Production of potassium-enriched biochar from Canna indica: Transformation and release of potassium

Addressing cadmium stress in rice with potassium-enriched biochar and Bacillus altitudinis rhizobacteria

Cadmium (Cd) is a potentially harmful metal with significant biological toxicity that adversely affects plant growth and physiological metabolism. Excessive Cd exposure in plants leads to stunted plant growth owing to its negative impact on physiological functions such as photosynthesis, nutrient uptake, and water balance. Potassium-enriched biochar (KBC) and Bacillus altitudinis rhizobacteria (RB) can effectively overcome this problem. Potassium-enriched biochar (KBC) significantly enhances plant growth by improving the soil structure, encouraging water retention, and enhancing microbial activity as a slow-release nutrient. Rhizobacteria promote plant growth by improving root ion transport and nutrient availability while promoting soil health and water conservation through RB production. This study examined the effects of combining RB + KBC as an amendment to rice, both with and without Cd stress. Four treatments (control, KBC, RB, and RB + KBC) were applied using a completely randomized design (CRD) in four replications. The results showed that the combination of RB + KBC increased rice plant height (38.40%), shoot length (53.90%), and root length (12.49%) above the control under Cd stress. Additionally, there were notable improvements in chlorophyll a (15.31%), chlorophyll b (25.01%), and total chlorophyll (19.37%) compared to the control under Cd stress, which also showed the potential of RB + KBC treatment. Moreover, increased N, P, and K concentrations in the roots and shoots confirmed that RB + KBC could improve rice plant growth under Cd stress. Consequently, these findings suggest that RB + KBC is an effective amendment to alleviate Cd stress in rice. Farmers should use RB + KBC to achieve better rice growth under cadmium stress.

Competitive adsorption of polycyclic aromatic hydrocarbons on phosphorus tailing-modified sludge biochar provides mechanistic insights

Biochar has been widely used to solve the wastewater pollution of polycyclic aromatic hydrocarbons (PAHs). However, the competition of PAHs with different benzene ring numbers (e.g., phenanthrene [Phe], pyrene [Pyr], and benzo[a]pyrene [BaP]) for adsorption sites on biochar has received little attention. In this study, biochar was produced by co-pyrolysis of sludge and phosphorus tailing at different temperatures (300, 500, or 800 °C) to adsorb PAHs. The results show that phosphorus tailing increased the adsorption of PAH by increasing the biochar's BET surface area (SBET), micropore volume, hydrophobicity (at low temperatures) and aromaticity (at high temperatures). The maximum adsorption capacities were 29.90 µmol/g for Phe, 25.58 µmol/g for Pyr and 20.45 µmol/g for BaP, respectively. Importantly, the types and functions of groups involved in the adsorption of various PAHs were discussed. Adsorption of Phe and Pyr on the biochar mainly involved C=O and C-O-C functional groups, and there was a certain degree of competition between these PAHs for those sites. In contrast, BaP mainly adsorbed at C-OH and C=C moieties, without competing with Phe or Pyr at C-OH sites. The competitive edge of BaP was also stronger than that of Phe and Pyr on C=C functional groups. The adsorption mechanisms involving pore filling, hydrophobic interactions, and π-π interactions governed the adsorption of the evaluated PAHs. Overall, the adsorption of PAHs on biochar followed a heterogeneous chemical adsorption process.

Evaluation of potassium-enriched biochar and GA3 effectiveness for Improving wheat growth under drought stress

Osmotic stress is a significant concern in agricultural crop production as it can harm crop growth, development, and productivity. Agriculture crops are particularly vulnerable to osmotic stress due to their reliance on water availability for various physiological processes. Organic amendments like activated carbon biochar and growth hormone gibberellic acid (GA3) can play a vital role. However, the time needed is to modify the established amendment to achieve better results. That's why the current study used potassium-enriched biochar (KBC = 0.75%) with and without GA3 (15 mg/L) as amendments under no osmotic stress and osmotic stress in wheat. Results showed that GA3 + KBC caused significant enhancement in germination (9.44%), shoot length (29.30%), root length (21.85%), shoot fresh weight (13.56%), shoot dry weight (68.38), root fresh weight (32.68%) and root dry weight (28.79%) of wheat over control under osmotic stress (OS). A significant enhancement in chlorophyll a, chlorophyll b and total chlorophyll, while the decline in electrolyte leakage of wheat, also validated the effectiveness of GA3 + KBC over control in OS. In conclusion, GA3 + KBC is the most effective among all applied treatments for improving wheat growth attributes under no osmotic and osmotic stress. Further research is needed at the field level, focusing on various cereal crops, to establish GA3 + KBC as the optimal treatment for effectively mitigating the impacts of osmotic stress.

Dynamics of potassium released from sewage sludge biochar fertilizers in soil

The solid product of sewage sludge (SS) pyrolysis, called SS biochar (SSB), is rich in carbon and nutrients, such as phosphorus (P), nitrogen (N), calcium (Ca), and zinc (Zn). However, SSB has a low potassium (K) concentration because it is released with water during the final stage of sewage treatment. The enrichment of SSB with mineral sources of K can solve the low supply of K in SSB and produce an organomineral fertilizer with a slow release of K. However, the dynamics of K release from these enriched fertilizers in different soil types remain unclear. This study investigated the dynamics of K release from biochar-based fertilizer (BBF) in the form of pellets and granules in two soil types (clayey and sandy) and natural silica. An incubation experiment was conducted for 60 days, and replicates were evaluated at prescribed time intervals. After the incubation period, the levels of K available in the solid fraction were determined, and the dynamics of K release were evaluated using four nonlinear regression models. BBFs achieved a slower release of K than the mineral KCl. The dynamics of K release were affected by the physical form of BBF, such that the pelleted BBF exhibited the slowest K release. Furthermore, regarding the concentration detected in the solid phase, the total released was highest in clayey soil, followed by sandy soil and natural silica. The enriched BBFs reduced K release throughout the experimental period, behaving as slow-release fertilizers with the potential to optimize K uptake by plants throughout the growth cycle. Further studies are required to evaluate K leaching and retention in the soil profile when biochar-based fertilizers are applied.