Distribution of Dry Matter and Chemical Constituents in Plant Parts of Four Florida Native Grasses

Abstract

Because of the selective nature of grazing livestock, the use of whole plant samples to estimate the nutritional potential of forages may be misleading. During this 2-year study, the distribution of dry matter (DM), crude protein (CP) in vitro organic matter digestibility (IVOMD), and concentrations of P, K, Ca, Mg, Mn, Fe, Cu, and Zn were determined in the individual leaf blades, leaf sheaths, nodes plus internodes, and infloresences of creeping bluestern (Schisachyrium stolonifenrm), lopsided indiangrass (Sorghastrum secundum), maidencane (Panicurn hemitomon), and wiregrass (Aristida stricta) when they were in the anthesis stage of + maturity. Most of the DM was in the nodes plus internodes (avg. 45%), while the leaf blades (avg. 18%) generally made up the smallest amount of the total plant DM. In a progression from the bottom to top of the plant the CP, IVOMD, and most of the mineral concentration of the different leaf blades, sheaths, and nodes plus internodes increased. Crude protein, IVOMD, and most of the minerals of the grasses were higher in leaf blades, followed by sheaths, and nodes plus internodes. When compared with other grasses, maidencane had a higher proportion of CP and minerals in the leaves and nodes plus internodes and a higher percentage of plant weight in these parts. Wiregrass was found to be similar to creeping bluestem and indiangrass in CP and most minerals, but IVOMD of wiregrass parts were lower. Dietary requirements for dry, pregnant cows for P, N, Mg, and Cu might not be met by any part of the 4 grasses, while apparently adequate levels of Fe, Mn, and Zn could be provided by each part. Leaf blades and infloresences had sufficient Ca concentrations for dry pregnant cows. When evaluating pasture quality, the nutritional potential of forage may be underestimated by analyzing whole plant samples. Cattle seldom consume whole plants, but rather selectively graze individual parts. The parts of a plant [infloresence, leaf blade, leaf sheath, and culm (nodes plus internodes)] differ in their chemical and physical properties depending on their role in the plant. Florida’s sub-tropical native forage grasses are low in protein, digestibility and mineral concentration (Kalmbacher 1981a, I98 I b). This is associated with low soil fertility and high temperature during the growing season and the advanced plant maturity in winter when most Florida range is grazed. Because evaluation of whole plant samples can be misleading, this study was initiated to examine the distribution of dry matter (DM), the variation in crude protein (CP), in vitro organic matter digestibility (IVOMD), and the concentration of certain minerals in parts of 4 important grasses. The major increaser on flatwoods range, wiregrass (Aristida stricta); 2 major decreasers on flatwoods, creeping bluestem (Schizachyrium stoloniferum) and lopsided indiangrass (Sorghastrum secundum); and the major decreaser on slough sites, maidenAuthor is associate agronomist, Ona Agricultural Research Center, Box 62, Ona,