Spatial distribution of dung patches under sheep grazing

Abstract

The spatial distribution of dung patches from sheep grazing pasture on a West Coast gley podzol near Greymouth was measured over four grazings in 2 years. During June four sheep stocking densities were used (900, 1200, 1500, and 1800 sheep/ha per day) with and without nitrogen (N) at 900 and 1800 sheep/ha per day. In an additional treatment, sheep were grazed for 4 days at 1800 su/ha per day on one area instead of 1 day on one-quarter of the area as for the other treatments. In October these grazings were repeated on pasture regrowth from the June grazings, but at one-third of the June stocking densities (300, 400, 500, and 600 sheep/ha per day). The spatial distribution of dung was best described by the negative binomial function. The Poisson Index which measures the aggregation of the dung patches showed that there was significantly more aggregation at the lowest stocking density than at the higher stocking densities. At the highest stocking density, grazing for 4 days resulted in more clumping of dung patches compared to grazing for 1 day. The correlation between the distribution of dung patches between grazings was generally low but there was a trend towards a higher correlation at higher stocking densities when the October 1985 and June 1986 grazings were compared. Most of the pasture yield response to urea was gained in the period from after application up to the first grazing with little response occurring after the first grazing. This indicated that the return of N from dung and urine affected an insufficient area to influence pasture growth even at a high stocking density. A technique of dosing sheep with sodium fluorescin and then detecting the affected urine patches with an ultraviolet lamp was used to measure the area of urea patches. Average area per mine patch was 0.03 m² which agreed closely with that measured from the alternative techniques. Using measured parameters from the trial and assumptions from other research, both the potassium (K) returned in urine and to a lesser extent the phosphorus (P) returned in dung, represented a significant input to the soil at higher stocking densities.

Keywords:

• distribution
• dung patch
• stocking density
• phosphorus
• potassium
• nitrogen
• sheep
• pasture
• urine
• negative binomial