By Glenn Concepcion
A study on alfalfa crops found that the co-application of biochar amendment and partial root-zone drying irrigation significantly improves plant water use efficiency in salt-affected soils, a finding that may contribute to IRRI’s research for sustainable rice cultivation in water-limited and degraded paddies.
A recent study featuring a researcher from the International Rice Research Institute (IRRI) has shown a powerful synergy between biochar amendment and advanced irrigation techniques, greatly enhancing the water use efficiency and biomass accumulation of crops grown in salt-affected soils.
The research investigated how combining biochar, a porous, carbon-rich soil amendment material produced through pyrolysis, with various deficit irrigation regimes impacts alfalfa (Medicago sativa L.), a crucial forage crop often constrained by water scarcity and salinity in arid and semi-arid regions.
The study, co-authored by Tovohery Rakotoson, a soil scientist at IRRI Vietnam, with other researchers from the Qingdao Agricultural University, the Chinese Academy of Sciences, and the Jiangxi University of Chinese Medicine, revealed that combining biochar with Partial Root-Zone Drying Irrigation (PRDI) substantially increased whole-plant water use efficiency by 39–56% compared to the PRDI treatment without biochar.
The findings, published in Environmental and Experimental Botany, offer promising strategies that could accelerate IRRI’s ongoing research into sustainable rice cultivation amidst global climate change challenges.
Mitigating stress and optimizing water use
Global climate change and human activities have intensified water scarcity and soil salinization, making improved water use efficiency a critical goal for sustainable agriculture. Deficit irrigation techniques, such as PRDI, aim to enhance water utilization by controlling the wetting and drying cycle of the root zone. While these techniques can improve water use efficiency, they often result in a trade-off: reduced stomatal conductance and lower net carbon dioxide (CO2) assimilation rate, leading to lower biomass accumulation.
The key finding of this research is that biochar effectively mitigates these negative consequences. Researchers utilized wheat straw biochar and corn straw biochar in a split-root pot experiment conducted in slightly salt-affected soil. They observed that biochar amendment dramatically improved the soil water-holding capacity and volumetric soil water content. This improved soil moisture environment alleviates stress on the plant.
Crucially, the combined strategy modulated the plant’s physiological response to stress. Deficit irrigation, particularly PRDI, typically triggers the accumulation of the key stress hormone abscisic acid, which acts as a root-to-leaf signal to close stomata, reducing water loss but also limiting carbon assimilation. While PRDI increased abscisic acid, biochar amendment significantly decreased abscisic acid across all irrigation treatments compared to the non-amended control, easing the stress on the plant.
The biochar application also optimized leaf stomatal traits, leading to enhanced leaf intrinsic water use efficiency and long-term water use efficiency (indicated by lower carbon isotope discrimination). Biochar improved the overall plant water status, leading to higher rates of net CO2 assimilation and ultimately promoting plant growth and total biomass. For instance, under PRDI treatment, biochar increased total biomass by 42% to 56% compared to the control without biochar. This demonstrates that the biochar-PRDI combination mitigates the typical trade-off, achieving high water use efficiency while sustaining greater productivity.
Advancing IRRI’s sustainable rice research
According to Dr. Rakotoson, the mechanisms observed in the alfalfa study directly align with and validate the goals of IRRI’s ongoing biochar research for rice cultivation. The core mechanism (biochar boosting water use efficiency by improving soil water retention and optimizing leaf hydration under water-saving irrigation) has significant implications for rice production, especially in challenging environments like saline and degraded paddies.
For irrigated lowland rice, the findings suggest that combining biochar with Alternate Wetting and Drying (AWD) could be highly effective. AWD aims to reduce water use, but if poorly timed, it can cause over-drying and yield penalties. Biochar’s ability to markedly enhance soil water-holding capacity could prevent yield penalties from over-drying caused by poorly timed AWD, enabling the system to sustain or even boost grain yields.
Furthermore, integrating biochar could deepen greenhouse gas (GHG) mitigation beyond the reductions achieved by AWD alone. Biochar also adds stable carbon content to the soil, improving soil health.
In rainfed upland or drought-prone lowland rice systems, where crops must contend with increasingly erratic rainfall, biochar is seen as a powerful drought-mitigation tool. It prolongs soil water availability during dry spells, which is critical for strengthening seedling survival and stabilizing yields during drought periods.
The collective evidence strongly suggests that biochar integration could simultaneously strengthen climate resilience, deepen GHG mitigation, and maintain rice productivity while requiring lower water and fertilizer inputs, making it a highly promising strategy for future rice-based systems.
While biochar effectiveness can vary based on feedstock and soil type, underscoring the need for tailored strategies, this study provides critical mechanistic understanding. Future research can focus on long-term field studies to determine the applicability of various biochar types and deployment strategies across diverse cropping systems and saline-alkali soils. The development of these sustainable irrigation and soil management strategies is essential for addressing the dual challenges of water scarcity and land degradation globally.
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Read the study:
Shangzhi Zhong, Xiang Zhang, Pengxin Hou, Jianghan Ouyang, Tovohery Rakotoson, Congcong Zheng, Qibo Tao, Juan Sun
Biochar amendment enhances water use efficiency in alfalfa (Medicago sativa L.) under partial root-zone drying irrigation by modulating abscisic acid signaling and photosynthetic performance
Environmental and Experimental Botany, Volume 238, 2025, 106244
https://doi.org/10.1016/j.envexpbot.2025.106244
