Organic Carbon and Nitrogen Associated with Soil Aggregates and Particle Sizes Under Different Land Uses in Tigray, Northern Ethiopia

Abstract

Soil aggregation serves as storage and cycling of soil organic carbon (SOC) and total nitrogen (TN), which are essential for the functioning of terrestrial ecosystems. Thus, aggregate and particle associated SOC and TN in 0‐ to 10‐cm and 10‐ to 20‐cm layers were estimated for five land uses: rainfed cultivation (RF), agroforestry (AF), open pasture (OP), silvopasture (SP), and irrigation (IR) each with five replications within a watershed in Ethiopia. OP had the highest WSA > 2 mm (88·7%) and SOC associated with macroaggregates (20·0 g kg−1), which were significantly higher (P < 0·0001; P = 0·0017 for WSA and SOC, respectively) than that in other land uses in 0‐ to 10‐cm depth. SOC associated with both macroaggregates and microaggregates decreased with depth. Macroaggregates contained higher SOC than microaggregates in both layers under all land uses. AF had the highest SOC associated with microaggregates (2·6 g kg−1) followed by that in SP (2·3 g kg−1), indicating its potential to stabilize SOC more than other land uses. TN associated with macroaggregates followed a trend similar to that of SOC. OP had also significantly higher SOC (P = 0·0001) and TN (P = 0·0004) associated with sand particles than RF, AF, and IR. Sand‐associated SOC and TN were the highest in uncultivated systems. Moreover, the higher SOC concentrations associated with clay particles in soils under OP, SP, and AF showed that grass‐based and tree‐based systems are rich in stable SOC as clay‐associated SOC has higher residence time than that associated with sand or silt fractions. Copyright © 2013 John Wiley & Sons, Ltd.

Soil Quality Indices for Evaluating Smallholder Agricultural Land Uses in Northern Ethiopia

“…Addition of more organic matter from leaf and root litters from the F. albida trees in AF than the other land uses likely explains the improved WSA in AF [36]. Similarly, a study by Gelaw et al [37] at the same site found that soils under natural grazing lands adjacent to cultivated lands were well structured, and contained higher SOC concentrations.…”

“…However, the difference among land uses was not statistically significant. Similarly, the detrimental effects of tillage may have offset the beneficial effects of SOC on TP [17,32,37]. …”

Ideas and perspectives: Can we use the soil carbon saturation deficit to quantitatively assess the soil carbon storage potential, or should we explore other strategies?

“…60% and 40% of total SOC of surface soil layers in Bavarian forests and grasslands, respectively. Several other studies have reported significant (>20%) contributions of >20 µm SOC to total SOC in various systems such as agricultural temperate soils 10 (Balesdent et al, 1998;Besnard et al, 2001) or cultivated tropical soils (Barthes et al, 2008;Gelaw et al, 2015). Moreover, several authors observed that increases in SOC stocks following a land management change were mostly due to an increase in sand-size particulate organic matter (e.g.…”

Effects of permanent grass versus tillage on aggregation and organic matter dynamics in a poorly developed vineyard soil

“…Munoz-18 Rojas et al 2012;De Moraes Sá et al 2013;Gelaw et al 2013;Parras-Alcántara et al 2013, 201419 Srinivasarao et al 2014;Yu and Jia 2014;Behera et al 2015;Peng 2015). Agriculture can strongly 20 limit SOM accumulation, influencing soil aggregate formation and turnover (Jastrow 1996;Cerdà, 21 2000;Jacobs et al 2010;Gosling et al 2013).…”