HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Figures Only Full Text Free Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Shuai, X. Articles by Yost, R. S. Search for Related Content PubMed Articles by Shuai, X. Articles by Yost, R. S. Agricola Articles by Shuai, X. Articles by Yost, R. S. Related Collections Soil Kinetics Other Approaches Soil Models Phosphorus Soil Chemistry

DIVISION S-8—NUTRIENT MANAGEMENT & SOIL & PLANT ANALYSIS

State-Space Modeling to Simplify Soil Phosphorus Fractionation

3190 Maile Way, Room 102, Dep. of Tropical Plant and Soil Sci., Univ. of Hawaii, Honolulu, HI 96822

^* Corresponding author (rsyost{at}hawaii.edu).

Soil P can be fractionated by methods such as the Hedley extraction method to help identify and quantify soil P. Measuring the increases in soil P fractions from P fertilizer does not indicate whether external P can control a P fraction because of transfers among P fractions. Similarly, correlations between soil P fractions and plant P uptake do not directly indicate whether a P fraction affects plant P uptake. The objectives of this research were to describe the transformation among fractions, the effect of P fertilizer on P fractions, and the relationship between plant P uptake and P fractions by a state-space modeling approach, and to minimize the dimension of the state-space model by introducing concepts of controllability and observability and by implementing the General Decomposition Theorem. A P fraction was said to be controllable if its size can be controlled directly by the amount of external P fertilizer, or indirectly through transformations among P fractions. A P fraction was considered observable if it contributed to plant P uptake directly, or indirectly through transformations among P fractions. The jointly controllable and observable P fractions identified by the General Decomposition Theorem were minimum to describe the measured soil P dynamics in selected soil-plant systems, while other fractions were redundant in the cases described. Results showed that only strip-P, inorganic NaHCO₃–Pi, organic NaHCO₃–Po, and inorganic NaOH-Pi of the seven fractions were necessary and sufficient to describe the P dynamics in example Mollisol, Vertisol, Ultisol, and Oxisol.