Sustainable fertilization: hydrochars transform crop growth and soil health

A new investigation reveals the significant potential of hydrochars, derived from common biowastes like sewage sludge and chicken manure, to function as effective slow-release phosphorus fertilizers. These findings offer a dual advantage for agriculture: enhancing crop productivity while simultaneously addressing challenges of waste management and environmental sustainability. Traditional phosphorus fertilizers often contribute to nutrient leaching and water pollution, prompting a global search for more environmentally sound solutions. This research presents a compelling case for hydrochars as a promising pathway toward a regenerative agricultural system.

To evaluate their performance, researchers developed various hydrochars from sewage sludge (SS) and chicken manure (CM) using hydrothermal carbonization at two temperatures: 125°C and 225°C. These SSCs (sewage sludge derived hydrochars) and CMCs (chicken manure derived hydrochars) were then meticulously characterized for their elemental composition, nutrient content, and surface structures. Subsequent pot and column greenhouse experiments cultivated corn (Zea mays) and soybean (Glycine max) in an acidic agricultural soil amended with these hydrochars, directly comparing their effects to un-amended soil and soil treated with triple super phosphate (TSP), a conventional phosphorus fertilizer. The experiments focused on assessing crop growth parameters and phosphorus availability within the soil over time.

Differentiated Crop Responses to Hydrochar Amendments

The study observed distinct impacts of hydrochar application on the growth of the two representative crops. For corn, both SSCs and CMCs substantially improved total dry biomass, increasing it by 32.8–92.4% and 21.8–69.7% respectively, when compared to control soils. Interestingly, hydrochars produced at the lower temperature (125°C) generally yielded more pronounced benefits for corn biomass. Soybean growth, however, responded more favorably to CMCs, with a 23.2–66.2% increase in total dry biomass, while SSCs showed minimal influence. This nuanced response underscores the importance of matching hydrochar type and processing conditions to specific crop requirements.

Enhancing Phosphorus Uptake and Soil Availability

A core finding pertains to the hydrochars' capacity to improve phosphorus dynamics. Both SSCs and CMCs significantly boosted shoot phosphorus uptake (SPU) and phosphorus use efficiency (PUE) in both corn and soybean. For instance, lower temperature hydrochars (SS125 and CM125) increased SPU in soybean by 45.3% and 52.2%, respectively, and even more dramatically in corn. This enhanced availability and uptake indicates that hydrochars effectively deliver crucial nutrients to plants, offering a viable alternative to purely chemical fertilizers. Notably, TSP showed minimal comparative impact on SPU, suggesting the superior efficacy of hydrochars in facilitating plant phosphorus acquisition.

Mitigating Environmental Phosphorus Runoff

Beyond promoting plant growth, the hydrochars demonstrated a crucial environmental benefit: effective phosphorus retention in the soil. Column experiments revealed that while hydrochars initially increased water soluble phosphorus (WSP) in the topsoil, these levels gradually stabilized over six months. This stabilization is attributed to the hydrochars' functional groups, elements, high surface area, and porosity, which facilitate phosphorus adsorption through mechanisms like precipitation, electrostatic attraction, and ion exchange. In stark contrast, TSP maintained persistently high WSP levels throughout the soil profile over time, indicating an elevated risk of phosphorus leaching and subsequent water pollution.

This work provides a robust framework for developing functionalized phosphorus-rich chars as sustainable alternatives to conventional chemical fertilizers. "Our research clearly demonstrates that hydrochars not only boost crop growth by providing essential phosphorus but also act as crucial agents in mitigating phosphorus leaching from agricultural soils," states Dr. Baoshan Xing, a co-corresponding author affiliated with the Stockbridge School of Agriculture at the University of Massachusetts, Amherst. "This dual benefit addresses critical issues in food security and environmental quality, moving us closer to more sustainable and cost-effective farming practices." The findings suggest that transforming agricultural waste into valuable soil amendments can significantly reduce reliance on finite mineral resources and decrease the ecological footprint of food production.

While this investigation compellingly establishes the efficacy of sewage sludge and chicken manure hydrochars as slow-release phosphorus fertilizers, further research will broaden its applicability. Future studies will explore the fertilization capacities of hydrochars for other essential macronutrients and micronutrients, evaluating their performance across a wider array of soil types and crop species. Additionally, examining the broader impact of hydrochar application on soil ecosystem multifunctionality, encompassing physical, chemical, and biological attributes, remains an important avenue for comprehensive understanding.

Corresponding Author: Baoshan Xing

Original Source: https://doi.org/10.1007/s44246-023-00086-w

Contributions: All authors contributed to the study conception and design. Hao Zheng and Baoshan Xing performed the supervision, conceptualization and funding acquisition. Material preparation, data collection and analysis were performed by Anahita Khosravi, Yanfei Yuan and Qiang Liu. The first draft of the manuscript was written by Anahita Khosravi. Yanfei Yuan, Qiang Liu, Masoud Hashemi, and Yuanzhi Tang commented on previous versions of the manuscript. The submitted version of the manuscript was finalized by Hao Zheng and Baoshan Xing. All authors read and approved the final manuscript.