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Stand Density, Shoot Weight, and Acetylene Reduction Activity of Alfalfa Populations Subjected to Field and Greenhouse Moisture Gradients 1
Author(s) -
Rumbaugh M. D.,
Johnson D. A.,
Rinehart D. N.
Publication year - 1983
Publication title -
crop science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.76
H-Index - 147
eISSN - 1435-0653
pISSN - 0011-183X
DOI - 10.2135/cropsci1983.0011183x002300040044x
Subject(s) - biology , agronomy , shoot , seedling , pasture , greenhouse , cultivar , water content , forage , moisture , horticulture , materials science , geotechnical engineering , composite material , engineering
The objective of this study was to determine if selection of alfalfa ( Medicago falcata L. and M. sativa L.) for increased forage yield has resulted in increased seedling stand density, shoot weight, and acetylene reduction rate in favorable environments but corresponding decreases in these characteristics in less favorable environments. Thirty‐eight alfalfa populations were divided into four groups differing in origin, breeding, and adaptation. They were grown in replicated field experiments in 2 successive years as well as in the greenhouse. Line‐source sprinkler systems were used to provide a range of water applications. Stand densities of alfalfa populations in the seedling year were related to the degree of selection by plant breeders but also were dependent upon water availability. Modern cultivars had higher stand densities of seedlings in more favorable environments, but exhibited lower stand densities than wild populations when subjected to increased moisture deficits. Shoot weight of field‐grown plants was also closely related to the intensity of breeding effort with the most highly bred cultivars achieving greater shoot weights than wild populations at all water applications. In the high moisture application treatment in the field in 1980, acetylene reduction activity was positively associated with the degree of agronomic selection of the populations. In the greenhouse environment the acetylene reduction activity of dryland pasture and range populations exceeded those of other types of alfalfas (P<0.05). However, we found no quantitative evidence of superior stand density, growth, or acetylene reduction activity of these dryland pasture and rangeland populations in their seeding year when grown in the field. At least for the seedling stage, the most highly bred germplasm would be more desirable for source material to improve shoot weight in either optimum or suboptimum environments than wild populations. Use of highly bred germplasm also would probably be most effective if the breeding objective is to increase field N 2 fixation and stand density at the seedling stage in favorable water environments.