Abstract
Soil structural stability is a vital aspect of soil quality and functions, and of maintaining sustainable land management. The objective of this study was to compare the contribution of four long-term land-use systems (crop, bush, grass, and forest) coupled with anionic polyacrylamide (PAM = 0, 25, and 200 mg L−1) application on the structural stability of soils in three watersheds of Ethiopia varying in elevation. Effect of treatments on soil structural stability indices were assessed using the high energy moisture characteristic (HEMC, 0–50 hPa) method, which provides (i) water retention model parameters α and n, and (ii) soil structure index (SI). Soil (watershed), land use and PAM treatments had significant effects on the shape of the water retention curves (α, n) and SI, with diverse changes in the macropore sizes (60–250; >250 μm). Soil organic carbon (SOC) content and SI were strongly related to soil pH, CaCO3 soil type-clay mineralogy, exchangeable Ca2+, and Na+ (negatively). The order of soil SI (0.013–0.064 hPa−1) and SOC (1.4–8.1%) by land use was similar (forest > grass > bush > cropland). PAM effect on increasing soil SI (1.2–2.0 times), was inversely related to SOC content, being also pronounced in soils from watersheds of low (Vertisol) and medium (Luvisol) elevation, and the cropland soil from high (Acrisol) elevation. Treating cropland soils with a high PAM rate yielded greater SI (0.028–0.042 hPa−1) than untreated bush- and grassland soils (0.021–0.033 hPa−1). For sustainable management and faster improvement in soil physical quality, soil properties, and land-use history should be considered together with PAM application.
Highlights
Soil structure and aggregation are central physical properties of soil that control a wide array of soil properties and functions including water retention and infiltration [1], susceptibility to erosion and the movement of associated contaminants [2], aeration, gaseous exchanges, and greenhouse gas emission [3], C sequestration, soil organic carbon (SOC)
The Upper Blue Nile basin of Ethiopia is characterized by a monsoon climate with a dry (November to April) and a wet (May to October) season, with >80% of the annual precipitation occurring from June to September
It emerged from our study that change of land use from cropland soils to land uses that do not require tillage has substantial positive effects on aggregate-structure stability indices in the studied acidic soils from the Ethiopian highlands
Summary
Soil structure and aggregation are central physical properties of soil that control a wide array of soil properties and functions including water retention and infiltration [1], susceptibility to erosion and the movement of associated contaminants [2], aeration, gaseous exchanges, and greenhouse gas emission [3], C sequestration, soil organic carbon (SOC). Protection [4], soil organic matter mineralization [5], and biogeochemical cycling of essential elements such as macro- and micronutrients [6]. Monitoring of soil structure and stability is vital in determining the sustainability of land use and management practices in both agricultural and natural ecosystems [7].
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