Monday, November 13, 2006

Dairy Effluent Rate Effects on Herbage Mass and Nutritive Value of Stargrass (Cynodon nlemfuensis Vanderyst var. nlemfuensis) Pastures.

Elide Valencia1, Rebecca Tirado-Corbalo1, Hector Diaz-Rios1, and Martin Adjei2. (1) University of Puerto Rico, Mayaguez, PO Box 5309, Mayaguez, PR 00681, (2) University of Florida, 3401 Experiment Station, Ona, FL 33865-9706, United States of America

Stargrass (Cynodon nlemfuensis Vanderyst var. nlemfuensis) is an important grass for the dairy industry in Puerto Rico.  However, high N fertilizer is needed to maintain Stargrass pastures productive year-round.  Earlier studies conducted in Puerto Rico in the 1970’s reported that Stargrass remove large amounts of N (as much as 400 kg ha-1 yr-1). The effect of increasing N from effluents on Stargrass is unknown.   A field study was conducted on 12 (0.50 ha) ten-year-old Stargrass growing on a Mabi soil series (Very-fine, mixed, active isohyperthermic Aquic Hapluderts), and arranged in a randomized complete block with three replicates.  The objective of the study was to assess the effects of four N rates (0, 200, 400, and 600 kg ha-1) on herbage mass (HM), crude protein (CP) and fiber concentration (NDF) of grazed Stargrass.  Effluents originating from anaerobic lagoon were split applied starting in June 2005 until June 2006.  Prior to the date of application, solids from the lagoons were sampled and analyzed for N to calculate rates.  Pastures were mobgrazed with dairy cows at 21-d intervals. Every 21 d, and prior to grazing, HM was estimated using a double sampling technique (30 disk height measurements and five height and clipping of grass in a 0.25 m2 in each pasture).  Average mean of ten harvest samples showed difference in HM as influenced by N effluent rate (3.2, 4.7, 5.4, and 5.9 Mg ha-1 for the control, L, M, and H rates, respectively). There was also differences in CP (6.7, 8.2, 9.2 and 10% for the control, L, M, and H rates, respectively), but no effect on NDF (65%).  This study suggests positive effects of effluents on HM and N concentration of Stargrass.  Futher studies should assess both P accumulation on soils and surface runoff, particularly on high rainfall areas of PuertoRico.