Numerous studies have concluded that carbon (C):nitrogen (N):phosphorus (P) stoichiometry in both soils and plants tends to be decoupled under global change. We consequently hypothesized that plants will adjust nutrient conservation strategies to balance the altered elemental stoichiometry accordingly. To test our hypothesis, we conducted two pot-cultured experiments (with 8-level water and 6-level N addition treatments) using N-fixing species Glycyrrhiza uralensis Fisch from a desert steppe in northwestern China. We observed that high water availability lowered total N content and the N:P ratio in soils, further promoting both N and P resorption from senescing leaves of G. uralensis. High N addition enhanced soil N availability and the N:P ratio, thereby reducing N resorption, but increasing P resorption of G. uralensis. Comparatively, there were also great changes in senescing leaf C:N:P stoichiometry while no clear changes were observed in either green leaf or root C:N:P stoichiometry of G. uralensis. As expected, the altered C:N:P stoichiometry may, in turn, modify N and P conservation strategies through their close linkages with N and P uptake in green leaves of G. uralensis. This modification may also further exert effects on N and P cycling of the desert steppe.

The effective and safe use of FGD gypsum in agricultural land is still debated in some countries even though its effectiveness in soil management has been reported in many studies. Thus, the changes in the levels of soil salinity, alkalinity, crop yield, and other physicochemical properties in different soil types and crops after reclamation and planting with FGD gypsum over four years are evaluated in this paper. The main aim of this paper is to review the effects of six treatment technologies in addressing soil salinity and sodicity and crop production in soils, with a focus on the basic theory, key technologies, and industrialized applications. This paper also shows that soil conditions can be improved and crop yields can be increased by using FGD alone or in combination with humic acid or fertilizer. FGD gypsum plus K–Zn–Mn fertilizer increased the yield of rice by 135%. In alkaline, salinized, and secondary salinized soils, FGD gypsum combined with organic fertilizer or organic plus chemical fertilizer increased the yield of rice by 21.2% and 60.4%, the yield of sunflower by 2.4% and 23.6%, and the yield of medlar by 18.81% and 20.78%, respectively. The application of FGD gypsum also increased the salt tolerance of salt-tolerant plants. Combined with drainage, laser field levelling and tillage decreased soil salinity by more than 63.76% and increased the yield of oil sunflower by up to 96.96%. This study provides convincing evidence of the benefits of the application of the six treatments to reclaim saline–alkali soils. It is suggested that comprehensive measures should be taken to improve saline–alkaline soil.

Biological improvement is a sustainable approach for saline–alkali land amelioration and utilization. Echinochloa frumentacea (Roxb.) link is a salt-tolerant gramineous forage, which plays an important role in improving saline–alkali land. The Hetao Ningxia Plain is located in the upper–middle reaches of the Yellow River with a large area of saline–alkali soil, where E. frumentacea has potential applications for improving saline–alkali land. Three experiments were conducted on saline–alkali land in Pingluo County, Ningxia, including soil-leaching experiments in pots as well as monoculture or intercropping experiments involving E. frumentacea in fields. The results showed that: (1) E. frumentacea had a strong leaching ability of Na⁺ and SO₄²⁻ in saline–alkali soil. (2) The planting of E. frumentacea decreased soil pH and total salt; enhanced the available N, P and K; and increased plant height, stem thickness and yields compared with the control. (3) The diversity of soil bacteria and land use efficiency could be improved by the intercropping of E. frumentacea with legume forages. Overall, E. frumentacea is an important pioneer species of biological improvement for the sustainable utilization of secondary saline–alkali land produced by irrigation around the world.

The use of chemical fertilizer along with organic fertilizer is an important agricultural practice that improves crop yield but also affects soil biogeochemical cycles. In this study, a maize field experiment was conducted to investigate the effects of NPK fertilizer (NPK), organic fertilizer (OF), and their combination (NPK+OF) on soil chemical properties, bacterial and fungal community structures, and diversity compared the control (CK, without any fertilizer). The results showed that the application of OF and NPK-combined OF increased soil organic matter (OM), total N, total P, available N, available P, and available K levels. For alpha diversity analyses, the application of fertilizers led to decreases in soil bacterial and fungal Shannon indices (except for NPK in fungi). Compared with CK, NPK, OF, and NPK+OF fertilization treatments significantly increased the abundances of Acidobacteriota, Gemmatimonadota, and Basidiomycota. Network analysis showed that fertilization produced fewer connections among microbial taxa, especially in the combination of NPK and OF. A redundancy analysis combined with Mantel test further found that the soil OM, available N and P were the main soil-fertility factors driving microbial community variations. Therefore, using organic fertilizer or biological fertilizer combined with chemical fertilizer to improve the status of soil C, N, and P is a promising method to maintain the balance of soil microorganisms in maize field.