Seasonal and diurnal relationship of forage nutritive value and mass in a tall fescue pasture under continuous stocking

Monitoring forage mass and nutritive value of pastures are encouraged to ensure adequate and efficient grazing management. For on‐farm monitoring, reliable instruments such as the rising plate meter (RPM) are useful and easy to achieve. The objective of this research was to verify the relationship between measurements of RPM (MRPM) to forage nutritive value based on seasonal and diurnal changes within a tall fescue sward under continuous stocking management. The study was conducted at the Plateau AgResearch and Education Center in Crossville, TN, from January 2015 to December 2016. The experiment was conducted in two 9‐hectare pastures consisting of a tall fescue [Schedonorus arundinaceus (Schreb.) Dumort., nom. cons., formerly Festuca arundinacea Schreb.] sward. During the 12‐month grazing period each year, total aboveground available forage was measured monthly in each pasture with a calibrated RPM. In addition, each month, several randomly placed 1‐m² sample areas were collected at 7 a.m., 9 a.m., 12 p.m. and 4 p.m. to characterize forage nutritive value. Neutral detergent fiber, crude protein and in vitro total dry matter digestibility (IVTDMD) were predicted by means of near‐infrared spectroscopy. During the entire year of 2015, all correlation coefficients of forage nutritive value variables with MRPM were significant. However, in 2016, only IVTDMD showed a significant correlation with MRPM. Of the nutritive value variables, we chose to focus on the IVTDMD and MRPM relationship because it had one of the highest correlations for most seasons and different times of day, especially in 2015. There was a strong relationship between RPM measurements of herbage mass with IVTDMD, and this relationship is especially useful during the spring, where rapid growth is occurring. The same relationship was not found to be consistent during periods of slow forage growth, especially if recovering from a drought event.