. Across soil depths, the uncultivated CL, SL and SCL soils had moderate to high > 2.00 mm WSA whose reduction due to cultivation impact was more pronounced in SL than in CL soil. Across soil depths and land uses, SOC content seemed higher in the macro- (> 0.50 mm) than in the micro- (< 0.50 mm) aggregates of all the soils while the reverse marked aggregate TSN content in almost all the soils. Cultivation mostly reduced macro-aggregate-associated SOC and TSN in L > CL > SL and in L > SL > CL > SCL soils, respectively. However, cultivation showed no reduction influence on micro-aggregate-associated SOC of all the soils. Cultivation-related reduction in micro-aggregate-associated TSN was more pronounced in the generally more ‘clayey’ CL and SCL than the L and SL soils. So, the potential of bush-fallowing to enhance micro-aggregateassociated TSN storage and stabilization against adverse influence of cultivation depends on soil texture.

Highlights

Soil organic carbon (SOC) and total soil nitrogen (TSN) are dynamic soil components that vary widely among soil types and land uses
Percent silt content declined with soil depth in Awgu and Okigwe cultivated soils while percent clay content tended to increase with soil depth in almost all the locations and under both land uses
The stability of the > 2.00 mm aggregates at 0-30 cm depth under both land uses is comparatively high in clay loam (CL) and sandy clay loam (SCL) and low in L and sandy loam (SL) soils

Summary

Introduction

Soil organic carbon (SOC) and total soil nitrogen (TSN) are dynamic soil components that vary widely among soil types and land uses. This is so because organic carbon (C) and nitrogen (N) contents in cropland are strongly influenced by the quantity of C inputs, cropping intensity, soil and crop management practices (Rahman, 2013). Increased SOC content improves soil structure and sustainability and enhances crop yield and productivity. SOC depletion has been associated with reduced soil aggregation and structural stability with attendant susceptibility to accelerated erosion in most tropical soils (Lal, 1991; 2019; BlancoCanqui and Benjamin, 2013; Liu et al, 2019)

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Conclusion