Advancing Sustainable Rice Production With Hydrochar And Animal-Waste Biochar Of Agronomic, Soil, And Environmental Impacts: A Systematic Review

Abstract

Rice cultivation is a critical component of global food security, particularly in Asia, Africa, and Latin America. However, rice paddies are substantial sources of methane (CH₄), nitrous oxide (N₂O), and ammonia (NH₃), while also contributing to soil acidification from prolonged fertilizer use. To address these challenges, this systematic review evaluates the impact of biochar and hydrochar amendments on agronomic performance, soil health, and environmental outcomes in rice production systems. A comprehensive literature search was conducted using Google Scholar, Scopus, ScienceDirect, and PubMed databases, following the PRISMA guidelines. Studies published in English that assessed the application of biochar (derived from animal waste) and hydrochar in rice cultivation were included. The review synthesizes data from 41 studies, covering a range of experimental designs (soil column, pot trials, field experiments) and material types (biochar, hydrochar, and co-amended forms). Key outcomes evaluated include grain yield, biomass, plant height, tiller count, soil pH, soil organic carbon (SOC), cation exchange capacity (CEC), microbial activity, greenhouse gas emissions (GHGs), and nutrient leaching. The results show that biochar, particularly from animal waste, consistently improves yield, nutrient retention, and pH, and reduces GHG emissions. Hydrochar, though more variable, demonstrates potential for enhancing nitrogen use efficiency and mitigating methane and nitrous oxide emissions when appropriately modified. The review underscores the need for multi-season, field-scale studies, standardized material specifications, and integrated measurements to optimize the use of these amendments in sustainable rice production.