Mineral Composition of 10 Tropical Forage Grasses in Puerto Rico

Abstract

Mineral composition—calcium (Ca), phosphorus (P), magnesium (Mg), and potassium (K)—in 60 samples of forage grasses representing 10 forages (African Crab, Digitaria swazilandensis; Venezuelan Elephant, Pennisetum setosum; Giant Pangola, Digitaria valida; Pangola, Digitaria decumbens; Signal, Brachiaria brizantha; Buffel, Cenchrus ciliaris; Jaragua, Hyparrhenia rufa; Limpo, Hemarthria altissima; Congo, Brachiaria ruziziensis; and Guinea, Panicum maximum) at 6 growth stages was analyzed statistically by variance, simple correlation, and simple regression analyses. Calcium, P, and Mg contents revealed highly significant differences while K presented significant differences with respect to grass species. Phosphorus, Mg and K contents, but not Ca, presented highly significant differences with respect to plant ages. Values ranged from 0.11 to 0.43 percent for Ca, 0.08 to 0.39 percent for P, 0.15 to 0.46 percent for Mg, and 0.68 to 7.33 percent for K. Calcium to P ratio ranged from 0.89 to 1.38 parts Ca to 1 part P, increasing as forages advanced in age. Phosphorus, Mg, K, and SA, but not Ca, were associated in a highly significant way to age, crude protein, lignin, in vitro true digestibility, and total ash. Phosphorus, K, and soluble ash were associated in a highly significant way to acid-detergent fiber and cellulose; Mg was significantly associated to acid-detergent fiber. It may be concluded that P, Mg, and K, but not Ca, declined with advance in plant age and that apparently the mineral composition of the grasses studied is nutritionally adequate for beef and dairy animals in Puerto Rico. The Ca to P ratios seemed generally adequate; however, they were somewhat low at younger growth stages. Additional mineral supplementation, either free-fed or mixed with the feed, is a routine feeding practice to insure optimum mineral intake.