Population sizes of clover rhizobia in soil in East Texas, influence of liming on rhizobial survival, and number of rhizobia needed for prompt nodulation of arrowleaf and crimson clovers /
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| Other Authors: | , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1992.
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| Subjects: | |
| Online Access: | Link to OAKTrust copy |
| Abstract: | Large populations of Rhizobium leguminosarum biovar trifolii in soil are important for prompt nodulation and seedling development of clovers. Counts of clover rhizobia capable of nodulating arrowleaf clover (Trifolium vesiculosum Savi.) were made on soils from 21 pastures having different inoculation and cropping histories. The variability of population sizes within four pastures was measured on nine soil samples from a 9 m^2 area. The influence of soil pH on rhizobial population size was determined, in the laboratory, by liming and inoculating acidic soil samples, and measuring changes in population densities. The population density of clover rhizobia needed for prompt nodulation of arrowleaf and crimson clovers was determined in pot and pouch studies under controlled conditions. The results showed that the numbers of clover rhizobia in soil, in 60% of the pastures surveyed, were more than 100 rhizobia g^-1 soil but populations ranged over two orders of magnitude in soil samples localized 1 m apart, in some pastures. Populations of indigenous rhizobia were affected by soil acidity. A homogeneous pH of 5.1 or below was very detrimental to survival of rhizobia. Liming of most soils having a pH of 5.4 or below improved survival of rhizobia. Numbers of nodules on the upper 2 cm zone of the taproot of clovers grown in soil correlated positively with rhizobial populations in soil. In pouches, rhizobial densities of at least 1,000 rhizobia per seedling were needed for one nodule to form near the position of the root tip at the time of inoculation. One nodule formed on the taproot approximately 7 days earlier for arrowleaf clover and 5 days earlier for crimson clover (Trifolium incarnatum L.) seedlings when clovers were inoculated with 1,000 rhizobia as compared to 10 rhizobia per seedling. Nodulation sites on the taproot of arrowleaf clover were susceptible to nodulation for at least 48 hours but less than 72 hours. Nodulation sites on the taproot of crimson clover were not susceptible to nodulation for longer than 24 hours. Populations of rhizobia in pastures are low enough in many cases to expect improved nodulation of clover seedlings by inoculation. Large populations of rhizobia are important to promote early nodulation and increase seedling vigor. |
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| Item Description: | Typescript (photocopy). Vita. "Major subject: Soil Science." |
| Physical Description: | xiii, 171 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references. |