Sequential Phosphorus Fractionation to Understand the Fate of Phosphorus Fertilizer in Sandy Ultisol, Amended with Biochar and Coal Fly Ash

The transfer of Phosphorus (P) in water draining from agricultural lands to surface and ground waters is regarded as one of the serious agronomic problems in sandy Ultisol soils that occur in the southeastern agricultural plain of the USA. Therefore, enhancement of the P fertilizer use efficiency is considered through the amendment of such soils with organic and inorganic soil amendments. We studied the effect of biochar and coal fly ash amendment on the retention efficiency of soluble fertilizer P added to Ultisols. A sequential P fractionation with a series of acid and alkali extracts was carried out to soil samples added with coal fly ash, bio char and coal fly ash + biochar, applied with soluble P fertilizer, and incubated for 30 days. As per our results, soil amendments reduced the readily leachable fractions of P in soil through a variety of retention and fixation pathways. Coal fly ash converted 41% of P into moderately labile Calcium (Ca) bound P. Biochar could retain 31% of P as less labile organic P and 26% as Ca bound P. The coal fly ash + biochar application significantly reduced the leachable P fraction by converting 93% of the P into labile, moderately labile and residual P pools. Coal fly ash and biochar soil amendments were recommended to reduce the leaching loss of P from acidic sandy Ultisol.

Automated summary

This study investigated the impact of biochar and coal fly ash amendments as soil amendments on the retention efficiency of soluble phosphorus fertilizer in Ultisols. The results showed that these amendments reduced the leachable phosphorus fractions in soil through various retention and fixation pathways, thereby reducing phosphorus leaching loss.