Abstract
The Sustainable Development Goals of the United Nations call for applying soil management practices that contribute land degradation neutrality. Our objectives were to investigate the effect of (i) soil management—conventional tillage (CT under crop) and no-tillage (NT under grass)—and (ii) an amendment (polyacrylamide (PAM)) application on the structure stability indices of soils from a semi-arid region. Two sets of experiments were conducted using the high-energy moisture characteristic (HEMC) method for the assessment of (i) land-use type (CT vs. NT) in soils (30 samples) varying in texture, and (ii) the effect of six PAM concentrations (0, 10, 25, 50, 100, and 200 mg L−1) on three typical soils (sandy clay loam, clay loam, and clay) under CT management; then, the contributions of PAM concentration (CT) and NT were compared. Water retention curves of samples were obtained at a matric potential from 0 to −5.0 J kg−1 and characterized by a modified van Genuchten model that yields (i) model parameters α and n, and (ii) a soil structure stability index (SI). The treatments affected the shape of the water retention curves. Change of land use from CT to NT and PAM application to CT soil increased the SI and ɑ, and decreased n compared to CT-managed soils. The magnitude of the NT and PAM effect was inversely related to soil clay content. CT-managed soils treated with a low PAM rate (10–25 mg L−1) gave SI comparable to that obtained for the NT-managed soils, while CT-managed soils treated with a high PAM rate (50–200 mg L−1) yielded 1.3–2.0 and 2–4 times higher SI than that for NT and CT-managed soils, respectively. Our findings suggest that both the change of land use to NT or the addition of small amounts of PAM are viable alternatives for stabilizing CT-managed weakly alkaline semi-arid soils, whose soil structure stability is a priori limited.
Highlights
Soil structure is an important soil property that is central to soil health; it plays vital roles in controlling land productivity, and carbon, nitrogen, and water cycles
A quantitative examination of the water retention curves is obtained from the analysis model parameters of the curves (α and n), and soil structural index (SI), all of which were significantly of the model parameters of the curves (α and n), and soil structural index (SI), all of which affected by soil texture, land use, and the interaction between them (Table S1)
It emerged from our study that the change of land use from conventional tillage (CT)-managed soils to no-till grass (NT)-managed soils has substantial positive effects on aggregate stability indices in the studied weakly alkaline semi-arid soils
Summary
Soil structure is an important soil property that is central to soil health; it plays vital roles in controlling land productivity, and carbon, nitrogen, and water cycles. In semi-arid and arid regions, which are abundant in Turkey, long-term intense cultivation led to degradation of soil structure, and to (i) a great reduction in soil organic matter (OM) and water-holding capacity, nutrient availability and fertility, and water-use efficiency, (ii) lessening of soil aeration and macro-aggregates fraction, and (iii) modification of aggregate- and pore size distribution (PSD) and soil hydraulic properties, a decrease in infiltration and an increase in runoff, erosion, and compaction [2,3,4,5,6,7]. In Turkey, similar to many other countries, land-use change (e.g., from forest or grassland to cropland) and long-term use of conventional tillage (CT) almost without conservation practices greatly reduced soil (physical) quality and altered the sustainability of soil function [8,9,10]. The residues left in the field provide inadequate soil cover (
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