Red clover (Trifolium pratense L.) is an important hay or pasture crop of the humid region of the United States, and its adaptability to acid infertile soils is still unknown. Research was undertaken to evaluate the effects of five levels of Al (0, 25, 50, 75, and 100 µmol L−1) on growth, uptake, and mineral nutrient efficiency ratios (ER) in 23 red clover cultivars. The ER is defined as milligrams of dry shoot weight produced per milligrams of element in the shoot. The initial solution pH of 4.5 changed due to crop growth, and such effects might have altered the concentrations of Al; however, relative comparisons between cultivar responses were possible. The growth of shoots and roots showed significant differences with respect to Al levels, cultivars, and their interactions. At 50 µmol L−1 Al, the average reduction of shoot and root growth was 73 and 57% of control, respectively. Overall shoot nutrient content showed a significant positive correlation with shoot and root dry weight, and inverse relations with treatment Al levels and shoot Al concentrations. The ER assisted in differentiating cultivars into efficient and inefficient utilizers of the absorbed nutrients. With the exception of the ER for Ca, Mg, and Mn, overall inverse relations were observed between Al levels and ER. The cultivars used in this study showed intraspecific genetic diversity in growth and ER values for the essential elements in the presence or absence of Al. ‘Kuhn’ and ‘Prosper I’ are the recommended cultivars for moderately acidic soils.
and B13-,{14, respectively. Cycles I and 2 were screened in Tatum clay-loam subsoil (36% AI saturation for cycle I and 6l% Al saturation for cycle 2), andcycles 3 and 4 were screened in a modified Steinberg solution (l11pmol Al, pH 4.5). Selection was based on root growth in the first two cycles and shoot growth in the latter two cycles. Selections were intercrossed with honey bees (,4pis mellifera L.) at the end of each cycle. Efficacy of the selection procedure was evaluated in pH 4.5 Steinberg solutions (Al concentration of 0 or 1 1 I ptmol), and in Tatum soil (0 or 68 % Al saturation). Regression analysis indicated that significant but minimal progress was made in developing synthetics with improved vigor under AI toxic conditions. B13-414 was among the least impaired of the entries in the ability to take up nutrients whereas AS-4 and Williamsburg (susceptible checks) were among the most impaired. It was concluded that tolerance to Al in nutrient solutions and soil could involve different mechanisms and that the screening procedure used here was much more effective in selecting for vigor than for Al tolerance. Alternative breeding approaches were proposed. (Rechcigl et al. 1986).In greenhouse experiments, the addition of monocalcium phosphate reduced aluminum concentration in acid soil and increased alfalfa growth four-fold (Horsnell 1985 for tolerance to ej in acid Bladen soil had sig-,"ff'ff,:i"i"tff:;,Wff:jil*|i]f#y;nificantly greater top and root vigor when Hapludult) which was collected from a wooded site grown in acid Tatum soil than did a popula-near Orange, Virginia; it is used routinely to screen tion (AS-3) which had been subjecteO to two plants for tolerance to A1 (Foy 1984
Alfalfa (Medicago sativa L.) is an important forage legume that is known to be sensitive to soil acidity. A nutrient solution experiment was conducted under controlled growth conditions to evaluate the effects of Al (0, 75, and 150 µmol L−1) on growth, nutrient uptake, and mineral nutrient efficiency ratios (ER = shoot dry weight produced per unit element in shoot) in 15 selected alfalfa cultivars and lines. Growth of shoots and roots differed with Al levels and cultivars/lines. At 75 µmol L−1 the mean reductions of shoot and root dry matter yield were 29 and 6% of the control, respectively. Shoot nutrient contents showed significant positive correlations with shoot and root weights, and negative correlations with Al level and shoot Al concentrations. The ER values were used to classify cultivars and lines into efficient and inefficient utilizers of absorbed nutrients. With the exception of the ER for Ca, negative correlations were observed between Al level and ER. The cultivars and lines used in this study showed intraspecific genetic diversity for dry matter yield and ER values for the elements when plants were grown with or without AL.
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