Influence of enhanced CO2 concentration and irrigation on sudangrass digestibility

Abstract

An experimental line of sudangrass (Sorghum bicolor L. Moench) was included in the free-air CO2 enrichment (FACE) project in 1991 at the University of Arizona Maricopa Agricultural Center to evaluate the effect of ambient (approximately 370 μmol mol−1) and enriched (550 μmol mol−1) CO2 in well-watered or water-stressed plots. Our specific objective was to determine modifications caused by these environmental effects on the percentages of morphological parts and the fiber components, and on the in vitro digestibility in vegetative and mature harvests. Enrichment with CO2 did not (P > 0.05) change the percentages of morphological parts or fiber components, or the digestibility of any of the morphological components. Protein levels tended to be lower in CO2-enriched plants. However, water-stressed plants tended to have a higher proportion of leaves (blades and sheaths) and a lower proportion of stems, were more digestible, and had lower amounts of anti-quality, aromatic compounds within the plant cell. Stems had the highest digestibility of all morphological components (about 75% in vegetative plants) despite the lowest levels of protein. Stems also showed the greatest changes caused by all treatments, including a 20% decline in digestibility from vegetative to mature samples. The results indicate that enriching CO2 to 550 μmol mol−1 did not reduce digestibility of sudangrass.