Changes in elemental concentrations in alfalfa herbage at two soil fertility levels with advance in maturity

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Abstract
A two‐year‐old stand of Vernal alfalfa (Medicago sativa L.) established in 45‐cm rows was used to study changes in elemental composition in fertilized (F) and nonfertilized (NF) herbage at different growth stages. Herbage was harvested weekly for eight weeks with the final stage at 85% flower. Herbage yields, as well as concentrations and accumulations of fourteen elements, were compared in F and NF alfalfa. Herbage yields increased from earliest vegetative stage to 60% flower in NF treatment and to 10% flower in F treatment with no yield increases thereafter. Yield of herbage at all growth stages was not increased significantly by fertilization. Concentrations of K, S, P, Mg, Zn, Mn, B, N, Fe, and Al in herbage from both fertility levels, and Cl in NF herbage, generally decreased with advance in maturity. Concentrations of Ca at both fertility levels, and Cl in F herbage increased during early stages of growth and then decreased. Concentrations of Na and Cu showed no significant changes. Concentrations of Mg, B, N, Ca, and Al decreased more in F than NF herbage, and was the reverse situation for K, Cl, P, Zn, Mn, and Fe. Elemental accumulation (uptake) is discussed.