Although a land consolidation project has increased arable land area in loess areas, the loessal soil has poor fertility and productivity. Soil degradation and the accompanying decline in crop yields are the main limiting factors for agricultural development on the Loess Plateau. Biochar has been used as an amendment to improve soil fertility and crop yields. A potted experiment was carried out to study the effects of biochar addition (0, 5, 15 and 25 t ha −1 ) on soil physicochemical properties as well as sunflower yield. The results showed that higher rates of biochar addition (15, 25 t ha −1 ) can significantly increase soil electrical conductivity, cation exchange capacity, nutrients and crop yields, while decreasing soil pH. The maximum soil nutrients were observed at 25 t ha −1 biochar addition. However, the lowest soil pH value and highest sunflower seed yield were obtained at 15 t ha −1 biochar addition. The highest net income was $985 ha −1 when the biochar addition rate was 15 t ha −1 . These results suggest that biochar can significantly improve soil fertility and sunflower yield. Soil salinity and alkalinity properties, organic carbon, nitrate nitrogen and available phosphorus were crucial factors that determined soil fertility and sunflower yield in loessal soil.

Soil is the largest pool of terrestrial organic carbon in the biosphere [1]. Statistically, the soil carbon (C) pool is 3.3 times the size of the atmospheric pool and 4.5 times the size of the biotic pool. The global soil C pool of 2500 gigatons (Gt) includes approximately 1550 Gt of soil organic carbon (SOC) [2]. Therefore, soil agro-ecological systems are considered potential C pools. SOC directly affects soil structure and soil fertility, and small changes in SOC will have a large

The stress–strain constitutive model under uniaxial compression is a basic element and important characterization method for determining physical and mechanical properties in cement-based materials research. In this study, a stress–strain constitutive model under uniaxial compression was established, which was based on a new nano-stabilized soil (NSS) through typical mechanical tests and constitutive relationship research. The results indicate that the unconfined compressive strength (UCS) of the nano-stabilized soil was enhanced with the increase in curing period and nano-stabilizer dosage, and that the strength growth rate reaches the maximum at a 12% dosage in the tested samples. The UCS of NSS under a 12% dosage is about 10~15% higher than that of ordinary stabilized soil (SS) without nano doping, and 25~40% higher compared with grade 42.5 cement-soil. The established constitutive model could accurately describe the linear-elastic and elastic-plastic deformation characteristics of NSS under uniaxial compression, which will be conducive to revealing the curve variation law of the stress–strain process. The research results could provide scientific support for the theoretical innovation and engineering application of green environmental protection materials.