Biochar reshapes phosphorus distribution in soil aggregates and improves rice phosphorus uptake

Abstract

Subtropical red paddy soils usually immobilize most phosphorus (P) in unavailable forms. Applying biochar to cropland is an effective measure to activate soil P. Soil aggregates are the main sites for P transformation and plant P uptake. However, the mechanisms through which biochar influences P dynamics within soil aggregates to enhance plant uptake remain unclear. The effects of biochar on P accumulation in aggregates and P uptake by rice were investigated by gradient application of biochar. Applying biochar increased total P by 44% to 97%, available P by 15% to 63%, inorganic P by 34% to 36%, and organic P by 71% to 249% in the bulk soil. In aggregate fractions, the total, organic, available P content in macroaggregates were increased by 47% to 87%, 112% to 229%, 61% to 93%, in microaggregates by 12% to 50%, 54% to 133%, 34% to 71%, and in silt-clay by 32% to 50%, 50% to 210%, 7% to 28%, respectively. A structural equation model showed that biochar mainly increased the organic P in macroaggregates and microaggregates to improve rice yield. In summary, biochar mainly increased rice yield by promoting the increase of organic P in macroaggregates, and 22.91 t hm^‒2 biochar application had the fastest effect on TP (78%) enrichment in red paddy soil layer. This study provides a theoretical basis for determining the optimal biochar application rate in red paddy soils.

Graphical abstract

Keywords

red paddy soil / rice straw biochar / aggregates / phosphorus compositions / rice uptake

Highlight

	● Biochar promotes the accumulation of organic and available P in micro-aggregates.
	● Non-linear response of P concentrations to rice straw biochar application.
	● 22.91 t hm‒2 biochar had the fastest effect on the P content in the tillage layer of red paddy soil.
	● 32.33 t hm‒2 biochar could make the soil P pool content reach saturation.

References

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