Alfalfa (Medicago sotiva L.) growing on K-depleted, semiarid, calcareous soil displays three K-deficiency symptoms: (i) white spots on leaflets 0, (u) marginal chlorosis 0, and (iu) normal leaflets on stunted plants (N). In a greenhouse study, we examined partitioning and heritability of K and Na nutritional traits in three alfalfa clones and their crosses, and also how K and Na soil fertility levels affected biomass production, genetic dependence of K and Na uptake and partitioning, and K use efficiency. Mother plants were propagated vegetatively and by seed from phenotype crosses in a low-K, low-Na, calcareous soil rooting medium. One trial used K- and Na-amended soil. Harvests were at early bloom. Leaves contained more K than stems, with no difference among phenotypes; Na was uniform in stems, but leaves of M contained much more Na than leaves of N and W. With nonamended soil, K and Na uptake and partitioning among leaves, stems, and roots were significantly affected by cross. The Na:K ratio in leaves, stems, and roots was strongly iduenced by phenotype and cross. Biomass production of leaves and stems differed among crosses and was increased by K fertilization; Na fertilization affected biomass only of leaves, and only in crosses M XM and N ✕ N (Na may have partially replaced K). The shoot:root ratio was affected only by cross. Potassium use efficiency was affected by cross and by Na fertilization. Broad-sense heritability for K and Na concentration was high, especially for Na in leaves and stems. Uptake and partitioning of Na and K in phenotype crosses supported narrow-sense heritability as well. Genetics, rather than soil K-Na competition, governed Na uptake, translocation, and utilization by phenotypes. Accordingly, characterization of K nutrition in alfalfa must consider Na levels. As phenotypes of alfalfa cultivars range widely in K-Na nutritional traits, it should be possible to select for high yield and K use efficiency
Contribution from the Utah Agric. Exp. Stn., Journal Paper no. 4538.