Nutrient composition and in vitro digestibility of cultivated and non-cultivated plant species found within a Southwestern forage production operation
Nutrient quality of non-cultivated plants in hay or grazing pasture may affect animal feeding behavior, digestive efficiency, forage quality, or a combination of these. Understanding nutritive composition of invasive plants may improve forage and weed management. A 2-year study was conducted to determine the nutrient composition and digestibility of invasive plants growing within the boundaries of 3 alfalfa hay fields and 7 grass pastures (9.75 ha) located at the University of Arizona’s West Agriculture Campus and Campus Agricultural Center (Tucson). Multiple whole above-ground samples of cultivated and non-cultivated species were collected at a maturity of mid-bloom for non-grasses (n = 53) and pre-shatter for grasses (n = 13). Samples were analyzed for DM, ash, NDF, ADF, ADL, CP, and IVTD. Species from 21 plant families were sampled, with the grass (Poaceae) family having the highest specie count (13), and 9 forb families having only 1 specie recorded. Compared to cultivated alfalfa, forb species had greater (P < 0.01) CP (20.2 vs. 15.5 ± 2.85%), ADL (8.5 vs. 3.0 ± 1.74%), and IVTD (75.1 vs. 67.3 ± 3.28%), and grass species had greater (P < 0.01) NDF (53.8 vs. 45.9 ± 3.76%) but lower (P < 0.01) ADF (25.7 vs. 33.6 ± 1.74%). Seven (7) plant families were represented by at least 3 species: amaranth (Amaranthaceae; n = 3), sunflower (Asteraceae; n = 7), mustard (Brassicaceae; n = 7), goosefoot (Chenopodiaceae; n = 5), knotweed (Polygonaceae; n = 4), nightshade (Solanaceae; n = 5), and grass. Within the 7 families, grasses had greatest NDF but least ADL, ash, and IVTD (54.7, 5.7, 11.9, and 64.3%, respectively; P < 0.01). Nightshade species had greatest CP (23.5%; P < 0.01), amaranth species had greatest IVTD and least NDF (84.0 and 29.3%, respectively; P < 0.01), and mustard species had greatest ADL (10.1%; P < 0.01). Greatest variation was observed with DM (SEM range = 2.47 to 16.98 %), and least variation was observed with ADL (SEM range = 0.93 to 4.33 %). Predominant species observed affecting grazing behavior or hay production included junglerice (Echinochloa colonum), bermudagrass (Cynodon dactylon), little mallow (Malva parviflora), and Palmer amaranth (Amaranthus palmerii). Results indicate the presence of non-cultivated plants growing within Southwestern hay and grazing fields may affect forage nutritive quality.
Keywords: forage, in vitro, invasive plants, nutrient composition