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ARS Home » Plains Area » Fort Collins, Colorado » Center for Agricultural Resources Research » Rangeland Resources & Systems Research » Research » Publications at this Location » Publication #328962
Title: Unified weak and strong soil tests to estimate latent plant available phosphorus pools

Author
item SHUAI, X - University Of Hawaii
item Ma, Liwang
item WENDROTH, O - University Of Kentucky

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/21/2018
Publication Date: 4/12/2018
Citation: Shuai, X., Ma, L., Wendroth, O. 2018. Unified weak and strong soil tests to estimate latent plant available phosphorus pools. Agronomy Journal. 110:859-867. doi:10.2134/agronj2017.11.0650.
DOI: https://doi.org/10.2134/agronj2017.11.0650

Interpretive Summary: Phosphorus (P) availability in tropical soils is important for plant growth and fertilizer P recommendation. Two intrinsic P pools (weakly and tightly adsorbed) recently proposed to quantify soil available P. The weakly adsorbed P pool can be measured with the Olsen method. The objective of this study was to quantify the tightly adsorbed P pool measured with the Truog method. P adsorption kinetics was obtained by applying five levels of fertilizer phosphate (0-1.6 lb P per ton of soil) to the seven tropical soils. Soil P was then extracted for half an hour with the Truog method after 2-180 days of adsorption under 77 oF. For all the seven soils, 15% to 62% of the weakly adsorbed P pool was extracted with the Truog method. For soils with low P sorption capacity, 15% to 36% of the tightly adsorbed P pool was extracted with the Truog method while only small portions were extracted from soils with high P sorption capacities. The extraction efficiencies of both P pools by the Truog method decreased as soil P sorption site density increased. The derived relationship between P extraction efficiency and soil P sorption site density may guide P recommendation in tropical soils.

Technical Abstract: Accurate quantification of available phosphorus (P) in tropical soils is important for fertilizer P recommendation. Two intrinsic P pools including weakly and tightly adsorbed P pools were recently proposed to quantify soil available P, and the weakly adsorbed P pool can be measured with the Olsen method. The objective of this study was to quantify the tightly adsorbed P pool measured with the Truog method. P adsorption kinetics was obtained by applying five levels of fertilizer phosphate (0-800 mg P kg-1 soil) to the seven tropical soils. Soil P was then extracted for half an hour with the Truog method after 2-180 days of adsorption under 25 oC. For all the seven soils, 15% to 62% of the weakly adsorbed P pool was extracted with the Truog method. For soils with low P sorption capacity, 15% to 36% of the tightly adsorbed P pool was extracted with the Truog method while only small portions were extracted from soils with high P sorption capacities. The extraction efficiencies of both P pools by the Truog method decreased as soil P sorption site density increased. The extraction of the tightly adsorbed P pool was described by a ligand exchange mechanism between sulfate and adsorbed phosphate as a first-order reactions. A linear model was derived to estimate the extraction efficiencies, i.e., the fractions of P extracted from the two P pools, from soil P sorption site density. This relationship may guide P recommendation in tropical soils.