Batch experiments were conducted to investigate the adsorption characteristics of tetracycline (TC), and the interactive effects of copper (Cu) on the adsorption of TC onto water hyacinth roots. TC removal efficiency by water hyacinth roots was ranging from 58.9% to 84.6%, for virgin TC, 1:1 TC-Cu and 1:2 TC-Cu. The Freundlich isotherm model and the pseudo-second-order kinetic model fitted the adsorption data well. Thermodynamics parameters ΔG⁰ for TC were more negative in the TC plus Cu than the TC-only treatments, indicating the spontaneity of TC adsorption increased with increasing of Cu concentrations. An elevated temperature was associated with increasing adsorption of TC by water hyacinth roots. The additions of Cu(II) significantly increased TC adsorption onto water hyacinth roots within the pH range 4 to 6, because copper formed a strong metal bridge between root surface and TC molecule, facilitating the adsorption of TC by roots. However, Cu(II) hindered TC adsorption onto water hyacinth roots on the whole at pH range from 6–10, since the stronger electrostatic repulsion and formation of CuOH⁺ and Cu(OH)₂. Therefore, the interaction between Cu(II) and TC under different environmental conditions should be taken into account to understand the environmental behavior, fate, and ecotoxicity of TC.

Returning residue to soils is not only an effective nutrient management method, but also can reduce the air pollution caused by residue burning, which has become an important factor in global warming. However, it is not clear whether returning residue to the soil can affect the nitrogen mineralization and the nitrogen cycle process, and the environmental impact caused by the nitrogen loss in gaseous forms. Therefore, a pot experiment was conducted to study the effects of residue placement on the nitrogen turnover process, including microbial biomass N (MBN) and C (MBC), inorganic N, crop N uptake, and the contribution of residue-derived N to maize at different maize growth stages. Three treatments were assessed: no residue addition (T0), residue addition to the soil surface (T1), and residue incorporation into the 0–10 cm soil layer (T2). Soil samples were taken at the 0–5 and 5–10 cm layers for all residue treatments. Residue retention (T1 and T2) significantly affected the MBC and MBN contents and decreased MBC/MBN ratio at different maize growth stages. MBC/MBN markedly increased at the R1 stage compared to other growth stages. The differences in total inorganic nitrogen (TIN) were attributed to the balance in net N immobilization and net mineralization in the different maize growth stages. In addition, T2 significantly increased the residue-derived N source for maize by 11.3% compared to T0 in the R3 growth stage. Overall, relative to T1, T2 is a better agriculture management measure to promote N transformation and supply, and enhance residue-derived N release and uptake in maize.

Soil aggregate-size distribution and soil aggregate stability are used to characterize soil structure. Quantifying the changes of structural stability of soil is an important element in assessing soil and crop management practices. A 5-year tillage experiment consisting of no till (NT), moldboard plow (MP) and ridge tillage (RT), was used to study soil water-stable aggregate size distribution, aggregate stability and aggregate-associated soil organic carbon (SOC) at four soil depths (0–5, 5–10, 10–20 and 20–30 cm) of a clay loam soil in northeast China. Nonlinear fractal dimension (D_m) was used to characterize soil aggregate stability. No tillage led to a significantly greater aggregation for >1 mm aggregate and significant SOC changes in this fraction at 0–5 cm depth. There were significant positive relationships between SOC and >1 mm aggregate, SOC in each aggregate fraction, but there was no relationship between soil aggregate parameters (the proportion of soil aggregates, aggregate-associated SOC and soil stability) and soil bulk density. After 5 years, there was no difference in D_m of soil aggregate size distribution among tillage treatments, which suggested that D_m could not be used as an indicator to assess short-term effects of tillage practices on soil aggregation. In the short term, > 1 mm soil aggregate was a better indicator to characterize the impacts of tillage practices on quality of a Chinese Mollisol, particularly in the near-surface layer of the soil.

Maize (Zea mays L.) is a valuable forage crop. It is also an essential and promising crop for the Republic of Kazakhstan, cultivated in the southern zone. Some new maize hybrids have been introduced, which have been beneficial for high yields with less fertilizer input. This study aims to introduce the new maize hybrid, Arman 689, for the judicial use of fertilizer and the high yield. This study was carried out in 2015 in the southeast region of Kazakhstan. There are five treatments with various mineral fertilizer and poultry manure doses: 1. control (T0), 2. P₆₀ K₁₀₀ (T1), 3. N₁₀₀P₆₀K₁₀₀ (T2). 4. N₁₀₀P₆₀K₁₀₀ + 40 tons of manure/ha (T3), and 5. N₁₀₀P₆₀K₁₀₀ + 60 ton of manure/ha (T4). The fertilizers used were ammonium nitrate (N—34.6%), amorphous (N—11.0%, P₂O₅—46.0%), and potassium chloride KCl (K₂O—56%). The results showed that the grain yield ranges from 5.51 t/ha (T0) to 8.49 (T4) t/ha. The protein contents in the maize grain varied from 9%(T0)–11.3%(T4). The grain nitrogen content accounted for 54.2 to 52.0%. The nutrient uptake results by different treatments indicated that nitrogen contributed to 41.5% of the total yield increase. Using manure in combination with mineral fertilizers reduced the payback of the applied resources, as the payback of T2–T4 was 8.8–9.1 kg of grain. With the application of recommended mineral fertilizer (NPK), the protein yield was 0.83 t/ha, 0.33, and 1.22 t/ha higher than T0 and T1 treatments, respectively. There was no significant yield difference under T3 and T4 treatments (p > 0.05). Overall, the treatment, NPK + 40 tons of manure, was proved the ultimate for the Arman hybrid in providing the optimum quantity and quality of maize, as well as reducing the payback cost (8.8–9.1 kg of grain). It is suggested to apply NPK-recommended doses along with manure in maize (Arman hybrid)-based intercropping systems to utilize the resources efficiently.

Oxalic acid is a key root exudate released by plants under phosphorus (P) deficiency and plays a direct role in solubilizing fixed soil P. However, its specific effects on soil microbial community assembly and ecological functions remain less clear. In this study, based on an ex planta soil microcosm incubation experiment, the impacts of oxalic acid input on soil bacterial and fungal community assemblage and functional profiles involved in P mobilization were explored. The results showed that oxalic acid input significantly changed soil bacterial and fungal community composition, decreased their diversity, and enriched bacterial taxa involved in P mobilization and fungal taxa associated with plants, showing the selective effects of oxalic acid on soil microorganisms. Further community assembly analyses (βNTI and NST) showed that oxalic acid input promoted a shift in bacterial community from a stochastic-process-dominated community to a deterministic-process-dominated community, while the fungal community exhibited a converse pattern. These findings reveal the important role of oxalic acid in shaping soil microbial community assembly and ecological functions under P deficiency, broadening our understanding of the role of oxalic acid in plant responses to low-P stress.