Author
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Staley, Thomas |
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Submitted to: Soil Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 11/21/2001 Publication Date: 3/3/2002 Citation: Staley, T.E. 2002. Low-level liming affects early white clover nodulation but not root development in a small-volume acidic soil model system. Soil Science 167:211-221. Interpretive Summary: Establishment of dinitrogen-fixing forage legumes on chemically-stressed soils is a serious problem for livestock producers in the south and east. A laboratory soil/plant/rhizobia model system was used to simulate symbiosis establishment on acidic (pH 4.7) soils. It was shown that nodulation can be significantly improved by an increase of only one-half pH Hunit. However, root growth and structure were not affected. It was concluded that the development of an improved symbiosis for chemically- stressful soils should focus on the root hair and/or rhizobial components to produce legume-based pastures that establish better and persist longer. Technical Abstract: Establishment, growth and persistence of forage legumes on shallow, infertile, and acidic hill-land pasture soils remains a problem, often because of the expense of optimal liming and fertilization. A better understanding of the mechanism of inhibition of symbiosis establishment in these soils, and its alleviation by minimal liming, could assist in the solution of this problem. White clover (Trifolium repens L.) seedlings were planted in two model systems (deepots or plates), utilizing an air- dried, nonsterile Ultisol limed from pHw 4.71 to 4.99, and inoculated with effective rhizobia (Rhizobium leguminosarum bv. trifolii). Both model systems demonstrated the stimulatory effect of low-level liming on nodulation 14 DAP, before differences in shoot mass and root length responses were apparent. Examination of roots at 3, 6, 8, 10, 12 and 14 DAP, grown in soil plates, revealed significant (P < 0.10) nodulation increases only at 14 DAP, relative to lime rate (soil pH). However, the consistent pattern of nodulation responses to liming nearly throughout the entire growth period suggests that nodulation was being affected as early as 6-8 days after planting. Only small differences were found at 12-14 DAP for total length, diameter, volume, surface area, tip and fork number. Root length, sorted into eight diameter classes, was similarly unresponsive to soil pH. Symbiosis establishment inhibition in our soil plate model system occurs at the cellular (root hair or nodule primordia) level. That rhizobial level interacted with soil pH on nodulation intensity suggests that, from a practical (field) perspective, the development of either an more acidic soil-tolerant plant cultivar or rhizobial strain would lead to a more robust symbiosis for infertile, acidic soils. |
