Soil salinity and alkalinity can inhibit crop growth and reduce yield, and this has become a global environmental concern. Combined changes in nitrogen (N) application and hill density can improve rice yields in sodic saline–alkaline paddy fields and protect the environment. We investigated the interactive effects of N application rate and hill density on rice yield and N accumulation, translocation and utilization in two field experiments during 2018 and 2019 in sodic saline–alkaline paddy fields. Five N application rates (0 (control), 90, 120, 150, and 180 kg N ha⁻¹ (N0–N4), respectively) and three hill densities (achieved by altering the distance between hills, in rows spaced 30 cm apart: 16.5 cm (D1), 13.3 cm (D2) and 10 cm (D3)) were utilized in a split-plot design with three replicates. Nitrogen application rate and hill density significantly affected grain yield. The mathematical model of quadratic saturated D-optimal design showed that with an N application rate in the range of 0–180 kg N ha⁻¹, the highest yield was obtained at 142.61 kg N ha⁻¹ which matched with a planting density of 33.3×10⁴ ha⁻¹. Higher grain yield was mainly attributed to the increase in panicles m^–2. Nitrogen application rate and hill density significantly affected N accumulation in the aboveground parts of rice plants and showed a highly significant positive correlation with grain yield at maturity. From full heading to maturity, the average N loss rate of the aboveground parts of rice plants in N4 was 70.21% higher than that of N3. This is one of the reasons why the yield of N4 treatment is lower than that of the N3 treatment. Nitrogen accumulation rates in the aboveground parts under treatment N3 (150 kg N ha⁻¹) were 81.68 and 106.07% higher in 2018 and 2019, respectively, than those in the control. The N translocation and N translocation contribution rates increased with the increase in the N application rate and hill density, whereas N productivity of dry matter and grain first increased and then decreased with the increase in N application rate and hill density. Agronomic N-use efficiency decreased with an increase in N application rate, whereas hill density did not significantly affect it. Nitrogen productivity of dry matter and grain, and agronomic N-use efficiency, were negatively correlated with grain yield. Thus, rice yield in sodic saline–alkaline paddy fields can be improved by combined changes in the N application rate and hill density to promote aboveground N accumulation. Our study provides novel evidence regarding optimal N application rates and hill densities for sodic saline–alkaline rice paddies.

The incorporation of straw in cultivated fields can potentially improve soil quality and crop yield. However, the presence of recalcitrant carbon compounds in straw slow its decomposition rate. The objective of this study was to determine the effects of different nitrogen sources, with and without the application of zinc, on straw decomposition and soil quality. Soils were treated with three different nitrogen sources, with and without zinc: urea (CO(NH2)2), ammonium sulfate ((NH4)2SO4), and ammonium chloride (NH4Cl). The combined treatments were as follows: maize (M) and wheat (W) straw incorporated into urea-, ammonium sulfate-, or ammonium chloride-treated soil (U, S, and C, respectively) with and without zinc (Z) (MU, MUZ, WU, WUZ; MS, MSZ, WS, WSZ; MC, MCZ, WC, WCZ, respectively); straw with zinc only (MZ, WZ); straw with untreated soil (MS, WS); and soil-only or control conditions (NT). The experiment consisted of 17 treatments with four replications. Each pot contained 150 g soil and 1.125 g straw, had a moisture content of 80% of the field capacity, and was incubated for 53 days at 25°C. The rates of CO2-C emission, cumulative CO2-C evolution, total CO2 production in the soils of different treatments were measured to infer decomposition rates. The total organic carbon (TOC), labile organic carbon (LOC), and soil microbial biomass in the soils of different treatments were measured to infer soil quality. All results were significantly different (P<0.05) with the exception of the labile organic carbon (LOC). The maize and wheat straw showed different patterns in CO2 evolution rates. For both straw types, Zn had a synergic effect with U, but an antagonistic effect with the other N sources as determined by the total CO2 produced. The MUZ treatment showed the highest decomposition rate and cumulative CO2 concentration (1 120.29 mg/pot), whereas the WACZ treatment had the lowest cumulative CO2 concentration (1 040.57 mg/pot). The addition of NH4Cl resulted in the highest total organic carbon (TOC) concentration (11.59 mg kg-1). The incorporation of wheat straw resulted in higher microbial biomass accumulation in soils relative to that of the maize straw application. The results demonstrate that mineral N sources can affect the ability of microorganisms to decompose straw, as well as the soil carbon concentrations.

Classical swine fever (CSF) and porcine reproduction and respiratory syndrome (PRRS) are both economically important, highly contagious diseases of swine worldwide. To develop an effective vaccine to control these two diseases, we constructed a recombinant adenovirus rAdV-GP52AE2, using a replication-defective human adenovirus serotype 5 as a delivery vector, to co-express the GP5 protein of highly pathogenic porcine reproduction and respiratory syndrome virus (PRRSV) and the E2 protein of classical swine fever virus (CSFV). Foot-and-mouth disease virus (FMDV) 2A peptide was used as a linker between the GP5 and E2 proteins to allow automatic self-cleavage of the polyprotein. The GP5 and E2 genes were expressed as demonstrated by immunofluorescence assay and Western blotting. Immunization of mice resulted in a CSFV-neutralizing antibody titer of 1:128 and a PRRSV-neutralizing antibody titer of 1:16. The lymphoproliferative responses were detected by Cell Counting Kit-8 assay and the stimulation index of CFSV-specific and PRRSV-specific lymphocytes in the rAdV-GP52AE2 group was significantly higher than that in the negative control group. The results show that rAdV-GP52AE2 can induce both effective humoral and cell-mediated immune responses in mice. The protective efficacy of the recombinant virus against CSF was evaluated in immunized rabbits, which were protected from fever induced by challenge with C-strain. Our study provides supporting evidence for the use of FMDV 2A to develop a bivalent genetically-engineered vaccine.