Soil salinization and secondary salinization have often occurred in the Yellow River irrigation area of northern Ningxia, China. As such, the regional food security is seriously constrained in sustainable agriculture. However, existing research has focused mainly on a single improvement. In this study, a systematic comparison was made of the different organic amendments on the water-salt transport, nutrient dynamics, and crop physiological responses. Three organic amendments were selected from the humic acid (HA), carboxymethyl cellulose (CMC), and amino acids (AA). Their efficacy was also evaluated to regulate the soil physicochemical properties and maize productivity. Specific regulatory mechanisms of these amendments were determined in deep soil. The optimal technical patterns were identified for the ecological restoration and yield enhancement of the saline-alkali land in the arid irrigation areas. A continuous three-year experiment of the field positioning was conducted from April 2022 to September 2024. A typical saline-alkali region was taken from the Pingluo County, Shizuishan City, Ningxia Hui Autonomous Region, China. A randomized complete block design was employed with four treatments: unamended control (CK), humic acid (HA, 1500 kg/hm²), carboxymethyl cellulose (CMC, 200 kg/hm²), and amino acids (AA, 1500 kg/hm²). Soil samples were collected from the 0-100 cm profile in 10 cm increments during the maize jointing, tasseling, and milking stages. Key parameters were measured, including the soil gravimetric water content, saturated paste extract electrical conductivity (EC), pH, sodium adsorption ratio (SAR), alkali-hydrolyzable nitrogen, available phosphorus, available potassium, and soil organic carbon. Additionally, some indicators were monitored annually, including the maize photosynthesis, agronomic traits, aboveground biomass, grain yield, and water use efficiency (WUE). Economic benefits were calculated using input costs and crop output values. The results indicated that all organic amendments were significantly optimized after the soil microenvironment, compared with the control. 1) The CMC treatment exhibited the strongest water retention capacity in the plow layer (0-40 cm) after the formation of a hydrophilic gel network. Among them, surface evaporation and deep percolation were significantly reduced by 40.49%. This physical barrier also inhibited the salt leaching in deeper layers. In contrast, the HA treatment demonstrated the most effective desalination. Cation exchange was also enhanced to displace the sodium ions. The HA was achieved in a desalination rate of 26.22-35.08 in the 0-50 cm active root zone, compared with the CK. While the soil SAR was reduced by 18.13%~21.64%. 2) All amendments significantly enhanced the soil fertility, where the soil organic carbon, alkali-hydrolyzable nitrogen, and available potassium contents also increased by 13.87%-56.99% over the 0-100 cm profile. The HA and AA treatments improved the nutrient availability, whereas the nutrient activation of the CMC was relatively lower. 3) While the amendments failed to significantly alter the vegetative traits, such as the plant height or stem diameter, they markedly improved the reproductive output. The average grain yield reached 13499 kg/hm² after 3 years of humic acid treatment, which was 27.67% higher than the control treatment, and the water use efficiency reached 24.46 kg/(hm²·mm). 4) The HA treatment also yielded the highest net income (21677.60 Yuan/hm²) and input-output ratio (3.04). Although the AA treatment increased the yield, the high marginal cost significantly lowered the input-output ratio (2.12), thus limiting its economic viability as a standalone amendment. In conclusion, the regulatory mechanisms were identified for the three amendments under saline-alkali conditions. Humic acid was the optimal choice for soil improvement. The sodium was effectively displaced to improve the soil structure and economic returns. Moreover, carboxymethyl cellulose was also required to prevent the deep-layer salt accumulation, suitable for the water-scarce areas. Amino acids served as the nutrient activators, indicating the economic constraints for the large-scale application. Future strategies should focus on the synergistic optimization of humic acid with the low-cost amendments in the Yellow River irrigation area, particularly for the cost-effectiveness and ecological benefits.

Based on an understanding of the differences in salt composition and nutrient availability, saline-alkali land improvement can be carried out to specifically improve the soil environment of saline-alkali land and increase crop yields. The objective of this study was to select an appropriate treatment of fertilizer application combined with improvement agents for maize planation in Ningxia, China. Given the unique characteristics of secondary saline-alkali soils in the Northwest Hetao Irrigation District, this study focused on the synergistic regulation of the “amendment-fertilizer-soil-crop” system. It investigated different types of amendment-organic fertilizer application patterns to address three key issues: 1) elucidate the synergistic mechanisms of composite amendments and fertilizer application on soil salinity migration and transformation, and clarify the interactive effects of each component in salinity regulation; 2) Reveal the coupled influence patterns of application patterns on soil physical and chemical properties and corn growth; 3) Select the optimal application scheme suitable for the Hetao Irrigation District, quantify its effect on reducing the annual accumulation rate of soil salinity, and assess its potential for increasing maize yields. This treatment was designed as the combinations of amendments (microbial agents, activated humic acid, and microsilica powder) and different types of fertilizers (conventional chemical fertilizers, organic fertilizers, and amino acid containing fertilizers) with no fertilization as the control. The field experiment of maize was carried out in 2023. Soil pH value, total salt, salt distribution, nutrients, and corn yield were analyzed at different stages of maize. The results showed that: 1) The application of activated humic acid in combination with amino acids can effectively reduce soil pH, alkalinity, and total salt content. Under this treatment, soil fertility levels improved most significantly, with organic matter and alkali-hydrolyzable nitrogen increasing by 80.92% and 86.07%, respectively, compared to pre-improvement levels. Activated humic acid combined with amino acids can improve soil quality by regulating salinity and alkalinity indicators, with Na⁺ and Cl⁻ levels decreasing by 83.34% and 57.27%, respectively, compared to pre-improvement levels. Under this treatment, the maize yield reached 137.77 kg/hm², increased by 3.97% to 29.52% compared to other treatments. 2) The soil quality index was the highest under the treatment of activated humic acid combined with amino acid treatment. This treatment outperformed other treatments in reducing saline-alkali indicators, improving soil fertility, and increasing maize yield. 3) The application of activated humic acid combined with amino acids improved soil quality by reducing soil salinity, increasing soil nutrients, and enhancing soil fertility. In summary, the use of activated humic acid combined with amino acids is recommended as a guideline for improving saline-alkali soils and achieving high maize yields in the study area.

The harmless treatment of livestock and poultry reduces the risk of water and soil pollution caused by untreated discard of sick and dead livestock. Chemical fertilizer increases crop yield, while its over-application will lead to serious problems such as agricultural non-point source pollution as well as land acidification and soil compaction. It is of great significance to explore the utilization potential of bio-organic matter originating from harmless treatment of livestock to improve the soil environment and enhance agricultural productivity. This study investigated the effects of different application rates of bio-organic matter (0, 1285, 1928, 2571 kg/hm²) and biochar addition (0, 10 000 kg/hm²) on soil properties and crop yield under 20% reduction of chemical nitrogen fertilizer. The results indicated that the application of bio-organic matter combined with biochar improved soil physical structure under fertilizer reduction by decreasing soil bulk density and increasing soil porosity and soil aggregate stability. Compared to that under CK, the soil bulk density was reduced by 1.42%-6.38%, and the soil porosity was increased by 1.17%-7.05%. Compared to conventional fertilization, applying bio-organic matter (1 928 kg/hm²) ensured sufficient soil nutrients for crop growth under 20% of fertilizer reduction. The soil fertility was further boosted by the addition of biochar. The alkaline nitrogen content peaked under BM3 with 42.08 mg/kg, and the total nitrogen content and soil organic matter content reached their peak values under NM4 treatment, which were 0.97 g/kg and 21.23 g/kg, respectively. The higher the amount of bio-organic matter applied, the higher the grain yield and crop water productivity. The yield gained with bio-organic matter application alone at the rate of 2571 kg/hm² under fertilizer reduction (NM4) was 7504 kg/hm², which can reach equal yield level with CK, while medium to high addition of bio-organic matter combining biochar (BM3 and BM4 treatments) produced higher grain yield than that under CK. The correlation analysis showed significant positive correlations between total nitrogen and maize yield and between soil organic matter and maize yield. Overall, under 20% fertilizer reduction, applying bio-organic matter at the rate of 1928 kg/hm² and combining biochar at the rate of 10 000 kg/hm² would be an economical plan to enhance soil physicochemical properties and ensure stable maize yield, and would also supply a scientific way to reuse bio-organic matter originating from harmless treatment of livestock carcasses.

Increasing the planting density can exacerbate crop competition for water, nutrients and space which results in a decline in the crop yields. However, the effect of increasing planting density on crop growth and soil biological characteristics in barren sandy land in the semi-arid regions are still unclear. In this study, we investigated the effects of six planting densities (5.4×10⁴, 6.45×10⁴, 7.95×10⁴, 9.5×10⁴, 9.75×10⁴ and 10.5×10⁴ plants/hm²) on maize growth, photosynthesis characteristics, yield and soil biological characteristics in barren sandy soil in the semi-arid region of Ningxia, China. The results indicated that the stem diameter and spike length decreased linearly with increasing planting density. The plant height, spike weight, grain weight and 100-grain weight decreased with increasing plating density. Moreover, the root length increased with increasing planting density. The diameter, volume and activity increased and then decreased with increasing planting density. There was no significant difference (p>0.05) in the effect of planting density on transpiration rate intercellular CO₂ concentration. As well, the soil microbial biomass carbon and microbial biomass nitrogen decreased with increasing planting density. The soil catalase activities increased and then decreased with increasing planting density. The alkaline phosphatase activity, the amounts of soil bacteria and actinomycetes increased with increasing planting density. Generally, a moderately increasing planting density can improve maize yield when water and nutrients are sufficient. The optimal planting density was 8.29×10⁴ plants/hm² and the highest yield was 15.84 t/hm² in barren sandy soil in semi-arid region of Ningxia, China. This study provides a theoretical basis for high yield and high efficiency of maize.

To understand the combined effect of organic and chemical fertilizers on soil carbon emissions and carbon balance of a farmland ecosystem, this study investigated the organic fertilizer nitrogen replacing different proportions of chemical fertilizer nitrogen. The results showed that, compared to F₁₀₀, the O₁₅F₈₅ treatment increased the yield and net ecosystem productivity carbon sequestration of silage maize under mild, moderate, and severe salinization levels, as well as the contents of soil organic carbon, microbial carbon, and humin carbon, while reducing plant carbon emissions. The O₁₅F₈₅ treatment did not significantly increase soil carbon emissions (CEC), but O₃₀F₇₀, O₄₅F₅₅ and O₁₀₀ treatments significantly increased CEC. The soil carbon balance analysis showed that the farmland ecosystem was a “sink” for atmospheric CO₂ under each treatment. The O₁₅F₈₅ treatment produced an “excitation effect” to enhance the carbon sink effect of silage maize farmland under mild, moderate and severe salinization levels while maintaining stable production and emissions. Although the O₁₀₀ treatment increased the carbon sink of farmland under different salinization levels, the yield was significantly reduced and did not represent practical production levels. Correlation analysis showed that soil organic carbon components and ecosystem carbon balance were closely related to soil total salt, pH and bulk density, while soil dissolved organic carbon, humus carbon components and carbon emissions were closely related to soil moisture and temperature. Therefore, the purpose of improving the carbon sink of saline-alkali land can be achieved through soil salt inhibition, soil structure remodeling and water supplement and warming regulation, which provides technical and theoretical support for reducing carbon emissions, achieving carbon neutrality and alleviating global warming.