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Paddy soil plays a vital role in sequestering carbon (C) and thereby contributes to mitigating the effects of global warming. The soil organic carbon (SOC) sequestration potential of paddy soil is estimated to be as much as 40% (Chen et al., 2021;Cui et al., 2020;Pan et al., 2004). Physical protection of SOC formation and its persistence in soil structure are the main mechanisms for building and maintaining C stocks in the long term (Cotrufo et al., 2015). In agricultural soil, sustainable agricultural management practices are a global priority for achieving food

In this study, we conducted field experiments to assess the effects of the combined application of Chinese milk vetch (Astragalus sinicus L., CMV) and red mud (RM) to remediate the cadmium-polluted acidic paddy soil. The results showed that the combined application increased the yield component index and improved the grain yields, compared with the control, RM1, RM2, and CMV treatments. However, the increased range of soil pH values in the CMV-RM1 and CMV-RM2 treatments was smaller than that of the RM1 and RM2 treatments at the different rice growth stages. The soil organic matter (SOM) contents of the RM-only treatments did not differ throughout the whole period, but were significantly different (p < 0.05) between CMV-RM2 and the control. Compared with the control, the combined application decreased the concentration of exchangeable Cd in the early rice soil. The combined application of CMV and RM substantially decreased the rice uptake of Cd. However, we found no significant difference (p < 0.05) between the CMV-RM1 and CMV-RM2 treatments. Therefore, compared with remediation with RM or CMV alone, we recommend the combined application of CMV and RM as an economical, highly effective, and replicable amendment for remediating acidic, Cd-polluted paddy soil. Considering the restorative effect and proper use of RM, we recommend CMV-RM1 treatment.

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Rational application of organic and chemical fertilizers is beneficial to improve crop yield and quality. However, the effect of combining these fertilizers on bacterial community structure and metabolic functions remains unclear, especially in reddish paddy soil. In the present study, absolute quantification 16S rRNA amplicon sequencing technology (AQS) was used to study the responses of soil bacterial community composition and its absolute abundance to environmental factors under different application ratios of organic and chemical fertilisers for two consecutive years in reddish paddy soil. The results showed that replacing the chemical fertiliser with organic fertiliser significantly increased the total nitrogen (TN), total potassium, hydrolysed nitrogen, and soil organic carbon (SOC), and significantly decreased the soil bulk density. These effects were more prominent in the treatment with 60% of organic fertilizer (60M). More importantly, AQS revealed that different fertilization treatments non-significantly affected soil bacterial diversity (Shannon) and richness (Chao1) but significantly changed the composition and abundance of bacterial communities. SOC, TN, and available potassium were the key factors shaping bacterial community structure under different fertilization regimes. The bacterial absolute abundance in the 60M treatment was 25.30% and 56.58% higher than that in the NPK and 30M treatments, respectively. Functional prediction analysis with PICRUSt2 revealed that the 60M treatment increased the abundance of species involved in xenobiotic biodegradation and metabolism, amino acid metabolism, and lipid metabolism, and further improved metabolic functions to a certain degree.

Declining earth resources, rising ore cost and pollution call for better recycling of wastewater in the context of the circular economy. In particular, urine is a potential huge source of phosphorus (P) and potassium (K) agricultural nutrients, yet the efficiency of actual methods for P and K recovery are limited. Here we designed a electrochemical crystallization system using sacrificial magnesium anodes to recover P and K in the form of K-struvite (MgKPO4·6H2O) from simulated urine at low (P/K=0.25) and high (P/K=0.6) phosphate levels, respectively. Results show optimal recoveries of 88.5% for P and 35.4% for K in the form of rod-shaped K-struvite at 3.5 mA/cm2, yet higher current density reduced recovery due to side reactions and pH increase. Adding phosphate to urine increased K recovery to 35.4% versus 15.0% without phosphate. Adding prefabricated struvite crystals at 1.6 g/L into urine enhanced the recovery of K by 14.7% and of P by 23.7% compared to the control group. Overall, our findings show that electrochemical crystallization is promising for the recovery of K-struvite fertilizers.