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Abstract
Plants grown in acidic soils often have reduced productivity because of limited mineral nutrients. For plants to obtain adequate nutrients under these conditions, some source of fertilizer is commonly added or a method to make nutrients more available to plants, such as mycorrhiza, is needed. Maize (Zea mays L.) was grown in acidic soil (pHW 4.7, soilwater, 1:1) with added phosphate rock (PR) and the arbuscular mycorrhizal fungus (AMF) Glomus clarum to determine the effectiveness of AMF and PR for supplying nutrients, especially P. Plants were grown in a growth chamber and harvested when plants had grown in treated soil 15, 22, 29, and 36 d. Plant dry matter (DM) was greatly enhanced by PR, and even more at each harvest when roots were colonized with AMF (AMF+PR). Shoot DM increased more than root DM with PR (PR and AMF+PR) treatments. Total root length (RL) was greater for plants grown with PR and AMF+PR compared to the Control (no added P or AMF) and AMF plants. Colonization of roots by AMF was higher for AMF+PR than for AMF plants. Acquisition of P followed the sequence of AMF+PR > PR >> AMF > Control. Other nutrients commonly limiting in acidic soil [e.g., calcium (Ca), magnesium (Mg), and potassium (K)] were greatly enhanced in AMF compared to nonmycorrhizal (nonAMF) plants. The AMF plants had 2-3-fold greater inflow rates [inflow = μg nutrient m−1 RL day−1] of Ca, Mg, copper (Cu), zinc (Zn), and boron (B) than nonAMF plants. The application of PR and/or AMF colonization decreased the concentrations of iron (Fe), manganese (Mn), and aluminum (Al) in the shoots. The lower specific accumulation rate [SAcR = μg nutrient g−1 shoot DM day−1] of Fe, Mn, and Al in the shoots indicated a possible precipitation or/and formation of metal-organic complexes in the roots. Application of PR to this acidic soil did not inhibit maize response to AMF, and both PR and AMF were important for optimal growth of maize in this acidic soil.
ACKNOWLEDGMENTS
Support of the Fulbright Exchange Program (CIES/USIA, No. 21133) to G.A. Alloush is gratefully appreciated. We also thank Dr. D. Bligh and Ms. B. White for ICP mineral analysis, and to Ms. M. Smith for technical assistance.
Notes
* Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.