Cattle Excreta Increases Herbage Rejection and Affects Herbage Nutrient Concentration.

Grazing animals return most of the ingested nutrients to the pasture via excreta deposition. This return is important to replenish soil fertility; however, irregular excreta distribution and herbage rejection due to fouling may occur. Herbage nutrient concentration and herbage mass may also be affected at excreta deposition sites. This experiment aimed to evaluate the effect of three stocking rates [2, 4, and 6 Animal Units (AU)/ha; 1 AU = 450 kg live weight] on herbage rejection, herbage mass, and herbage nutrient concentration around cattle dung pads on signal grass (Brachiaria decumbens Stapf.) pastures. Response variables measured included herbage rejection, herbage mass, and herbage N, P, and K concentrations from herbage collected at concentric zones away from the dung pad (0-20 cm; 20-40 cm; and 40-60 cm away from the dung border). Herbage rejection was measured in five different evaluations by comparing the height of paired samples at the pre- and post-grazing evaluations. Herbage mass and herbage nutrient concentration was performed in eight evaluations. Herbage rejection occurred when more herbage mass was available, which happened for the lowest stocking rates at the peak of the forage growing season. Herbage P was higher (P < 0.05) at the zone closer to the dung and decreased it values at further zones. Herbage nutrient concentration (N, P, and K) varied with evaluation and there was a treatment x evaluation interaction for N and K concentrations. Herbage nutrient tended to be higher for the higher stocking rates (4 and 6 AU/ha). Herbage mass around dung pads was affected by a treatment x evaluation interaction, with more herbage mass observed for the lowest stocking rate (2 AU/ha) in three out of eight evaluations. Higher stocking rate decreased herbage rejection which caused more immature herbage regrowth, affecting herbage nutrient concentration as a result.