Jesús Jarillo-Rodríguez

Does Stocking Rate Manipulation Promote Pasture Sustainability in the Humid Tropics

Abstract Stocking rate manipulation was examined as a means of improving plant diversity (as a measure of pasture sustainability and forage value) in a native grass pasture used for dairy production in the humid tropics of Veracruz, Mexico. Given that environmental impact reduces biotic diversity, plant phylogenetic and functional diversity should decline with increased stocking rate. Stocking rates of 2, 3, and 4 cows · ha−1 and a rotational grazing plan of 3 d of occupation and 27 d of rest per pasture were applied continuously over 5 yr. Across 200 quadrats in each of two replicate paddocks per treatment, observed species richness, phylogenetic diversity (average taxonomic distinctness based on species presence/absence), and functional diversity (life-cycle duration and growth habit) were assessed. Most species were forb/herbs and forb/herb-subshrubs. Perennial species declined with increased stocking rate (F = 16.36, 0.05 > P > 0.02) while annual-perennial species increased (F = 76.88, 0.01 > P > 0.005); the proportion of annual species was least prominent and did not differ significantly. Observed species richness and phylogenetic diversity did not differ significantly with stocking rate. The correlation between functional diversity for life-cycle duration and phylogenetic diversity was significant and positive, suggesting that plant communities were predominantly assembled randomly from the surrounding species pool rather than through interspecies interactions acting to naturally filter immigrant species, thus leading to more opportunistic and undesired species. Although grazing pressure was not sufficient to alter indices or production measures, they did reveal shifts that may precede further pasture decline, indicating pasture sustainability was not being achieved. These rapid assessment methods permit monitoring for early warnings of reductions in pasture sustainability and forage quality for cattle.

Cratylia argentea: un arbusto forrajero potencial en sistemas silvopastoriles: Rendimiento y calidad de accesiones según las edades de rebrote y estaciones climáticas

In silvopastoral systems, high nutritional quality shrub legumes represent an alternative to shortage of grasses in dry periods of the year. The effect of different regrowth ages (6, 9, 12 and 15 weeks) in three climatic seasons (rainy, winter and dry seasons, 2007-2008) of four Cratylia argentea accessions (18516, 18666, 18668 and 18676) were evaluated in Veracruz, Mexico, for dry matter yield (DMY), neutral detergent fiber (NDF), acid detergent fiber (ADF), lignin (Lig), crude protein (CP) and in situ DM degradation (ISDMD). Dry matter yield (mean ± standard error) was affected by season and regrowth age, but not by accession or interactions. The dry season showed the largest DMY (3632 ± 306 kg·ha-1), representing 45 % of total forage yield, followed by the rainy (33 %, 2615±188 kg·ha-1) and winter (22 %; 1733 ± 61 kg·ha-1) seasons. For NDF, ADF, Lig and CP, statistical effects were found for regrowth age in all three seasons. The largest ISDMD occurred in the rainy and dry seasons, reaching average values of 66 and 65 % at 72 h of incubation, respectively. The dry season was the best period for DMY and ISDMD, making Cratylia argentea a reliable feed resource for silvopastoral systems. Recibido: 22 de octubre, 2013 Aceptado: 26 de junio, 2014 doi: 10.5154/r.rchscfa.2013.11.040 http://www.chapingo.mx/revistas PALABRAS CLAVE: Rendimiento de materia seca, composición química, efectos estacionales, leguminosas forrajeras arbustivas, Veracruz, México.