Mineral Concentrations in Whole Crop and Pressed Forage of Three Legumes
Mechanical dewatering of fresh herbage produces a pressed forage (PF) suitable for ensiling without field drying. A 2-yr field experiment was conducted to compare concentrations of minerals in initial whole crop (WC) and pressed forage of alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.), and birdsfoot trefoil (Lotus corniculatus L.) harvested at four first-harvest maturity stages. Plots of each species were grown on Plano silt loam soil (fine-silty, mixed, mesic Typic Argiudolls) and were harvested beginning 1 wk after early bud and continuing at 1 wk intervals for 4 wk. Pressed forages of all species were lower in P, K, Ca, and Mg than their respective WC. Potassium decreased the most and, averaged over all species, was 26.5% lower in the PF. Pressed forages averaged 21% lower in Mg than the WC, but remained above the critical concentration of 2.0 g kg−1 at all maturity stages. Pressed forage from the most mature alfalfa and red clover had P concentrations insufficient for some classes of livestock. Pressing and shoot maturation reduced S concentrations of all species, but pressing affected S more in alfalfa than in the other species. Alfalfa, red clover, and birdsfoot trefoil N/S ratios differed widely and averaged 11.8, 14.7, and 17.7, respectively. Pressed forages from the last two harvest dates had higher N/S ratios that WC from the same harvests. Pressing significantly reduces P, K, Ca, and Mg concentrations in alfalfa, red clover, and birdsfoot trefoil and, with the exception of red clover, reduces S concentration. Pressing effects on mineral concentrations vary across minerals and legume species.
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