Effects of Cutting Management on Eight Subtropical Pasture Mixtures

Rhodesgrass (Chloris gayana Kunth) and ‘Pangola’ digitgrass (Digitaria decumbens Stent.) were grown with desmodium (Desmodium intortum (Mill.) Urb), glycine (Glycine jevanica L. ‘Tinaroo’), lotononis (Lotononis bainesii Baker), or ‘Siratro’ (Macroptilium atropurpureum (D.C.) Urb) on an Oxisol near Porto Alegre, Grande do Sul. They were cut every 3 or 6 weeks at 5 or 13-cm stubble heights to simulate different grazing pressures during two growing seasons. Herbage samples were hand separated to ascertain botanical composition. Crude protein (CP) and in vitro dry matter disappearance (IVDMD) analyses were determined for each species for cutting-frequency treatments during the first year only. Cutting at 5 cm, at either frequency, increased legume content more than cutting at 13 cm. Exceptions were glycine, which increased most with rhodesgrass when cut at 13 cm, and ‘Siratro’, which decreased under all treatments when grown with ‘Pangola’. Legume contents increased from an average of 14% in the seeding year to 31% by the beginning of the third year. During the same period, grasses increased from 50% to 63% and weeds decreased from 36% to 5%. Weed-free, dry forage yields from all mixtures ranged from 1.24 to 7.26 metric/ha during the first year, and from 3.69 to 10.26 metric tons/ha during the second year. Yields generally were highest when mixtures were cut every 6 weeks at 5 cm, and were lowest when mixtures were cut every 3 weeks at 13 cm. The CP concentration in legumes averaged 26% when they were cut every 3 weeks at either stubble height, and 23% when they were cut every 6 weeks. Concentration in CP in grasses averaged 15% for 3 weeks, and 13% for 6-week cutting treatments. Yields of CP from mixtures ranged from 196 to 972 kg/ha. Yields of CP were greater from rhodesgrass mixtures than from Pangola mixtures, except for the Pangola-desmodium mixture, which had CP yields equal to, or greater than, some rhodesgrass mixtures. Estimated digestible dry matter (EDDM), determined by IVDMD, in legumes averaged 54% when they were cut every 3 weeks at either stubble height, and 51% when they were cut every 6 weeks. EDDM in grasses averaged 73% for 3-week cuttings. Yield of EDDM was greater from rhodesgrass mixtures than from Pangola mixtures. Considering all aspects studied, we believe that mixtures of rhodesgrass with desmodium or lotononis would be best choices for improving pastures in Rio Grande do Sul. Responses to cutting indicated that rhodesgrass-desmodium should be grazed every 3 weeks to about a 13-cm stubble height during the growing season. Grazing to higher stubble height, rather than the lower height, should result in a well-balanced grass-legume mixture for grazing. A well-balanced rhodesgrass.lotononis mixture should be maintained in a pasture by grazing every 3 weeks to about a 13-cm stubble height, or every 6 weeks to either stubble height. Frequent, close grazing would probably result in higher percent legume in the mixture.