Robusta coffee, a vital cash crop for Vietnamese smallholders, significantly contributes to the national economy. Vietnam is the largest exporter of Robusta coffee, supplying 53% of the global market. However, this success has come at a cost. Decades of intensive Robusta coffee cultivation in Vietnam have led to severe soil acidification and biodiversity loss, favoring soil-borne pathogens. There is a lack of literature analyzing how intensive management causes soil acidification, advances the spread of soilborne pathogens, and the application of soil amendments to address these issues. Therefore, this review explores the causes of acidification, pathogen proliferation, and sustainable amendments like lime and biochar to mitigate these effects. The study synthesizes findings from studies on soil acidification, soil-borne pathogen dynamics, and sustainable soil amendments in Robusta coffee systems. We found that the overuse of nitrogen-based chemical fertilizers to grow coffee is the primary driver of soil acidification, consequently increasing soilborne diseases and the severity of plant diseases. Additionally, the effects of soil amendments as a sustainable solution to reduce soil acidity, enhance soil health, and better control soilborne pathogens. The implementation of sustainable coffee farming systems is strongly recommended to meet the increased demand for safe and green products worldwide. Locally available resources (lime, biochar, and agricultural wastes) present immediate solutions, but urgent action is required to prevent irreversible damage. However, the effects of amendments significantly vary in field conditions, suggesting that further studies should be conducted to address these challenges and promote sustainability.

Inappropriate fertilization and poor management practices in citrus orchards can cause soil acidification, which may result in potential proton (H+) toxicity to citrus roots. It has been reported that boron (B) can mediate H+ detoxification in citrus; however, the mechanisms remain limited. Herein, a hydroponic experiment was employed to unravel the alleviation mechanism of B on H+ toxicity at pH 4 in trifoliate (Poncirus trifoliate (L.) Raf.) seedlings. H+ toxicity reduced cytoplasmic pH from 7.2 (control) to 6.9 and vacuolar pH from 5.6 (control) to 5.4. This severely damaged the plasma membrane (PM) and inhibited root activity by 35%. However, B supplementation restored cytoplasmic pH to 7.1 and vacuolar pH to 5.6, enhancing root activity by 52% and reducing membrane permeability (relative conductivity decreased by 28%). Mechanistically, B upregulated phosphorylated-type adenosine triphosphatase activity by 14%; conversely, it suppressed vacuolar-type adenosine triphosphatase hyperactivity by 9% to stabilize vacuolar pH. Furthermore, B restored PM integrity by increasing phospholipid (40%), glycolipid (50%) and sulfhydryl group (28%) content, critical for membrane structure and function. It is concluded that B can alleviate root growth inhibition induced by H+ toxicity via increasing the content of key components of PM, which not only repairs the damaged PM but also maintains cellular pH homeostasis through enzyme regulation. The improvement of citrus growth correspondingly safeguards the production capacity.

Aluminium (Al) stress is the second-leading abiotic stress on crops. An improved understanding of the response mechanisms of plants to Al stress will provide scientific guidance for enhancing the crops' tolerance to Al stress. In this study, Al stress (50-200 mu M AlCl3) caused visible damage to broad bean (Vicia faba L.) roots rather than shoots, which was attributed to Al accumulation and distribution in different tissues. Root transcriptomic analysis revealed that Al stress altered cell wall properties by downregulating lignin synthesis and several xyloglucan endotransglucosylase/hydrolase-, expansin- and peroxidase (POD)-encoding genes, which likely weakened cell extensibility to inhibit root growth. Additionally, Al stress impeded reactive oxygen species scavenging pathways involving POD activity and flavonoid biosynthesis, leading to oxidative damage characterised by malondialdehyde accumulation. These results indicate that optimising cell wall properties and/or enhancing antioxidant processes are crucial for alleviating Al toxicity to broad beans. Interestingly, exogenous application (500 and 1000 mu M) of the flavonoid apigenin effectively alleviated Al toxicity in broad bean roots by partially improving the total antioxidant capacity of the roots. This study contributes to understanding the interaction between plants and Al and provides new strategies to alleviate Al toxicity in crops.

Acidification of slurry is a promising approach for reducing ammonia emissions during the application procedure. Since only a few studies have been conducted focusing on ammonia emissions during the application of liquid organic fertilizers on the soil surface, a suitable incubation system was developed to evaluate the effects of acidification under controlled conditions. This incubation system was used to measure the ammonia emissions of various liquid organic fertilizers. The substrates were acidified with sulfuric and citric acid to different pH values to determine both the influence of the pH value of the substrates and of the type of acid on the ammonia emissions. The emissions decreased with declining pH value, and the reduction in emissions compared to the initial pH of the substrate was over 86% for pH 6.5 and over 98% for pH 6.0 and below. At the same pH value, the ammonia emissions did not differ between substrates acidified with citric acid and sulfuric acid, although more than twice as much 50% citric acid was required compared to 96% sulfuric acid to achieve the same pH value. Overall, our results demonstrate that the incubation system used is suitable for measuring ammonia emissions from surface-applied liquid organic fertilizers. The system allows for the differentiation of emission levels at various pH levels and is therefore suitable for testing the effectiveness of additives for reducing ammonia emissions from liquid organic fertilizers.

Little was known about the leaching behavior of potentially toxic elements (PTEs) from soils under the interaction between freeze-thaw (F-T) cycle and the solutions of varying pH values. In this study, PTEs leachability from soils before and after F-T tests was evaluated using toxicity characteristics leaching procedure (TCLP) test. The microstructure and mineralogical evolution of soil mineral particles were conducted using pores (particles) and cracks analysis system (PCAS) and PHREEQC. The results indicated that during 30 F-T cycles, the maximum leaching concentrations of PTEs were 0.22 mg/L for As, 0.61 mg/L for Cd, 2.46 mg/L for Cu, 3.08 mg/L for Mn, 29.36 mg/L for Pb and 8.07 mg/L for Zn, respectively. Under the coupled effects of F-T cycle and acidification, the porosity of soil particles increased by 4.79%, as confirmed by the microstructure damage caused by the evolution of pores and cracks. The anisotropy of soil particles increased under F-T effects, whereas that decreased under the coupled effects of F-T cycle and acidification. The results from SEM-EDS, PCAS quantification and PHREEQC modeling indicated that the release mechanism of PTEs was not only associated with the microstructure change in mineral particles, but also affected by protonation, as well as the dissolution and precipitation of minerals. Overall, these results would provide an important reference for soil remediation assessments in seasonal frozen areas.

Magnesium plays a crucial role in plant physiological processes. However, the specific mechanisms underlying the response of tea plants to altered magnesium nutrition under acid stress remain unclear. This study investigates how root environment acidification impacts tea seedlings and the role of magnesium (Mg) in mitigating these effects. We examine varying pH and Mg levels' influence on tea seedlings' resistance to abiotic stress, focusing on antioxidant capacity and nutritional content. In a hydroponic experiment, we varied root pH (3.5, 5.0, 6.5) and Mg concentrations (0.01, 0.4, 0.8 mM), assessing parameters like antioxidant capacity, peroxidative damage, and nutritional content at 1, 7, 15, and 30 days post treatment. Root environment acidification and Mg deficiency worsened peroxidative damage in tea plant leaves and roots. Increased Mg supplementation enhanced antioxidant enzyme activity, reducing malondialdehyde and mitigating oxidative damage from root environment acid stress. Under acid stress, 0.8 mM Mg significantly increased tea leaf polyphenols, amino acids, and water-soluble extracts. Mg notably boosted chlorophyll content, surpassing lower Mg levels at pH 5. Additionally, Mg reversed root vitality inhibition induced by acid stress, leading to increased nitrogen, potassium, and Mg concentrations in leaves, promoting balanced nutrient absorption. Mg supplementation is crucial for enhancing tea plant antioxidant capacity, alleviating growth inhibition from root-environment acid stress, and improving chlorophyll content and root vitality, highlighting Mg's significance in tea cultivation and broader agricultural practices.

Over -application of nitrogen fertilizer induces soil acidification, which activates heavy metals availability and poses significant challenge to crop production and food safety. In this study, we prepared a clay-based material by ball-milling bentonite with NH4Cl (NH4Cl@bentonite) and assessed its synergistic performance in enhancing nitrogen fertilizer utilization efficiency, immobilizing heavy metals, and improving crop yield and safety. The results showed that the optimal performance of NH4Cl@bentonite was achieved by milling bentonite with NH4Cl at a 4:1 mass ratio for 9 h. NH4Cl@bentonite significantly improved soil water holding and retention capacity by 1.6 and 4.3 times, respectively. In comparison to NH4Cl alone, NH4Cl@bentonite led to a 22.3% increase in N -use efficiency and a 1.5 times enhancement in crop yield. The Pb and Cd content in water spinach shoots decreased by 55.3% and 57.5%, respectively, attributed to the transformation of heavy metals into lower bioavailability states by NH4Cl@bentonite. Experiments and Density Functional Theory (DFT) calculations indicated that NH4Cl@bentonite could immobilize Pb and Cd through processes such as cation exchange, surface adsorption, complexation, and enhancement of soil pH. This work proposes a simple and efficient method for improving cropland fertilizer utilization while ensuring healthy and sustainable development. Environmental implication: Soil acidification, caused using chemical fertilizers, especially nitrogen -based ones, threatens crop production and food safety by damaging soil structure, speeding up nutrient loss, and increasing the solubility of heavy metals. To tackle this problem, we made a clay material by mixing bentonite with NH4Cl (NH4Cl@bentonite) in a ball mill. NH4Cl@bentonite increased N -use efficiency by 22.3%, boosted crop yield by 1.5 times, and reduced the Pb and Cd levels in water spinach shoots by 55.3% and 57.5%, respectively. This work suggests a simple and effective way to enhance fertilizer use in croplands while ensuring healthy and sustainable development.