Enhancement Effect of Cassava Starch Manufacturing Wastes on Availability and Fate of P from Thai Phosphate Rocks in Sandy Typic Paleusults: An Incubation Study

Abstract

ABSTRACT Direct application of phosphate rock (PR) can be an alternative to phosphorus (P) fertilizer in highly weathered tropical soils, but the low solubility of PR obstructs its use. The use of cassava peel (CP) and cassava starch waste (CSW) to enhance two Thai PRs (Kamphaeng Phet, KP-PR; 20.3% P2O5 and Lamphun, LP-PR; 14.7% P2O5) was investigated for P availability in two sandy Typic Paleusults in laboratory. Both PRs had low reactivity but similar dissolution behavior as most P dissolved in 2% formic acid (22.2% and 19.0%, respectively, of total P2O5). The CP promoted better PR solubility than did the CSW, resulting in significantly more available P in the soils but P majorly occurred in moderately labile and chemically relatively stable fractions. The labile fraction was still lower than other forms of soil P, especially NaHCO3-Po, but both wastes, especially CP, increased NaHCO3-Pi and -Po to some extent while the soluble Pi (NH4Cl-Pi) became more soluble after 4 months. The relative distributions of the Pi and Po fractions varied over the incubation period with no definite trends detected, but the PR and wastes were correlated variably in all P fractions.