Management strategies to improve nutrient cycling in grazed Pensacola bahiagrass pastures

Efficient nutrient cycling plays a major role in pasture sustainability in low-input systems and in preservation of the environment in high-input systems. In this work, we studied the effect of a range of management practices on aspects of nutrient return to pastures via animal excreta and plant litter. There were two grazing experiments. In Experiment 1, bahiagrass pastures were continuously stocked and the treatments were three management intensities: Low (40 kg N ha-1 and 1.4 AU [animal units] ha-1), Moderate (120 kg N ha-1 and 2.8 AU ha-1), and High (360 kg N ha-1 and 4.2 AU ha-1). Patterns of excreta deposition, changes in soil nutrient concentration, and herbage responses were measured. Litter production and decomposition rates were also assessed. In Experiment 2, rotational and continuous stocking methods were compared in terms of their effect on animal grazing behavior, uniformity of excreta distribution in the pasture, changes in soil nutrient concentration, and herbage responses. Finally, the effect of management intensity and grazing method on soil organic matter (SOM) was determined. Based on the herbage responses to N fertilizer it is concluded that under continuous stocking the use of more than 120 kg N ha-1 yr-1 is not justified for Pensacola bahiagrass in North Central Florida. In terms of stocking methods, rotational stocking promoted greater herbage accumulation (70 kg DM ha -1 d-1) than continuous stocking (40 kg DM ha -1 d-1). Soil nutrient concentration was greater closer to shade and water, but rotational stocking with short grazing periods promoted a more uniform excreta distribution across the pasture. The litter results showed that the above-ground plant litter pool does not supply a large amount of nutrients for plant and microbial growth, but it does act as a buffering pool reducing potential N losses to the environment, particularly in more intensive systems. Finally, the SOM results demonstrated that increasing management intensity increased C and N accumulation in grazed pastures. These data aid in assessing potential environmental impacts and nutrient-use efficiency of various grazing management practices as well as providing data needed for modeling nutrient cycling in forage-livestock systems.