Impacts of Aggregate size, soil moisture and residence time on phosphorus solubility in highly weathered soils

Name: Jureewan Boonplong

LCSH: Kasetsart University -- Theses. M.S. (Soil Science) 2019

Classification :.LCCS: S592.6.P5

LCSH: Kasetsart University. -- Department of Soil Science -- Theses

LCSH: Soils -- Phosphorus content

LCSH: Soil temperature

LCSH: Soil physics

LCSH: Soil moisture

LCSH: Phosphorus -- Dissolution

LCSH: Phosphorus -- Solubility

Abstract: Strong phosphorus (P) fixation by iron (Fe) and aluminum (Al) (oxyhydr)oxides in wellaggregated soils particularly highly weathered tropical soils has been documented a severely limits for crop production. To overcome this constraint, soil factors that govern P solubility in such Fe/Al-rich soils are indispensably required to be elucidated. Therefore, the goals of this study are to 1) quantify total and available P pools in seven size aggregates (2000-8000, 1000-2000, 500-1000, 250-500, 125-250, 53-125, and <53 µm) of eight highly weathered soils (Pc1-2, Ak1-2, Ci1-2, and Ti1-2), and to 2) identify the effects of soil moisture contents and residence time on P pools with diverse solubility using a six-step sequential extraction. The seven size aggregates were clustered together into three subgroups including macroaggregate (MA: 250-8,000 µm), microaggregate (MiA: 53-250 µm), and silt and clay fractions (SC: <53 µm) for data comprehension. The results showed that the MA fraction was the most dominant fraction in all studied soils corresponding to 73% of the total soil fraction (range = 43-84%), whereas the MiA and SC fractions occurred in minor extents. Total P content in size fractions varied substantially between the soil samples and size fractions (81-3,461 mg kg-1 ), resulting from a great diversity of land uses and historical P fertilizer use. Extraordinary P content was observed in orchard soils (Ti1-2), whereas left-idle (Pc2), para-rubber growing (Ak1-2), cassava growing (Ci1-2) and maize growing soils (Pc1) contained lower P contents. Meager amounts (median = 2.2% of total soil P) of Bray-II extractable P (Pb) for most soils, except for the Pc1 soil, indicated abundant recalcitrant P pools in the soil that are sparingly available for plant uptake. However, there were positive relationships of Pb in all size aggregates with various forms of Fe, Al and Mn oxides in particular poorly crystalline phases (ρP b –Feo , ρP b –Alo , and ρP b –Mno = 0.52, 0.66, and 0.75), pH (ρP b –pH = 0.65) and OM (ρP b –pH = 0.75). These associations suggest that even Fe/Al/Mn oxides are believed to be primary P fixing minerals, but P adsorbed to microcrystalline phases of such minerals are dissolvable and potentially available for plant use. Alleviating soil acidity and organic matter addition can improve soil P availability. The incubation results revealed that P bound to Fe oxide (F3) and residual P (F6) fractions were the most dominant P pools in the respective Ak1 and Ci1 soils accounting for 34-47% and 36-54% of the total soil P. The pronounced effect of soil moisture on changes in P pools was disregarded. Soluble P was quickly removed after one day of the incubation, but the large F3 and F6 fractions substantially increased, suggesting the profound influence of poorly crystalline Fe oxides on P sorption and a rapid P transformation to more recalcitrant phases. Over 60 days, soluble and loosely bound P fraction (F1) gradually declined, corresponding to half-life times (t1/2) of 28 and 29 days for the respective Ak1 and Ci1 soils. This result suggests that P fertilizer should be supplied every month to satisfy crop production. As the macroaggregates and poorly crystalline Fe oxides play an active role in P sequestration in highly weathered soils; management measures to enhance P availability from these sinks are imperative to be further investigated.

Kasetsart University. Office of the University Library

Address: Bangkok

Email: tdckulib@ku.ac.th

Name: Worachart Wisawapipat

Role: Thesis Advisor

Name: Natthapol Chittamart

Role: Thesis CO-Advisor

Created: 2019

Modified: 2025-07-02

Issued: 2025-07-02

วิทยานิพนธ์/Thesis

application/pdf

URL: https://www.lib.ku.ac.th/KUthesis/2562/jureewan-boo-all.pdf

CallNumber: S592.6.P5 .J87

eng

DegreeName: Master of Science

Level: Master's Degree

Descipline: Soil Science

Grantor: Kasetsart University

©copyrights Kasetsart University

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