Soil salinization is a significant threat to soil health, especially to the agricultural ecosystem; it reduces vegetation biomass, destroys ecosystem diversity, and limits land use efficiency. This area of investigation has garnered extensive attention in China, especially in the arid and semi-arid areas, totaling 7.66 × 10⁶ ha. A variety of theoretical research and technology developments have contributed to soil water and salt regulation and the screening of salt-tolerant varieties to improve nutrient utilization efficiency and microbial control and reduce ecological problems due to saline-based obstacles. These techniques can be classified into physical treatments, chemical treatments, biological treatments, and combined treatments; these different measures are all aimed at primarily solving saline–alkali stress. In general, the improvement and utilization of saline–alkali soil contribute to soil health improvement, concentrating on high-quality development, food security, ecological security, cultivated land protection, and agricultural upgrading. However, the risks of various technologies in the practical production process should be highlighted; green and healthy measures are still expected to be applied to saline–alkali land.

Biochar has been widely recognized as an effective and eco-friendly ameliorant for saline soils, but information about the mechanism of how biochar influences nitrification in salt-affected agroecosystem remains fragmented. An incubation experiment was performed on the salt-affected soil collected from a three-consecutive-year experiment at biochar application gradients of 7.5 t⋅ha⁻¹, 15 t⋅ha⁻¹ and 30⋅t ha⁻¹ and under nitrogen (N) fertilization. Responses of the nitrification rate (NR), numbers of ammonia monooxygenase (amoA) gene copies, and community structures of ammonia-oxidizing bacteria (AOB) and archaea (AOA) to biochar application were investigated. The results indicated that, under N fertilization, the NR and numbers of amoA-AOB and amoA-AOA gene copies negatively responded to biochar addition. Biochar application increased the community diversity of AOB but decreased that of AOA. Biochar addition and N fertilization shifted the AOB community from Nitrosospira-dominated to Nitrosospira and Nitrosomonas-dominated, and altered the AOA community from Nitrososphaera-dominated to Nitrososphaera and Nitrosopumilus-dominated. The relative abundance of Nitrosospira, Nitrosomonas and Nitrosopumilus decreased, and that of Nitrosovibrio and Nitrososphaera increased with biochar application rate. Soil SOC, pH and NO₃⁻-N explained 87.1% of the variation in the AOB community, and 78.1% of the variation in the AOA community was explanatory by soil pH and SOC. The SOC and NO₃⁻-N influenced NR through Nitrosovibrio, Nitrosomonas, Norank_c_environmental_samples_p_Crenarchaeota and amoA-AOB and amoA-AOA gene abundance. Therefore, biochar addition inhibited nitrification in salt-affected irrigation-silting soil by shifting the community structures of AOB and AOA and reducing the relative abundance of dominant functional ammonia-oxidizers, such as Nitrosospira, Nitrosomonas and Nitrosopumilus.

The summer maize-winter barley (or wheat) rotation system is a conventional farming method in coastal areas of east China. However, researchers have paid little attention to the increasing soil degradation after successive crop rotation in coastal saline agriculture. In the current study, a two-year field experiment was conducted to investigate the changes in soil physio-chemical properties and crop grain yields under the maize-barley rotation system. Wheat straw derived biochar (BC) was applied to topsoil (0~20 cm) at four different rates (0, 7.5, 15 and 30 Mg ha⁻¹) before summer maize cultivation, and no biochar was added in the cultivation of the winter barley. Bulk density (BD), water holding capacity (WHC), water stable aggregate (WSA), soil electrical conductivity (EC), pH (1:5 water w/v) and soil organic carbon (SOC), at the harvesting time of maize and barley, were analyzed. The application of biochar increased WHC and macro-aggregate (>2 mm) content after barley harvest. Soil EC was mainly affected by the rain during maize cultivation and increased only slightly under BC treatments. However, no difference in EC was found among all treatments after barley harvest. The application of BC at 30 Mg ha⁻¹ increased the maize yield by 66% but produced no difference in the barley yield. We concluded that biochar could be an effective option to mitigate soil degradation and improve crop productivity in coastal saline agriculture.

In newly reclaimed coastal soil, saline conditions and nutrient deficiency are the restraining factors for crop yield. Manure and plastic film mulch are proved to play a vital role in reducing soil salt, increasing soil water, and improving soil nutrients and plant growth. A field experiment was carried out with plastic film mulch, manure, and their combinations in the Tiaozini reclamation area; four treatments were set up as (1) control treatment (CK), (2) plastic film mulch (PM), (3) farmyard manure (FM), and (4) combined application of plastic film mulch and farmyard manure (PM+FM). The main results showed that, compared with CK treatment, the average soil water content under the FM+PM treatment was increased by 5.8% and 3.6%, and the average soil salt content was reduced by 20.2% and 10.0% at 0–20 cm and 20–40 cm soil layers, respectively. This was because of the decrease in soil bulk density and increase in saturated hydraulic conductivity and saturated water content. Meanwhile, soil organic matter, total nitrogen, available nitrogen, and available phosphorus were significantly increased under the PM+FM treatment, except that for AN, which was significantly decreased at the 0–10 cm soil layer owing to plant uptake. Based on the decrease in soil salt, there was an improvement in soil hydraulic properties and soil nutrients, which resulted in summer maize biomass and yield being increased by 106% and 137%, respectively, and barley biomass and yield were increased by 133% and 106%, respectively, under FM+PM treatment. Consequently, combined manure and plastic film mulch application was better at reducing soil salt; increasing soil water content; and improving soil nutrients, plant growth, and yield production in newly reclaimed salt-affected soils.

A field experiment was conducted to investigate the effects of biochar (BC), fulvic acid (FA) and Bacillus subtilis (BS) on soil properties and crop growth in the coastal salt-affected soil. Four levels of BC (0, 7.5, 15, 30 t ha⁻¹), two levels of FA (0, 1.5 t ha⁻¹) and BS suspension (0, 108 CFU mL⁻¹) were designed during the maize cultivation. The results showed that 30 t ha⁻¹ BC treatment was the most beneficial for improving the soil qualities. The grain yields in treatments containing FA and BS were lower than that in the BC treatments, and they were lower than that in the CK treatment. The treatment of 15 t ha⁻¹ BC + BS obtained the highest grain yield, which was 1.75 times more than CK. An antagonism effect of the combination of FA and BS induced a grain yield decrease, and a higher content application of BC alleviated the negative effects.

Salt-affected soils is an important soil resource. Understanding fertilizer and salinity interaction are of great economic importance for improving crop yield and fertilizer use efficiency. A pot experiment was carried out to study the application of nitrogen (N) for ameliorating salt stress in wheat grown in the coastal saline soil of the Yellow River delta. Several controlling levels of salinity and nitrogen (0.7, 1.7, 2.7 g/kg, and 135, 270, and 405 kg/ha) were designed in a pot experiment in a stable water content state to investigate the N and salt interaction on soil properties and winter wheat growth characteristics. The results showed that the dry weight of winter wheat was promoted by salinity in the early growth stage (20 days), then it was gradually inhibited by nitrogen fertilizer. When winter wheat was grown by 54 days, the N and salinity had significant effects on the biomass of winter wheat. The nitrogen content of wheat shoot and root was mainly affected by N addition usage, and the largest value was obtained in 270 kg/ha N dosage treatments. The higher the salt content existed in the soil, the lower the growth rate shown in wheat cultivation. Under saline conditions, the N fertilizer application amount should be controlled to no more than 270 kg/ha, so that it could greatly promote wheat growth. Reasonable fertilizer usage could significantly contribute to crop yield and food quality of the saline agriculture in the Yellow River delta.