Researchers from National Chung Hsing University (NCHU) in Taiwan found that combining two natural bio-inputs, biochar and a specially prepared chitosan xerogel, created a synergistic effect that fully restored the growth of water spinach under conditions of both water scarcity and nutrient deficiency.
The findings offer a viable, low-input strategy for vegetable producers to mitigate the mounting challenges of global warming, which is intensifying water scarcity, and the environmental impact of excessive fertiliser use.
Globally, water scarcity is projected to affect between 1.7 and 2.4 billion people by 2050.
At the same time, only 30% to 50% of applied nitrogen and 10% to 20% of applied phosphorus are actually absorbed by crops, leading to significant environmental contamination.
Improving the efficiency of both water and fertiliser use is, therefore, essential for the future of sustainable agriculture.
Single amendments fell short of providing full protection
The study focused on water spinach (Ipomoea aquatica), a staple crop known for its sensitivity to soil moisture and nutrient availability, making it an ideal indicator for testing the amendments. The NCHU team initially investigated the effects of biochar and chitosan xerogel separately.
Biochar, a carbon-rich product derived from pyrolysed biomass, is known for its porous structure and ability to improve soil water retention. Chitosan, derived from crustacean shells, is a natural polymer used as a soil conditioner and bio-stimulant.
When tested individually, their improvements were limited. Under water deficit, biochar alone did not significantly enhance growth. Similarly, while chitosan xerogel on its own did offer some drought mitigation, the overall plant performance was not restored to the level of the optimally grown control group.
The biochar used in the study was produced from mushroom waste bags, while the chitosan xerogel was formulated using chitosan derived from shrimp and crab shells dissolved in wood vinegar — a byproduct of biomass pyrolysis — and mixed with diammonium hydrogen phosphate. The researchers explained that this composite created a highly efficient, water-retaining gel that also introduced a major macronutrient, phosphorus, in a water-soluble form.
Dual treatment proved to be a powerful synergistic solution
The true breakthrough came when the researchers tested the combined application of the two amendments. They found that a dual application of 4% biochar and 0.8% chitosan xerogel was required to unlock the full potential.
The two materials worked together in a complementary way. The porous biochar primarily improved the physical structure of the substrate, enhancing aeration and making it easier for roots to grow. Concurrently, the hydrophilic chitosan xerogel acted as a water-retaining, controlled-release polymer right near the root zone.
In the water-deficient test groups, the combined treatment significantly increased the fresh weight, stem weight and leaf weight of the water spinach by 1.2, 1.3 and 1.7 times, respectively, compared to the untreated, stressed plants.
Under fertiliser-deficient conditions, the results were equally impressive, with a 1.3-fold increase in fresh weight, a 2.0-fold increase in stem weight, and a 1.4-fold increase in leaf weight. Crucially, the growth performance in the combined treatment groups was comparable to that of plants receiving full irrigation and fertiliser application.
The most significant finding was the synergy. The biochar was the stable, high-surface area sorbent, and the xerogel was the moisture-retaining, nutrient-stabilising polymer. Together, they essentially created a sophisticated, controlled-release nutrient and water matrix that sustained the plant under stress.
Higher nutrient uptake and improved efficiency
The scientists also confirmed that the combined amendment enhanced the plants’ physiological function and nutrient uptake, allowing them to thrive even when resources were scarce.
Under both water and fertiliser stress, the dual application led to significantly higher levels of chlorophyll and beta-carotene in the leaves, indicating improved photosynthetic efficiency and nutritional quality.
Furthermore, the combined treatment demonstrably increased the uptake and concentration of essential mineral nutrients in the water spinach tissues, including nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), and manganese (Mn). This highlighted the dual treatment’s ability to act as a catalyst for nutrient-use efficiency.
The researchers found that the combined treatment could increase the concentrations of these critical elements, especially phosphorus and manganese, even higher than in the control group that received normal fertilisation. This meant they were not just compensating for the lack of fertiliser but also making the plant’s nutrient acquisition system more effective.
The research suggests that this approach could allow commercial vegetable producers to achieve current yields with reduced fertiliser application and water usage, leading to significant cost savings and reduced environmental pollution.
Next steps: Field trials and broader applications
The researchers indicated plans to move the study from controlled greenhouse conditions to open-field environments to validate the long-term agronomic and ecological performance of the biochar–chitosan system under real-world subtropical climatic variability.
The integration of bio-inputs like the one in the study represents a sustainable agricultural strategy that could simultaneously address soil degradation, water scarcity and nutrient inefficiency. It would likely fulfil the goals of climate-resilient and resource-efficient agriculture, which is paramount in the face of climate change. The researchers believe this combination has enormous potential for sustainable, cost-efficient crop production for B2B growers globally.
In conclusion, they wrote: “The findings support the integration of chitosan xerogel and biochar as a sustainable, low-input strategy to enhance crop productivity and maintain yield stability. This strategy is particularly relevant for mitigating the effects of climate change and can be tailored for semi-arid regions or controlled-environment cultivation systems where maintaining optimal soil water and nutrient balance is critical.”
Source: Horticulturae “Improving Sustainable Vegetable Production with Biochar and Chitosan Xerogel Combination Under Water and Fertilizer Stress” https://doi.org/10.3390/horticulturae11121448 Authors: Pan I-Chun, et al.
