Enrichment of primary macronutrients in biochar for sustainable agriculture: A review

Abstract

Macronutrient-enriched biochars have potential for nutrient recycling from waste, enhance soil fertility, reduce consumption of fertilizers, and thereby promoting sustainable agriculture. The focus of the recent research studies has been on exploring different methods for production of macronutrients (nitrogen [N], phosphorus [P], and potassium [K]) enriched biochar fertilizers. There is now an urgent need to comprehend the work carried out on biochar fertilizers for a proper scientific understanding and advancement. This review provides crucial information about nutrients enriched biochars production and the underlying mechanisms toward its use in agriculture. The production methods, nutrient characteristics, potential major challenges and future perspectives of using these nutrients enriched biochars have also been dealt in the present review. Among primary macronutrients, the main focus of nutrients enriched biochar are on N and P. Total N, P, and K enriched up to 10%, 15.32%, 25.85% in biochar through controlled (primarily temperature) pyrolysis and utilization of specific feedstock. Although total macronutrients content in nutrients enriched biochar were thoroughly studied, but the bio-labile and plant available fractions of these nutrients are yet to be extensively researched. Nutrients transformation in biochars revealed about comparatively higher bio-available K fraction due to formation of water soluble kalicinite (KHCO₃) minerals. The efficacy of biochars toward soil fertility and plant growth was widely studied (mainly as pot experiments) and there results varied. Overall, the prospects of nutrients enriched biochars toward sustainable agriculture has gained momentum with time and further engineered biochars hold great potential to cater for specific soil-plant-environment system.

Graphical abstract

KEYWORDS:

• Agriculture
• biochar fertilizers
• macronutrients
• soil fertility
• waste

Acknowledgments

All the authors express sincere thanks to all the reviewers and editor for valuable guidance, which helped in improving the content and quality of the manuscript. Authors also acknowledge the support of Prof. S. Basu, Director, CSIR-IMMT, Bhubaneswar. Manish Kumar would like to highlight the financial support provided by CSIR (OLP-86 and MLP-75) and DST, Government of India [(DST/TDT/WM/2019/51 (g))] as GAP-335 projects related to biochars theme at CSIR-IMMT.