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Effects of Magnesium Fertilization on Mineral Utilization and Nutritional Quality of Alfalfa for Lambs^1,2,

West Virginia University, Morgantown 26506 and U. S. Regional Pasture Research Laboratory, University Park, PA 16802

Abstract

Alfalfa treated with four levels (0, 112, 224, 448 kg Mg/ha) of kieserite (MgSO₄.H₂O) fertilizer was harvested in first and regrowth cuttings in three years following initial application, and fed in digestibility, intake and mineral balance trials to growing lambs. Fertilization markedly increased the concentration of magnesium (from .20 to .32% in the 0 and 448 Mg/ha treatments, respectively, over all cuttings), with lesser effects on sulfur concentration (from .21 to .24%), and no effect on concentration of other minerals measured. Concentration increases declined with time after application. Over all trials with ad libitum feeding, magnesium fertilization had no effect on apparent absorption (AA) or availability of magnesium but increased magnesium retention (from .39 to .74 g/day at the 0 and 448 kg Mg/ha levels, respectively). Retention was found to be a curvilinear function of magnesium intake. Fertilization increased the AA of sulfur, had no effect on AA of calcium, phosphorus, potassium and nitrogen, and did not affect retention of calcium, phosphorus or nitrogen. In two trials in which regrowth alfalfa was fed at both ad libitum and restricted levels, lower dry matter intake resulted in an increased AA of magnesium, calcium, sulfur, potassium and nitrogen, and a decreased retention of magnesium, calcium, phosphorus and nitrogen. Level of kieserite fertilization had no effect on dry matter digestibility of the alfalfa, but intake was increased at the highest level (448 kg Mg/ha) of fertilization in the first 2 years after fertilizer application, with no effect in the third year. The increase in intake over the 0 treatment averaged 8.8 and 11.7% in the first and second years, respectively, with increases in individual cuttings ranging from 3.1 to 18.9%. Intake effects may have resulted, in part, from lower levels of cell-walls noted in alfalfa fertilized at higher levels of kieserite.

¹ Published with the approval of the Director of the West Virginia Agricultural Experiment Station as Scientific Paper No. 1546. Contribution No. 466 from the U. S. Regional Pasture Research Laboratory, University Park, PA.

² The authors acknowledge the assistance of Mr. John Hedges in feeding and metabolism trials, and thank Dr. W. V. Thayne for his help with statistical analysis of data. They also express their appreciation to Mr. Lynn Hofmann, Superintendent of the Agronomy Farm, Rock Springs Agricultural Research Center, PA, and to the Potash Import and Chemical Corp., New York, for the donation of fertilizer used in this study.

³ Division of Animal and Veterinary Sciences, W. V. U.

⁴ U. S. Regional Pasture Research Laboratory.