Pore structures of physically amended sandy soils exhibit significant multifractal characteristics, which are influenced by many soil physical properties. This study investigated the influences of adding fly ash and Montmorillonite-enriched sandstone (MS) on the physical properties and multifractal characteristics of pore structures in a sandy soil. Scanning electron microscope (SEM) was used to obtain the pore structures. MATLAB scripts were developed for calculating the Hölder index (α_q) and generalized dimensions (D_q) of binary SEM images. The results showed that particle compositions and water retention capacity are improved after adding the two materials. The amplitudes of D_q (ΔD) was reduced by 6.9% to 35.6% in the amended soils, which means smaller scaling diversities of pore structures. The right branches of multifractal spectrum (α_r) showed higher amplitudes than that of left branches (α_l), indicating that smallest pores were more diverse than the largest pores after adding the two materials. Multifractal parameters showed significant linear relationships with the sand and silt content, bulk density and total porosity. The result indicate that multifractal parameters could be used to describe the changes of pore characteristics and to quantify the characteristics of pore structures in the amended sandy soils.

The efficient use of organic amendment (OM) is considered an economic, environmental and sustainable practice to improve soil quality, especially the accumulation of organic carbon (C) and water use efficiency (WUE) in dryland agriculture. However, the effect of different OM on soil nutrients, organic carbon fractions, water content and maize yield is unclear in arid and semi-arid regions with sandy soil. Field experiments with four OM, grass peat (GP), biochar (BC), organic fertilizer (OF) and maize straw (MS), were conducted with an equivalent amount of C input on the southeastern edge of Mu Us Sandy Land in China. Results indicated that the soil nutrients and labile organic carbon (DOC, MBC, KMnO₄-C and POC) concentrations were higher under OM (GP, BC, OF and MS) treatments than in CK in the 0–0.10 m soil layers. GP treatment remarkably improved carbon pool index values (1.63, 2.51 and 2.24, respectively) in all layers compared to CK (1.00). At maturity stages of maize, the soil water content (SWC) under GP and OF treatments (11.3–13.4%) was remarkably higher than that in CK treatment (around 10.0%). Yield and WUE were remarkably greater in GP and OF treatments compared to CK. The results proved that GP amendment is superior for barren sandy soil than BC, OF and MS treatments in improving soil nutrients, organic carbon sequestration, WUE and crop yield in China.

Spatial distribution of soil organic carbon (SOC) is important for the development of ecosystem carbon cycle models and assessment of soil quality. In this study, a total of 732 soil samples from 122 soil profiles (0–10, 10–20, 20–40, 40–60, 60–80, and 80–100 cm) were collected by a combination of fixed-point sampling and route surveys in an agro-pastoral ecotone of northern China and the spatial variation of the SOC in the samples was analyzed through classical statistical and geostatistical approaches. The results showed that the SOC contents decreased from 4.31 g/kg in the 0–10 cm to 1.57 g/kg in the 80–100 cm soil layer. The spatial heterogeneity of the SOC exhibited moderate and strong dependence for all the soil layers owing to random and structural factors including soil texture, topography, and human activities. The spatial distributions of the SOC increased gradually from northeast to southwest in the 0–40 cm soil layers, but there was no general trend in deep soil layers and different interpolation methods resulted in the inconsistent spatial distribution of SOC. The storage of SOC was expected to be 25 Tg in the 0–100 cm soil depths for the whole area of 7692 km². The SOC stocks estimated by two interpolation approaches were very close (25.65 vs. 25.86 Tg), but the inverse distance weighting (IDW) interpolation generated a more detailed map of SOC and with higher determination coefficient (R²); therefore, the IDW was recognized as an appropriate method to investigate the spatial variability of SOC in this region.