Soybean root growth in acid subsoils in relation to magnesium additions and soil solution chemistry

Description

Aluminum tolerance of soybean [Glycine max (L.) Merr.] by citrate secretion from roots, leading to external complexation of toxic Al species in solution, is enhanced by addition of μM Mg²⁺ to hydroponic solutions. The objectives of this dissertation were to assess ameliorative effects of μM Mg additions on soybean root growth in acidic subsoils and to relate the soil solution ionic compositions to soybean root growth. Roots of soybean cultivar Plant Introduction 416937 extending from a limed surface soil compartment grew for 28 days into a subsurface compartment containing acid subsoils [Cecil (oxidic and kaolinitic), Creedmoor (montmorillonitic) and Norfolk (kaolinitic)]. The three Mg treatments consisted of the native equilibrium soil solution concentrations in each soil (50 or 100 μM) and MgCl₂ additions to achieve 150 and 300 μM Mg (Mg150, Mg300, respectively) in the soil solutions. Root elongations into Mg-treated subsoils were compared with a CaCO₃ treatment limed to achieve a soil pH value of 5.5. Subsoil root length for the treatments without added Mg or lime decreased in the order of the Cecil followed by Norfolk and Creedmoor subsoils, and corresponded to the increasing order of percent Al saturation (27, 61 and 83%, respectively). Subsoil root growth and dry matter responses to the Mg treatments were less than the lime treatments, and there were no differences for the Mg150 and Mg300 treatments as compared to the treatments without added Mg or lime. Citrate adsorption experiments found that over 66% citrate added in the subsoils were adsorbed and biodegraded, suggesting that root secreted citrate in the soil might readily be unavailable to complex Al for ameliorating its rhizotoxicity. Root length relative to the limed treatments for all subsoils (RRL) was poorly related to the activity of soil solution Al species (Al³⁺ and Al-hydroxyl species) and Mg²⁺. However, the RRL values were more closely related to the parameters associated with soil solution Ca activity including Ca²⁺, Al³⁺/Ca²⁺, and Al³⁺/(Ca²⁺ + Mg²⁺), suggesting that Ca could be a primary factor ameliorating Al and H⁺ rhizotoxicity in these subsoils. Increased tolerance to Al rhizotoxicity of soybean by μM Mg additions to hydroponic solutions, inducing citrate secretion from roots to externally complex toxic Al species, may be less important in the acid subsoil with a poor native Ca available to root growth.

Links & Downloads

1. http://www.lib.ncsu.edu/theses/available/etd-05222006-212404/

Tags

Soil Science

Additional Fields

Identifer	oai:union.ndltd.org:NCSU/oai:NCSU:etd-05222006-212404
Date	30 May 2006
Creators	Hashimoto, Yohei
Contributors	Daniel W. Israel, Paul V. Nelson, T. Jot Smyth, Dean Hesterberg
Publisher	NCSU
Source Sets	North Carolina State University
Language	English
Detected Language	English
Type	text
Format	application/pdf
Source	http://www.lib.ncsu.edu/theses/available/etd-05222006-212404/
Rights	unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to NC State University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report.