Dung decomposition in temperate dairy pastures - I. Changes in soil chemical properties

The effect of dung from cows grazing low and high input systems ( 2 cows/ha, 35 kg P/ha; 4 cows/ha, 140 kg P/ha) on soil chemical properties in temperate dairy pastures was investigated. Dung was used to create pads, and their effect on soil at 2 depths compared with control areas to which nothing was applied. Most dung had decomposed after 40 days in autumn, and was completely degraded by Day 60 in this temperate environment. Large quantities of the nutrients P, K, Ca, Na, Mg, and S were applied to the soil in these dung pads. The mechanism of movement of these nutrients from the pads into soil appeared to be based on their solubility in water. Phosphorus did not leach from the pads but was incorporated into the soil with the decomposing pad. Calcium, Mg, and S concentrations declined slowly in the decomposing pads. On the other hand, K and Na appeared to leach from the pads, as significant decreases in concentrations occurred during decomposition. Soil pH ( 1 : 20 soil : water) decreased under dung pads, although the effect did not last beyond 60 days and was linked to the observed increase in soil EC with depth. Extractable P and K increased considerably in soil under dung pads, but only in the upper 0 - 5 cm layer. Soil exchangeable aluminium and total organic P were not affected by the presence of dung pads. These results are discussed in relation to nutrient cycling in temperate Australian dairy pasture soils.