Dung pads increase pasture production, soil nutrients and microbial biomass carbon in grazed dairy systems

In grazing systems dung is an important source of nutrients which can increase soil fertility and contribute to nutrient cycling through increased pasture production. Changes in soil chemical and biological properties and pasture production were measured below and around dung pads created in the field. Almost 65% of the total dung P remained after 45 days and about two-thirds of the pad fresh weight had disappeared in that time, indicating that physical degradation is the mechanism of incorporation of dung P. All the pads bar one were completely degraded by 112 days. At this time, soil pH and EC increased under dung pads as did Olsen extractable inorganic phosphorus (Pi) and total phosphorus (Pt), with these changes observed at 0-5 and 5-10 cm depths. Bicarbonate extractable soil organic phosphorus (Po) was not affected by dung and the observed differences in soil Po:Pi ratios were largely influenced by the substantial addition of inorganic P from dung. Dung increased the P buffering capacity of the 0-5 cm soil samples collected at the end of the experiment, potentially contributing to the increased extractable soil P measured under the pads. Dung also changed soil properties in 0-10 cm samples with increases in soil pH, EC, Colwell P and Colwell K recorded even long after the dung had completely disappeared. Microbial biomass carbon increased under dung pads in the 0-10 cm soil samples in the first 45 days after pads were applied. Total herbage production and ryegrass biomass increased significantly under and around the pads by 112 days after dung was applied. The botanical composition changed significantly with increased ryegrass contents observed, but only under the dung pads. This experiment demonstrated that increases in pasture around dung pads in the field are not solely due to animal rejection.